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Thermometers, one of the most commonly used instruments at home, are normally adapted to measure temperature directly with high accuracy but rarely adopted to act as readout in the biosensors. It is necessary to find some ways to establish a relationship between the concentration of the target and the temperature change. In this study, a common thermometer was used as readout to develop a convenient immunosensor. The designed immunosensor comprises three components, including target recognition area, water flow system, and exothermic reaction bottle. The capture antibody for the target [carcinoembryonic antigen (CEA) was selected as a model target] was preloaded on the bottom of the recognition area. In the presence of CEA, a sandwich-type structure was formed between the capture antibody, CEA, and biotinylated detection antibody. Then, the streptavidin-functionalized platinum nanoparticles were labeled on the detection antibody due to biotin-avidin interaction. The captured platinum nanoparticles can effectively catalyze the decomposition of H2O2 into O2. The continuous production of gas resulted in pressure increment inside the reaction bottle and further pushed the water flow into the exothermic reaction bottle. Finally, the water reacted with calcium oxide to generate a large amount of heat in the exothermic reaction bottle; thereby the temperature inside the bottle was enhanced and recorded by a common thermometer easily. The temperature enhancement has a linear relationship with the CEA concentration in the range of 7.81-500 pg/mL with a detection limit of 0.6 pg/mL. Furthermore, by taking advantage of simplicity, compatibility, stability, and high sensitivity, our temperature-based immunoassay has been applied to detect CEA in human serum samples with satisfactory results.

Hydrogen sulfide (H2S) is a highly toxic gas, which poses a serious threat to human health and safety. It is necessary to develop some simple and highly selective and sensitive approach for the detection of hydrogen sulfide. In this study, a highly selective and sensitive fluorescence sensor for H2S detection has been developed on the basis of Cu(II)-dependent DNAzyme. The catalytic DNA strand (Cu-enzyme) was labeled with a quencher (black hole quencher, BHQ1) at the 5′-termini and its corresponding DNA substrate strand (Cu-substrate) was labeled with a 6-carboxyfluorescein (FAM fluorophore) at the 3′-end and an additional quencher was attached on the 5′-end. Cu-enzyme and Cu-substrate could hybridize with each other to form a triplex structure firstly and the FAM emission was quenched by the labeled quenchers. The present of Cu(II) could catalyze the oxidative cleavage of the Cu-substrate and hence caused the releasing of the quencher from the FAM fluorophore and the enhanced fluorescence of the system. However, in the presence of H2S, Cu(II) reacted with H2S to form CuS firstly, hindering the cleavage and the fluorescence enhancement. The decrease of fluorescence intensity had a linear relationship with the concentration of H2S in the range between 0.5 and 25 μM with a detection limit of 0.2 μM (S/N = 3). The proposed method innovatively used fluorescent labeling technology and DNAzyme sensing to detect gaseous hydrogen sulfide, and it has been successfully applied to detect the contamination of hydrogen sulfide gas in the refuse collectors with a simple purification procedure.

A comprehensive survey of recent developments and applications of capillary electromigration techniques for enantioseparations from January 2006 to June 2010 is presented. The techniques include capillary electrophoresis, chip capillary electrophoresis and capillary electrochromatography. The separation principles and the chiral recognition mechanisms are discussed. Additionally, on-line preconcentrations in chiral capillary electrophoresis are also reviewed.

A novel molecular imprinting sensor based on TiO

Based on the adsorption of a metal-organic framework (MOF) to DNA, a fluorescent biosensor for H

Graphene oxide (GO) has many exciting advantages such as easy preparation, low toxicity, good solubility and stability in aqueous solution. However, GO itself has a low near-infrared (NIR) absorption, and thus is not suitable for photothermal therapy and photoacoustic imaging. To overcome this limitation, a novel dye-enhanced GO is prepared utilizing the π–π stacking interactions between GO and indocyanine green (ICG). The ICG–GO complex has a high optical absorbance in the NIR region and exhibits excellent photothermal properties under NIR irradiation. In order to improve the cancer-targeting activity, GO was modified with folic acid (FA). In vitro experiments showed that the ICG–GO–FA nanocomposite could be used for targeted photothermal cancer cell destruction. Moreover, the application of the ICG–GO–FA nanocomposite for photoacoustic imaging was also demonstrated.

A pH-responsive controlled release system is proposed using acid-decomposable layered double hydroxides (LDHs) as inorganic nanovalves by virtue of the electrostatic adsorption of LDH nanosheets on the surface of mesoporous silica nanoparticles (MSNs). Guest molecules (Ru(bpy)3Cl2 in this case) are loaded and encapsulated in a neutral environment. The dissolution of the LDH coatings in an acidic environment triggers the release of the guest molecules from the MSNs.

A kind of surface glycoprotein imprinting over magnetic Fe

A novel imprinting strategy using reversible covalent complexation of glycoprotein is described for creating glycoprotein-specific recognition cavities on 3-acrylamidophenylboronic acid-immobilized silica nanoparticles (SiO2@AAPBA). Two kinds of organic silanes (3-aminopropyltriethoxysilane (APTES) and n-octyltrimethoxysilane (OTMS)) were then polymerized on the surface of SiO2@AAPBA after the template (horseradish peroxidase (HRP)) was covalently immobilized by forming cyclic boronate complexes and their influence was examined. The results showed that not only the silane composition but also the relative proportions play an important role in glycoprotein imprinting. The template recognition properties were evaluated by single-protein or competitive batch rebinding experiments, and the results showed that the HRP-imprinted silica nanoparticles (HRP-MIP silica NPs) exhibited higher recognition ability and selectivity towards the template than the nonimprinted silica NPs and their corresponding imprinted factor (a) reached 2.71. The as-prepared HRP-MIP silica NPs could not only differentiate the template from another glycoprotein, but also enrich HRP from spiked human serum. The good results demonstrated their potential in glycoproteomic analysis.

