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This paper presents an innovative application of chitosan material to be used as pH-responsive valves for the precise control of lateral flow in microfluidic paper-based analytical devices (μPADs). The fabrication of μPADs involved wax printing, while pH-responsive valves were created using a solution of chitosan in acetic acid. The valve-forming solution was applied, and ready when dry; by exposure to acidic solutions, the valve opens. Remarkably, the valves exhibited excellent compatibility with alkaline, neutral, and acidic solutions with a pH higher than 4. The valve opening process had no impact on the flow rate and colorimetric analysis. The potential of chitosan valves used for flow control was demonstrated for μPADs employed for nitrate determination. Valves were used to increase the conversion time of nitrate to nitrite, which was further analyzed using the Griess reaction. The μPAD showed a linear response in the concentration range of 10–100 μmol L−1, with a detection limit of 5.4 μmol L−1. As a proof of concept, the assay was successfully applied to detect nitrate levels in water samples from artificial lakes of recreational parks. For analyses that require controlled kinetics and involve multiple sequential steps, the use of chitosan pH-responsive valves in μPADs is extremely valuable. This breakthrough holds great potential for the development of simple and high-impact microfluidic platforms that can cater to a wide range of analytical chemistry applications. [Display omitted] • The development of pH-responsive valves offers a simple fabrication method and operational advantage in paper-based devices. • Control over the chitosan valve is achieved by adjusting the proton concentration using acid solutions • Chitosan is a biocompatible material for constructing valves, enabling precise control over nitrate reduction • A proof-of-concept study using urban park water analysis demonstrates the effectiveness of chitosan valves. [ABSTRACT FROM AUTHOR]

In this work, we present a dual-mode assay system consisting of a nanozyme and a luminogen with the aggregation-induced emission (AIE) feature. In the assay system, the chosen nanozyme named CuCo-0 catalyzes the substrate to produce colorimetric signals, while the aggregates of H 4 ETTC (4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl) tetrakis ([1,1′-biphenyl]-4-carboxylic acid), a typical AIE luminogen, generate fluorescent signals. The peroxidase-like activity of the CuCo-0 nanozyme can be remarkably suppressed with sequential additions of antioxidants, leading to a dual-signal response characterized by enhanced fluorescence emission and reduced UV-vis absorbance. On this basis, a dual-mode assay capable of producing both colorimetric and fluorescent signals for the assessment of antioxidant capacity using gallic acid as a representative antioxidant was exploited. Good linearity can be obtained in the 0–60 μM range for both colorimetric analysis and fluorescent analysis, with detection limits of 1.3 μM and 0.35 μM, respectively. Furthermore, this dual-mode assay was successfully applied to real gallnut samples, yielding satisfactory results. A colorimetric/fluorescent dual-mode assay was proposed by integrating a luminogen with aggregation-induced emission features and a CuCo nanozyme catalyzed reaction system, and it was successfully applied in antioxidant capacity of gallic acid and gallnuts samples. [Display omitted] • A colorimetric/fluorescent dual-mode assay that integrated AIEgen with a nanozyme catalyzed reaction system was developed. • The effect of chelating agents on the peroxidase-like activity of CuCo nanozymes was investigated. • H 4 ETTC was introduced to the CuCo nanozyme catalyzed assay system to yield fluorescent signals. • The antioxidant capacity of Chinese gallnut was detected by our dual-mode assay system. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is a chronic neurodegenerative disease that threatens to the health of global elderly population. Acetylcholinesterase (AChE) inhibitors are an effective therapeutic agent for AD, and screening of these substances is important for AD treatment. In this work, a Pd-Pt MXene nanoenzyme was successfully synthesized by using the in-situ reduction technique. A colorimetric method for sensitive AChE inhibitor detection was designed based on enzymatic cascade reaction between Pd-Pt MXene and AChE. Briefly, The Pd-Pt MXene material exhibited excellent peroxidase (POD)-like activity due to its bimetallic composition, effectively catalyzing the oxidation of colorless 3,3,5,5-tetramethylbenzidine (TMB) to generate blue oxidized TMB (oxTMB). Under the presence of AChE and acetylthiocholine chloride (ATCh), the POD-like activity of Pd-Pt MXene was significantly inhibited. The activity of this nanoenzyme could be restored after the addition of AChE inhibitors. Using donepezil as an example, colorimetric detection was conducted within a linear range of 0.1 nmol/L to 10 nmol/L and the lowest detection boundary was only 0.35 nmol/L (S/N = 3). Finally, a paper-based platform was designed and constructed, and it has been successfully employed for AChE inhibitor detection in real samples with the aid of a smartphone. In all, this work paves a new way for designing nanoenzyme-based devices towards medicine determination or screening like AChE inhibitor., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

A novel fluorescence/colorimetric dual-mode sensor, based on enhancement of the oxidase-like activity of CeO 2 /Cu x O nanozyme towards the oxidation of o -phenylenediamine (OPD) induced by thiourea (TU), has been proposed for TU detection. The catalytic activity enhancement on CeO 2 /Cu x O can be attributed to the strong electron-donation ability of TU, which promoted hydroxyl radical generation and amplified OPD oxidization with enhanced dual-signal readout. By integrating a portable paper-chip and smartphone system, this CeO 2 /Cu x O-OPD system achieved on-site visual colorimetric analysis of TU. The dual-mode sensor demonstrated high sensitivity and specificity in recognizing TU, with a detection limit (LOD) of 1.90 μM and a linear range (LR) 2.5–80 μM in fluorescent mode; as well as an LOD of 6.69 μM and an LR 10–250 μM in colorimetric mode. Furthermore, the CeO 2 /Cu x O-TU-OPD system has been designed for dual-mode glutathione (GSH) detection with enhanced sensitivity, achieving an LOD of 0.19 μM and an LR 0.5–10 μM in fluorescent mode; as well as an LOD of 1.24 μM and an LR 1.25–25 μM in colorimetric mode. Additionally, GSH discrimination (fluorescent mode) was successfully achieved in different biological samples, showing good consistency with the standard method. The recoveries ranged from 96.8 % to 116.7 % in serum samples and from 97.3 % to 107.7 % in cell lysates, with RSDs less than 2 %. This work not only introduced a novel approach to enhance oxidase-like activity of nanozymes but also provided an efficient field-suitable tool for enhanced dual-mode response towards TU and GSH. [Display omitted] • CeO 2 /Cu x O nanozyme was synthesized via a deep eutectic solvent strategy with l -proline as a ligand. • A dual-mode fluorescence/colorimetric sensor was developed for thiourea and glutathione detection. • The on-site visual colorimetric sensing was achieved by integrating a portable paper-chip and smartphone system. • TU interact with CeO 2 /Cu x O nanozyme to facilitate redox couples' circulation and enhance ·OH generation. [ABSTRACT FROM AUTHOR]

Heparin, a widely studied glycosaminoglycan, plays crucial roles in the regulation of various physiological and pathological processes. Therefore, it's important to develop highly selective and sensitive methods for convenient monitoring of heparin levels in biological systems. We report the design and synthesis of Fe 3 O 4 @PDA@MnO 2 nanoparticles (FPM-NPs), which exhibit dual enzymatic activities, enabling quantitative detection of heparin. The FPM-NPs feature a unique tri-layer spherical shell structure, possessing both peroxidase-like and oxidase-like activities, and catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence or absence of H 2 O 2. Remarkably, upon co-incubated with heparin, the oxidase activity of FPM-NPs decreases, while the peroxidase activity increases. By leveraging these dual enzymatic properties of FPM-NPs, a highly sensitive and specific colorimetric detection of heparin is achieved, with a detection limit reaching 6.51 nM and a good linear response to quantify heparin ranging 10–800 nM. Additionally, the developed FPM-NPs are successfully applied to measure heparin in fetal bovine serum samples. We also extend this detection method to a paper-based chip, enabling portable detection of heparin through grayscale analysis of mobile phone photographs. The multi-nanozyme-based heparin detection approach provides a new perspective for future research on expanding the application of nanocomposite materials in biomedical detection and analysis. Quantitative heparin assay through the evaluation of differential regulation effect of heparin on peroxidase (POD) and oxidase (OXD)-like activities of Fe 3 O 4 @PDA@MnO 2 nanoparticles. [Display omitted] • FPM-NPs with tri-layer spherical shell exhibit peroxidase and oxidase activities. • Heparin inhibits oxidase activities, but enhances peroxidase activities of FPM-NPs. • FPM-NPs enable colorimetric detection for heparin with high sensitivity (>6.7 nM). • The method offers wide dynamic range (10–1500 nM) and high linearity (R2 > 0.99). • FPM-NPs have been adapted for paper-based chip for portable detection of heparin. [ABSTRACT FROM AUTHOR]

