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Polydiacetylene (PDA) holds promise as a versatile material for biosensing applications due to its unique optical properties and self-assembly capabilities. In this study, we developed a colorimetric detection biosensor system utilizing PDA and aptamer for the detection of microcystin-LR (MC-LR), a potent hepatotoxin found in cyanobacteria-contaminated environments. The biosensor was constructed by immobilizing MC-LR-specific aptamer on magnetic beads, where the aptamer was hybridized with a urease-labelled complementary DNA (cDNA-urease). Upon binding MC-LR, the aptamer undergoes a conformational change to release cDNA-urease. The released cDNA-urease is subsequently captured by PDA bearing a single-stranded DNA (ssDNA). The enzymatic reaction triggers a distinctive color transition of PDA from blue to red. The results demonstrate exceptional sensitivity, with a linear detection range of 5–100 ng/mL and a limit of detection as low as 1 ng/mL. The practicability of the colorimetric method was demonstrated by detecting different levels of MC-LR in spiked water samples. The recoveries ranged from 77.3 to 102% and the color change, visible to the naked eye, underscores the practical utility for on-site applications. Selectivity for MC-LR over other microcystin variants (MC-RR and MC-YR) was confirmed. The colorimetric detection platform capitalizes on the properties of PDA and nucleic acid, offering a robust method for detecting small molecules with potential applications in environmental monitoring and public health. [ABSTRACT FROM AUTHOR]

Metal–organic-frameworks (MOFs) have emerged as promising candidates in different scientific disciplines owing to their intriguing characteristics. Their unique structural properties, including large surface area to volume ratio with multi-functionalities and ultra-high porosity, tunability, uniformity, and easy derivation and fabrication, render them effective materials for sensing applications. The detection of heavy metals in different environmental matrices using various MOF-based sensors is in practice. They include luminescent, electrochemical, electrochemiluminescent, colorimetric, and surface-enhanced Raman scattering, are of great interest. This review elaborates on selected synthetic methods for the fabrication of MOF-based sensors, modification routes for tailoring and enhancing the desired properties, basic characterization techniques, and their limitations in the detection of heavy metals. Also, it emphasizes the use of various types of MOF-based sensors alternatively for the detection of different heavy metals such as Fe(III), Cr(III), Hg(II), Cd(II), and Pb(II) in addition to a normal metal Al(III). A collection of recent references is provided for researchers interested in such applications. Results from the literature have been summarized in tables which give an easy comparison and will help to develop efficient materials. [ABSTRACT FROM AUTHOR]

AbstractCurrently, the use of metal-organic framework (MOF)-based peroxidase (POD) mimics has been attempted for the development of colorimetric biothiol detection sensors. Furthermore, Ni/Co layered double hydroxides (NiCo-LDH), as sourced from MOF, have attracted increasing interest as enzyme mimics for colorimetric detection due to their low cost, adjustable layered structure, and composition. Herein, the hollow cubes of NiCo-LDH were synthesized with zeolitic imidazolate framework-67 (ZIF-67) as a sacrificial template. NiCo-LDH nanosheets were used to construct the hollow cubes with additional active sites exposed by the hollow structure. A series of experiments were conducted to confirm the superior catalytic activities of NiCo-LDH nanozymes as peroxidase (POD)-like inhibitors to horseradish peroxidase. The enzymatic kinetic constant Km values for NiCo-LDH nanozyme were 0.70 mM (H2O2) and 0.16 mM (TMB). Glutathione (GSH) was determined with a detection limit of 0.263 μM and a detection range from 5 to 60 μM. Meanwhile, the platform exhibited exceptional selectivity and stability. The mechanism and application of NiCo-LDH nanozymes were explored to promote the development of nanozymes with multi-metal active sites. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) is a reliable biomarker for various diseases, making the development of new detection methods highly significant. Herein, we report a simple and accurate dual-signal optical detection strategy for measuring ALP activity across the entire clinical range in adults. Based on this, we designed a smartphone app to eliminate the limitations of large instruments, enabling real-time field detection. In this work, ALP catalyzes the conversion of the phosphate monoester of 2-phospho-L-ascorbic acid (PAA) into ascorbic acid (AA), a compound with strong reducing properties. AA facilitates the in-situ reduction of Ag+ to form Au@Ag core-shell nanoparticles, accompanied by significant changes in the ultraviolet-visible absorption spectra and color. These changes allow for the qualitative and quantitative detection of ALP activity. In UV absorption spectroscopy and colorimetric detection, the signal shows good linearity with ALP activity concentrations, with detection ranges of 0 U/L to 200 U/L (R2=0.9961) and 25 U/L to 250 U/L (R2=0.9771), respectively. Subsequent selective analysis and serum sample analysis demonstrated the high selectivity and accuracy of the proposed method, highlighting its potential for field application. [ABSTRACT FROM AUTHOR]

Designing metal nanoparticles with oxidase‐mimicking capabilities has garnered significant attention due to their promising attributes. However, understanding the intricate catalytic mechanisms underlying these nanoparticles poses a formidable challenge. In this study, a straightforward pyrolysis procedure was employed to synthesize nitrogen‐doped iron‐based nanoparticles (Fe NPs‐N@C) with Fe8−N2 serving as active sites. The confirmation of these sites was thoroughly confirmed through density functional theory (DFT) calculations complemented by experimental validation. The resulting Fe NPs‐N@C nanoparticles, averaging 5.45 nm in size, exhibited excellent oxidase‐mimicking activity, with vmax=1.11×10−7 M s−1and km=1.67 mM, employing 3,3′,5,5′‐tetramethylbenzidine as a substrate. The oxidation pathway and catalytic mechanism of Fe NPs‐N@C involved 1O2⋅ radicals, validated through electron paramagnetic resonance analysis and DFT calculations. Furthermore, Fe NPs‐N@C/TMB system was devised for ascorbic acid and nitrite quantitative detection. This method demonstrated the capability to detect ascorbic acid within concentrations ranging from 1 to 55 μM, with a limit of detection (LOD) of 0.81 μM, and nitrite within concentrations from 1 to 160 μM, with a LOD value of 0.45 μM. These findings offer a comprehensive understanding of the catalytic mechanisms of Fe NPs‐N@C nanoparticles at the atomic level, along with its potential for colorimetric sensor in future. [ABSTRACT FROM AUTHOR]

The high catalytic activity of Cu-based nanozymes mainly depends on the efficient Fenton-like reaction of Cu+/ H2O2, but Cu+ cannot exist stably. Trying to find a material that can stably support Cu+ while promoting the electron cycle of Cu2+/Cu+ still faces serious challenges. C60 is expected to be an ideal candidate to solve this problem due to its unique structure and rich physicochemical properties. Here, we designed and synthesized a C60-doped Cu+-based nanozyme (termed as C60-Cu-Bpy) by loading high catalytic active site Cu+ onto C60 and coordinating with 2,2′-bipyridine (Bpy). The single crystal diffraction analysis and a series of auxiliary characterization technologies were used to demonstrate the successful preparation of C60-Cu-Bpy. Significantly, the C60-Cu-Bpy exhibited superior peroxidase-like activity during the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB). Then, the catalytic mechanism of C60-Cu-Bpy as peroxidase was elucidated in detail, mainly benefiting from the dual function of C60. On the one hand, C60 acted as a carrier to directly support Cu+, which has the ability to efficiently decompose H2O2 to produce reactive oxygen species. The other was that C60 acted as an electron buffer, contributing to promoting the Cu2+/Cu+ cycle to facilitate the reaction. Furthermore, a colorimetric sensor for the quantitative analysis of bleomycin was established based on the principle of bleomycin specific inhibition of C60-Cu-Bpy peroxidase-like activity, with satisfactory results in practical samples. This study provides a new strategy for the direct synthesis of Cu+-based nanozymes with high catalytic performance. Schematic illustration of the preparation of C60-Cu-Bpy (a) and the colorimetric detection of bleomycin based on specific inhibition of C60-Cu-Bpy peroxidase-like activity (b) [ABSTRACT FROM AUTHOR]