The quality of Pseudostellaria heterophylla depends on the growing area of the plants greatly. Compared with near infrared spectroscopy employed to discriminate the geographic regions before, the Raman signal is more obvious. So far, discrimination of P. heterophylla from different regions by Raman spectroscopy has not yet been realized. Hence, Raman spectroscopy coupled with chemometric methods to rapidly and effectively discriminate P. heterophylla from different regions was studied. Original spectra of P. heterophylla in wavenumber range of 4000–100 cm−1 were acquired. Then, a steady and exact model, partial least squares discriminant analysis (PLS-DA), was constructed. And competitive adaptive reweighted sampling (CARS) was further used to extract effective wavelength spectral characteristic variables. Results show that CARS-PLS-DA model is an appropriate model to discriminate the P. heterophylla, with determination coefficient of calibration (R2C), root mean square error of cross validation (RMSECV), determination coefficient of prediction (R2P), and root mean squared error of prediction (RMSEP) are 0.9468, 0.1979, 0.9665, and 0.1120, respectively. These results demonstrated that the built method is useful and effective to discriminate P. heterophylla from different regions, which provide a new idea in the application of rapid field test.

Common colorimetric immunoassays only show monochromatic intensity variations, and the absorbance intensity is utilized for the quantitative detection of the analytes. Herein, we demonstrate for the first time that Au Nanobipyramid@Ag Nanorods (Au NBP@Ag) is an ideal multicolor chromogenic substrate for immunoassays which combines the absorbance intensity with the Localized Surface Plasmon Resonance (LSPR) peak shifts are utilized for quantitative detection of the analytes, and vivid color variations are used for semi-quantitative detection. Our investigation reveals that unlike the single metallic nanoparticles such as gold nanorods which show one-way LSPR peak shifts, Au NBP@Ag Nanorods shows an interesting multi-way peak shifts: the LSPR peak would initially blue shift, and then red shift, finally blue shift again during the etching process. As a result, a series of vivid colors can be observed. The results indicate that the correlation linear range for the detection of Squamous cell carcinoma antigen (SCCA) was 2.5–105 ng/mL. Although only the detection of SCCA is demonstrated in this work, this method is easy to expand to detect other biomarkers since our method is based on conventional immunoassay strategy.

The amino-functionalized metal organic framework (NH2-Cu-MOF) was fabricated via bottom-up synthesis strategy. Detailed characterization using electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy demonstrated that the as-synthesized NH2-Cu-MOF was two-dimensional nanosheet (a thin thickness ∼4.2 nm). Results showed that the as-synthesized NH2-Cu-MOF nanosheet possessed fluorescence property (λem = 425 nm) as well as peroxidase mimic activity. On the basis of these two properties, we proposed a biosensor for hypoxanthine detection. The fluorescence intensity had a linear relationship with the hypoxanthine concentration in the range of 10–2000 μM. The limit of detection was 3.93 μM (S/N = 3). This work contributes to the synthesis of a new two-dimensional MOF nanosheet and extends the application of two-dimensional MOF nanosheet on biological luminescent sensors.

A specific and label-free “on-off-on” luminescence biosensor based on a novel heterometallic cluster [Ag6Au6(ethisterone)12]-estrogen receptor α (Ag6Au6Eth-ERα) aggregation utilizing graphene oxide (GO) as a quencher to lead a small background signal was firstly constructed to detect immunoglobulin G (IgG) with a simple process and high selectivity. The efficient photoluminescent (PL) Ag6Au6Eth-ERα aggregation is strongly quenched by GO. In the presence of IgG, the PL of this system will be restored, and perceivable by human eyes under UV lamp excitation (365 nm). The quenching mechanism of GO on Ag6Au6Eth-ERα and enhancement mechanism of IgG on Ag6Au6Eth-ERα-GO were investigated in detail. Under the optimum conditions, the biosensor for high sensitive IgG detection expressed a wider linear range of 0.0078–10 ng/mL and a lower detection limit of 0.65 pg/mL with good stability and repeatability, which provided a new approach for label-free IgG detection.

Hydrogen sulfide (H2S) is important for normal neural functions, which involves protecting neurons from oxidative stress and neuronal transmission modulation in brain. The detection of H2S is significant for revealing its role in the diagnosis of various disease. In this study, a novel multicolor colorimetric assay based on the etching of gold nanorods (Au NRs) is proposed to evaluate H2S level with the naked eye. This measurement relies on the catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) via horseradish peroxidase (HRP) to produce TMB2+, which could etch the Au NRs quickly and accompany with a distinct color change. The vivid colors can be easily distinguished with the naked eye without any sophisticated instruments. The presence of H2S can cause the deactivation of HRP, which affects the amount of TMB2+ produced and consequently affects the color changing of the system. Based on this mechanism, a simple but sensitive multicolor colorimetric assay is developed for H2S detection with a line...

A simple, low-cost, and sensitive liposome-based colorimetric aptasensor has been developed to detect ochratoxin A (OTA). Specifically, a dumbbell-shaped probe was designed, including magnetic beads (MBs), double-stranded DNA (dsDNA), and enzyme-encapsulated liposome. The dsDNA formed by the hybridization between OTA aptamer and its complementary probe. And the dsDNA was used to contact the MBs and the enzyme-encapsulated liposome. In the presence of OTA, the aptamer preferred to combine with OTA to form G-quadruplex, resulting in the release of the detection probe and the enzyme-encapsulated liposome. Each liposome contained a large amount of HRP. Thus, when the liposome was lysed by adding the mixed solution of 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2, a large number of HRP were released. HRP could catalyze the H2O2-mediated oxidation of TMB and hence resulted in the color change from colorless to blue with the OTA concentration varying, and this variation can be observed by naked eyes easily. The result showed that the absorption intensity at 652 nm enhanced with the increase of OTA concentration ranging from 0.05 to 2.0 ng mL−1, and the limit of detection was calculated to be 0.023 ng mL−1 (S/N = 3). The developed colorimetric aptasensor has been applied to detect OTA concentration in corn samples with satisfied results.