Escherichia coli (E. coli) is a prevalent pathogen that is frequently associated with the foodborne illness. It causes various infections and poses a significant threat to human health. A rapid and sensitive assay for detecting E. coli is essential for timely diagnosis. Herein, a simple and sensitive colorimetric analysis method for detecting E. coli was developed based on the formation of Au@Ag core-shell nanoparticles facilitated by p -benzoquinone (BQ). E. coli reduced p -benzoquinone to generate hydroquinone (HQ), which could reduce the added Tollens' reagent to silver elemental and grow on the surface of gold nanoparticles (AuNPs). As the E. coli concentration increased, the silver layer thickess on the AuNPs surface growed, resulting in a stronger silver absorption peak observed at 390 nm. The color of the solution changed from red to orange, which could be used to detect E. coli by the naked eye. As a result, E. coli was detected with a linear range from 1.0 × 101 to 1.0 × 107 CFU/mL based on the absorbance intensity. In addition, this method accurately detected E. coli in real milk sample, demonstrating promising applications in foodborne pathogen detection. With satisfactory accuracy, the proposed colorimetric method holds excellent prospects in detecting pathogens in actual food samples. A simple and sensitive colorimetric analysis method for detecting Escherichia coli was proposed based on the formation of Au@Ag core-shell nanoparticles facilitated by p -benzoquinone. [Display omitted] • The color changes related to E. coli concentration were observable by the naked eye. • The colorimetric method avoided complex instruments and label procedure. • The method had a wide linear range and a low detection limit. • The method was applied in real milk samples with satisfactory accuracy. [ABSTRACT FROM AUTHOR]

Breast cancer is the most common malignant tumor in women, which accounts for 6.9% of all cancer-related deaths. Early diagnosis is crucial for making the best clinical decision and improving the prognosis of patients. Circulating tumor cells (CTCs) have been regarded as significant tumor biomarkers. Herein, we designed a colorimetric biosensor for breast cancer CTCs quantification based on ladder-branch hybridization chain reaction (HCR) and DNA flowers/gold nanoclusters (DFs/AuNCs) nanozyme. With the assistance of complementary DNA labeled on magnetic beads (MBs), the cleavage products of RNA-cleaving DNAzymes (RCDs) could be rapidly captured, subsequently triggering ladder-branch HCR. In addition, the DFs/AuNCs nanozyme was applied for colorimetric analysis, which further improved the sensitivity for the detection of target CTCs. Benefiting from specific RCDs, ladder-branch HCR and DFs/AuNCs, we achieved a superior detection limit of 3 cells/mL as well as a broad linear range of 10 cells/mL to 104 cells/mL. Conclusively, this colorimetric biosensor achieved sensitively and selectively detection of breast cancer CTCs without the participation of enzymes at room temperature, which might provide new insight into the early detection of breast cancer. [Display omitted] • A colorimetric biosensor for breast cancer CTCs quantification was developed. • Ladder-branch HCR was constructed for effective signal amplification. • DFs/AuNCs was synthesized with high peroxidase-like activity. • The proposed sensor showed good sensitivity, selectivity and real sample detection ability. [ABSTRACT FROM AUTHOR]

In this study, a novel integrated liposome-based microfluidic platform combined with a smartphone was designed for the rapid colorimetric detection of microRNA-21 (miRNA-21) in real samples. The flowing surface-functionalized liposomes were first captured by nucleic acid-functionalized Au nanoparticles in the microfluidic chip. In the presence of miRNA-21, the DNA strand modified on the surface of Au nanoparticles hybridized with the target to form double-stranded products and was cleaved by duplex-specific nuclease (DSN) enzyme, causing the liposomes to be re-released. Then, as the liposomes in the colorimetric module were lysed and the "cellular" contents were released, a step-by-step "glucose-glucose oxidase-3,3′,5,5′-tetramethylbenzidine (TMB)" colorimetric reaction process catalyzed by the G-quadruplex/hemin was triggered. The grayscale values were recorded and recognized by the smartphone camera for miRNA-21 analysis. The advantages of the present strategy included the portability of smartphone-based colorimetric assay, the encapsulation and transport of reactants by liposomes and the low solvent usage of microfluidic chip. Under optimal conditions, this assay exhibited a wide linear range from 1 pM to 1 nM (r2 = 0.9981), and the limit of detection of miRNA-21 was as low as 0.27 pM. Moreover, the high specificity of this strategy allowed its successful application to the rapid analysis of miRNA-21 in real blood serum samples of people with type 2 diabetes. [Display omitted] • A novel liposome-based microfluidic system combined with a smartphone was designed. • Rapid colorimetric strategy was based on the liposome-triggered sequential reaction. • The simple method was highly sensitive for the specific recognition of microRNA-21. [ABSTRACT FROM AUTHOR]

The significant role of cell-free DNA (cfDNA) for disease diagnosis, including cancer, has garnered a lot of attention. The challenges of creating target-specific primers and the possibility of false-positive signals make amplification-based detection methods problematic. Fluorescent biosensors based on CRISPR-Cas have been widely established, however they still require an amplification step before they can be used for detection. To detect cfDNA, researchers have created a CRISPR-Cas12a-based nucleic acid amplification-free fluorescent biosensor that uses a combination of fluorescence and colorimetric signaling improved by duplex-specific nuclease (DSN). DSN-assisted signal recycling is initiated in H1@MBs when the target cfDNA activates the CRISPR-Cas12a complex, leading to the degradation of single-strand DNA (ssDNA) sequences. This method has an extremely high detection limit for the BRCA-1 breast cancer gene. In addition to measuring viral DNA in a field-deployable and point-of-care testing (POCT) platform, this fast and highly selective sensor can be used to evaluate additional nucleic acid biomarkers. [Display omitted] • The approach output both colorimetry and fluorescence signals. • The approach is highly-possible to greatly reduce outside noise and increase the precision of the analysis. • The approach displays remarkable selectivity thanks to CRISPR-Cas12a system based accurate target recognition. [ABSTRACT FROM AUTHOR]

Fabric-based microfluidic analytical devices (μADs) have emerged as a promising material for replacing paper μADs thanks to their superior properties in terms of stretchability, mechanical strength, and their wide scope of applicability in wearable devices or embedded in garments. The major obstacle in their widespread use is the lack of a technique enabling their massive fabrication at a negligible-to-nil cost. In response, we report the development of a wax ink with proper thixotropic and hydrophobic properties, fully compatible with automatic screen-printing that allows the one step massive fabrication of microfluidics on a cotton/elastane fabric, with a printing resolution 400 μm (hydrophilic channel) and 1000 μm (hydrophobic barrier), without being necessary any post curing. The cost of the ink (50 g) and of each microfluidic device is ca. 2.3 and 0.007 €, respectively. The active component of the ink was a refined beeswax in a matrix based on ethyl cellulose in 2-butoxy ethyl acetate. Screen-printed fabric μADs were used for the simultaneous colorimetric determination of pH and urea in untreated human sweat by using multivariate regression analysis. This method enabled the direct measurement of urea using urease, regardless of the sweat's pH, and shows strong agreement with a reference method. [Display omitted] • Wax screen-printable ink for massive fabrication of negligible-to-nil cost μFADs. • Printing resolution: 400 μm (hydrophilic channel) and 1000 μm (hydrophobic barrier). • Thermal or UV post curing is not necessary. • Simultaneously determination of pH and urea in untreated human sweat. • Determination of urea, despite the sweat acidity, by multivariate regression analysis. [ABSTRACT FROM AUTHOR]

Sensitively, accurately, and rapidly evaluating edible oils' peroxide value (PV) is significant for safeguarding food quality and safety. However, the conventional detection methods are challenging to meet the above demands due to their complex operation, poor reproducibility, and professional personnel. The colorimetric method is an emerging technique to rapidly and on-site determine the PV of edible oils. CsPbBr 3 NCs, as a novel fluorescent-sensing material, have been applied in the chemical colorimetric analysis. However, the heavy use of high-toxic solvents (toluene, chloroform) in the CsPbBr 3 NCs colorimetric system significant-negatively influences the environment. This study evaluated the performances of CsPbBr 3 NCs in nine low-toxic solvents and investigated the potential response mechanism to PV. The results presented that CsPbBr 3 NCs in ethyl acetate displayed the highest photoluminescent intensity and the most uniform distribution. The results performed that the micro-morphology and crystal structure of CsPbBr 3 NCs in ethyl acetate were similar to that in toluene, demonstrating the potential excellent performance. Under optimum conditions, three methods, including photoluminescence (PL)-decreased, wavelength-shifted, and phone-based colorimetric methods, were established to evaluate PV with the LOD of 0.0034 g/100 g. The PV recovery rates in Soybean oil, Camellia oil, Linseed oil, and Olive oil were from 75.0% to 100.0%, with a relative error below 25%. Furthermore, it was believed that the decreased PL and shifted wavelength originated from the halogen substitution with the crystal-structure destructions and the surface-defect formations. Thus, developing the low-toxic colorimetric CsPbBr 3 NCs system with ethyl acetate could reduce the environmental influence and even enlighten the rise of other green detection methods for PV in edible oils. [Display omitted] • CsPbBr 3 NCs in ethyl acetate displayed the highest performance among 9 reagents. • The structure of CsPbBr 3 NCs in ethyl acetate was similar to that in toluene. • PL-decreased, wavelength-shifted, and phone-based methods were built to detect PV. • The LOD of the as-established methods was 0.0034 g/100 g. • The mechanism of CsPbBr 3 NCs to PV was crystal destruction and defects dot formation. [ABSTRACT FROM AUTHOR]

