Search

The development of efficient, accurate, and high-throughput technology for gut microbiota sensing holds great promise in the maintenance of health and the treatment of diseases. Herein, we developed a rapid fluorescent sensor array based on surface-engineered silver nanoparticles (AgNPs) and vancomycin-modified gold nanoclusters (AuNCs@Van) for gut microbiota sensing. By controlling the surface of AgNPs, the recognition ability of the sensor can be effectively improved. The sensor array was used to successfully discriminate six gut-derived bacteria, including probiotics, neutral, and pathogenic bacteria and even their mixtures. Significantly, the sensing system has also been successfully applied to classify healthy individuals and colorectal cancer (CRC) patients rapidly and accurately within 30 min, demonstrating its clinically relevant specificity., Competing Interests: Declaration of competing interest We declare that we have no financial and relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Urinary tract infections (UTIs) have greatly affected human health in recent years. Accurate and rapid diagnosis of UTIs can enable a more effective treatment. Herein, we developed a multichannel sensor array for efficient identification of bacteria based on three antimicrobial agents (vancomycin, lysozyme, and bacitracin) functional gold nanoclusters (AuNCs). In this sensor, the fluorescence intensity of the three AuNCs was quenched to varying degrees by the bacterial species, providing a unique fingerprint for different bacteria. With this sensing platform, seven pathogenic bacteria, different concentrations of the same bacteria, and even bacterial mixtures were successfully differentiated. Furthermore, UTIs can be accurately identified with our sensors in ∼30 min with 100% classification accuracy. The proposed sensing systems offer a rapid, high-throughput, and reliable sensing platform for the diagnosis of UTIs.

Technological advances and methodological innovations in cell signaling pathway analysis will facilitate progress in understanding biological processes, intervening in diseases, and screening drugs. In this work, an elaborate strategy for visualizing and monitoring the transient receptor potential melastatin 7 (TRPM7)-Mg 2+ signaling pathway in living cells was constructed through the logical analysis of upstream mRNA and downstream molecules by two individual DNA sensors. The DNA sensors are constructed by modifying the dye-labeled DNA sequences on the surface of gold nanoparticles. By hybridizing with upstream mRNA, Cy5-modified DNA sensor 1 can detect and silence it simultaneously, outputting a red fluorescence signal. When the upstream mRNA is silenced, the concentration of downstream molecules of Mg 2+ will be affected and down-regulated. The FAM-modified DNA sensor 2 detects this change and emits a green fluorescence as a signal. Therefore, the dynamic information on TRPM7 mRNA and the Mg 2+ -mediated signaling pathway can be successfully obtained by fluorescence imaging methods. Furthermore, the TRPM7 mRNA-Mg 2+ signaling pathway also affects cell activity and migratory function through cell scratching and other experiments. More importantly, the proposed sensor also shows potential for screening signaling pathway inhibitors. Our work provides a simple and general strategy for the visualization of signaling pathways, which helps to understand the changes in the physiological activities of cancer cells and the causes of carcinogenesis and is crucial for cancer diagnosis and prognosis.

In this work, near-infrared fluorescent silver nanoclusters (Ag NCs) were prepared based on the in situ formed poly methacrylic acid (PMAA) as the template and stabilizer, which is synthesized by methacrylic acid (MAA) and hydroxyl radical (·OH) that is generated by the cascade nanoenzyme reaction of cupric oxide nanoparticles (CuO NPs). CuO NPs possess the intrinsic glutathione-like (GPx-like) and peroxidase-like (POD-like) activities, which can catalyze glutathione (GSH) and O 2 to produce hydrogen peroxide (H 2 O 2 ), and then transform into ·OH. The fluorescence intensity of Ag NCs decreases with the addition of GSH, because the -SH can easily anchor on the surface, resulting in the PMAA leaving the Ag NCs, and the coeffect of GSH and PMAA results in the aggregation to form larger Ag NPs. A good linear relationship between the fluorescence quenching rate and the GSH concentration was found in the range 0.01-40 μM with the detection limit 8.0 nM. The Ag NCs can be applied in the detection of GSH in the serum, as well as bioimaging of endogenous and exogenous GSH in cells with high sensitivity. Moreover, the normal and cancer cells can be distinguished through bioimaging because of the different GSH levels. The new method for the preparation of biocompatible nanoprobe based on the nanozyme tandem catalysis and the in situ formed template can avoid the direct usage of polymers or protein templates that hinder preparation and separation, providing a reliable approach for the synthesis, biosensing, and bioimaging of nanoclusters.