A promising and novel electrochemiluminescence (ECL) aptasensor equipped with an electrically heated indium tin oxide (ITO) electrode was constructed. Temperature control was achieved by heating the ITO electrode, avoiding the tedious operation and substantial increase in noise experienced when heating the bulk solution. Using the heated ITO electrode, an order of magnitude improvement in ECL sensitivity was obtained by operating the electrode at 65 °C compared to 25 °C, and this can be used to further enhance the performance of the biosensor. Keywords: Temperature control, Heated indium-tin-oxide electrode, Electrochemiluminescence, Hyperbranched rolling circle amplification, Ochratoxin A

Aflatoxin B1 (AFB1) can cause great threat to human health, so the development of convenient and portable device for sensitive detection of AFB1 is highly desired. The portable pH meter has the characters of facile operation, low cost, and easy availability. Therefore, in this study, we investigate the applicability of utilizing a pH meter as the readout to develop a portable sensor for AFB1. The specific detection of AFB1 is realized via the combination of AFB1-responsive aptamer-cross-linked hydrogel. Upon the addition of AFB1, AFB1 binds to its aptamer with high affinity in lieu of aptamer/DNA complex, causing the collapse of hydrogel network and results in the releasing of urease into the solution. The released urease can catalyse the hydrolysis of urea and result in the rise of pH value. The change of pH value has a direct relationship to the concentration of AFB1 in the range of 0.2-20µM with a detection limit of 0.1µM (S/N = 3). The proposed portable device is successfully applied to assay AFB1 in the food samples with satisfied results.

Visual detection method is a means of quantitative analysis by the naked eye through the comparison of color intensity or type of change. Owing to its simplicity, low-cost, rapid operation, and equipment-free, visual detection was widely used in the detection of numerous targets. Gold nanomaterials were widely used in the construction of visual biosensors due to its unique optical properties when compared to other nanomaterials. The local surface plasmon resonance absorption peak would change with the variety in the distance or the morphology. Herein, this paper reviewed the application of gold nanomaterials in the construction of visual biosensors for the detection of target molecules. Meanwhile, we pointed out the main problems of gold nanoparticles based colorimetric methods in the determination of actual samples. The forecast of gold nanoparticles based biosensor was also provided at the end of this article.

The pH meter, one of the most common sensors for laboratory measurements, has the advantages of excellent sensitivity, low price, high reliability, and ease of use. In this study, the high sensitivity of the pH meter was coupled with the high selectivity of immunosorbent assay to develop a simple and portable biosensor for aflatoxin B1 (AFB1) determination. Urease was first labelled on the AFB1 antigen, in the presence of AFB1; the target competed with the urease-labeled AFB1 antigen to be captured by the antibody. Urease could catalyse the hydrolysis of urea into ammonia and induce the pH increase of the solution; the change could easily be detected using a handheld pH meter or pH-sensitive dye. Under optimized conditions, the pH value enhancement had a linear relationship with the logarithm of the concentration of AFB1 in the range of 0.62 to 23.42 ng mL−1. The proposed biosensor has been applied to detect AFB1 in real samples with satisfactory results.

Vascular endothelial growth factor (VEGF) is a crucial signaling protein for the tumor growth and metastasis, which is also acted as the biomarkers for various diseases. In this research, we fabricate an aptamer-antibody sensor for point-of-care test of VEGF. Firstly, target VEGF is captured by antibody immobilized on the microplate, and then binds with aptamer to form the sandwich structure. Next, with the assist of glucose oxidase (GOx)-functionalized ssDNAs, hybridization chain reaction occurs using the aptamer as the primer. Thus, GOx are greatly gathered on the microplate, which catalyzes the oxidization of glucose, leading to the pH change. As a result, the detect limit at a signal-to-noise was estimated to be 0.5 pg/mL of target by pH meter, and 1.6 pg/mL of VEGF was able to be distinguished by naked eyes. Meanwhile, this method has been used assay VEGF in the serum with the satisfactory results.

Hypochlorite (ClO–) is one of the most important reactive oxygen species (ROS), which plays an important role in sustaining human innate immunity during microbial invasion. Moreover, ClO– is a powerful oxidizer for water treatment. The safety of drinking water is closely related to its content. Herein, m-phenylenediamine (mPD) is used as a precursor to prepare carbon dots (named m-CDs) with highly fluorescent quantum yield (31.58% in water), and our investigation shows that the strong fluorescent emission of m-CDs can be effectively quenched by ClO–. Based on these findings, we developed a novel fluorescent nanoprobe (m-CDs) for highly selective detection of ClO–. The linear range was from 0.05 to 7 μM (R2 = 0.998), and the limit of detection (S/N = 3) was as low as 0.012 μM. Moreover, a portable agarose hydrogel solid matrix-based ratiometric fluorescent nanoprobe (m-CDs@[Ru(bpy)3]2+) sensor was subsequently developed for visual on-site detection of ClO– with the naked eyes under a UV lamp, suggesting it...

Hexagonal boron nitride nanosheets (BNNS), one kind of inorganic graphene analogue, exhibit high fluorescence quenching ability via the photo-induced electron transfer (PET) and different affinity toward single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). As a proof of concept, the BNNS was first used as a sensing platform for the rapid detection of DNA and small molecules with high sensitivity and selectivity in this study. This strategy is versatile and quick fluorescence sensing of DNA and extensive DNA related analytes such as metal cations and small molecules. Moreover, this strategy might be available for the practical application in future. This work provides an avenue for understanding the interaction between two-dimensional nanomaterials and biomolecules and designing novel sensing strategies for extending the applications of nanomaterials in bioanalysis.