The facile detection of total antioxidant capacity (TAC) is limited by in-situ analysis, because it usually requires complex laboratory equipments. Here, a colorimetric assay for TAC detection is developed based on the peroxidase-like activity of iron-doped carbon nitride (Fe/NC) and the smartphone platform. The peroxidase-like activity of carbon nitride is greatly improved by the introduction of Fe atoms, and the active sites turn to Fe-N x coordination groups in the Fe/NC. The inhibition mechanism of the chromogenic reaction for different kinds of antioxidants is also studied. The colorimetric assay is fabricated by the relationship of absorbance-color-antioxidant content and applied successfully to the TAC detection of several fruit juicesand commercial beverages. This work not only provides a promising approach for convenient in-situ TAC assay without the use of large instruments, but also expands the application of nanozymes in nutritional value assessment of foods. The Fe atom-containing carbon nitride shows greatly improved peroxidase-like activity and can be conveniently used for the on-site smartphone-based colorimetric assay of total antioxidant capacity of foods. [Display omitted] • The peroxidase-like activity of C 3 N 4 is greatly improved by Fe atom doping. • The newly formed Fe-N x serve as the main active sites in the Fe/NC nanozyme. • The antioxidants content are tested and different mechanisms are proposed for AA or GSH/Cys. • RGB model of smartphone can be used for on-site colorimetric assay of TAC in food samples. [ABSTRACT FROM AUTHOR]

The use of the RGB color model in colorimetric chemical sensing via imaging techniques is widely prevalent in the literature. However, the lack of specificity in the selection of RGB color space during capture and analysis presents a significant challenge in creating standardised methods for this field and possible discrepancies. In this study, we conducted a comprehensive comparison and contrast of a total of 68 RGB color spaces to evaluate their respective impacts on colorimetric bio/chemical sensing. We explore the impact of dynamic range, sensitivity, and limit of detection, and show that the lack of specificity in RGB color space selection can significantly impact colorimetric chemical sensing by 42–77%. We also explore the impact of underlying RGB comparisons and demonstrate a further 18.3% discrepancy between RGB color spaces. By emphasising the importance of proper RGB color space selection and handling, our findings contribute to a better understanding of this critical area and present valuable opportunities for future research. We further provide valuable insights for creating standardised methods in this field, which can be utilised to avoid discrepancies and ensure accurate and reliable analysis in colorimetric bio/chemical sensing. [Display omitted] • Unspecified RGB color spaces can compromise chemical sensing via imaging techniques. • Sensory characteristics significantly affected by RGB color space selection (42–77%). • Conversion between RGB spaces can lead to further discrepancies (18%). • 68 RGB color spaces compared - proper selection is critical for accurate analysis. • Proposed method herein can contribute to standardised methods/analysis in the field. [ABSTRACT FROM AUTHOR]

The reliable and accurate detection of glyphosate is urgently demanded because it is related to food and environmental safety. In this contribution, a PDA-PEI/Cu2+ complex that possesses peroxidase-mimetic activity and stimulus-responsive fluorescence was fabricated by coordinating Cu2+ with polydopamine-polyethyleneimine copolymer dots (PDA-PEI CPDs). With the introduction of Cu2+, the fluorescence intensity of PDA-PEI CPDs dropped sharply owing to the electron transfer effect. As a peroxidase-mimicking nanozyme, the PDA-PEI/Cu2+ complex owns catalytic capacity to oxidize the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue oxTMB, leading a further fluorescence quenching by internal filtering effect by oxTMB. Once the glyphosate participated, the fluorescence signal of PDA-PEI CPDs is recovered significantly because of the formation of more stable Glyp-Cu2+ complexes, meanwhile the peroxidase-mimicking activity of PDA-PEI/Cu2+ complex could be strongly hindered. According to this principle, a novel and extremely convenient 'turn off' colorimetric and 'turn on' fluorescence sensing platform can be established for dual-mode detection of glyphosate. The favorable sensitivity and selectivity and were verified in the analysis of glyphosate in the environment through the marriage of dual-signal sensing platform. The detection limit of the dual-mode glyphosate sensing platform was 103.82 ng/mL for colorimetric assay and 16.87 ng/mL for fluorescent assay, respectively. Satisfactory recoveries in the range of 96.40%–104.66% were obtained, indicating the potential of this method for application in complicated real sample. Thereby, this strategy broadens the applications of polydopamine nanomaterials and holds a promising application in determination of pesticide residues. A dual-mode colorimetric-fluorescent sensing platform based on bifunctional Cu(II)-containing polydopamine-polyethyleneimine copolymer dots (PDA-PEI CPDs) for detection of glyphosate in the environment has been reported. This dual-mode strategy enables high sensitivity and selectivity for quantitative analysis of glyphosate. The reliable and accuracy detection of glyphosate in the real samples has also been proved. Taking the advantages of the specific bifunction feature of bifunctional Cu(II)-containing polydopamine-polyethyleneimine copolymer dots, it is anticipated that such a novel strategy based on dual-mode sensing platform with stimulus-responsive fluorescence and peroxidase-mimetic activity could enable hold promising applications in environmental analysis. Furthermore, it is believed that the proposed method can provide a new paradigm for the exploration and represent a development of polydopamine nanomaterials, which open a new window for the design of multifunctional materials with a simple composition. [Display omitted] • Novel bifunctional PDA-PEI/Cu2+ complex based sensing strategy was developed. • PDA-PEI/Cu2+ complex serve as fluorescent indicator and peroxidase mimetic. • Dual-mode glyphosate sensing platform is reported. • The high selectivity and sensitivity were achieved. • This strategy enables detection of glyphosate in the environment. [ABSTRACT FROM AUTHOR]

The microbial environment greatly affects the performance of colourimetric sensors, especially the interference of bacteria in the sample detected. This paper reports the fabrication of an antibacterial colorimetric sensor based on V 2 C MXene synthesized via simple intercalation and stripping. The prepared V 2 C nanosheets can mimic oxidase activity towards 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation without exogenously adding H 2 O 2. Further mechanistic studies showed that V 2 C nanosheets could effectively activate the oxygen adsorbed on their surface, which in turn causes an increase in the bond length and a decrease in the magnetic moment of oxygen through electron transfer from the nanosheet surface to O 2. The V 2 C nanosheets also exhibited excellent broad-spectrum antibacterial activity through the outbreak of reactive oxygen species. Owing to its unique catalytic activity and the inherent antibacterial ability for mimicking oxidase, a colorimetric sensing platform was developed to effectively determine L-cysteine levels at a detection limit of 30.0 nM (S/N = 3). It is impressive that the detection results of L-cysteine in various complex microbial environments are also very satisfactory. This study broadens the biological use of MXene-based nanomaterials through their satisfactory enzymatic activity and provides a simple and efficient colorimetric strategy for detection techniques used in complex microbial environments. The V 2 C MXene nanosheets possessed specific oxidase-like activity towards 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation avoiding the use of H 2 O 2. The characterization and simulation indicated that V 2 C nanosheets can effectively activate the oxygen adsorbed on its surface, in turn, causes an increase in bond length and a decrease in magnetic moment of oxygen through electron transfer from nanosheets surface to O 2. Due to exceptional ROS production capability, V 2 C nanosheets also has the significant antibacterial effect on gram-positive bacteria and gram-negative bacteria. Therefore, an effective colorimetric sensing of L-cysteine sensing has been developed in complex media with high selectivity and sensitivity. [Display omitted] • An antibacterial colorimetric sensor based on V 2 C MXene was developed. • The V 2 C nanosheets have distinctive oxidase-like activity avoiding the use of H 2 O 2. • The V 2 C nanosheets exhibit excellent broad-spectrum antibacterial activity. • The role of V 2 C is to effectively activate O 2 through electron transfer. • The L-cysteine detection system have the excellent anti-interference ability. [ABSTRACT FROM AUTHOR]

Automated, colorimetric analysis of nutrients in samples with high and variable salinity can be time consuming due to the need to matrix match calibration and reference solution matrices with those of samples—particularly when using flow-based analyzers that are prone to detector artifacts caused by optical inhomogeneities, "schlieren," that form at interfaces between samples and deionized water carrier or wash solutions. Such detector artifacts do not occur in discrete analyzers. Here we report spike recoveries when nitrite plus nitrate, nitrite, ammonia, orthophosphate, and silica were determined in estuarine waters, seawater, and hypersaline surface water samples without calibrator matrix matching using an automated discrete analyzer set up with standard colorimetric methods. Salinities of these samples varied from 0 to 22%. Spike recoveries and precision were excellent for nitrite and nitrite plus nitrate analyses in samples with salinities up to 15%, for ammonia in samples with salinities up to about 1.7%, and for orthophosphate in samples with salinities up to about 3.5%. Orthophosphate spike recoveries were high biased in hypersaline matrices (salinity >3.5%), likely due to an unidentified sample matrix interference. After applying linear correction factors to account for chemistry-related salt effects, spike recoveries were acceptable for ammonia analyses in samples with salinities in the range of 1.7–3.5%, and for silica analyses in samples with salinities in the range of 0–3.5%. Image 1 • Measurement of nutrients in samples with variable salinity can be challenging when using flow-based colorimetry. • The need for matrix matching in nutrient methods for estuarine and seawater samples is eliminated with discrete analyzer. • Analysis of nutrients in hypersaline waters is simplified with discrete analyzer. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen sulfide (H 2 S) plays a vital role in numerous biological processes in living organisms. To better understand its functions, a fluorescent probe to fast and sensitively detect H 2 S is imminently needed. Keep this in mind, we reasonably designed probe DHC for detecting H 2 S based on α, β-unsaturated ethanoylcoumarin fluorophore. The limit of detection (LOD) is found to be as low as 5 × 10−8 M, which is superior to most reported fluorescent probes to detect H 2 S. Furthermore, the wide pH range of 4–11 makes it capable of application in biological systems. Most importantly, MTT assays and cell imaging experiments indicate that probe DHC has hypotoxicity and outstanding membrane permeability, which makes DHC successful imaging of H 2 S in Baby Hamster Syrian Kidney (BHK) cells. Graphical abstract A coumarin-based colorimetric fluorescent probe for rapid response and highly sensitive detection of hydrogen sulfide in living cells. fx1 Highlights • Spectroscopic studies show that DHC has excellent specificity and a short reaction time (＜1 min). • The detection limit of DHC is found to be 50 µM, which is superior to the most reported fluorescent probes to detect H 2 S. • The cytotoxic activity suggests that DHC has low cytotoxicity. • Confocal fluorescence imaging shows that DHC can be applied to monitor intracellular H 2 S. [ABSTRACT FROM AUTHOR]