An electrochemiluminescence (ECL) sensor provides a sensitive and convenient method for early diagnosis of diseases; however, it is still a challenge to develop simple and sensitive sensing platforms based on efficient ECL signals and luminophore groups. Porphyrin-based metal-organic frameworks (MOFs) show great potential in ECL sensing; however, the mechanism and structure-activity relationship, as well as application, are rarely reported. Herein, hydrothermal reactions obtained porphyrin Zr-MOFs (PCN-222) with different specific surface areas, pore sizes, structures, and surface charge states by tuning the reaction time were developed, which served both as the ECL luminophore, coreaction promoter for S 2 O 8 2- , and a connection in the ECL immunoassay. By progressively controlling the condition of the hydrothermal reaction, PCN-222 with large surface area-abundant micropores can be obtained, which has good conductivity and positively charged surfaces, obtaining excellent ECL performance. The ECL performance and the enhancement mechanism were investigated in detail. Using PCN-222-6h with the best ECL intensity as the immobilization matrix for the aptamer, a highly sensitive and selective assay for thrombin was developed. The decrease of the ECL signal was logarithmically linear with the concentration of thrombin in the range from 50 fg mL -1 to 100 pg mL -1 with a low detection limit of 2.48 fg/mL. This proposed strategy provides a brand new approach for tuning of the structures of MOFs as effective ECL signal probes, thus providing wider possibilities for effective ECL immunoassays in the detection of other biomarkers in diagnosis of diseases.

Pathogenic bacterial infections in freshwater-farmed fish have high morbidity and mortality. As an effective broad spectrum antibacterial agent, silver nanoparticles (AgNPs) have great application potential in the field of aquaculture. However, due to the easy aggregation and oxidation properties of AgNPs, their practical applications are rather limited. Herein, nanocomposites of AgNPs and carbon nanodots (AgNPs@C-dots) were synthesized by using carbon nanodots as a reductant and a stabilizer. Their antibacterial activity and biosafety were systematically investigated. AgNPs@C-dots exhibit superior aggregation stability, excellent biocompatibility, and enhanced antibacterial activity compared to common AgNPs (reduced by sodium citrate). In vitro antibacterial results show that AgNPs@C-dots can completely kill Aeromonas salmonicida at a concentration of 9.5 μg mL -1 . The possible antibacterial mechanism of AgNPs@C-dots was thoroughly clarified by scanning electron microscopy, gel imaging, and laser scanning confocal imaging. The AgNPs@C-dots have been successfully applied to enhance the resistance of zebrafish to A. salmonicida with satisfactory results. Moreover, AgNPs@C-dots did not result in detectable residues of silver in the muscles after 30 days of exposure. It is well demonstrated that AgNPs@C-dots could be used for the development of antibacterial agents in aquaculture.

It remains an unanswered question whether the flux of K + and H + in lysosomes are correlated due to difficulties in simultaneously imaging these two ions. This question is of great value for understanding lysosomal acidification. Herein, we designed DNA quadruplex and triplex based luminescent nanosensors that can, respectively monitor K + and pH in lysosomal lumen. Each sensor contained an upconversion nanoparticle luminophore and a gold nanoparticle quencher, producing green and blue luminescence signals for K + and H + , respectively. The sensors were tested in buffers showing dynamic ranges of 5 to 200 mM K + and pH 5.0 to 8.2. Co-imaging using these two sensors in cells indicated that the influx of H + was accompanied with the efflux of K + , solving this long-standing question of the lysosomal biochemistry., (© 2020 Wiley-VCH GmbH.)

In recent years, germanium nanoparticles (Ge NPs) have attracted considerable research attention because of its excellent electrical and optical properties. However, it is mainly applied in the field of solar cells, photodetectors and photothermal therapy. Actually, Ge NPs have the advantages of low toxicity and excellent biocompatibility, which means that they have great potential in biosensing applications. However, there are few related reports. In this paper, we discovered that Ge NPs have the intrinsic peroxidase-like catalytic activity and can significantly accelerate the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) by H 2 O 2 for the first time. Compared with natural enzyme (horseradish peroxidase, HRP), Ge NPs maintain higher catalytic stability after treatment at different pH, temperature and ionic strength. Furthermore, a Ge NPs-based colorimetric platform was established for the first time to detect biomolecules with favourable sensitivity and selectivity, such as uric acid, glucose and choline. This work finds the new property of Ge NPs and extends its application in biosensing., (Copyright © 2018 Elsevier B.V. All rights reserved.)