α-Glucosidase (α-Glu) is implicated in the progression and pathogenesis of type II diabetes (T2D). In this study, we developed a rapid colorimetric technique using platinum nanoparticles stabilized by chitosan (Ch-PtNPs) to detect α-Glu activity and its inhibitor. The Ch-PtNPs facilitate the conversion of 3,3′,5,5′-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB) in the presence of dissolved O2. The catalytic hydrolysis of 2-O-α-d-glucopyranosyl-l-ascorbic acid (AA-2G) by α-Glu produces ascorbic acid (AA), which reduces oxTMB to TMB, leading to the fading of the blue color. However, the presence of α-Glu inhibitors (AGIs) hinders the generation of AA, allowing Ch-PtNPs to re-oxidize colorless TMB back to blue oxTMB. This unique phenomenon enables the colorimetric detection of α-Glu activity and AGIs. The linear range for α-Glu was found to be 0.1–1.0 U mL−1 and the detection limit was 0.026 U mL−1. Additionally, the half-maximal inhibition value (IC50) for acarbose, an α-Glu inhibitor, was calculated to be 0.4769 mM. Excitingly, this sensing platform successfully detected α-Glu activity in human serum samples and effectively screened AGIs. These promising findings highlight the potential application of the proposed strategy in clinical diabetes diagnosis and drug discovery. [ABSTRACT FROM AUTHOR]

Anions play an important role in our life, from storing our genetic code on the polyanion DNA, to being the active ingredient in agricultural fertilisers and other industrial processes. Consequently, chemists have been designing systems that can sense anionic species through a variety of methods, such as unimolecular chromophores or sensor arrays. Nonetheless, most existing sensing approaches still have some drawbacks, particularly related to obtaining adequate selectivity and achieving sensing of anions in aqueous environments. In this manuscript, we report a liquid–liquid extraction (LLE)-based sensing approach that allows the conversion of non-selective optical anion sensors that only work in organic media, into selective sensing systems that allow detection of anions in water. We tested this approach on deprotonation-based anion sensors (alizarin, naphthol AS, 4-nitrophenol, BI-Lawsone, and chromophore 1) and hydrogen bonding-based anion sensors (1,2-diaminoanthraquinone and 4-nitro-1,2-phenylenediamine). In general, the deprotonation-based sensors could be converted from a non-selective sensor for basic anions (NCO¯, H2PO4¯, AcO¯ and F¯) to a selective sensing system for NCO¯ with the aid of carefully chosen tetraalkylammonium salts as extracting agents. On the other hand, the hydrogen-bonding based sensors could be converted to a selective sensing system for the hydrophobic anion ClO4¯ using similar tetraalkylammonium salts. [ABSTRACT FROM AUTHOR]

Chronic immunoinflammatory rheumatic diseases, such as axial spondyloarthritis (AxSpA), are accompanied by a dysregulation of bone remodeling. Among potential biomarkers of bone metabolism, the Wnt pathway antagonist, Dickkopf-1 (DKK-1), is of particular interest because of its potential to reflect a shift towards joint ossification or osteoporosis, but its diagnostic value needs validation. There is still a lack of stable and efficient methods of measuring serum DKK-1 levels suitable for longitude studies. The use of aptamer-based diagnostic assays could be very promising for this purpose. We generated novel anti-DKK-1 DNA aptamers from a combinatorial library with a pre-defined sequence pattern in the randomized region. This approach showed high efficacy, as only four SELEX rounds of selection produced high-affinity aptamers with dissociation constants ranging from 1.3 to 3.7 nM. A family of their truncated versions was also developed by rational design. Novel DNA aptamers functioned as capture components in a microplate ELISA-like assay with HRP-conjugated anti-DKK-1 antibody as a reporter component. We succeeded in revealing the aptamer/aptamer sandwich pairs that provided an aptamer-only sandwich colorimetric assay. The aptamer/antibody colorimetric test systems were also examined in the analyses of blood serum from AxSpA patients and shown sufficient workability. However, in a number of cases we registered significant differences between assays based on TD10 and DK4 aptamers and made some suggestions about the origin of this effect. [ABSTRACT FROM AUTHOR]

Background: Brucellosis is a major worldwide zoonotic disease that is caused by Brucella spp. and threatens the health of communities. Novel methods for rapid detection of Brucella bacteria are beneficial and necessary in preventing infection and subsequent economic losses. Constructing biosensors with nanoparticles is a promising approach for identification of pathogenic bacteria in a short time. This study aimed to introduce a new detection method of Brucella cells using a biosensor, based on gold nanoparticles and a specific aptamer, via a colorimetric reaction. In this work, gold nanoparticles (GNPs) were synthesized and attached to the aptamer through electrostatic bonding. The binding of aptamer to gold nanoparticles was confirmed by Uv/vis spectrophotometry, FT-IR, transmission electron microscope (TEM) and zeta sizer (DLS). Results: In the presence of the bacterial cells, aptamers were bound to their targets, and the surfaces of the nanoparticles were depleted from aptamers resulting in intensified peroxidation activity of GNPs, and with the addition of 3, 3′, 5, 5′-tetramethylbenzidine (TMB), the color of the solution was changed from red to purple, which indicated the presence of Brucella. The sensitivity of the aptasensor was investigated using different concentrations of Brucella cells and its specificity was confirmed against several species of bacteria. The results showed that the designed aptasensor was more sensitive compared to PCR assay method with the ability to detect 1.5 × 101 CFU/mL of the bacterial cells. Conclusion: These findings indicate that the designed aptasensor can be used as a simple and rapid diagnostic tool to detect Brucella cells without need to experts and expensive laboratory equipment. [ABSTRACT FROM AUTHOR]

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A paper-based colorimetric sensor array mediated by a novel nanozyme (CuCo2O4) was developed using a screen-printing technology. The aim was to facilitate the identification of different kinds of alkaloids. Typically, three chromogenic substrates (3,3′,5,5′-tetramethylbenzidine, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), and o-phenylenediamine) were selected as sensing elements, which can be catalyzed by a CuCo2O4 nanozyme with peroxidase-like activity to yield corresponding oxidized products, thereby inducing color changes. Owing to the varying inhibitory ability of different alkaloids on acetylcholinesterase (AChE), a decrease in choline (Ch) concentration occurs and subsequently results in the restoration of color within the units of sensor array. Color data can be transformed into hue information with a smartphone. The above color variations generated a unique "fingerprint" pattern on five alkaloids (berberine, palmatine, jatrorrhizine, eserine, and harmane), which can be successfully discriminated through linear discriminant analysis in the range 0.2 to 20 µM. Furthermore, the sensor arrays allowed successful discrimination of the above five alkaloids in Chinese herbal medicine samples and recognition of 22 blind samples. This work presents a novel nanozyme-based paper sensor array, which is a user-friendly and reliable platform for probing different alkaloids. In addition, the developed sensing strategy enables the identification of AChE-related diseases, positively contributing to the screening available of AD-associated drugs. [ABSTRACT FROM AUTHOR]