Abstract A novel colorimetric nanosensor has been developed for high sensitive and selective detection of cysteine (Cys) based on the intrinsic oxidase-like activity of cerium nanotube coordinated with aspartic acid (Asp/Ce-NT). Under the function of Asp/Ce-NT, colorimetric reaction of TMB (3,3′,5,5′-tetramethylbenzidine) takes place within five minutes without the assistance of additional oxidizing agents (e.g. H 2 O 2). The oxidase-like activity of Asp/Ce-NT can be modulated by adjusting the ratio of Asp to Ce(NO 3) 3 during preparation process as well as the chirality of Asp (levogyration/ L and dextrorotation/ D). Compared with D -Asp/Ce-NT, L -Asp/Ce-NT exhibits more excellent activity which can be specifically depressed by Cys. According to the developed strategy, limit of detection for Cys reaches as low as 33.2 nM. The avoiding use of H 2 O 2 would improve the repeatability and reliability. Nice recoveries from 92.5% to 100.8% are found for Cys detection in serum samples. The developed sensing assay is cost-effective and operated in H 2 O 2 -free and enzyme-free condition, providing an effective rapid detection way for practical application in disease monitoring and diagnosis. Graphical abstract fx1 Highlights • A novel Asp/Ce nanotube-based nanosensor for cysteine (Cys) has been developed. • Asp/Ce nanotube can catalyze colorimetric reaction of TMB in H 2 O 2 -free condition. • The peroxidase-like activity of Asp/Ce nanotube can be depressed by cysteine. • The Cys detection presents excellent sensitivity, selectivity and repeatability. • The assay offers an effective mix-then-test way for rapid detection Cys in serum. [ABSTRACT FROM AUTHOR]

Abstract Acetate ion was widely used in pH buffer to control pH environment. Here we firstly found that acetate ion had mimic peroxidase activity. Acetate ions are capable of catalyzing the decomposition of hydrogen peroxide and play a similar role to that of horseradish peroxidase (HRP). Acetate catalyzes the oxidation of tetramethylbenzidine (TMB) by H 2 O 2 , which is the product of the reaction of glucose and glucose oxidase. A colorimetric sensor for H 2 O 2 and glucose was developed using acetate ions. The linear regression equation for H 2 O 2 was A = 0.0029 C + 0.0530 (C (μmolL−1), R = 0.9978), and the detection limit was 3.0 μmolL−1, whereas that for glucose was A = 0.0021 C + 0.0709 (C (μmol L−1), R = 0.9977), and the detection limit was 4.0 μmol L−1. Moreover, the proposed method was successfully applied for the detection of H 2 O 2 in human urine and glucose in human serum; thus, the proposed method could be used for the diagnosis of illness or disease. A single-enzyme-based glucose test paper was firstly prepared and tested for semi-quantitative analysis of glucose. Graphical abstract fx1 Highlights • The authors firstly discovered the peroxidase-mimicking activity of acetate ion. • Acetate ion was applied to develop colorimetric sensor for H 2 O 2 and glucose based upon its catalysis oxidation of TMB. • Single-enzyme based test paper for glucose was firstly prepared according to the novel characteristics of acetate ions. [ABSTRACT FROM AUTHOR]

Abstract In this work, a simple, rapid, and highly sensitive colorimetric assay for the determination of glutathione (GSH) was developed. It employs human serum albumin (HSA)-templated MnO 2 nanosheets as an artificial oxidase. HSA-templated MnO 2 nanosheets can oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue oxTMB product with a significant increase in absorbance at 652 nm in the absence of H 2 O 2. When GSH is introduced, the MnO 2 nanosheets are reduced to Mn2+ ions, thereby inhibiting the formation of oxTMB. Based on these findings, a simple colorimetric assay was developed for the detection GSH in the range of 10 nM to 5 μM with a low detection limit of 5.6 nM. Importantly, the proposed method was successfully used for quantitative determination of GSH in biological fluids, such as human serum samples. Graphical abstract A colorimetric method for facile sensing of GSH based on HSA-templated MnO 2 nanosheets with oxidase-like activity. fx1 Highlights • We developed a simple, rapid, and highly sensitive colorimetric assay for the determination of glutathione (GSH). • The colorimetric assay is based on human serum albumin (HSA)-templated MnO 2 nanosheets as an artificial oxidase. • The practicality of the proposed method was demonstrated by the detection of GSH in complex matrix. [ABSTRACT FROM AUTHOR]

Abstract The present paper describes a laboratory investigation conducted with the main aim to compare two colorimetric methods (1-(2-pyridylazo)-2-naphthol (PAN) from HACH® and porphyrin ligand (T-(4CP)P)) with ICP analyses for the evaluation of low concentrations of manganese in water. The colorimetric porphyrin method was found to provide reliable results compared to those obtained by inductively coupled plasma - optical emission spectroscopy (ICP-OES) even at low Mn2+ concentrations (<10 µg L−1). The presence of MnO 2 particles results in an overestimation of the dissolved Mn2+ if unfiltered samples are analyzed by ICP and PAN methods. The presence of particles does not significantly impact sample analysis by porphyrin (T-(4CP)P) colorimetry. Although ICP-OES is still the analytical approach of reference, the porphyrin colorimetric method displays a high detection range and precision and could be a suitable on-site alternative to the current widespread use of the PAN method. In all cases, for both colorimetric methods, the use of Rochelle salt is recommended to alleviate calcium cation interference. Graphical abstract fx1 Highlights • The Porphyrin method had a lower LOD (0.84 µg L−1) and LOQ (2.80 µg L−1) than the PAN method. • As opposed to the PAN method, the porphyrin method is selective toward dissolved Mn(II) detection. • The Porphyrin method exhibits high selectivity to dissolved Mn(II). • Filtration can interfere with Mn2+ detection due to issues related to adsorption phenomena. • The Porphyrin method is a simple, low-cost and robust method to confirm Mn concentration below 20 µg L-1. [ABSTRACT FROM AUTHOR]

Abstract In this work, a novel fluorescence (FL) probe for selective and sensitive detection of Cys with colorimetric and FL dual signal changes was reported. The probe was synthesized by two step of sulfonamide reaction coupling between a sulfonyl benzoxadiazole (SBD) dye and dansyl chloride linked with rigid piperazine group. The probe showed a specific off-on response to Cys in aqueous solution with nanomolar LOD, and without interference by a range of amino acids and several competing analytes. Upon addition of Cys, the probe will undergo sequential substitution and intramolecular rearrangement reactions, yielding a 4-amino SBD derivative, which results in generation of strong yellow fluorescence emission at 575 nm accompanied by a two-step red shift in the absorption spectral. Moreover, it can be used for imaging of endogenous Cys in living cells. Graphical abstract fx1 Highlights • A fluorescence probe for highly discriminating detection of Cys. • The probe detects Cys selectively and sensitively with dual signal changes. • The probe has proven suitable for monitoring endogenous Cys in living cells. [ABSTRACT FROM AUTHOR]

Abstract In the present study, a microfluidic platform was exploited for electromembrane extraction. For device integration as a lab-on-a-chip system, the detection step was carried out by a colorimetric method based on fluorescence quenching of quantum dots. The model analyte was transferred under a pulsed applied electrical field across a polypropylene membrane, impregnated with 1-Octanol, into a final aqueous acceptor phase. The obtained acceptor phase was added into a solution containing CdTe quantum dots. Quenching of the quantum dots was tracked by analyzing the main three color components of red, green, and blue in different concentration levels of the analyte. All effective parameters on the extraction efficiency, fluorescence detection, and synthesis of quantum dots were optimized. Under the optimal conditions, the detection was accomplished by three different detection methods including HPLC-UV, spectrofluorometric detection, as well as colorimetry detection via a smartphone. Calibration curves were linear in the range of 2.0–500 µg L−1 for LC-UV, 30–2500 µg L−1 for fluorescence detection, and 2.5–20 µg mL−1 for image analysis. Inter- and intra-assay relative standard deviations were less than 10.1% in all detection modes. Graphical abstract fx1 Highlights • A microfluidic platform was exploited for pulsed electromembrane extraction. • Portable colorimetric detection of ciprofloxacin was done based on RGB analysis. • The efficiency of extraction system was studied with respect to the sample flow. • The system paves a new way for point-of-care colorimetric detections. [ABSTRACT FROM AUTHOR]