An immunosensor is described for the voltammetric determination of α-fetoprotein. It is making use of an AuNP-dendrimer conjugate and an ionic liquid. A gold electrode was first modified with chitosan. Then, the AuNP-dendrimer conjugate was covalently immobilized on the electrode. Following this, an ionic liquid was placed on the electrode via formation of a covalent bond between the amino groups of PAMAM and the aldehyde groups of an ionic liquid containing ferrocene. Thus, the redox probe ferrocene becomes immobilized on the electrode surface. PAMAM increases the amount of ferrocene immobilized on the electrode due to its globular shape and rich amino groups. The use of AuNPs improves the conductivity of the electrode. The modified electrode was applied to the determination of α-fetoprotein in human serum and has a linear response that covers the 0.05 to 30 ng mL -1 α-fetoprotein concentration range, with a detection limit of 0.02 ng mL -1 . This assay is stable, selective and reproducible. It is perceived to provide a powerful tool for the early detection of cancer markers. Graphical abstract Schematic of a voltammetric immunoassay for α-fetoprotein based on a gold nanoparticle/dendrimer conjugate and ionic liquids anchored with both aldehyde and ferrocene. Chit: chitosan; GA: glutaraldehyde ; PAMAM: G4 polyamidoaminic dendrimers; AuNP: Au nanoparticle; Fc: ferrocene; IL: ionic liquid. PB: phosphate buffer solution.

The selective and sensitive detection of dopamine (DA) is of great significance for the identification of schizophrenia, Huntington's disease, and Parkinson's disease from the perspective of molecular diagnostics. So far, most of DA fluorescence sensors are based on the electron transfer from the fluorescence nanomaterials to DA-quinone. However, the limited electron transfer ability of the DA-quinone affects the level of detection sensitivity of these sensors. In this work, based on the DA can reduce Ag + into AgNPs followed by oxidized to DA-quinone, we developed a novel silicon nanoparticles-based electron transfer fluorescent sensor for the detection of DA. As electron transfer acceptor, the AgNPs and DA-quinone can quench the fluorescence of silicon nanoparticles effectively through the synergistic electron transfer effect. Compared with traditional fluorescence DA sensors, the proposed synergistic electron transfer-based sensor improves the detection sensitivity to a great extent (at least 10-fold improvement). The proposed sensor shows a low detection limit of DA, which is as low as 0.1 nM under the optimal conditions. This sensor has potential applicability for the detection of DA in practical sample. This work has been demonstrated to contribute to a substantial improvement in the sensitivity of the sensors. It also gives new insight into design electron transfer-based sensors., (Copyright © 2018. Published by Elsevier B.V.)

In this paper, the colorimetric sensing of H 2 O 2 related molecules and biothiols based on etching and anti-etching strategy was firstly proposed. Ag/carbon nanocomposite (Ag/C NC) was served as the sensing nanoprobe, which was synthesized via carbon dots (C-dots) as the reductant and stabilizer. The characteristic surface plasmon resonance (SPR) absorbance of Ag nanoparticles (AgNPs) was sensitive to the amount of hydrogen peroxide (H 2 O 2 ). It exhibited strong optical responses to H 2 O 2 with the solution colour changing from yellow to nearly colourless, which is resulted from the etching of Ag by H 2 O 2 . The sensing platform was further extended to detect H 2 O 2 related molecules such as lactate in coupling with the specific catalysis oxidation of L-lactate by lactate oxidase (LOx) and formation of H 2 O 2 . It provides wide linear range for detecting H 2 O 2 in 0.1-80μM and 80-220μM with the detection limit as low as 0.03μM (S/N=3). In the presence of biothiols, the etching from the H 2 O 2 can be hampered. Other biothiols exhibit anti-etching effects well. The strategy works well in detecting of typical biothiols including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH). Thus, a simple colorimetric strategy for sensitive detection of H 2 O 2 and biothiols is proposed. It is believed that the colorimetric sensor based on etching and anti-etching strategy can be applied in other systems in chemical and biosensing areas., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Construction of a new multifunctional chemo/biosensing platform for small biomolecules and tumor markers is of great importance in analytical chemistry. Herein, a novel universal multifunctional nanoplatform for biomolecules and enzyme activity detection was proposed based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and target-inducing enlarged gold nanoparticles (AuNPs). The reductive molecule such as H 2 O 2 can act as the reductant to reduce HAuCl 4 , which will make the Au seeds grow. The enlarged AuNPs can effectively quench the fluorescence of UCNPs owing to the good spectral overlap between the absorption band of the AuNPs and the emission band of the UCNPs. Utilizing the FRET between the UCNPs and enlarged AuNPs, good linear relationship between the fluorescence of UCNPs and the concentration of H 2 O 2 can be found. Based on this strategy, H 2 O 2 related molecules such as l-lactate, glucose, and uric acid can also be quantified. On the basis of UCNPs and PVP/HAuCl 4 , a general strategy for other reductants such as ascorbic acid (AA), dopamine (DA), or enzyme activity can be established. Therefore, the universal multifunctional nanoplatform based on UCNPs and the target-inducing in situ enlarged Au NPs will show its potential as a simple method for the detection of some life related reductive molecules, enzyme substrates, as well as enzyme activity.