A unique approach is introduced for constructing gold nanocrystals (AuNCs) with RNA motif–directed morphologies in a sequence-independent manner and its applications in the clinical area are described. By using this method, a label-free LSPR-based detection method for the SOX2OT transcript, long non-coding RNAs (lncRNAs), which is a prognostic indicator of poor survival in lung cancer patients is presented. For the first time, we examined how the structural changes of RNA after the heteroduplex formation with a specific DNA probe can change the morphology and LSPR band of AuNCs. Using this method, is was possible to differentiate lung squamous cell carcinoma from adenocarcinoma samples without a need for a prior amplification of the target lncRNA. The approach of using specific DNA probe enables the in situ synthesis of nanocrystals in a different way and expands this method for future translational medicine, particularly detection of specific RNA. [ABSTRACT FROM AUTHOR]

By self-assembly of MnCl2 and arginine under alkaline conditions, ultra-small MnArg nanoparticles were successfully constructed as oxidase (OXD) mimics for intelligent detection of the Ginkgo toxin 4′-O-methylpyridoxal (MPN). The obtained MnArg nanozymes possessed excellent OXD-like activity and thermal stability. Based on the inhibitory effect of MPN for the catalytic activity of MnArg, this system was utilized for the colorimetric sensing of MPN with a low limit of detection (LOD) of 2.16 µg mL−1. The detection system exhibited good selectivity against other potential interferents. FTIR data showed that the presence of MPN binds with MnArg and shields the active sites, thereby interfering with the oxidase-like activity. Combined with a smartphone and the ColorMax software, this nanozyme-based intelligent detection platform could effectively detect MPN with a LOD of 2.1 µg mL−1. Our MnArg nanozyme–based system was applied to detect real ginkgo nut samples with recoveries of 92.4–108.7%, and the relative standard deviations were less than 0.7%. This work may promote the development of novel nanozymes and expand their applications in the field of food safety detection. [ABSTRACT FROM AUTHOR]

Cobalt-doped Prussian blue composite nanocubes (Co-PB NCs) were synthesized, which can quickly convert O2 to O2•− and 1O2. Due to the presence of cobalt and iron transition metal redox electron pairs, Co-PB NCs with high oxidase mimetic activity can rapidly oxidize the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) to produce blue products (ox-TMB) without the assistance of unstable H2O2. Using ascorbic acid-2-phosphate trisodium salt (AAP) as a substrate, it can be converted to reduced ascorbic acid (AA) under acid phosphatase (ACP) hydrolysis, resulting in suppression of TMB oxidation. Therefore, an enzyme cascade signal amplification strategy for rapid colorimetric detection of AA/ACP was developed based on the high-efficiency oxidase-like activity of Co-PB NCs combined with the hydrolysis effect of ACP. The color changes at low concentrations of AA and ACP could be observed by the naked eye, and the detection limits of AA and ACP were 1.67 μM and 0.0266 U/L, respectively. The developed colorimetric method was applied to the determination of AA in beverages and ACP in human serum, and the RSDs were less than 3%, showing good reproducibility. This work provides a promising strategy for the use of metal-doped Prussian blue composite material for the construction of rapid colorimetric sensing platforms that avoid the use of unstable hydrogen peroxide. [ABSTRACT FROM AUTHOR]

Isothermal amplification (IA) techniques like rolling circle amplification (RCA) and loop-mediated isothermal amplification (LAMP) have gained significant attention in recent years due to their ability to rapidly amplify DNA or RNA targets at a constant temperature without the need for complex thermal cycling equipment. Such technologies, combined with colorimetric systems rendering visual confirmation of the amplification event, are ideal for the development of point-of-need detection methods suitable for field settings where access to specialized laboratory equipment is limited. The utility of these technologies, thus far limited to DNA and RNA targets, could be broadened to a wide range of targets by using aptamers. Composed of DNA or RNA themselves, aptamers can bind to substances, including proteins, metabolites, and inorganic substances. Their nucleic acid nature can potentially allow them to serve as a bridge, extending the reach of DNA/RNA-centric technologies to the broader molecular world. Indeed, the change in aptamer conformation occurring during ligand interaction can be used to elaborate ligand-responding RCA or LAMP templates. By using an existing aptamer targeting SARS-CoV-2 Spike protein as a model, we explored the possibility of establishing ligand-responsive IA systems. Our study used aptamers with simple sequence modifications as templates in LAMP assays and hyperbranched RCA (HRCA) by exploiting the dynamic nature of the model aptamer to trigger these IA systems. Importantly, our work uniquely demonstrates that this aptamer's dynamic response to ligand binding can regulate both RCA and LAMP processes. This novel approach of using aptamer conformational changes to trigger LAMP paves the way for new aptamer-based detection assays. Our system detects 50 nM of Spike protein, with LAMP occurring within 30 min in the presence of Spike. The colorimetric readout showed clear results, allowing for the detection of Spike protein presence. [ABSTRACT FROM AUTHOR]

The market size of biosurfactants (BSs) has been expanding at an extremely fast pace due to their broad application scope. Therefore, the re-construction of cell factories with modified genomic and metabolic profiles for desired industrial performance has been an intriguing aspect. Typical mutagenesis approaches generate huge mutant libraries, whereas a battery of specific, robust, and cost-effective high-throughput screening (HTS) methods is requisite to screen target strains for desired phenotypes. So far, only a few specialized HTS assays have been developed for BSs that were successfully applied to obtain anticipated mutants. The most important milestones to reach, however, continue to be: specificity, sensitivity, throughput, and the potential for automation. Here, we discuss important colorimetric and fluorometric HTS approaches for possible intervention on automated HTS platforms. Moreover, we explain current bottlenecks in developing specialized HTS platforms for screening high-yielding producers and discuss possible perspectives for addressing such challenges. [ABSTRACT FROM AUTHOR]

Recent years have witnessed an exponential increase in the research on gold nanoparticles (AuNPs)-based colorimetric sensors to revolutionize point-of-use sensing devices. Hence, this review is compiled focused on current progress in the design and performance parameters of AuNPs-based sensors. The review begins with the characteristics of AuNPs, followed by a brief explanation of synthesis and functionalization methods. Then, the mechanisms of AuNPs-based sensors are comprehensively explained in two broad categories based on the surface plasmon resonance (SPR) characteristics of AuNPs and their peroxidase-like catalytic properties (nanozyme). SPR-based colorimetric sensors further categorize into aggregation, anti-aggregation, etching, growth-mediated, and accumulation-based methods depending on their sensing mechanisms. On the other hand, peroxidase activity-based colorimetric sensors are divided into two methods based on the expression or inhibition of peroxidase-like activity. Next, the analytes in environmental and food samples are classified as inorganic, organic, and biological pollutants, and recent progress in detection of these analytes are reviewed in detail. Finally, conclusions are provided, and future directions are highlighted. Improving the sensitivity, reproducibility, multiplexing capabilities, and cost-effectiveness for colorimetric detection of various analytes in environment and food matrices will have significant impact on fast testing of hazardous substances, hence reducing the pollution load in environment as well as rendering food contamination to ensure food safety. [ABSTRACT FROM AUTHOR]