Poly(glutamic acid) (P-GLU)/carboxyl functionalized multiwalled carbon nanotubes (MWCNTs-COOH)/polyvinyl alcohol (PVA) modified glassy carbon electrode (GCE) has been successfully prepared and the electrochemical behavior of procaterol hydrochloride (ProH) was studied. The results show that the as-prepared modified electrode exhibits a good electrocatalytic property towards the oxidation of ProH in 0.2M phosphate buffer solution (PBS) (pH 6.0) due to the enhanced oxidation peak current at ~+0.59V. Under optimal reaction conditions, the oxidation peak current of ProH is proportional to its concentration in the linear dynamic ranges of 0.060 - 8.0μM (R = 0.9974), with a detection limit of 8.0 × 10-9M. Finally, this method was efficiently used for the determination of ProH in tablets and human urine with recoveries of 88.5~98.7% and 89.2 ~ 108.0%, respectively.

Fish product is one of the main seafood with the disadvantage of easy to perish. Various indexes and diverse methods have been developed to evaluate the fish freshness, but most of them are complex and cannot be applied for on-field detection. In this study, we reported a simple, visual and economical multicolor biosensor based on the etching of gold nanorods (GNRs) to evaluate the fish freshness with the naked eye. Hypoxanthine (Hx) is chosen as the index of fish freshness and it react with the dissolved oxygen to produce H 2 O 2 at the presence of xanthine oxidase (XOD). Then GNRs are etched quickly by the H 2 O 2 in the presence of Fe 2+ . Correspondingly, the GNRs surface plasmon resonance (SPR) is regulated and results in a distinctly color change of the system, which can be easily distinguished with the naked eye. Therefore, the concentration of Hx in the fish samples can be semi-quantitatively analyzed with the naked eye. The proposed multicolor Hx sensor has been successfully applied to the detection of Hx in fish samples.

The authors describe a biosensor for histidine that is based on the use of a DNAzyme catalytic beacon. The Cu(II)-dependent DNA-cleaving DNAzyme (Cu-Enzyme) was modified with a quencher (BHQ1) at its 5′ end, and the corresponding substrate strand (Cu-Sub) was modified with a quencher and the FAM fluorophore at its 5′ and 3′ ends, respectively. The green FAM emission of the system is completely quenched after the Cu-Enzyme is hybridized with Cu-Sub. The presence of Cu(II) triggers the cleavage of the Cu-Sub so that fluorescence recovers. Histidine forms a complex with Cu(II) ion. The complex is not capable of cleaving Cu-Sub effectively so that the fluorescence of the system is not restored. These findings were exploited to design a robust and sensitive assay for the determination of histidine. Fluorescence intensity is linearly related to the concentration of histidine in the range between 0.05 and 40 μM, and the detection limit is 20 nM. The method has been successfully applied to the determination of histidine in (spiked) human urine and gave satisfying results.

A fluorescent biosensor for ochratoxin A was fabricated on the basis of a new nanocomposite (Fe3O4/g-C3N4/HKUST-1 composites). Fe3O4/g-C3N4/HKUST-1 was synthesized in this work for the first time, which combined HKUST-1 with g-C3N4 to improve its chemical stability. Fe3O4/g-C3N4/HKUST-1 composites have strong adsorption capacity for dye-labeled aptamer and are able to completely quench the fluorescence of the dye through the photoinduced electron transfer (PET) mechanism. In the presence of ochratoxin A (OTA), it can bind with the aptamer with high affinity, causing the releasing of the dye-labeled aptamer from the Fe3O4/g-C3N4/HKUST-1 and therefore results in the recovery of fluorescence. The fluorescence intensity of the biosensor has a linear relationship with the OTA concentration in the range of 5.0-160.0ng/mL. The LOD of sensor is 2.57ng/mL (S/N=3). This fluorescence sensor based on the Fe3O4/g-C3N4/HKUST-1 composites has been applied to detect OTA in corn with satisfying results.

A label-free, ultra-sensitive and turn-on fluorescence method to detect melamine has been developed. The strategy uses the DNA-Ag nanoclusters (DNA-AgNCs) as the fluorescence probe. The fluorescence of DNA-AgNCs can be quenched in presence of Hg2+. However, When Hg2+ and melamine were reacted for 15 min at 1000 rmp then introduced into DNA-AgNCs solution, a strong fluorescence recovery could be found. Based on this methodology, the changing fluorescent intensity has a linear relationship with melamine in the range of 0.2 μM to 4 μM (R2=0.997). The detection limit down to 0.1 μM was obtained, which is 200 times lower than the melamine safety limit of 20 μM estimated by the US Food and Drug Administration. In addition, we had been successfully applied this method to detect melamine in milk powder and raw milk.

A novel electrochemiluminescence (ECL) biosensor was developed for high sensitive and selective detection of miRNA-21 based on the efficient and specific toehold-mediated strand displacement (TMSD) amplification with Ru(phen)

Thermometers, one of the most commonly used instruments at home, are normally adapted to measure temperature directly with high accuracy but rarely adopted to act as readout in the biosensors. It is necessary to find some ways to establish a relationship between the concentration of the target and the temperature change. In this study, a common thermometer was used as readout to develop a convenient immunosensor. The designed immunosensor comprises three components, including target recognition area, water flow system, and exothermic reaction bottle. The capture antibody for the target [carcinoembryonic antigen (CEA) was selected as a model target] was preloaded on the bottom of the recognition area. In the presence of CEA, a sandwich-type structure was formed between the capture antibody, CEA, and biotinylated detection antibody. Then, the streptavidin-functionalized platinum nanoparticles were labeled on the detection antibody due to biotin-avidin interaction. The captured platinum nanoparticles can effectively catalyze the decomposition of H