Clenbuterol (CLB), a member of β-agonist family, has now been a serious threat to human health due to its illegal usage in the animal feed. In this paper, we designed a fluorescence resonance energy transfer (FRET) system consisting of carbon dots (C-dots) and gold nanoparticles (AuNPs) for recovered fluorescence detecting of CLB. In the presence of CLB, CLB molecules can interact with AuNPs via Au-N bonds, preventing the interaction of C-dots and AuNPs, which induced the recover of the fluorescent intensity. Under the optimal conditions, the limit of detection for CLB was 3 nM, with a wide concentration linear range of 8-200 nM (S/N = 3). Meanwhile, the proposed method was successfully applied to detect CLB in pork samples, illustrating it could be used as a reliable, rapid, and cost-effective method for the determination of CLB residues in pork samples.

In this work, a novel immunosensor was constructed based on the alkaline phosphatase (ALP) in situ generating an electroactive substance by enzymatic hydrolysis the inactive substrates. The new signal-amplified strategy for sensitive detection of HIgG was based on the catalytic oxidation of ALP-generated products, ascorbic acid (AA), using carbon-based Ag-Au bimetallic as the catalyst and signal enhancer. Through a sandwich reaction, ALP-Ab 2 bioconjugates were captured on the electrode surface and the amplified signal can be obtained as follows: the ALP catalyzed the inactive substrate L-ascorbic acid 2-phosphate (AAP) to in situ produce AA; AA as an electroactive product then can be directly electro-oxidized to generate electrochemical signal; At the same time, AA could be catalytic oxidized by Ag-Au bimetallic and resulted in the amplification of electrochemical signal; Finally, the oxidation of Ag on the Ag-Au bimetallic maybe further enhance the detection signal. The proposed immunosensor achieved good linear in the range of 0.005-100ngmL -1 with the detection limit of 0.0009ngmL -1 (S/N =3). The proposed immunosensor was successfully applied in the analysis of human IgG in real samples and got satisfied results. The present work demonstrates a general strategy for the design of multifunctional nanomaterials based on carbon-based bimetallic nanoparticles for different applications, such as biosensors, immunosensors and nanocatalysts., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Herein we report a novel switch-off fluorescent probe for highly selective determination of uric acid (UA) based on the inner filter effect (IFE), by using poly-(vinylpyrrolidone)-protected gold nanoparticles (PVP-AuNPs) and chondroitin sulfate-stabilized gold nanoclusters (CS-AuNCs) as the IFE absorber/fluorophore pair. In this IFE-based fluorometric assay, the newly designed CS-AuNCs were explored as an original fluorophore and the hydrogen peroxide (H 2 O 2 ) -driven formed PVP-AuNPs can be a powerful absorber to influence the excitation of the fluorophore, due to the complementary overlap between the absorption band of PVP-AuNPs and the emission band of CS-AuNCs. Under the optimized conditions, the extent of the signal quenching depends linearly on the H 2 O 2 concentration in the range of 1-100μM (R 2 =0.995) with a detection limit down to 0.3μM. Based on the H 2 O 2 -dependent fluorescence IFE principle, we further developed a new assay strategy to enable selective sensing of UA by using a specific uricase-catalyzed UA oxidation as the in situ H 2 O 2 generator. The proposed uricase-linked IFE-based assay exhibited excellent analytical performance for measuring UA over the concentration ranging from 5 to 100μM (R 2 =0.991), and can be successfully applied to detection of UA as low as 1.7μM (3σ) in diluted human serum samples., (Copyright © 2017 Elsevier B.V. All rights reserved.)

A dual-functional platform for the sensing of acetylcholinesterase (AChE) activity and cadmium ions (Cd 2+ ) was developed based on the fluorescence resonance energy transfer (FRET) between NaYF 4 :Yb,Er upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) via glutathione regulation. The detection mechanism is based on the fact that AuNPs can quench the fluorescence of UCNPs. AChE catalyzes the hydrolysis of acetylthiocholine (ATC) into thiocholine which reacts with AuNPs by S-Au conjunction and results the aggregation of AuNPs and change in fluorescence of UCNPs. Therefore, the AChE activity can be detected through the changes of the color of solution and fluorescence recovery of UCNPs. However, the presence of glutathione (GSH) can protect AuNPs from aggregation and enlarge the inter-particle distance between AuNPs and UCNPs. When Cd 2+ is added into the stable mixture of AuNPs, GSH and AChE/ATC, Cd 2+ could interact with GSH to form a spherical shaped (GSH) 4 Cd complex, which decreases the free GSH on the surface of AuNPs to weaken the stability of AuNPs and lead to the easily aggregation of them in the system. The aggregated-AuNPs are released from the surface of UCNPs, which results in the fluorescence of UCNPs gradually recovered. Under the optimized conditions, the detection limits of AChE activity and Cd 2+ are estimated to be 0.015mU/mL and 0.2µM, respectively. The small molecules regulated dual-functional platform based on UCNPs/AuNPs is a simple, label-free method and can be applied for the turn-on fluorescence detection of AChE activity in human serum and Cd 2+ in real water samples. The present work demonstrates a general strategy for the design of small molecules regulated multifunctional platform and will be expanded for different areas in the future., (Copyright © 2016 Elsevier B.V. All rights reserved.)