Abstract In this study, the asymmetrically modified gold nanoparticles (AuNPs) with relatively large size are proposed for highly sensitive detection of melamine in raw milk. At first, we found that the sensitivity of colorimetric detection of melamine based on the conventional citrate-stabilized AuNPs could be significantly increased (limit of detection by visual observation: from 1 μmol L−1 to 1 nmol L−1) via enlarging the size of AuNPs (from 13 to 42 nm). However, the large-sized AuNPs are unstable in the solution, and the accuracy of relevant aggregation-based colorimetric detection method is dramatically decreased due to the rapid evanishment of the color of solution caused by the precipitation of large-scaled AuNPs aggregates after introducing melamine. In view of this limitation, the stabilizing agent polyethylene glycol (PEG) is introduced onto the selected area at the surface of AuNPs to stabilize the large-sized AuNPs sensor and further adjust the aggregation behavior in an oriented and controllable manner. As a result, the addition of melamine into asymmetrically PEGylated AuNPs with large size could still induce a color change from purple to blue, but the color change could be maintained in aqueous solution for a long time. This improvement is mainly caused by forming stable and oriented oligomers of AuNPs taking advantage of the asymmetrical modification of AuNPs with PEG chain in this system. Such a way of aggregation leads to remarkably enhanced long-term stability and an at least 2 orders of magnitude wider dynamic detection range (1.05 nmol L−1 to 1 mmol L−1) compared with conventional AuNPs sensors. Finally, such a novel asymmetrically modified AuNPs sensor is successfully applied to detect melamine in the raw milk with the satisfactory spiked recovery from 99.6% to 103.7% and RSD of about 3.0%. This work provides a sensitive and reliable method to detect melamine in pretreated milk, indicating a new avenue to make innovation on colorimetric sensors for real sample detection. Graphical abstract fx1 Highlights • The large-sized PEGylated AuNPs are prepared for detection of melamine with a low LOD and an extremely wide linear range. • The asymmetrically PEGylated AuNPs aggregate in an oriented and controlled manner, improving the stability of detection. • This is the first example for sensitive and accurate detection of melamine in raw milk using the PEGylated AuNPs. [ABSTRACT FROM AUTHOR]

Abstract We report the colorimetric detection of dopamine (DA) on microfluidic paper-based analytical devices (μPADs) using an oxidation-reduction method. Here, dopamine reacts with ferric chloride forming reduced Fe2+ that subsequently reacts with phenanthroline to form the red tris(1,10-phenanthroline)iron(II) complex. The devices were fabricated by wax printing and changes in color intensity were recorded using a common cell phone. Subsequent analysis using Photoshop software, yielded a limit of detection (LOD) for DA of 0.37 μmol/L with a linear range of 0.527–4.75 μmol/L and relative standard deviation of 0.11% (inter-day) and 0.15% (intra-day) for n = 15 paper chips. The effects of detection conditions have been investigated and are discussed. Cow serum samples and human blood serum and plasma samples were detected. The work, herein, demonstrates the potential of this method as a low cost and rapid colorimetric technique to detect DA in real samples. Graphical abstract fx1 Highlights • A colorimetric detection of dopamine (DA) on microfluidic paper-based analytical devices (μPADs) was developed. • The changes in color intensity were recorded using a common cell phone and analysis using Photoshop software. • The method provide an inexpensive and selective determination of DA with low LOD. It does not need other assistances. • The relative standard deviation (RSD) of inter-day (n =15) and intra-day (n =15) is no more than 0.2%. • Cow serum samples and human serum and plasma samples were detected. [ABSTRACT FROM AUTHOR]

Abstract Fluorescent eggshell membrane-templated gold nanoclusters (Au-ESM) can be obtained in a facile and low-cost manner in this study. The fluorescence of the Au-ESM may be significantly quenched by mercapto-compounds and peroxidase-like activity of Au-ESM could be regulated by the reaction process with glutathione. Moreover, the catalytic activity of the mimetic enzyme membrane could be modulated by immunoreactions. An immunoassay for colorimetric determination of staphylococcal enterotoxins B (SE-B) using colored gold nanoparticles was established based on the catalytic activity adjusted by the target molecules. This colorimetric assay can detect SE-B at the concentration range of 0.4–20 ng/mL and the limit of detection (LOD) is 0.12 ng/mL. As a practical application, the proposed colorimetric assay was further utilized to detect SE-B in food samples such as flour, corn and rice, requiring very low volume of sample and exhibiting great sensitivity and high accuracy, which provides promising platform for development of point-of-care diagnostic devices with biomedical and food safety applications. Graphical abstract fx1 Highlights • A regulatable peroxidase-like egg shell membrane embedded gold nanoclusters (Au-ESM) was prepared with simple method. • The Au-ESM serves as substrate to develop plasmonic colorimetric assay for detecting staphylococcal enterotoxin B. • The colorimetric assay provides rapid detection of staphylococcal enterotoxin B in food samples. [ABSTRACT FROM AUTHOR]

Abstract We present a fluorescence turn-on and colorimetric dual-readout sensing system for the sensitive detection of alkaline phosphatase (ALP) activity via self-assembled gold nanoclusters (AuNCs) based on fluorescence resonance energy transfer (FRET). The positively charged polyallylamine hydrochloride (PAH)-crosslinked AuNCs (PAH-AuNCs) with aggregation-induced enhancement (AIE) characteristics can electrostatically adsorb the negatively charged 2, 6-dichlorophenolindophenol (DCIP). Thus, the fluorescence of PAH-AuNCs can be significantly quenched by the occurrence of FRET from PAH-AuNCs to DCIP. However, the reduction reaction of DCIP from blue to colourless by L -ascorbic acid (AA) which is generated by the ALP catalyse hydrolysis of 2-Phospho- L -ascorbic acid (AAP) disturbs the FRET between PAH-AuNCs to DCIP. The quenched PAH-AuNCs fluorescence can be recovered efficiently. The strategy of first creating AIE-enhanced PAH-AuNCs, followed by the effective FRET manipulation, is an important contribution to the sensitive detection of ALP. More importantly, the distinct colorimetric signal change can be used to visually distinguish the presence of ALP. More importantly, the distinct colorimetric signal change can be used to visually distinguish the presence of ALP. Good linear relationships of fluorescence and colorimetric sensing towards ALP were obtained in the range from 0.5 to 100 U/L, and the detection limits were 0.2 U/L and 0.5 U/L, respectively. In addition, the proposed FRET sensing system was applied to the detection of ALP in human serum samples with satisfactory results. The simple and efficient sensing approach proposed here has the potential to promote the development of chemo/biodetection methods using fluorescence and colorimetric dual-readout. Graphical abstract Sensitive fluorescence turn-on and colorimetric dual-readout sensing of ALP based on the DCIP mediated FRET on PAH-AuNCs was reported. fx1 Highlights • PAH-AuNCs with AIE characteristic were formed based on electrostatic self-assembly. • The fluorescence of PAH-AuNCs can be quenched 97% by DCIP due to FRET. • The fluorescence and colorimetric dual-readout assay for ALP detection was developed. • The LODs of the dual-readout assay are 0.2 U/L and 0.5 U/L, respectively. • The recoveries for spiked human serum samples are in the range from 96.4% to 105.5%. [ABSTRACT FROM AUTHOR]

Abstract A non-invasive textile-based colorimetric sensor for the simultaneous detection of sweat pH and lactate was created by depositing of three different layers onto a cotton fabric: 1.) chitosan, 2.) sodium carboxymethyl cellulose, and 3.) indicator dye or lactate assay. This sensor was characterized using field emission scanning electron microscopy and fourier transform infrared spectroscopy. Then, this sensor was used to measure pH and lactate concentration using the same sweat sample. The sensing element for sweat pH was composed of a mixture of methyl orange and bromocresol green while a lactate enzymatic assay was chosen for the lactate sensor. The pH indicator gradually shifted from red to blue as the pH increased, whereas the purple color intensity increased with the concentration of lactate in the sweat. By comparing these colors with a standard calibration, this platform can be used to estimate the sweat pH (1−14) and the lactate level (0–25 mM). Fading of the colors of this sensor was prevented by using cetyltrimethylammonium bromide (CTAB). The flexibility of this textile based sensor allows it to be incorporated into sport apparels and accessories hence potentially enabling real-time and continuous monitoring of sweat pH and lactate. This non-invasive sensing platform might open a new avenue for personal health monitoring and medical diagnosis as well as for determining of the physiological conditions of endurance athletes. Graphical abstract fx1 Highlights • Non-invasive textile-based colorsensor for detection of sweat pH and lactate was created. • This sensor was simplifyfabricated by coating of cotton with chitosan, sodium carboxymethyl cellulose,indicator dye or lactate assay. • The sensor was able to differentiate sweat pH and lactate levels in human sweat. • This sensor was applied for simultaneous detection of sweat pH and lactate in human volunteers. [ABSTRACT FROM AUTHOR]