Background: Salmonella, is one of the most important pathogens causing foodborne illnesses worldwide. The early detection of Salmonella is essential to minimize the risk. Herein, the nanoprobe (CS-AuNPs@phage-T156) for Salmonella was obtained by functionalizing cysteamine (CS) stabilized gold nanoparticles (CS-AuNPs) with phage T156. Results: In the presence of target Salmonella, the CS-AuNPs@phage-T156 specifically recognized and adsorbed on the surface of Salmonella, then induced the aggregation of gold nanoparticles and the color changes from red to purple, which enabled visual detection. The concentration of Salmonella was quantified by the absorption ratio (A680/A526), with a wide linear range from 1.2 × 101 CFU/mL to 1.2 × 106 CFU/mL. Under the optimal experimental conditions, this assay possessed a potent selectivity characteristic quickly toward Salmonella, with a detection limit of 12 CFU/mL. Conclusion: This simple and rapid detection method is expected to provides a novel identification element for the detection of Salmonella by intuitive visualization judgment and quantitative analysis. [ABSTRACT FROM AUTHOR]

The pH detection helps control food quality, prevent spoilage, determine storage methods, and monitor additive levels. In the previous studies, colorimetric pH detection involved manual capture of target regions and classification of acid–base categories, leading to time-consuming processes. Additionally, some researchers relied solely on R*G*B* or H*S*V* to build regression models, potentially limiting their generalizability and robustness. To address the limitations, this study proposed a colorimetric method that combines pH paper, smartphone, computer vision, and machine learning for fast and precise pH detection. Advantages of the computer vision model YOLOv5 include its ability to quickly capture the target region of the pH paper and automatically categorize it as either acidic or basic. Subsequently, recursive feature elimination was applied to filter out irrelevant features from the R*G*B*, H*S*V*, L*a*b*, Gray, XR, XG, and XB. Finally, the support vector regression was used to develop the regression model for pH value prediction. YOLOv5 demonstrated exceptional performance with mean average precision of 0.995, classification accuracy of 100%, and detection time of 4.9 ms. The pH prediction model achieved a mean absolute error (MAE) of 0.023 for acidity and 0.061 for alkalinity, signifying a notable advancement compared to the MAE range of 0.03–0.46 observed in the previous studies. The proposed approach shows potential in improving the dependability and effectiveness of pH detection, specifically in resource-constrained scenarios. [ABSTRACT FROM AUTHOR]

A significant hypsochromic or bathochromic shift of photoabsorption bands of dyes may be observed only in halogenated solvents. Such specific solvatochromism is termed organohalogenochromism (OHC), which has been recently recognized as a photophysical phenomenon. However, few studies have been carried out on the elucidation of OHC and thus there is a limited insight into the mechanism for expression of OHC, although the phenomenon not only is of a great scientific interest in photochemistry, photophysics, analytical chemistry, and synthetic organic chemistry but also has great potential for development of colorimetric detection technique for organohalogen compounds; this technique is expected to be facile operation and simple analysis with sufficient accuracy, high sensitivity, and fast response, and thus allows visualization and real‐time monitoring for toxic volatile organohalogen compounds (VOHCs). In this Concept, we first review OHC of dyes which have been reported so far. Second, the elucidation of OHC based on the interactions between dye and organohalogen molecules are discussed. In particular, we propose the explanation for a pronounced OHC of donor‐π‐acceptor‐type cationic dye from the viewpoint of halogen bond (XB) between halogenated solvents and counter anion of cationic dye. Moreover, an application of organohalogenochromic dyes to colorimetric sensors for VOHCs is presented. [ABSTRACT FROM AUTHOR]

In this study, a novel colorimetric method is developed for the detection of arsenic and mercury ions, utilizing the surface plasmon resonance (SPR) properties of AuNPs (AuNPs=gold nanoparticles) functionalized with APT (APT=5-(3-aminophenyl) tetrazole). Theoretical calculations confirm the findings from UV–Visible spectroscopy and transmission electron microscopy analyses, indicating that APT is electrostatically bound to the surfaces of the AuNPs. The introduction of As3+ and Hg2+ ions triggers a coordination reaction with APT, resulting in a reduced interparticle distance among the AuNPs. This change leads to a visible color shift of the solution from wine red to bluish-gray. The detection limits for As3+ and Hg2+ are determined to be 0.6 and 0.24 μ g⋅mL−1, respectively, distinguishable to the naked eye. A robust linear correlation is observed between the absorbance ratios and the ion concentrations, with correlation coefficients (R2) of 0.990 for As3+ and 0.998 for Hg2+. These findings demonstrate that AuNPs functionalized with APT are effective for the quantitative analysis of arsenic and mercury ions. The sensor exhibits high selectivity and excellent resistance to interference, indicating its potential applicability for monitoring As3+ and Hg2+ in tap water and cosmetic products. [ABSTRACT FROM AUTHOR]

Antioxidants are substances that have the ability to resist or delay oxidative damage. Antioxidants can be used not only for the diagnosis and prevention of vascular diseases, but also for food preservation and industrial production. However, due to the excessive use of antioxidants, it can cause environmental pollution and endanger human health. It can be seen that the development of antioxidant detection technology is important for environment/health maintenance. It is found that traditional detection methods, including high performance liquid chromatography, gas chromatography, etc., have shortcomings such as cumbersome operation and high cost. In contrast, the nanozyme-based detection method features advantages of low cost, simple operation, and rapidity, which has been widely used in the detection of various substances such as glucose and antioxidants. This article focuses on the latest research progress of nanozymes for antioxidant detection. Nanozymes for antioxidant detection are classified according to enzyme-like types. Different types of nanozyme-based sensing strategies and detection devices are summarized. Based on the summary and analysis, one can find that the development of commercial nanozyme-based devices for the practical detection of antioxidants is still challenging. Some emerging technologies (such as artificial intelligence) should be fully utilized to improve the detection sensitivity and accuracy. This article aims to emphasize the application prospects of nanozymes in antioxidant detection and to provide new ideas and inspiration for the development of detection methods. [ABSTRACT FROM AUTHOR]

Gold-platinum (Au@Pt) nanozymes with high catalytic activity and stability were designed to improve the stability of the enzyme-linked immunosorbent assay (ELISA), and a two-mode signal output was used to enhance the sensitivity and confidence of the assay. This study reports the two-mode signal output based on Au@Pt nanozyme to catalyzed 3,3′,5,5′-tetramethylbenzidine (TMB) reaction. Oxidized 3,3′,5,5′-tetramethylbenzidine (ox-TMB) has wide absorption spectrum, providing excellent optical density capabilities and fluorescence quenching. The detection limits of imidacloprid were 0.88 μg/L and 1.14 μg/L in colorimetric and fluorescence modes, respectively. Multiple-mode strategy improves detection accuracy, increases the confidence of experimental results, and broadens detection modes. Two modes can meet the requirements of accurate and flexible multi-mode sensing in different application situations. [ABSTRACT FROM AUTHOR]

A novel colorimetric approach specifically designed to effectively identify the presence of 3-aminophenol (3-AP) in environmental water is introduced. Briefly, a nitrogen-doped carbon-supported cobalt nanozyme (Co@CN-1) was synthesized and utilized to improve the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of peroxymonosulfate (PMS). Comparative catalytic reactions confirmed that the performance of PMS as an activator exceeds that of hydrogen peroxide catalytically by a factor of 3.5. The catalytic reaction parameters underwent optimization, further resulting in the derivation of a linear detection equation for 3-AP, expressed as inhibition rate (IR%) = 3.35[3-AP]—4.36 (0–20 μM, R2 = 0.994) and IR% = 1.43[3-AP] + 31.87 (20–36 μM, R2 = 0.992), with the limit of detection (LOD) of 2.84 μM. The linear relationship between 3-AP concentration and the conversion of color to grayscale value (GSV) was established by smartphones, expressed as GSV = 1.28[3-AP] + 147.10 (R2 = 0.972). Density functional theory calculations revealed that Co acts as the preferred active site for donating electrons in PMS activation. This work provides a rapid and accurate approach for monitoring 3-AP concentration, enabling real-time analysis and potentially contributing to environmental and ecological studies. [ABSTRACT FROM AUTHOR]