A new ratiometric nanosensor is developed for selective and ultrasensitive detection of melamine based on conjugated polyelectrolyte (CPE)-stabilized silver nanoparticles (P1-AgNPs) by perfectly combining the advantages of CPE and AgNPs. P1 featuring a π-delocalized backbone bearing pyridinyl groups can act as an excellent dual-emission fluorescent probe as well as a polymer localizer for AgNPs. In the presence of melamine, the fluorescence intensity at 386nm increases owing to the turn-on of the fluorescence of P1, whereas FL intensity at 488nm decreases due to the melamine-induced aggregation and subsequent aggregation-enhanced emission quenching of P1-AgNPs, therefore leading to the ratiometric fluorescent sensing of analyte. Moreover, analyte-induced aggregation of P1-AgNPs also allows the ratiometric colorimetric measurement of melamine. Under the optimum conditions, this facile ratiometric nanosensor favors the fluorescent and colorimetric determination of melamine in liquid milk products with the detection limit as low as 0.1 and 0.45nM, respectively., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this paper, a double signal electrochemical Human immunoglobulin G (HIgG) immunosensor based on AgNPs/carbon nanocomposite (Ag/C NC) as the signal probe and catalytic substrate was developed for fast and sensitive detection of HIgG. The as-prepared AuNPs-PDA-rGO nanocomposite and Ag/C NC were confirmed by UV-vis, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical properties of the proposed immunosensor. The AuNPs-PDA-rGO nanocomposite can improve the electron transfer rate and capture more Ab1. In the sandwich-type immunoassay process, the Ag/C NC functionalized bioconjugates were captured on HIgG/Ab1/AuNPs-PDA-rGO surface and the electrochemical double-signal strategy was employed. These double electrochemical detection signals were directly monitored the oxidation current originated from Ag/C NC and indirectly detected the reduction current of benzoquinone which was produced from the reaction of H2O2 and HQ by catalysis of Ag/C NC in electrochemical detection of HIgG. Under the optimized conditions, the current responses were changed with the concentrations of HIgG for the proposed immunosensor with wide linear ranges of 0.1 to 100 ngmL(-1) and 0.01-100 ngmL(-1) with the lowest detection concentration of 0.001 ng mL(-1) in the absence and presence of H2O2 and HQ. The double-signal strategy is used for detection of HIgG, and the results came from the two signals were well consistent with each other. The proposed immunosensor was successfully applied in analysis of human IgG in real samples and this strategy may provide a relative simple and effective method for construction of other immunsensors in detection of other biomarkers in clinical medicine., (Copyright © 2015 Elsevier B.V. All rights reserved.)

We have found that hydroxyl-rich carbon dots (C-dots) have the ability to reduce Au(3+) to form gold nanoparticles (AuNPs). Thiocyanate (SCN(-)) can be absorbed on the surface of the AuNPs due to its high affinity toward the AuNPs, which inhibits the growth of the AuNPs. Meanwhile, SCN(-) has the ability to etch the as-synthesized big AuNPs to small AuNPs, which can also cause the absorption peak of the AuNPs to decrease. Therefore, an optical sensor is developed for the detection of SCN(-) based on measuring the plasmon resonance absorption peak change of the AuNPs. Under optimal conditions, this method yields excellent sensitivity (the limit of detection is 0.16 μM) and selectivity toward SCN(-). This method can detect SCN(-) in raw milk with satisfactory results. This work gives new insight into monitoring the quality of milk.