Gold nanoparticles (AuNPs) have been frequently utilized for the construction of diverse colorimetric biosensors. Normally, AuNPs with sharp edges could have better sensitivity. However, the poor monodipersity of AuNPs with sharp edges seriously confines their utility for colorimetric biosensing. Herein, we demonstrate the utility of highly uniform gold nanobipyramids (Au NBPs) for ultrasensitive colorimetric detection of H5N1 virus. The proposed method is based on the fact that alkaline phosphatase (ALP) could catalyze the decomposition of 4-aminophenyl phosphate (4-APP) to generate 4-aminophenol (4-AP), which would then reduce silver nitrate to metal silver and then deposited on Au NBPs. The metal silver shell coated on the Au NBPs changed the refractive index of gold and thus resulted in a blue shift of longitudinal localized surface plasmon resonance (LSPR) and accompanied a vivid color change. This method exhibited a higher sensitivity than that of other Au NPs such as gold nanorods due to the high-i...

Herein, an electrochemiluminescence (ECL) biosensor for ultrasensitive and specific detection of Kras mutant genes has been developed on the basis of the high discrimination capability of locked nucleic acid (LNA) and dual signal amplification techniques including DNA walkers and hyperbranched rolling circle amplification (HRCA).

A readily available aminoquinoline derivative (5-(quinolin-8-yliminol)pentanal, QYP) is used as a new cost-effective colorimetric probe for Cu2+ ion detection by forming a complex with a stoichiometry of 1 : 2. The QYP conjugated with Cu2+ ions induces a discernable color change from light yellow to red-brown in the solution, and the corresponding UV-Vis absorption shifts from 380 nm to 510 nm dramatically. The detection limit for Cu2+ ions is 2.0 μM by the naked eye, approaching other previously reported colorimetric methods, and without tedious conditions. Other possible contaminated metal ions cause no significant interference to detecting Cu2+ ions with the proposed probe. The stability constant of the complex is estimated to be 7.87 × 1010 M−2, which suggests the high stability of the conjugation of QYP with Cu2+ ions. Besides, it was successfully applied to assay Cu2+ ions in river water samples, indicating that the probe may become a great potential candidate in complex sample determination.

A kind of protein imprinted over magnetic Fe3O4@Au multifunctional nanoparticles (NPs) with multiple binding sites was synthesized and investigated. Magnetic Fe3O4@Au NPs as carrier materials were modified with 4-mercaptophenylboronic acid (MPBA) and mercaptopropionic acid (MPA) to introduce boronic acids and carboxyl groups. Using Bovine Hemoglobin (BHb) as a template, a polydopamine(PDA)-based molecular imprinted film was fabricated to produce a kind of magnetic molecularly imprinted nanoparticle (MMIP), possessing multiple binding sites with benzene-diol, amino groups, boronic acids and carboxyl groups. The MMIPs exhibited an excellent imprinting effect and adsorption capacity (89.65± 0.38 mg g−1) toward the template protein. The results show that the MMIPs reached saturated adsorption at 0.5 mg mL−1 within 90 min. The synthesized MMIPs are suitable for the removal and enrichment of the template protein in proteomics. The strategy of multiple binding sites paves the way for the preparation of functional nanomaterials in molecular imprinting techniques.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs), as one of the derivatives of polybrominated diphenyl ethers (PBDEs), have received extensive concern recently. In this paper, the interaction of OH-PBDEs and human serum albumin (HSA) was investigated using 4-OH-2,2′,3,4′-tetrabromodiphenyl ether (4-OH-BDE-42) as a representative. The binding constant, the number of binding sites and the binding site were investigated using fluorescence spectroscopy. The predominant forces of the interaction were van der Waals and hydrogen bonds, which was made clear by the calculation of thermodynamic parameters. The alterations of HSA protein secondary structure in the presence of 4-OH-BDE-42 were confirmed by UV-Vis and circular dichroism (CD) spectroscopy. The distance between HSA and 4-OH-BDE-42 was studied by Forster's non-radioactive energy transfer theory. An equilibrium dialysis experiment was performed, which indicated that 4-OH-BDE-42 severely affects the physiological function of HSA in transportation of 3,3′,5-triiodothyronine (T3), Trp and VB2. This paper has made deep investigation and detailed interpretation of the interaction of 4-OH-BDE-42 and HSA.

A highly sensitive and selective fluorescence biosensor for inorganic pyrophosphatase (PPase) activity has been developed based on special click ligation trigger hyperbranched rolling circle amplification (CLT-HRCA). Pyrophosphate ion (PPi) can coordinate with Cu2+ to form stable PPi/Cu2+ complex and Cu2+ in the complex cannot be reduced to Cu+. The addition of PPase causes the hydrolysis of PPi into orthophosphate (Pi) and therefore induces the releasing of Cu2+ from the stable PPi/Cu2+ complex, and the free Cu2+ is easily reduced to Cu+ by sodium ascorbate. Then Cu+ catalyzes the cyclization reaction between the specially designed 5′-azide and 3′-alkyne tagged padlock probes through Cu+ catalyzed azide-alkyne cycloaddition (CuAAC), which in turn initiates the hyperbranched rolling circle amplification (HRCA). Given that the CLT-HRCA products contain large amounts of double-stranded DNAs (dsDNAs), the addition of SYBR Green I resulted in the enhanced fluorescence signal. There was a linear relationship between the enhanced fluorescence intensity and the logarithm PPase activity ranging from 0.05 to 25 mU with a detection limit of 0.02 mU. Such proposed biosensor has been successfully applied to screen the potential PPase inhibitors and has accessed the related inhibit ability with high efficiency.