A colorimetric sensor for the rapid and sensitive detection of GSH was developed. The hydrothermal method was utilized to synthesize chitosan-stabilized gold nanoparticles (CS-AuNPs). The synthesized CS-AuNPs were characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), X-ray diffractograms (XRD), and Fourier transform infrared spectroscopy (FTIR). The CS-AuNPs are well-dispersed and possess a spherical shape with an average particle size of 10.05 ± 2.26 nm in aqueous solution. They show an intrinsic peroxidase-like activity, which could efficiently catalyze the decomposition of H2O2 to produce •OH radicals. These radicals then oxidized 3, 3´, 5, 5´-tetramethylbenzidine (TMB), resulting in the formation of the blue oxidized product oxTMB, observed a visible color change (from colorless to blue), and oxTMB had an obvious absorption peak at 652 nm. The presence of GSH could inhibit the peroxidase-like activity of CS-AuNPs, thereby reducing the formation of oxTMB. The solution's blue hue underwent a reduction in absorption intensity. Based on this fact, a novel and sensitive colorimetric sensor for detection of GSH was constructed. Under optimal conditions, the results of detection had an excellent linear relationship between the concentration of GSH and ∆A within the range 0.5 ~ 50.0 × 10−6 mol/L. The limit of detection (LOD) for GSH was 2.10 × 10−7 mol/L, which was much lower than those in most previous works. Furthermore, for detection in real human serum samples, the recoveries of GSH and the relative standard deviations (RSD) in the serum were in the range 98.40 ~ 103.32% and 1.85 ~ 3.54%, respectively. Thus, this visual colorimetric method has good precision and can be used for GSH detection in practical applications, promising in the fields of bioanalysis and illness diagnostics. [ABSTRACT FROM AUTHOR]

Abstract Alkaline phosphatase (ALP) is a reliable biomarker for various diseases, making the development of new detection methods highly significant. Herein, we report a simple and accurate dual-signal optical detection strategy for measuring ALP activity across the entire clinical range in adults. Based on this, we designed a smartphone app to eliminate the limitations of large instruments, enabling real-time field detection. In this work, ALP catalyzes the conversion of the phosphate monoester of 2-phospho-L-ascorbic acid (PAA) into ascorbic acid (AA), a compound with strong reducing properties. AA facilitates the in-situ reduction of Ag+ to form Au@Ag core-shell nanoparticles, accompanied by significant changes in the ultraviolet-visible absorption spectra and color. These changes allow for the qualitative and quantitative detection of ALP activity. In UV absorption spectroscopy and colorimetric detection, the signal shows good linearity with ALP activity concentrations, with detection ranges of 0 U/L to 200 U/L (R2=0.9961) and 25 U/L to 250 U/L (R2=0.9771), respectively. Subsequent selective analysis and serum sample analysis demonstrated the high selectivity and accuracy of the proposed method, highlighting its potential for field application.

In foods, there are many types and sources of harmful substances that can accumulate in the human body, thereby posing a threat to human health. Therefore, it is crucial to develop efficient, rapid and portable visual detection devices with low detection limits. In recent years, nanozymes, nanomaterials with natural enzyme-like activity, have played an important role in the construction of colorimetric sensors due to their tunable enzyme activity and high stability, enabling efficient and rapid visual detection of harmful substances in foods. Redox-type nanozymes are the most researched nanozymes. Therefore, this paper introduces the types of redox-type nanozymes and elucidates their catalytic mechanisms. It focuses on reviewing the application of redox-type nanozymes in constructing colorimetric sensors for detecting common representative harmful substances (heavy metals, pesticide residues, and mycotoxins) in foods. Finally, we summarize the advantages and disadvantages of colorimetric assays based on redox-type nanozymes in the field of food safety detection, and propose some solutions to the problems in order to provide a reference for future research.

Abstract Background Brucellosis is a major worldwide zoonotic disease that is caused by Brucella spp. and threatens the health of communities. Novel methods for rapid detection of Brucella bacteria are beneficial and necessary in preventing infection and subsequent economic losses. Constructing biosensors with nanoparticles is a promising approach for identification of pathogenic bacteria in a short time. This study aimed to introduce a new detection method of Brucella cells using a biosensor, based on gold nanoparticles and a specific aptamer, via a colorimetric reaction. In this work, gold nanoparticles (GNPs) were synthesized and attached to the aptamer through electrostatic bonding. The binding of aptamer to gold nanoparticles was confirmed by Uv/vis spectrophotometry, FT-IR, transmission electron microscope (TEM) and zeta sizer (DLS). Results In the presence of the bacterial cells, aptamers were bound to their targets, and the surfaces of the nanoparticles were depleted from aptamers resulting in intensified peroxidation activity of GNPs, and with the addition of 3, 3′, 5, 5′-tetramethylbenzidine (TMB), the color of the solution was changed from red to purple, which indicated the presence of Brucella. The sensitivity of the aptasensor was investigated using different concentrations of Brucella cells and its specificity was confirmed against several species of bacteria. The results showed that the designed aptasensor was more sensitive compared to PCR assay method with the ability to detect 1.5 × 101 CFU/mL of the bacterial cells. Conclusion These findings indicate that the designed aptasensor can be used as a simple and rapid diagnostic tool to detect Brucella cells without need to experts and expensive laboratory equipment.

After high-temperature etching of metal-free porous N -doped carbon with NaCl, the doped Cl atoms significantly enhance the peroxidase-like activity of the nanozyme. [Display omitted] Metal-free carbon-based nanozymes often exhibit superior chemical stability and detection reliability compared to their metal-doped counterparts. However, their catalytic activity remains an area ripe for further enhancement. Herein, we successfully prepared a chlorine (Cl)-modified, metal-free, and porous N -doped carbon nanozyme (Cl x -pNC) via NaCl molten etching. The incorporation of Cl induced an increase in the intrinsic defects of sp3-hybridized carbon within Cl x -pNC and optimized the electronic structure of the N -connected carbon atoms. Remarkably, the peroxidase (POD)-like activity of Cl x -pNC was enhanced twelvefold compared to porous N -doped carbon (pNC). Theoretical simulations highlighted that the introduction of Cl not only promoted H 2 O 2 adsorption but also lowered the energy barrier for its decomposition, facilitating the generation of active intermediates and thus boosting POD-like activity. Based on the POD mimic activity of Cl x -pNC, we developed a colorimetric platform for OPs detection utilizing a cascade amplification strategy. This work provides insights into the rational design of carbon-based nanozymes and the development of nanozyme-based colorimetric biosensors. [ABSTRACT FROM AUTHOR]

Silver nitrate (AgNO3), trisodium citrate dihydrate (C6H5Na3O7 · 2H2O), sodium borohydride (NaBH4), and L-ascorbic acid (C6H8O6) were combined in distilled water to create a triangular silver nanoprism particle (AgNPRP) solution. UV-visible (UV-vis) spectroscopy at wavelengths of 350–460 nm and 580–700 nm was observed, and as a result of them, the successful formation of the triangular AgNPRPs was confirmed. The prepared silver nanoprism particles were characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy(SEM), and transmission electron microscopy(TEM) and employed for the colorimetric detection of platinum(IV) ions in an aqueous solution containing Pt4+ ions. The color of the aqueous silver nanoprism particle solution, containing Pt4+ ions, changed from blue to light brown before turning colorless. Using UV-vis spectrophotometry, the detection limit of the Pt4+ ion concentration was determined to be 6.23 μM in an aqueous solution of silver nanoprism particles. The proposed method was applied for detecting Pt4+ ions in tap water samples.