Abstract A rapid and sensitive colorimetric detection method for the determination of Hg2+ has been successfully developed in this research. Citrate−functionalized silver nanotriangles (AgTrngs) were synthesized via one−pot sodium borohydride method with the edge−length range of 30 − 40 nm. The obtained AgTrngs were fully characterized using UV−Vis spectrophotometry, transmission electron microscopy (TEM), energy dispersed spectroscopy (EDS) and X−ray diffractometer. The efficiency of the developed sensor was optimum at pH= 8 due to interfering effect of H+ ions for Hg2+ under acidic conditions. The successful detection of mercury in aqueous solutions in the concentration range of 10 nmol L−1–50 μmol L−1 indicated the applicability of the developed sensor for effective monitoring and controlling the level of Hg2+ in industrial effluents. The ability of Hg2+ ion to interact with Ag and form the Hg−Ag alloy (amalgam) over the surface of AgTrngs resulted in an obvious color change from blue to violet. UV−Vis spectrophotometry showed that the sensor has the limit of detection (LOD) value of as low as 4 nmol L−1 which was below the safety level of Hg2+ions (10 nmol L−1) in drinking water. The proposed method can be used for on−line determination of Hg2+ in the complex aqueous solutions. Graphical abstract fx1 Highlights • Development of a label−free colorimetric approach for the determination of Mercury ion as a toxic chemical. • In-plane dipole and in-plane quadrapole resonances of Ag nanotriangles wereimproved the sensitivity of developed sensor. • The developed colorimetric sensor has a wide dynamic range of 10 nmol L−1–50 μmol L−1 with the LOD as low as 4 nmol L−1. [ABSTRACT FROM AUTHOR]

A two-dimensional (2D) Ni based metal-organic framework (MOF) nanosheets were synthesized using a one-step solvent-thermal method. The as-prepared nanosheets were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and energy disperse spectroscopy (EDS) mapping. Ni-MOF nanosheet was first time found to used as a peroxidase mimetic with catalytic activities and could catalyze the oxidation of the substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H 2 O 2 ). Catalytic mechanism analysis suggested the enzymatic kinetics of Ni-MOF nanosheets followed typical Michaelis-Menten theory and Ni-MOF nanosheets possess a higher affinity for two substrates (TMB and H 2 O 2 ) than horseradish peroxidase (HRP). Furthermore, Ni-MOF nanosheet was applied to establish an H 2 O 2 colorimetric sensor which deserves a wide linear range of 0.04 ~ 160 μM and a low detection limit of 8 nM. Also the application of this sensor for H 2 O 2 detection in human serum and disinfectant was demonstrated and satisfactory results were obtained. Thus, the simple and sensitive Ni-MOF/TMB/H 2 O 2 colorimetric system has great promising applications in clinical medicine and food environment analysis. [ABSTRACT FROM AUTHOR]

A highly sensitive colorimetric method for detection of alkaline phosphatase (ALP) and carbohydrate antigen (CA125) was developed, which was achieved by ascorbic acid (AA) - mediated enhanced growth of silver nanoparticles (AgNPs) promoted with NaBH 4 as pre-reducing agent. With prereduction by NaBH 4 , the AA controlled growth of AgNPs was promoted and the localized surface plasmon resonance absorbance was much higher compared with that without prereduction. ALP could hydrolyze L -ascorbic acid 2-phosphate trisodium salt (AAP) to form AA, which could then reduce Ag + to AgNPs resulting in the enhancement of localized surface plasmon resonance peak of AgNPs and accompanying the color change from colorless to bright yellow. Benefiting from the highly sensitive response of Ag + to AA, the detection limit for ALP could be lowered to 0.003 U L −1 , and the proposed plasmonic ELISA could achieve a low detection limit of 1.75 U mL −1 for CA125. Moreover, this method was validated for the analysis of ALP and CA125 in human serum samples, giving results matched well with conventional method, demonstrating the potential application of the developed method in clinical diagnosis. [ABSTRACT FROM AUTHOR]

Aroma affects the quality of black tea, and the rapid evaluation of aroma quality is the key to realize the intelligent processing of black tea. A simple colorimetric sensor array coupled with a hyperspectral system was proposed for the rapid quantitative detection of key volatile organic compounds (VOCs) in black tea. Feature variables were screened based on competitive adaptive reweighted sampling (CARS). Furthermore, the performance of the models for VOCs quantitative prediction was compared. For the quantitative prediction of linalool, benzeneacetaldehyde, hexanal, methyl salicylate, and geraniol, the CARS–least-squares support vector machine model's correlation coefficients were 0.89, 0.95, 0.88, 0.80, and 0.78, respectively. The interaction mechanism of array dyes with VOCs was based on density flooding theory. The optimized highest occupied molecular orbital levels, lowest unoccupied molecular orbital energy levels, dipole moments, and intermolecular distances were determined to be strongly correlated with interactions between array dyes and VOCs. [Display omitted] • A novel method was used for quantitative monitoring black tea fermentation aroma. • A simple CSA consisting of four dyes enables quantitative monitoring of five VOCs. • The best Rp value of CARS-LSSVM quantitative model for VOCs was 0.95. • DFT was applied to investigate the binding mechanism of CSA with VOCs. [ABSTRACT FROM AUTHOR]

The biological molecules used in the sandwich detection method have problems such as complex extraction processes, high costs, and uneven quality. Therefore we integrated glycoprotein molecularly controllable-oriented surface imprinted magnetic nanoparticles (GMC-OSIMN) and boric acid functionalized pyrite nanozyme probe (BPNP) to replace the traditional antibody and horseradish peroxidase for sensitive detection of glycoproteins through sandwich detection. In this work, a novel nanozyme functionalized with boric acid was used to label glycoproteins that were captured by GMC-OSIMN. The substrate in the working solution catalyzed by the nanozyme labeled on the protein underwent visible color changes to the naked eye, and the generated signal can be quantitatively detected by a spectrophotometer, and the best color development conditions of the novel nanozyme under the influence of many factors were determined through multi-dimensional investigation. The optimum conditions of sandwich are optimized with ovalbumin (OVA), and it was extended to the detection of transferrin (TRF) and alkaline phosphatase (ALP) in the application. The detection range for TRF was 2.0 × 10−1-1.0 × 104 ng mL−1 with a detection limit of 1.32 × 10−1 ng mL−1, The detection range for ALP was 2.0 × 10−3-1.0 × 102 U L−1 with the detection limit of 1.76 × 10−3 U L−1. This method was subsequently used to detect TRF and ALP levels in 16 liver cancer patients, and the standard deviation of the test results of each patient was less than 5.7%. [Display omitted] • Capture unit with dual recognition of boron affinity and imprinted cavity. • Hydrophilic molecules on capture unit reduce non-specific adsorption of proteins. • Pyrite nanoenzyme with high catalytic activity is used to rapidly output signals. • Combination of physiological pH and low non-specific labeling pH environments. [ABSTRACT FROM AUTHOR]

We report here for the first time a self-powered biosensing platform based on graphene/graphdiyne/graphene (GDY-Gr) heterostructure substrate material for ultrasensitive hepatocarcinoma marker (microRNA-21) detection in both electrochemical and colorimetric test modes. The dual-mode signal intuitively displayed on a smartphone fundamentally improves the detection accuracy. In electrochemical mode, the calibration curve is established in the linear range of 0.1–10000 fM, and the detection limit is as low as 0.333 fM (S/N = 3). Simultaneously, colorimetric analysis of the miRNA-21 is realized by using ABTS as an indicator. The detection limit is confirmed as 32 fM (S/N = 3), and miRNA-21 of concentration from 0.1 pM to 1 nM exhibit a linear relationship with R2 = 0.9968. Overall, the combination of GDY-Gr and multiple signal amplification strategy significantly improved the sensitivity by 310 times compared with traditional enzymatic biofuel cells (EBFCs) based detection platform, showing broad application prospects for on-site analysis and future mobile medical services. [Display omitted] • Ultra-sensitive self-powered biosensor platform based on graphdiyne/graphene heterogeneous is designed for liver cancer markers detection. • Dual-mode signal intuitive displayed on a smartphone and fundamentally improve the detection accuracy. • Detection limit are as low as 0.33 fM and 32 fM (S/N = 3) in electrochemical and colorimetric analysis mode, respectively. [ABSTRACT FROM AUTHOR]

Iodine intake remains a major public health concern, as both iodine excess and deficiency are related to adverse effects on health. Therefore, developing simple and economical methods to detect I− is still in great demand. Herein, we constructed a visual I− sensing platform based on the uncoated Ag–Ti 3 C 2 nanohybrids using methyl orange (MO) as a colorimetric indicator. Plasmonic nanostructures are frequently employed in colorimetric analysis, but uncoated Ag nanoparticles (NPs) are unstable because their surface energies are usually high. Considering that Ag NPs can be etched by I− via forming Ag–I bond, we introduce Ag–Ti 3 C 2 nanohybrids because uncoated Ag NPs with immaculate surfaces are more conducive to binding with I− and being etched. Dissolved O 2 molecules adsorbed on Ti3+ of Ti 3 C 2 MXenes enable the in situ generation of H 2 O 2 by iodine-etching of uncoated Ag–Ti 3 C 2 nanohybrids. ∙OH radicals promote the degradation of MO through a self-driven Fenton-like process, exhibiting the color variation from orange to transparent. Under optimal conditions, the absorbance of MO at 465 nm decreases linearly with the concentration of I− in the range of 0.5–300 μM, with a limit of detection as low as 0.31 μM. This work opens the feasibility of iodine-etching of Ag in developing novel probes for facile colorimetric determination of I−. [Display omitted] • H 2 O 2 is generated in situ through the iodine-etching of Ag–Ti 3 C 2 nanohybrids. • Ti 3 C 2 promotes the H 2 O 2 -initiated MO degradation for colorimetric reactions. • The extent of degradation of the MO indicator depends on the concentration of I−. • This colorimetric method has good sensitivity and selectivity for real samples. [ABSTRACT FROM AUTHOR]