Based on the strong enhancement effect of procaterol hydrochloride on the electrochemiluminescence (ECL) of Ru(bpy)32+ (bpy = 2,2′-bipyridine) in an alkaline H3PO4–NaOH buffer solution on a bare Pt electrode, a simple, rapid and sensitive method was developed for the determination of procaterol hydrochloride. The optimum conditions for the enhanced ECL have been developed in detail in this work. Under optimum conditions, the logarithmic ECL enhancement vs. the logarithmic concentration of procaterol hydrochloride is linear over a wide concentration range of 2.0 × 10−7 to 2.0 × 10−4 M (r = 0.9976), with a limit of detection of 1.1 × 10−8 M (S/N = 3), and a relative standard deviation of 2.1% (n = 7, c = 5.0 × 10−6 M). The proposed method was applied to the determination of this drug in tablets with recoveries of 89.7%–98.5%. In addition, a possible mechanism for the enhanced ECL of Ru(bpy)32+, which is caused by ProH, has also been proposed.

A new label-free DNA sensing protocol was designed for fluorescent detection of mercury(II) (Hg(2+)), coupling hairpin DNA-scaffolded silver nanocluster (DNA-AgNC) with exonuclease III-assisted target recycling amplification. The assay was carried out through target-induced conformational change of hairpin DNA, while the signal derived from the formed silver nanoclusters on hairpin DNA probes. Initially, target Hg(2+) was specifically coordinated with thymine-thymine (T-T) mismatches to form an intact hairpin DNA. Then, the newly formed hairpin DNA was digested through exonuclease III from blunt 3' termini and restrained at 3' protruding terminus, thus resulting in the release of target Hg(2+) from hairpin DNA. The liberated target Hg(2+) initiated the next cycling, thereby causing the conformational change of numerous hairpin probes from the stem-loop DNA structure to single-stranded DNA. Under the optimal conditions, the fluorescent intensity of the as-produced DNA-AgNCs decreased with the increasing Hg(2+) concentration within a dynamic range from 0.1 nM to 10nM with a detection limit (LOD) of 24 pM. Moreover, the low-cost fluorescent sensing system exhibited high reproducibility and good specificity, thus representing an optional sensing platform for rapid screening of Hg(2+) in environmental water samples.

In this work, a sensitive and specific electrochemical biosensor for lead ion (Pb(2+)) detection was developed by coupling with synergetic catalysis of porous Au-Pd bimetallic nanoparticles and hemin/G-quadruplex-based DNAzyme. In the presence of target Pb(2+), the substrate strand was cleaved and the enzyme strand was released. Subsequently, G-rich DNA-labeled Au-Pd bimetallic nanoparticle was linked with the released enzyme strand through the helper DNA. Upon addition of hemin, a large number of hemin/G-quadruplex-based DNAzyme molecules were formed on the electrode to serve as nicotinamide adenine dinucleotide hydrogen (NADH) oxidase and peroxidase mimics. DNAzyme could catalyzed the reduction of H2O2, generated from NADH in the presence of O2, to produce an electrochemical signal when using thionine as the electron mediator. Introduction of porors Au-Pd bimetallic nanoparticles could enhance the detectable signal and cause the increase in the sensitivity. Experimental results showed that the variations (∆I) in the cathodic peak currents of the biosensor were linearly dependent on target Pb(2+) concentrations from 1.0 pM to 100 nM with a detection limit (LOD) of 0.34 pM. The excellent performance of the sensing platform indicated its promising prospect as a valuable tool for simple and cost-effective Pb(2+) detection in practical application.

A simple, low-cost transducer with glucometer readout was designed for sensitive detection of mercury(II) (Hg(2+)), coupling with thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination chemistry and invertase-functionalized gold-dendrimer nanospheres for the signal amplification. Initially, nanogold-encapsulated poly(amidoamine) dendrimers (Au DENs) were synthesized by in-situ reduction of gold(III). Thereafter, the as-prepared Au DENs were utilized for the labeling of invertase and T-rich signal DNA probe. In the presence of target Hg(2+), the functionalized Au DENs were conjugated to capture DNA probe-modified electrode via T-Hg(2+)-T coordination chemistry. Accompanying the Au DENs, the labeled invertase could hydrolyze sucrose into glucose, which could be quantitatively monitored by an external personal glucometer (PGM). The PGM signal increased with the increasing target Hg(2+) in the sample. Under the optimal conditions, our designed sensing platform exhibited good PGM responses toward target Hg(2+), and allowed the detection of Hg(2+) at a concentration as low as 4.2 pM. This sensing system also displayed remarkable specificity relative to target Hg(2+) against other competing ions, and could be applied for reliable monitoring of spiked Hg(2+) into the environmental water samples with satisfactory results. With the advantages of cost-effectiveness, simplicity, portability, and convenience, our strategy provides a tremendous potential to be a promising candidate for point-of-use monitoring of non-glucose targets by the public.

Background Liquid biopsy based on 5-hydroxymethylcytosine (5hmC) signatures of plasma cell-free DNA (cfDNA) originating from tumor cells provides a novel approach for early diagnosis in hepatocellular carcinoma (HCC). Here, we sought to develop a reliable model using cfDNA 5hmC signatures and protein biomarkers for diagnosis and prognosis of HCC. Patients and methods We carried out genome-wide 5hmC sequencing of cfDNA samples collected from 165 healthy volunteers, 62 liver cirrhosis (LC) patients and 135 HCC patients. A sensitive 5hmC diagnostic model was developed based on 5hmC signatures selected by sparse Partial Least Squares Discriminant Analysis and cross-validation to define the weighted diagnostic score (wd-score). Then, we combined protein biomarkers with the wd-score to build a more robust score (HCC score) by logistic regression. Results The distribution pattern of differential 5hmC regions could clearly distinguish HCC patients, LC patients and healthy volunteers. The wd-score based on 64 5hmC signatures in cfDNA achieves 93.24% of area under the curve (AUC) to distinguish HCC patients from non-HCC patients, and the HCC score by combing protein biomarkers achieves 92.75% of AUC to distinguish HCC patients from LC patients. Meanwhile, the HCC score showed high capacity for screening high recurrence risk patients after receiving surgical resection, and appeared to be an independent indicator for both relapse-free survival (P = 0.00865) and overall survival (P = 0.000739). Furthermore, the values of the HCC score in patients' longitudinal plasma samples were positively associated with tumor burden dynamics during follow-up. Conclusion We have developed and validated a novel non-invasive liquid biopsy strategy for HCC diagnosis, prognosis and surveillance during HCC progression., Highlights • A novel liquid biopsy approach was developed for HCC diagnosis, prognosis, and surveillance. • Novel HCC score defined here showed excellent capacity in distinguishing HCC patients from liver cirrhosis patients. • HCC score could predict the early recurrence risk for HCC patients after receiving surgical operation. • HCC score could sensitively monitor tumor burden and progression of HCC in longitudinal.