Total antioxidant capacity of food is one of the critical parameters to evaluate its efficacy. Establishment of a fast and sensitive analytical method for the detection of total antioxidant capacity of food has great significance. In this paper, a metal-organic framework complex nanozyme (Fe-HHTP@ZIF-8) with peroxidase-like activity was firstly designed and successfully synthesized. Then, the morphology, structure and catalytic activity were characterized in detail. The results showed that Fe-HHTP@ZIF-8 possessed a two-dimensional ultra-thin layer structure while its Km and Vmax values towards H2O2 were 0.67 mmol/L and 3.55×10−8 mol/L·s−1, respectively. Ascorbic acid (AA) as a typical antioxidant, an efficient colorimetric biosensor was constructed based on its inhibitory effect on chromogenic reaction catalyzed by nanozyme. Comprehensive validation showed that the colorimetric biosensor had low limit of detection (1.67 μmol/L), wide linear range (5.0~3000.0 μmol/L) and high accuracy (recovery rate of 98.62%~103.13%). By using this colorimetric method, total antioxidant capacity of different beverages was detected and the obtained results were basically consistent with labeled values. Therefore, this study provided a simple, fast and effective colorimetric method for the evaluation of the total antioxidant capacity of food.

Abstract Chronic kidney disease (CKD) is a widespread condition with considerable health and economic impacts globally. However, existing methodologies for serum creatinine assessment often involve prolonged wait times and sophisticated equipment, such as spectrometers, hindering real-time diagnosis and care. Innovative solutions like point-of-care (POC) devices are emerging to address these challenges. In this context, there is a recognized need for remote, regular, automated, and low-cost analysis of serum creatinine levels, given its role as a critical parameter for CKD diagnosis and management. This study introduces a miniaturized system with integrated heater elements designed for precise serum creatinine measurement. The system operates based on the Jaffe method and accurate serum creatinine measurement within a microreservoir chip. Smartphone-based image processing using the hue-saturation-value (HSV) color space was applied to captured images of microreservoirs. The creatinine analyses were conducted in serum with a limit of detection of ~ 0.4 mg/dL and limit of quantification of ~ 1.3 mg/dL. Smartphone-based image processing employing the HSV color space outperformed spectrometric analysis for creatinine measurement conducted in serum. This pioneering technology and smartphone-based processing offer the potential for decentralized renal function testing, which could significantly contribute to improved patient care. The miniaturized system offers a low-cost alternative ($87 per device), potentially reducing healthcare expenditures (~ $0.5 per test) associated with CKD diagnosis and management. This innovation could greatly improve access to diagnosis and monitoring of CKD, especially in regions where access to sophisticated laboratory equipment is limited.

Artemisinin (Art) is the first‐choice medicine for treating malaria. It also shows good therapeutic effects in antibacterial and antitumor treatment. Therefore, a simple and efficient method for detecting Art is of great significance. Mn‐functionalized ZIF‐67 (Mn@ZIF‐67) hybrid materials were synthesized using a post‐synthesis modification method. Due to the introduction of Mn2+, Mn@ZIF‐67 possesses higher peroxidase/oxidase like dual‐mimic enzymes activity than ZIF‐67, which can catalyze Art and generate peroxyl radicals. Based on this fact, Mn@ZIF‐67 was used to detect Art in the presence of TMB. A good linear relationship between absorption intensities at 652 nm and Art concentrations was obtained in the range of 0–22 μM with a detection limit of 200 nM. Ascorbic acid (AA), due to its reducibility, can inhibit peroxidase/oxidase mimetics activity of Mn@ZIF‐67 and the blue Mn@ZIF‐67‐TMB solution fades gradually with the addition of AA. Mn@ZIF‐67‐TMB acting as a colorimetric sensor, AA can be sensitively detected ranging from 0–30 μM, and the detection limit is 50 nM. Coexisting substances don't interfere with the detection of Art or AA. This sensing platform provides a highly sensitive and selective colorimetric method for monitoring AA and Art in serum, thereby demonstrating remarkable practicality. [ABSTRACT FROM AUTHOR]

The development of sensitive and accurate glucose biosensors is significant in diabetic patient monitoring. Here, we synthesize carbon-decorated Fe3O4 nanotubes (Fe3O4@C NTs) using a rational designed template method. Through catalytic oxidation of a typical colorimetric reaction, the prepared Fe3O4@C NTs showed significantly better peroxidase-like and oxidase-like performances than other similar Fe3O4-based nanomaterials. Moreover, the optimal pH, temperature, and concentration for Fe3O4@C NTs were 4.0, 60 °C, and 40 μg/mL, respectively. We additionally investigated the steady-state kinetics of Fe3O4@C NTs, and their catalyzed reactions were found to follow the typical Michaelis–Menten model. Based on the peroxidase-like activity of Fe3O4@C NTs, they were employed for label-free, rapid, selective, and highly sensitive colorimetric detection of H2O2 and glucose, demonstrating a potential application for glucose determination. [ABSTRACT FROM AUTHOR]

Staphylococcus aureus (S. aureus) is a common foodborne pathogen, posing a serious threat to public health. Consequently, it is crucial to establish a platform for sensitive and specific determination of S. aureus in food. Herein, phage SapYZUH5, isolated by our lab, was covalently immobilized on Co3O4 to synthesize SapYZUH5@Co3O4. Notably, SapYZUH5@Co3O4 exhibited remarkable oxidase-like activity, enabling the catalysis of dissolved oxygen to generate superoxide anion free radicals and accelerate the TMB chromogenic reaction. Upon introduction of S. aureus, specific capture by SapYZUH5@Co3O4 resulted in inhibiting its oxidase-like activity and decelerating the 3,3′,5,5′-tetramethylbenzidine (TMB) chromogenic reaction. Moreover, S. aureus can be lysed to release the reductive bacterial contents, which can further inhibit the TMB chromogenic reaction. Based on this principle, SapYZUH5@Co3O4 + TMB reaction system was employed for detection with enhanced sensitivity of S. aureus, yielding an equation: A = − 0.092 Log (CSA) + 0.79 (R2 = 0.987), with an ultralow limit of detection (LOD) of 28 CFU mL−1. This system exhibited remarkable specificity and anti-interfere towards S. aureus, owing to the excellent affinity of SapYZUH5 towards S. aureus. In addition, S. aureus in the actual food samples was detected using this system, yielding recoveries ranging from 96.34 to 109.43%, demonstrating its exceptional accuracy. Hence, our proposed covalent immobilization of phage on the nanozyme can realize sensitive and specific colorimetric determination of S. aureus in food samples. [ABSTRACT FROM AUTHOR]