A simple colorimetric method using gold nanoparticles (AuNPs) was developed as an efficient strategy for specific and sensitive detection of insecticides that are analogs of nereistoxin (NRT). The AuNPs were synthesized by a surfactant-free sonochemical reaction with ultrasonication at 430 kHz. A color change occurred in the presence of NRT because the AuNPs aggregated if they were coated with a small amount of thioctic acid (TA). At a pH of around 5, the TA adsorbed on the AuNPs was deprotonated, whereas NRT was protonated (NRT-H + ). Adsorption of NRT-H + onto the TA-coated AuNPs surface would decrease the surface charge of the AuNPs, and this resulted in aggregation. Because the aggregation of the TA-coated AuNPs could not be induced by amine compounds without thiol groups, this provided a surface-limited aggregation mechanism for specific sensing of NRT. The absorbance at 700 nm was dependent on the concentration of NRT, and the calibration curve was linear over the concentration range 85 nM (12 ng/mL) to 1000 nM (140 ng/mL). The applicability of the proposed method to detection of trace levels of NRT in environmental water samples was successfully demonstrated using a simple liquid–liquid reverse extraction technique. [ABSTRACT FROM AUTHOR]

A new colorimetric and fluorescent chemosensor for visual determination of carbonate ions was developed by the microwave assisted solvent free synthesis of 7,8-dihydroxy-3-(4-methylphenyl) coumarin ( DHMC ). The structural characterization of DHMC was confirmed by microanalysis and spectroscopy methods (MALDI-TOF, FT-IR, 1 H NMR, 13 C NMR, and 2D HETCOR). The binding behaviors of DHMC were investigated towards various anions by UV–vis and fluorescence spectroscopy. DHMC showed a selective and sensitive fluorometric and colorimetric responses towards carbonate ion over other anions. The detection limit of CO 3 2- was found to be 1.03 µM. Moreover, the fluorescence imaging in living cells suggests that DHMC has a great potential in the biological imaging application. It has been demonstrated that DHMC can be used as a rapid and reliable sensor for the determination of carbonate anion in a variety of practical applications. [ABSTRACT FROM AUTHOR]

A highly sensitive and selective colorimetric assay is proposed for the detection of mercury ions (Hg 2+ ), cadmium ions (Cd 2+ ) and ascorbic acid (AA) using trithiocyanuric acid (TMT) functionalized gold nanoparticles (TMT-AuNPs). TMT-AuNPs are dispersed in 40 mM NaCl solution, while the presence of Hg 2+ and Cd 2+ can induce TMT-AuNPs aggregate due to the strong interaction of Hg 2+ and Cd 2+ with TMT. Then the quantitative detection of Hg 2+ and Cd 2+ can be realized in the linear range from 5 × 10 −9 to 1 × 10 −6 M and 1 × 10 −8 to 3 × 10 −7 M, with a lower detection limit of 2.8 nM for Hg 2+ and 3.5 nM for Cd 2+ (S/N = 3), respectively. To distinguish Hg 2+ from Cd 2+ , a reductive biological small molecule ascorbic acid (AA) was used based on the different redox interaction of AA with Hg 2+ and Cd 2+ . When the mixture of AA and Hg 2+ was added into TMT-AuNPs solution, the state of TMT-AuNPs was still dispersed because Hg 2+ was reduced by AA. On the contrary, when the mixture of AA and Cd 2+ was added into TMT-AuNPs solution, the TMT-AuNPs was aggregated and the color of the solution has no obvious change compared to the system of Cd 2+ -TMT-AuNPs since the weak interaction between AA and Cd 2+ . Thus, AA could be detected. A linear correlation exists between the ratio of A 640 /A 520 and the concentration of AA in the range from 1 × 10 −8 to 1 × 10 −6 M with a detection limit of 4.8 nM (S/N = 3). Importantly, it has been successfully applied to determine Hg 2+ , Cd 2+ in lake water and AA in vitamins C tablet. [ABSTRACT FROM AUTHOR]

We have synthesized new colorimetric hydrogen-sensing materials, PdO/metal oxide hybrid nanoparticles, in which palladium oxide was loaded upon surface of substrate materials via an acid-base reaction between a H 2 PdCl 4 solution and substrate materials, ZnO, MgO, TiO 2 , and SiO 2 respectively at 25 °C. The colorimetric hydrogen gas sensing properties of all the samples, PdO/ZnO, PdO/MgO, PdO/TiO 2 and PdO/SiO 2 , were characterized and compared in order to investigate how hydrogen gas sensitivity would be affected by surface property of substrate materials. It was confirmed that the amount of the loaded PdO, which was thought to be closely related with the colorimetric hydrogen sensitivity, was quite different according to the substrate materials and was increased with increasing of the basicity of substrate materials (ZnO > MgO > TiO 2 > SiO 2 ). Consequently, among the PdO/metal oxide hybrid nanoparticles, the largest amount of PdO was observed to be loaded on ZnO substrate nanoparticles due to its highest basicity. The best colorimetric hydrogen gas sensing properties (color difference, ΔE = 71.57) was observed in PdO/ZnO hybrid nanoparticles, showing the most prominent color change from brown to black, when the sample was exposed to hydrogen gas of 4 vol% balanced with nitrogen for 2 min. [ABSTRACT FROM AUTHOR]

The accurate and rapid ochratoxin A (OTA) detection at early stage can prevent people from getting cancer to a great extent due to its strong liver toxicity and renal toxicity. The development of an efficient strategy to detect OTA without sophisticated instruments is highly desired, but still remains a severe challenge. In this communication, a sandwich type point-of-care testing (POCT) immunoassay is developed for OTA detection. The 3-aminopropyltrimethoxysilane-glutaraldehyde (APTMS-GA) is used as color matrix and Au-N-TiO 2 as labels for loading more captured antibodies and glucose oxidases (GOD). When glucose is added, GOD can be catalyzed to produce H 2 O 2 which can weaken the color strength to quantify OTA concentrations. The mean gray values of reacted ITO-based immunosensors can be calculated by the software of Image J. The linear range of OTA is 0.0001–1 ng mL –1 with a low detection limit of 28 fg mL –1 at a signal-to-noise ratio of 3 s. This strategy can achieve the excellent performance without sophisticated instruments. This POCT method may has a potential application in the undeveloped countries with only a camera-equipped cellphone. [ABSTRACT FROM AUTHOR]

An ultrasensitive colorimetric aptasensor was developed for antibiotics detection, with chloramphenicol (CAP) as model target, using DNAzyme labeled Fe-MIL-88-Pt as novel peroxidase mimic signal tags and target-triggered circular strand-displacement polymerization (CSDP) for signal amplification. The system consists of two components which can partially hybridize with each other: one is capture probe which was formed through immobilizing hairpin DNA containing aptamer sequence on magnetic beads (MB-cDNA), another is signal tag which was constructed through labeling single strand DNAzyme (G-quadruplex/Hemin) which can partially hybrid with cDNA on platinum nanoparticles functionalized Fe-MIL-88 (MIL-88-Pt-DNAzyme). All components of MIL-88, Pt and DNAzyme in the tag can act as peroxidase mimic to triply catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H 2 O 2 into a blue-colored oxidized TMB (oxTMB) for the colorimetric readout. Thus distinctive signal can be observed by naked eye even in presence of 0.02 nM tags. In the presence of target and primer, cDNA loop can open to form cDNA/CAP intermediates, enabling primer to hybridize with the exposed sequences of the cDNA, which initiated target assisted CSDP recycles. Then numerous signal tags were released into supernatant to catalyze TMB for color development. There was a liner relationship between the absorbance and the concentration of CAP in the range of 0.1 pM (0.0323 pg/mL) to 1000 pM (323 pg/mL) with the detection limit of 0.03 pM (0.0097 pg/mL). The ultra-high sensitivity was ascribed to the multiplex catalytic activities from the tags and CSDP based signal amplification. Furthermore, this method can produce signals being observed by naked eye to facilitate in-situ detection and be further extended to detect other antibiotics in food just by simply replacing cDNA on the sensing system. [ABSTRACT FROM AUTHOR]

To develop a simple and sensitive sensor for gamma radiation is of great importance not only for public safety, but also for rational utilization of ionizing radiation. In this study, a simple and sensitive method for colorimetric detection of low dose gamma radiation has been developed based on the single-strand DNA modified AuNPs (ssDNA-AuNPs), which were synthesized by immobilizing the sulfhydryl ssDNA on the surface of AuNPs. After the gamma radiation, the colors of ssDNA-AuNPs changed from wine-red to blue-purple gradually, and this can be easily distinguished by the naked eyes. Over a range from 0 to 30 Gy, a good linear relationship between the ratio of absorbance at 625 nm to that at 521 nm (A 625 /A 521 ) in the UV–vis spectrum and radiation dose was obtained. The detection limit was as low as 0.5 Gy. The colorimetric mechanism was ascribed to the generation of hydroxyl radical during the gamma radiation. As a result, ssDNA was cut off and released from the AuNPs. Then the salt effect caused the aggregation leading to the distinct color change. The capability of the method has also been demonstrated for anti-radiation efficiency comparison of different radioprotectors. In addition, lymphocytes irradiation expriment indicated that the ssDNA-AuNPs prepared in this work can be successfully used for an indicator during blood irradiation to avoid transfusion associated graft vs. host disease (TA-GVHD). [ABSTRACT FROM AUTHOR]