Here we report a nanosensor based on fluorescence resonance energy transfer (FRET) between upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) for melamine detection. The positively charged UCNPs as donor and the negatively charged AuNPs as acceptor bound together through electrostatic interaction, which caused the fluorescence quenching of UCNPs. Upon addition of melamine, AuNPs were released from the surface of UCNPs and aggregation due to the N-Au interaction between melamine and AuNPs, which results in the fluorescence of UCNPs gradually recovered. Under the optimal conditions including media pH (7.0), the concentration of AuNPs (1.23nM) and incubation time (12min), the fluorescence enhanced efficiency shows a linear response to the melamine concentration ranging from 32.0 to 500nM with a detection limit of 18.0nM. Compared with other fluorescence methods, the fluorimetric nanosensor shows high sensitivity of 0.968, ease of operation and can be used for the determination of melamine in raw milk samples., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In this study, we synthesized a new fluorescence probe which was used to detect melamine by coupling with gold nanoparticles (AuNPs). The new fluorescence probe has good optical stability and high fluorescence intensity, which can greatly improve the detection sensitivity. Compared to the traditional fluorophore, it is less dependent on the pH value. It has a very strong fluorescence emission peak at 550 nm, which has larger overlap with the absorption peak of AuNPs. When the probe incubates with the AuNPs, the fluorescence of the probe can be effectively quenched by AuNPs. Adding melamine into a probe-AuNPs mixture caused aggregation of AuNPs and released the adsorbed probe; the fluorescence intensity of the probe was recovered. By measuring the changes of the fluorescence intensity of the probe, the detection of melamine can be realized. Under optimized conditions, the linear response to melamine is in the range of 1.0 × 10(-8)-4.0 × 10(-6) mol L(-1) and lowers the detection limit down to 3.0 nmol L(-1) with the sensor. This method can detect melamine in milk and milk-based productions.

Biological thiols play a critical role in biological processes and are involved in a variety of diseases. The discrimination detection of biological thiols is of increasing importance in clinical diagnosis. In this paper, a novel nanosensor was developed to discriminate cysteine (Cys) from homocysteine (Hcy) and glutathione (GSH) with multiple signals: colorimetric, photoluminescence (PL), and up-conversional photoluminescence (UCP). The nanosensor (NC-dots/AuNPs) was constructed by nitrogen-doped carbon dots (NC-dots) and gold nanoparticles (AuNPs) through assembling NC-dots "shell" on AuNPs and showed the obvious different response to Cys, Hcy, and GSH with colorimetric, PL, and UCP signals. The discrimination effect for Cys is originated from conformations and interaction difference of the thiols groups in Cys and Hcy and/or GSH with AuNPs. Among them, only Cys can quickly penetrate into the NC-dots "shell" of the composite and induce the dispersing of the aggregated NC-dots/AuNPs, which lead to the color change from purple to red and the recovery of PL and UCP of NC-dots. This assay was successfully applied for the detection of Cys in human serum with the detection limit of 4 nM.

A new sensing system is developed for selective and ultrasensitive detection of iodide based on the inner filter effect (IFE) between conjugated polyelectrolyte-stabilized silver nanoparticles (P1-AgNPs) and 4-oxo-4-(pyren-1-ylmethoxy) butanoic acid (probe 1). P1-AgNPs are designed to be capable of functioning as a composite light-absorber. Meanwhile, probe 1 is selected as an ideal fluorophore because its emission spectrum can perfectly overlap with the absorption band of P1-AgNPs. The intense fluorescence of probe 1 quenched by P1-AgNPs can be efficiently recovered after adding H2O2 and I(-) via the oxidation-etching and regeneration of P1-AgNPs. Under the optimum conditions, this facile IFE-based approach allows the sensitive and selective determination of I(-) in tap water, iodized salt and urine with the detection limit as low as 0.3 nM (S/N=3). Interestingly, the regenerated AgNPs is in smaller size and well-dispersed perhaps due to the particular role of P1 as a polymer localizer containing pyridinyl and sulfonate groups., (Copyright © 2014 Elsevier B.V. All rights reserved.)

In this paper, a novel electro-active graphene oxide (GO) nanocomposite was firstly prepared by covalently grafted (4-ferrocenylethyne) phenylamine (Fc-NH2) onto the surface of GO. The synthesized hybridized nanocomposite of GO-Fc-NH2 coupled with HAuCl4 simultaneously electrodeposited on the glassy carbon electrodes (GCE) to obtain rGO-Fc-NH2/AuNPs/GCE. The covalently grafted material of the rGO-Fc-NH2/AuNPs film can effectively prevent the electron mediator leaking from the electrode surface, which can hold the advantage of both the nanomaterials and electron mediator. By employing the catalysis effect of the nanomaterial and electron mediator coupling with large active surface area and high accumulation capacity of rGO-Fc-NH2/AuNPs, a synergetic signal amplification platform for ultra-sensitive detection of bisphenol A (BPA) was successfully established. With this novel sensor, the oxidation peak currents of BPA were linearly dependent on the BPA concentrations in the range of 0.005-10 μM with the detection limit of 2 nM. Modification of electron mediators on nanomaterials can greatly enhance the electrochemical performance of the sensors and will provide a new concept for fabricating newly electro-active nanomaterials-based electrochemical biosensors., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Here we report a novel label-free fluorescent sensor for ultrasensitive detection of protamine and heparin based on the high quenching ability of gold nanoparticles to the fluorescence of fluorescein. The fluorescence was significantly quenched when fluorescein molecules were attached to the surface of gold nanoparticles by electrostatic interaction. Upon addition of protamine, the fluorescein molecules were detached from the surface of the gold nanoparticles due to the stronger adsorption of protamine on the surface of AuNPs, and resulting in the recovery of the fluorescein molecules fluorescence. Heparin is able to bind with Protamine specifically. In the presence of heparin, the interaction of heparin with protamine makes the AuNPs de-aggregate and the fluorescein molecules re-attach to the AuNPs, which lead to marked fluorescence quench again. By measuring the changes in the fluorescence of the fluorescein molecules, the concentration of protamine and heparin were sequentially determined. The linear response range was obtained over the concentration range from 0 to 0.8 μg/mL and 4 to 1.6 μg/mL with the low detection limit 0.0067 μg/mL and 0.0013 μg/mL for protamine and heparin, respectively., (Copyright © 2013. Published by Elsevier B.V.)