Nanozymes based on manganese oxide (MnO2) are demonstrated to be promising probes in colorimetric sensing applications. In this study, the r-MnO2/β-MnO2 heterophase nanostructure was simply prepared by a calcination process with controllable temperature. The characterization of the nanostructured material was confirmed by SEM, UV–vis spectroscopy, Raman, TGA–DSC, and XRD analysis. The r-MnO2/β-MnO2 exhibits a remarkably good catalytic activity in the oxidation process of 3,3′,5,5′-tetramethylbenzidine (TMB) compared with the r-MnO2 or Mn2O3 nanostructure owing to its heterophase junctions. The enhanced performance of the colorimetric sensor for ascorbic acid (AA) detection was investigated using the r-MnO2/β-MnO2 heterophase nanostructure as probe. The r-MnO2/β-MnO2 material enhanced the monitoring of AA in the wide linear range from 1 µM to 50 μM with a limit of detection of 0.84 µM. This work presents a promising and straightforward approach for the construction of MnO2-based colorimetric sensor and their practical application in plant growth monitoring. [ABSTRACT FROM AUTHOR]

This study introduces a novel method for the rapid and efficient detection of paracetamol, leveraging a colorimetric sensing mechanism predicated on the utilization of TMB-MnO2 nanosheets. The interaction of paracetamol with MnO2 is characterized by a selective reaction mechanism, leading to the reduction of MnO2 to Mn2+ ions and consequent attenuation of the oxidase-mimetic activity of MnO2. The developed colorimetric sensor exhibits a linear detection range for paracetamol extending from 5 × 10−4 to 10−2 M, with a lower detection limit quantified at 5.24 × 10−7 M. Empirical assessments conducted to ascertain the influence of potential interferents prevalent in actual samples revealed a negligible impact on the colorimetric sensor. Furthermore, the application of this sensor system to real-world samples demonstrated its capability to detect paracetamol with a notable recovery rate and a relative standard deviation of < 6.65%. This approach manifests significant promise for the efficacious detection of paracetamol in various sample matrices. [ABSTRACT FROM AUTHOR]

Calcium ions (Ca2+) are essential for a myriad of physiological functions, including excitability, neurotransmitter release, gene transcription, cell proliferation, synaptic plasticity, and hormone secretion. Consequently, the detection of Ca2+ concentrations in water is of fundamental and practical significance. In this study, a novel method for the simple, visual, and rapid colorimetric detection of Ca2+ is introduced, leveraging the surface plasmon resonance (SPR) absorbances of gold nanoparticles (AuNPs) modified with 5‐Pyrimidinylboronic acid (5‐PBA). A color change from wine‐red to gray‐blue was observed with increasing concentrations of Ca2+, indicative of the agglomeration of AuNPs. This agglomeration displayed favorable anti‐interference properties and selectivity. The limits of detection (LOD) were determined to be 0.08 mM by the unaided eye and 3.29 μM by UV‐visible spectroscopy. Moreover, an excellent linear relationship (R2=0.9879) was maintained within the Ca2+ concentration range of 0.0 to 0.5 mM. These results suggest that AuNPs modified with 5‐PBA are suitable for the quantitative determination of Ca2+. Subsequent testing on actual samples confirmed that this new method could be effectively applied to the monitoring of Ca2+ in water. [ABSTRACT FROM AUTHOR]

Alpha-fetoprotein (AFP) is a key marker for early cancer detection and assessment. However, the current detection methods struggle to balance accuracy with the need for decentralized medical treatment. To address this issue, a new AFP analysis platform utilizing digital image colorimetry has been developed. Functionalized gold nanoparticles act as colorimetric agents, changing from purple-red to light gray-blue when exposed to different AFP concentrations. A smartphone app captures these color changes and calculates the AFP concentration in the sample. To improve detection accuracy, a hardware device ensures uniform illumination. Testing has confirmed that this system can quantitatively analyze AFP using colorimetry. The limit of detection reached 0.083 ng/mL, and the average accuracy reached 90.81%. This innovative method enhances AFP testing by offering portability, precision, and low cost, making it particularly suitable for resource-limited areas. [ABSTRACT FROM AUTHOR]

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Chronic kidney disease (CKD) is a widespread condition with considerable health and economic impacts globally. However, existing methodologies for serum creatinine assessment often involve prolonged wait times and sophisticated equipment, such as spectrometers, hindering real-time diagnosis and care. Innovative solutions like point-of-care (POC) devices are emerging to address these challenges. In this context, there is a recognized need for remote, regular, automated, and low-cost analysis of serum creatinine levels, given its role as a critical parameter for CKD diagnosis and management. This study introduces a miniaturized system with integrated heater elements designed for precise serum creatinine measurement. The system operates based on the Jaffe method and accurate serum creatinine measurement within a microreservoir chip. Smartphone-based image processing using the hue-saturation-value (HSV) color space was applied to captured images of microreservoirs. The creatinine analyses were conducted in serum with a limit of detection of ~ 0.4 mg/dL and limit of quantification of ~ 1.3 mg/dL. Smartphone-based image processing employing the HSV color space outperformed spectrometric analysis for creatinine measurement conducted in serum. This pioneering technology and smartphone-based processing offer the potential for decentralized renal function testing, which could significantly contribute to improved patient care. The miniaturized system offers a low-cost alternative ($87 per device), potentially reducing healthcare expenditures (~ $0.5 per test) associated with CKD diagnosis and management. This innovation could greatly improve access to diagnosis and monitoring of CKD, especially in regions where access to sophisticated laboratory equipment is limited. [ABSTRACT FROM AUTHOR]

AbstractThe development of affordable, easy-to-use methods holds promise to broaden access to food analysis in resource-limited settings that will enhance food safety monitoring and the assessment of public health interventions. In this study, we propose a green extraction method called deep eutectic solvent liquid-liquid microextraction (DES-LLME), coupled with a simple detection technique referred to as the smartphone digital image colorimetry (SDIC), for the quantification of iodate in table salt. Optimization of the DES-LLME-SDIC method was conducted to enhance performance. At the optimum conditions, the proposed method achieved an enrichment factor between 6.1 and 27.8, with a limit of detection (LOD) between 0.52 and 0.84 µmol L−1, and a limit of quantitation (LOQ) between 1.73 and 2.81 µmol L−1. The concentration of iodate exhibited a satisfactory linear correlation with absorbance, as demonstrated by a well-fit regression model as verified by lack of fit test (p > 0.05), within a linear dynamic range from 1.73 to 25.00 µmol L−1. The precision of the method was validated through the relative standard deviation (%RSD) for intraday (3.6%) and interday (6.3%) precision. The developed method was applied for the determination of iodate in various salt samples. Additionally, the accuracy of the proposed SDIC method was evaluated with a separate ultraviolet-visible spectrometry method. Both methods exhibited statistical agreement. [ABSTRACT FROM AUTHOR]

Interleukin-6 (IL-6) detection and monitoring are of great significance for evaluating the progression of many diseases and their therapeutic efficacy. Lateral flow immunoassay (LFIA) is one of the most promising point-of-care testing (POCT) methods, yet suffers from low sensitivity and poor quantitative ability, which greatly limits its application in IL-6 detection. Hence, in this work, we integrated Aushell nanoparticles (NPs) as new LFIA reporters and achieved the colorimetric and photothermal dual-mode detection of IL-6. Aushell NPs were conveniently prepared using a galvanic exchange process. By controlling the shell thickness, their localized surface plasmon resonance (LSPR) peak was easily tuned to near-infrared (NIR) range, which matched well with the NIR irradiation light. Thus, the Aushell NPs were endowed with good photothermal effect. Aushell NPs were then modified with IL-6 detection antibody to construct Aushell probes. In the LFIA detection, the Aushell probes were combined with IL-6, which were further captured by the capture IL-6 antibody on the test line of the strip, forming a colored band. By observation with naked eyes, the colorimetric qualitative detection of IL-6 was achieved with limit of 5 ng/mL. By measuring the temperature rise of the test line with a portable infrared thermal camera, the photothermal quantitative detection of IL-6 was performed from 1~1000 ng/mL. The photothermal detection limit reached 0.3 ng/mL, which was reduced by nearly 20 times compared with naked-eye detection. Therefore, this Aushell-based LFIA efficiently improved the sensitivity and quantitative ability of commercial colloidal gold LFIA. Furthermore, this method showed good specificity, and kept the advantages of convenience, speed, cost-effectiveness, and portability. Therefore, this Aushell-based LFIA exhibits practical application potential in IL-6 POCT detection. [ABSTRACT FROM AUTHOR]