Sensing of total antioxidant capacity (TAC) as an integrated parameter showing the collective action of various antioxidants is an important challenge in food, biochemical and drug analysis. A novel heparin-stabilized gold nanoparticles (AuNPs)-based ‘cupric reducing antioxidant capacity’ (CUPRAC) colorimetric sensor was designed for TAC measurement. Heparin, a sulfated polysaccharide, was both the reducing and stabilizing agent for distinct negatively-charged AuNPs synthesis. The stabilized AuNPs were added to the copper(I)-neocuproine (Cu(I)-Nc) solution formed from the reaction of Cu(II)-Nc with antioxidants, and the absorbance of the resulting Cu(I)-Nc-AuNPs (Cu(I)-Nc cationic chelate electrostatically adsorbed on gold nanoparticles) was measured at 455 nm. As opposed to other similar AuNPs-based sensors, the proposed nano-sensor exhibited excellent (1000-fold) tolerance toward inert electrolytes without aggregation. The linear range was wider than that of conventional CUPRAC, with lower LOD (0.2 µM for trolox) and higher molar absorptivity (8.36 × 10 4 M −1 cm −1 for quercetin). The ‘trolox equivalent antioxidant capacity’ (TEAC) values and activity order for a number of antioxidants were in accordance with those of the reference CUPRAC assay. Antioxidant additions to black tea extract gave recoveries of 93–97% and RSD 2–6%. This green sensor significantly reduced reagent consumption, and operated in complex food samples with a simple, reliable and robust methodology. [ABSTRACT FROM AUTHOR]

A sensitive and artful colorimetric immunosensor based on horseradish peroxidase (HRP) was designed by labelling metal–organic frameworks (Cu-MOFs) on the second antibody (Cu-MOFs@Ab 2 ) as signal amplification for the detection of trace dibutyl phthalate (DBP). In this system, when Cu-MOFs@Ab 2 was captured by antigen- primary antibody (Ab 1 ) complex, tremendous Cu(II) will be released from Cu-MOFs in the presence of nitric acid (HNO 3 ), and Cu(II) will be further reduced to Cu(I) after the addition of sodium ascorbate (SA), consequently, inhibiting the HRP to catalyse the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) into blue oxidized TMB (ox TMB). Under the optimized conditions, the limit of detection (LOD) was 1 μg L −1 , which was almost 60 times lower than that using a conventional ELISA with the same antibody. In addition, our method showed good accuracy and reproducibility (recoveries of 87.73–103.4%; CV values of 1.46–5.95%) through a spike-recovery analysis. The proposed immunosensor indicated great potential for trace DBP determination from environmental and food samples. [ABSTRACT FROM AUTHOR]

Various DNA-modulated photosensitization schemes have been reported for various applications, but DNAzyme has not yet been included. Here, we found the DNAzyme with metal ion as cofactor could also be efficient in modulation of photosensitization process. The UO 2 2 + -specific DNAzyme can switch between double strand DNA (dsDNA) and single strand DNA (ssDNA) upon UO 2 2 + cleavage, which can regulate the photosensitization process of SYBR Green I. Coupling with photosensitization-induced chromogenic reaction (TMB oxidation), a simple colorimetric sensor for UO 2 2 + was developed accordingly. To increase the visual resolution of the proposed assay, a background color was supplied. Compared with the previous DNAzyme-based UO 2 2 + sensors, the proposed assay featured label-free and simple. Besides, the tolerance for high salinity of this assay is appealing. The proposed assay offered a detection limit of 0.08 μg/L with UV−vis detection and 0.5 μg/L with the naked eye. With the proposed colorimetric assay, UO 2 2 + levels in the range of 0.7–1.2 μg/L (2.9–5.0 nM) were identified in high salinity seawater samples, with spike-recoveries ranging from 93% to 104%. [ABSTRACT FROM AUTHOR]

This paper reported a novel colorimetric assay strategy for avidin and biotin interactions based on terminal protection of the biotinylated single-stranded DNA and the surface plasmon resonance adsorption of gold nanoparticles (AuNPs). In this assay, it was firstly found that biotin-ssDNA specifically bound to the target protein avidin with strong affinity could be protected from hydrolysis by exonuclease I (Exo I). Furthermore, a colorimetric strategy was designed for the detection of avidin and biotin interactions. In the process, in the presence of avidin, the interaction of avidin and biotin protected the digestion of Exo I towards the biotin-ssDNA. The biotin-ssDNA with negatively charged would attach to the surface of AuNPs with positively charge in high salt solution through electrostatic interactions, which prevented AuNPs to aggregate. With the increased addition of avidin, the absorbance of AuNPs in 520 nm increased gradually and the color showed gradually wine red. By taking advantage of terminal protection, the developed strategy could offer high sensitivity for detecting small molecule-protein interactions. The results revealed that the developed strategy was highly sensitive for detecting avidin in the concentration ranging from 0.01 to 0.2 μg/mL with the detection limit of 4 × 10 −3 μg/mL.The developed assay also showed highly specific, cost-efficient and convenient. Moreover, this strategy only required labeling the small molecule on a single-stranded DNA, circumventing protein modifications that might be harmful for activity. In view of these advantages, this new colorimetric method could have potential to become a universal, sensitive, and selective platform for detection of small molecule−protein interactions. [ABSTRACT FROM AUTHOR]

Developing fluorescent probes for specific detection of extremely toxic thiophenols is pretty significant in the field of environment, chemistry and biology. We report herein a turn-on red fluorescent xanthene-based probe ( RD-Probe ) for detecting thiophenol with high selectivity over other analytes including aliphatic thiols. The probe could play the part of a “naked-eye”colorimetric indicator toward thiophenol. Moreover, the relative fluorescence intensity at 653 nm displayed good linearity with the concentration of thiophenol ranging from 0 to 6 μM, and the limit of detection for thiophenol could be as low as 15 nM. Furthermore, the practicability of RD-Probe has been successfully proved through the quantitative thiophenol detection in real water samples and fluorescence bioimaging of thiophenol in HeLa cells. [ABSTRACT FROM AUTHOR]

The recent growing interest in peracetic acid (PAA) as disinfectant for wastewater treatment demands reliable and readily-available methods for its measurement. In detail, the monitoring of PAA in wastewater treatment plants requires a simple, accurate, rapid and inexpensive measurement procedure. In the present work, a method for analyzing low concentrations of PAA, adapted from the US EPA colorimetric method for total chlorine, is assessed. This method employs N,N-diethyl-p-phenylelnediamine (DPD) in the presence of an excess of iodide in a phosphate buffer system. Pink colored species are produced proportionally to the concentration of PAA in the sample. Considering that PAA is available commercially as an equilibrium solution of PAA and hydrogen peroxide (H 2 O 2 ), a measurement method for H 2 O 2 is also investigated. This method, as the one for the determination of PAA, is also based on the oxidation of iodide to iodine, with the difference that ammonium molybdate Mo(VI) is added to catalyze the oxidation reaction between H 2 O 2 and iodide, quantifying the total peroxides (PAA+ H 2 O 2 ). The two methods are suitable for concentration ranges from about 0.1–1.65 mg L −1 and from about 0.3–3.3 mg L −1 , respectively for PAA and H 2 O 2 . Moreover, the work elucidates some relevant aspects related to the operational conditions, kinetics and the possible interference of H 2 O 2 on PAA measurement. [ABSTRACT FROM AUTHOR]

Fabrication of core-shell nanostructured catalyst is a promising way for tuning its catalytic performance due to the highly active interface and rich redox properties. In this work, hierarchical Co 3 O 4 @NiO core-shell nanotubes are fabricated by the deposition of NiO shells via a chemical bath treatment using electrospun Co-C composite nanofibers as templates, followed by a calcination process in air. The as-prepared Co 3 O 4 @NiO core-shell nanotubes exhibit a uniform and novel hollow structure with Co 3 O 4 nanoparticles attached to the inner wall of NiO nanotubes and excellent catalytic activity toward the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 . Due to the synergistic effect, the peroxidase-like activity of the Co 3 O 4 @NiO core-shell nanotubes is much higher than that of individual Co 3 O 4 and NiO components. Owing to the superior peroxidase-like activity, a simple and rapid colorimetric approach for the detection of dopamine with a detection limit of 1.21 µM and excellent selectivity has been developed. It is anticipated that the prepared Co 3 O 4 @NiO core-shell nanotubes are promising materials applied for biomedical analysis and environmental monitoring. [ABSTRACT FROM AUTHOR]

Thiophenols are a class of highly toxic environmental pollutant, hence it is very necessary to monitor thiophenols in environment and living cells with an efficient and reliable method. Herein, a novel fluorescent probe for thiophenols has been developed, which exhibited a colorimetric and fluorescence turn-on dual response towards thiophenols with good selectivity and fast response. The sensing mechanism for thiophenols was attributed to nucleophilic substitution reaction, which was confirmed by HPLC. The probe exhibited good recovery (from 90% to 107%) and low limit of detection for thiophenols (37 nM) in industrial wastewater. Moreover, the probe has been successfully employed to visualize thiophenol in living cells. Therefore, the fluorescent probe has good capability for monitoring thiophenols in environmental samples and biological systems. [ABSTRACT FROM AUTHOR]