A new ferrocene benzyne derivative (Fc-SAc) that contained oligo-(phenylene-ethynylene) skeleton, ferrocene and thiolate terminal groups was firstly synthesized. The hydrolysis product of Fc-SAc (Fc-SH) was immobilized onto gold nanoparticles (AuNPs) modified glass carbon electrode (GCE) as sensing element for rutin detection with high sensitivity. The new sensing strategy was proposed by using two Fc-SH modified electrodes: Fc-S/AuNPs/GCE (Electrode1) and Fc-S/AuNPs/graphene-chitosan/GCE (Electrode2). The electrochemical oxidation of rutin on Electrode2 was a diffusion-controlled process, which was different from a mass-controlled process on Electrode1. Under the optimal conditions, the peak currents of the sensors were linearly related to the concentrations of rutin. The linear responses ranges were 0.05-30 μM and 0.04-100 μM with the regression coefficients of 0.998 and 0.997 on Electrode1 and Electrode2, respectively. Electrode2 presented wider linear range, superior high sensitivity, lower detection limit and better stability on determination of rutin., (Copyright © 2012 Elsevier B.V. All rights reserved.)

A highly sensitive and selective electrochemical aptasensor for thrombin was developed. By introducing chitosan-gold nanoparticles and horseradish peroxidase (CS-AuNPs-HRP) conjugates to the sensitive union, the thrombin detection signal was dual amplified. The capture probe was prepared by immobilizing an anti-thrombin aptamer on core-shell Fe(3)O(4)-Au magnetic nanoparticles (AuMNPs) and which was served as magnetic separation material as well. The detection probe was prepared from another anti-thrombin aptamer, horseradish peroxidase (HRP), thiolated CS nanoparticle and gold nanoparticle (CS-AuNPs-HRP-Apt2). In the presence of thrombin, the sandwich structure of AuMNPs-Apt1/thrombin/Apt2-CS-AuNPs-HRP was formed and abundant HRP was captured in it. The resultant conjugates are of magnetic characters and were captured onto the surface of a screen printed carbon electrode (SPCE) to prepare the modified electrode by a magnet located on the outer flank of the SPCE. It was demonstrated that the oxidation of hydroquinone (HQ) with H(2)O(2) was dramatically accelerated by the captured HRP. The electrochemical signal, which correlated to the reduction of BQ (the oxidation product of HQ), was amplified by the catalysis of HRP toward the reaction and the enrichment of HRP on the electrode surface. Under optimized conditions, ultrasensitive and high specific detection for thrombin was realized with the proposed assay strategy. The signal current was linearly correlated to the thrombin concentration in the range of 0.01-10 pM with a detection limit of 5.5 fM (S/N = 3). These results promise extensive applications of this newly proposed signal amplification strategy in protein detection and disease diagnosis.

A three-dimensional network PAMAM-Au nanocomposite (3D-PAMAM-Au NC) was prepared by using the first generation polyamidoamine dendrimer (G1 PAMAM) as the dispersant agent. The resultant 3D-PAMAM-Au NC was successfully used as an immobilization matrix for the construction of a reagentless mediator-free horseradish peroxidase (HRP)-based H(2)O(2) biosensor on a multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode. With the advantages of the three-dimensional network, the organic-inorganic hybrid materials dramatically facilitate the direct electron transfer of HRP, and good bioelectrocatalytic activity towards H(2)O(2) was demonstrated. Under optimum conditions, the current response of the enzyme modified electrode at -0.30 V was detected. The current response is linearly correlated to H(2)O(2) concentration within the range of 18.00 μM to 20.80 mM with a correlation coefficient of 0.9992 and a sensitivity of 377.78 μA mM(-1) cm(-2). The detection limit was down to 6.72 μM (S/N = 3). Furthermore, the biosensor exhibits some other excellent characteristics, such as high selectivity, short response time, and long-term stability. The 3D-PAMAM-Au NC has proved to be a promising biosensing platform for the construction of mediator-free biosensors, and may find wide potential applications in biosensors, biocatalysis, bioelectronics and biofuel cells.