A copper(II)-based two-dimensional metal-organic framework with nanosheet structure (CuBDC NS) that possesses peroxidase (POx) mimicking activity was prepared. In the presence of hydrogen peroxide, the system catalyses the oxidation of terephthalic acid to a blue-fluorescent product (excitation = 315 nm; emission = 425 nm). Pyrophosphate has a very strong affinity for Cu2+ ion and blocks the POx-mimicking activity of the CuBDC NS. If, however, inorganic pyrophosphatase is present, the POx mimicking activity is gradually restored because pyrophosphate is hydrolyzed. The findings were used to design a method for the determination of the activity of inorganic pyrophosphatase by fluorometry. Fluorescence increases linearly in the 1–50 mU·mL−1 inorganic pyrophosphatase activity range. The limit of detection is 0.6 mU·mL−1 (S/N = 3).

A surface-enhanced Raman scattering (SERS) substrate with good flexibility and high water absorbing capacity is reported. It consists of a calcium alginate sponge incorporating gold nanoparticles. These are in close contact with the sponge without the need for amino or sulfhydryl modification. The substrate is capable of detecting the dyes crystal violet (CV) and malachite green (MG) in water directly and rapidly by immersing it into the liquid sample. Preconcentration and separation are not required. The dyes absorbed on the sponge can be detected without drying and thus the whole analytical process can be completed within 3 min. The results show that the lowest detectable concentrations are 0.1 and 0.25 μg⋅L-1 for CV and MG, respectively. This is lower than the minimum required performance limits set by the European Commission and the US EPA. Moreover, MG and CV can be simultaneously detected in liquid samples due to their different SERS bands (at 1216 and 1534 cm-1, respectively). It should be noted that the molecular structures of MG and CV are very similar. Therefore, the method has a large potential for determination of several analytes simultaneously even in complex sample metrics. Graphical abstract Schematic presentation of the fabrication of a sodium alginate sponge loaded with gold nanoparticles. Gold nanoparticles together with gel-like alginate were freeze-dried to form the sponge. The sponge was cross-linked by CaCl2 solution and then it was freeze-dried again.

Foodborne contaminants widely exist in foods, which can lead to various foodborne diseases and food safety issues. The development of quick, sensitive and universal analytical approaches for foodborne contaminants is imperative. Electrochemiluminescent functional nucleic acids (ECL FNAs)-based sensors are a series of sensing devices using FNAs as the recognition elements and ECL as the transducer. Contributing to the specific recognition ability of FNA and the high sensitivity of ECL, ECL FNA-based sensors are considered to be of great application potential for foodborne contaminants monitoring. This review mainly presents the applications of ECL FNA-based sensors for foodborne contaminants (including microorganisms, mycotoxins, allergens, antibiotics, heavy metal ions, pesticides and some illegal additives). In general, the application of ECL FNA-based sensors in the field of food analysis is just in its infancy. Although there are several limitations and challenges, it is envisaged that ECL FNA-based sensors will have broad prospects for food analysis in the future.

A new heated thiol-functionalized ionic liquid (TFIL)/Au composite electrode, which possessed the advantages of a heated electrode technique and ionic liquids (ILs), was designed and fabricated in this study. The electrode temperature (Te) could be accurately controlled by indirect electrical heating. Attributed to the stable Au–S bone and the very low vapor pressure of IL, the immobilized TFIL was stable on the electrode at high Te. The heated TFIL/Au electrode could be expediently used to study the electrochemical behavior of thermally unstable material at high temperature. The analytical performances of electrochemical (EC)/electrochemiluminescence (ECL) detection systems based on the heated TFIL/Au electrodes were evaluated by HSO3− and phenol, respectively. Higher electron-transfer rates, enhanced sensitivities, and improved reproducibilities were obtained compared with the bare Au electrode. The heated TFIL/Au composite electrode presented a promising platform for EC or ECL sensors.

Biomolecular immobilization and construction of the sensing platform are usually crucial for the successful development of a high-efficiency detection system. Herein we report on a novel and label-free signal-amplified aptasensing for sensitive electrochemical detection of small molecules (adenosine triphosphate, ATP, used in this case) by coupling with target-induced hybridization chain reaction (HCR) and the assembly of electroactive silver nanotags. The system mainly consisted of two alternating hairpin probes, a partial-pairing trigger-aptamer duplex DNA and a capture probe immobilized on the electrode. Upon target ATP introduction, the analyte attacked the aptamer and released the trigger DNA, which was captured by capture DNA immobilized on the electrode to form a newly partial-pairing double-stranded DNA. Thereafter, the exposed domain at trigger DNA could be utilized as the initator strand to open the hairpin probes in sequence, and propagated a chain reaction of hybridization events between two alternating hairpins to form a long nicked double-helix. The electrochemical signal derived from the assembled silver nanotags on the nicked double-helix. Under optimal conditions, the electrochemical aptasensor could exhibit a high sensitivity and a low detection limit, and allowed the detection of ATP at a concentration as low as 0.03 pM. Our design showed a high selectivity for target ATP against its analogs because of the high-specificity ATP-aptamer reaction, and its applicable for monitoring ATP in the spiking serum samples. Improtantly, the distinct advantages of the developed aptasensor make it hold a great potential for the development of simple and robust sensing strategies for the detection of other small molecules by controlling the apatmer sequence.