In this study, a chemical sensor based on silver nanoparticles (AgNPs) synthesized with Cucumis melo juice extract was presented for the determination of sulfide ions. The biosynthesized AgNPs, whose solution color was yellow, exhibited a sharp surface plasmon resonance peak at 405 nm. The addition of sulfide ions changed the surface properties of the AgNPs, resulting in a decrease in the absorbance intensity of the AgNPs, and the color of the solution changed from yellow to colorless. The response of the sensor to sulfide ions was linear in the concentration range of 0.5–11.5 µM, and the detection limit for this determination was 0.1 µM. The developed sensor was applied to detect sulfide ions in real water samples and showed excellent recoveries in the range of 98.7–103.5%. Furthermore, the AgNPs showed excellent selectivity toward sulfide ions. This assay is capable of qualitative and quantitative assessment of sulfide ions in environmental samples. [ABSTRACT FROM AUTHOR]

miRNA-21 (miR-21) is a potential biomarker for the monitoring of diseases through its expression levels. Simple, portable and sensitive miR-21 detection of is advantageous for health monitoring in Point of Care Testing (POCT). Gold nanoparticles (AuNP) as excellent colorimetric sensors are widely used in the POCT. However, their low sensitivity is a limitation of their clinical use. Herein, we developed an AuNPs-based miR-21 assay with enzyme-assisted amplification reaction to construct the colorimetric platform capable of detecting as low as 0.1nM. In this platform, template ssDNA as a signal molecule could hybridize with ssDNA-modified AuNPs to generate the color reaction. The target miR-21 specifically hybridized to the template ssDNA, which was then cleaved by exonuclease III (Exo III) to release the target miR-21. As a trigger, miR-21 catalyzed the degradation of the template ssDNA to amplify the signal by Exo III. By hybridizing miR-21 and template ssDNA in the presence of Exo III, R-21 induced a significant decrease in the level of template ssDNA to reduce the aggregation of AuNPs. There is a clear color difference in the presence/absence of miR-21 in the assay. In this assay, the optimal concentration of templated ssDNA and Exo III were 100nM and 0.06U/μL in a 100μL detection system. The LoD for UV–Vis spectrum and colorimetric reaction were 0.1nM and 0.5nM, respectively. The detection system has good selectivity and can be used to detect miR-21 in the simulated saliva. It has great potential for application in biomedical research as well as in clinical diagnostics. [ABSTRACT FROM AUTHOR]

In this study, nanosilica was utilized as a substrate for the deposition of polymeric layers imprinted with copper-(II) ions, which were used for the colorimetric detection of Cu-(II). The nanosilica was first prepared using the Stober method and then used in an in situ polymerization of aminopropyltriethoxysilane and tetraethyl orthosilicate in the presence of the template copper ions. Following the elution process, the polymer was washed with a proper solution to obtain the Cu-(II)-imprinted polymers on nanosilica (SiO2@MIP), which were characterized by transmission electron microscopy to reveal the diameter of the silica core to be approximately 350 nm, and the polymeric layers were about 40 nm in thickness. The SiO2@MIP was successfully employed in the colorimetric detection of Cu-(II) in aqueous solutions with concentrations ranging from 0.001 to 0.1 M, using xylenol orange as the colorimetric indicator. The color change could be easily observed by the naked eye, with colors shifting from yellowish-orange to dark purple. The sensing signal was quantitatively assessed using UV–vis absorbance, and the limit of detection for Cu-(II) was determined to be 0.064 mg/mL. Additionally, SiO2@MIP was demonstrated to be highly specific for the adsorption of Cu-(II) with the imprinted cavities. The proposed Cu-(II) imprinted polymers show promise in real-world detection of Cu-(II) with advantages of low cost, user-friendliness, and high selectivity. [ABSTRACT FROM AUTHOR]

As promising alternatives for natural enzymes, much attention has been paid to nanozymes. And our recent study showed that the medium acid sites on the support are the active sites for the adsorption and oxidation of the substrate. Thus, in this work, due to the abundance of medium acid sites, Al2O3 was chosen as the support to prepare Pt/Al2O3 nanozymes. Through the Pt/Al2O3 samples, we further proved that the distribution of the Pt clusters and the amount of the medium acid sites can significantly influence the peroxidase‐like activity. Then the Pt/Al2O3 sample was used for the detection of glucose. And as low as 0.96 μM glucose could be detected with a linear range from 5–60 μM via our method. This work showed the great potential applications of the easily prepared Pt/Al2O3 samples in varieties of simple, robust, and easy‐to‐make analytical approaches in the future. [ABSTRACT FROM AUTHOR]

Multifunctional N, Fe-doped carbon dots (N, Fe-CDs) were synthesized by the one-step hydrothermal method using ferric ammonium citrate and dicyandiamide as raw materials. The N, Fe-CDs exhibited peroxidase-like (POD) activity by catalyzing the oxidization of 3,3′,5,5′-tetramethylbenzidine (TMB) to the green oxidation state ox-TMB in the presence of hydrogen peroxide (H2O2). Subsequently, based on the POD activity of N, Fe-CDs, an efficient and sensitive colorimetric method for the detection of H2O2 and ascorbic acid (AA) was established with a limit of detection of 0.40 µM and 2.05 µM. The proposed detection method has been successfully applied to detect AA in fruit juice, vitamin C tablets, and human serum samples and has exhibited excellent application prospects in biotechnology and food fields. Furthermore, N, Fe-CDs also showed a protective effect on the cell damage caused by H2O2 and could be used as an antioxidant agent. [ABSTRACT FROM AUTHOR]

In this study, V2O5 nanoparticles with flake or prism‐like morphology were synthesized using a two‐step solvothermal synthesis and calcination process for the first time. These nanoparticles exhibited intrinsic oxidase‐like activity, catalyzing the oxidation of 3,3′,5,5′‐tetramethylbenzidine to produce blue oxidized 3,3′,5,5′‐tetramethylbenzidine even in the absence of H2O2, with a characteristic absorption peak at 652 nm. Upon the introduction of glutathione (GSH), the solution color gradually lightened, correlating with a reduction in absorbance. Leveraging these properties, we developed a simple, sensitive, and highly selective colorimetric biosensor utilizing V2O5 nanoparticles for GSH detection in human serum. The developed method demonstrated excellent linearity over a range of 1–30 μM, with a low detection limit of 4.04 nM. Additionally, it exhibited outstanding selectivity against common interfering substances in human serum. Furthermore, this biosensor enabled both naked‐eye detection and spectrophotometric quantitative analysis of GSH. Successful application to spiked serum samples yielded recoveries ranging from 97.1% to 101.7%. Overall, this method offers a promising approach for determining GSH content in human serum, with significant potential for biomedical testing applications. Its rapid and accurate detection capability may contribute to early diagnosis and treatment of various fatal diseases, including cancer and cardiovascular diseases. [ABSTRACT FROM AUTHOR]