A new method for the detection of point mutation in DNA based on the monobase-coded cadmium tellurium nanoprobes and the quartz crystal microbalance (QCM) technique was reported. A point mutation (single-base, adenine, thymine, cytosine, and guanine, namely, A, T, C and G, mutation in DNA strand, respectively) DNA QCM sensor was fabricated by immobilizing single-base mutation DNA modified magnetic beads onto the electrode surface with an external magnetic field near the electrode. The DNA-modified magnetic beads were obtained from the biotin-avidin affinity reaction of biotinylated DNA and streptavidin-functionalized core/shell Fe(3)O(4)/Au magnetic nanoparticles, followed by a DNA hybridization reaction. Single-base coded CdTe nanoprobes (A-CdTe, T-CdTe, C-CdTe and G-CdTe, respectively) were used as the detection probes. The mutation site in DNA was distinguished by detecting the decreases of the resonance frequency of the piezoelectric quartz crystal when the coded nanoprobe was added to the test system. This proposed detection strategy for point mutation in DNA is proved to be sensitive, simple, repeatable and low-cost, consequently, it has a great potential for single nucleotide polymorphism (SNP) detection., (2011 © The Japan Society for Analytical Chemistry)

A novel DNA detection platform based on a hairpin DNA switch, nanoparticles, and enzyme signal amplification for ultrasensitive detection of DNA hybridization has been developed in this work. In this DNA assay, a "stem-loop" DNA probe dually labeled with a thiol at its 5' end and a biotin at its 3' end, respectively, was used. This probe was immobilized on the gold nanoparticles (AuNPs) anchored by a protein, gamma-globulin, on a 96-well microplate. In the absence of target DNA, the immobilized probe with the stem-loop structure shields the biotin from being approached by a bulky horseradish peroxidase linked streptavidin (streptavidin-HRP) conjugate due to the steric hindrance. However, in the presence of target DNA, the hybridization between the hairpin DNA probe and the target DNA causes significant conformational change of the probe, which forces biotin away from the surface of AuNPs. As a result, the biotin becomes accessible by the streptavidin-HRP, and the target hybridization event can be sensitively detected via the HRP catalyzed substrate 3,3',5,5'-tetramethylbenzidine using a spectrophometric method. Some experimental parameters governing the performance of the assay have been optimized. At optimal conditions, this DNA assay can detect DNA at the concentration of femtomolar level by means of a signal amplification strategy based on the combination of enzymes and nanoparticles. This approach also has shown excellent specificity to distinguish single-base mismatches of DNA targets because of the intrinsic high selectivity of the hairpin DNA probe.

• FeCo alloy doped carbon sphere (FeCo@C) was obtained from the carbonization of FeCo-ZIF. • FeCo@C exhibits satisfactory mimetic dual-enzyme activity. • The mimetic dual-enzyme activity can be controlled and used as bifunctional colorimetric biosensor for HQ and H 2 O 2. • The FeCo@C solves the defect of instability of non-precious metal nanoparticles owing to the protection of C sphere. • The FeCo@C has strong magnetic which could achieve multiple recycling. Extensive attention has been paid to rationally control the artificial nanoenzyme activities via suitable strategies to prepare various nanoscale functional materials. Herein, FeCo co-doped carbon sphere (FeCo@C) with intrinsic oxidase-like and peroxidase-like activity has been obtained from the carbonization of FeCo-ZIF. The unique dual-enzyme catalytic property of FeCo@C can be simply regulated and utilized for bifunctional colorimetric platforms. At pH 3.6 and catalytic reaction time of 6 min, the FeCo@C possesses strong oxidase-like activity which can catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) owing to the production of O 2 ·− with the participation of O 2 to result in typical color change of the system. Hydroquinone (HQ) as a reducing agent can induce the color fading, and therefore, a novel colorimetric biosensing platform for HQ was constructed with the linear range of 1–30 μM and detection limit of 0.8 μM. However, with the pH of 4.4 and catalytic reaction time of 3 min, the oxidase-like activity of FeCo@C was obviously weakened, and the peroxidase-like activity of FeCo@C is still high. Hence, a facile analytical method was developed to detect H 2 O 2 based on the peroxidase-like activity of FeCo@C with the linear range of 1–240 μM and detection limit of 1 μM. Moreover, the FeCo@C has high stability and strong magnetism with the activity being kept well after several cycles of recycling, which shows great prospect in biosensing and catalysis areas. [ABSTRACT FROM AUTHOR]