MicroRNAs (miRNAs) have attracted enormous interest due to their involvement in complex regulatory functions and for being closely linked to some cancers. Thus, qualitative and quantitative detection of miRNAs has become an urgent necessity. In this study, we report an enzyme-free fluorescent biosensor for miRNA-21 detection based on MnO2 nanosheets and catalytic hairpin assembly amplification. Results showed that the detection limit for miRNA-21 was 0.33 nM (S/N = 3) and the linearity range was from 1 to 50 nM. Compared with traditional methods, such strategy is convenient, rapid, and low-cost and it can have a promising potential for miRNA detection in cancer.

A new impedimetric sensing strategy based on enzyme-triggered formation of enzyme-tyramine concatamers on the nanogold-functionalized poly(amidoamine) (PAMAM) dendrimer was designed for sensitive detection of mercury(II) (Hg(2+)) ion, coupling with enzymatic biocatalytic precipitation towards 4-choloro-1-naphthol (4-CN) on thymine (T)-rich single-stranded DNA1-modified electrode. Initially, nanogold-decorated PAMAM dendrimer (AuNP-PAMAM) was synthesized by the in-situ reduction method, and then functionalized with horseradish peroxidase (HRP) and another T-rich oligomer (DNA2). Upon target Hg(2+) introduction, probe DNA2 on the AuNP-PAMAM bound to the DNA1 on the electrode owing to the T-Hg(2+)-T coordination chemistry between the two DNA strands. Accompanying the AuNP-PAMAM, the carried HRP could trigger the formation of HRP-tyramine concatamer via the classical tyramine signal amplification strategy in the presence of HRP-tyramine conjugates and hydrogen peroxide. The concatenated HRP molecules in the concatamer catalyzed the 4-CN oxidation to produce an insoluble precipitation on the electrode, thereby resulting in the local alteration in the conductivity. Under optimal conditions, two signal-generation tags including HRP-AuNP-DNA2 and HRP-AuNP-PAMAM-DNA2 with or without tyramine signal amplification strategy (i.e., four schemes) were used for impedimetric detection of target Hg(2+) on the basis of the same assay format. A low detection limit (LOD) of 0.4pM and a wide dynamic working range of 0.001-100nM Hg(2+) by using HRP-AuNP-PAMAM-DNA2 with tyramine signal amplification strategy were obtained in comparison with those of other strategies. The assay had a good repeatability and showed an intermediate precision of down to 9.6%. In addition, the methodology also exhibited high specificity and selectivity towards target Hg(2+) against other metal ions, and was applicable for monitoring Hg(2+) in the spiked drinking water samples.

Mesoporous silica nanoparticles (MSN) based controlled release system had been coupled with diverse detection technologies to establish biosensors for different targets. Chemiluminescence (CL) system of luminol/H2O2 owns the characters of simplicity, low cost and high sensitivity, but the targets of which are mostly focused on some oxidants or which can participate in a chemical reaction that yields a product with a role in the CL reaction. In this study, chemiluminescent detection technique had been coupled with mesoporous silica-based controlled released system for the first time to develop a sensitive biosensor for the target which does not cause effect to the CL system itself. Cocaine had been chosen a model target, the MSN support was firstly loaded with glucose, then the positively charged MSN interacted with negatively charged oligonucleotides (the aptamer cocaine) to close the mesopores of MSN. At the present of target, cocaine binds with its aptamer with high affinity; the flexible linear aptamer structured will become stems structured through currently well-defined non-Waston-Crick interactions and causes the releasing of entrapped glucose into the solution. With the assistant of glucose oxidase (GOx), the released glucose can react with the dissolved oxgen to produce gluconic acid and H2O2, the latter can enhance the CL of luminol in the NaOH solution. The enhanced CL intensity has a relationship with the cocaine concentration in the range of 5.0-60μM with the detection limit of 1.43μM. The proposed method had been successfully applied to detect cocaine in serum samples with high selectivity. The same strategy can be applied to develop biosensors for different targets.

Most electrochemical biosensors for microRNA (miRNA) detection need the immobilization of DNA on the electrode; first, the process is tedious and the DNA/RNA hybridization occurs on the electrode/solution interface, resulting in low efficiency. In this study, a homogeneous electrochemical biosensor has been proposed for sequence-specific miRNA in pancreatic cancer cells and lung adenocarcinoma cells, which combines the advantages of the simplicity of immobilization free and high efficiency of duplex-specific nuclease (DSN) assisted target recycling amplification. A DNA probe modified with a methylene blue group at the 3′ terminal (eMB) contains negative charges on its backbone, which cannot diffuse easily to the surface of the negatively charged indium tin oxide (ITO) electrode because of electrostatic repulsion, so a low electrochemical signal was detected. In the presence of miRNA, eMB can recognize and hybridize with miRNA to form a DNA–RNA heteroduplex. The eMB can be hydrolysed by DSN, so miRNA is retained. miRNA can cause a new cycle of hybridization–cleavage–releasing, and this recycling process generates numerous short MB-labelled oligonucleotide fragments (MB-OFs). The MB-OFs with less negative charges can diffuse easily to the surface of the ITO electrode, so an enhanced electrochemical signal was detected. Under the optimal conditions, the differential pulse voltammetric (DPV) response of the system had a linear relationship with the logarithm of the target miRNA concentration in the range of 0.1 pM to 10 nM. The proposed biosensor has been successfully applied to detect miRNA in real samples.