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Abstract Proteases, as one of the most significant kind of digestive enzymes, are closely related to a variety of physiological processes and diseases. Herein, a black phosphorus nanosheets (BPs) based sensitive fluorometric method for protease detection and inhibitor screening is proposed. The aqueous solution of perylene probe (probe 1) displays a strong fluorescence. BPs, as novel discovered two-dimensional (2D) materials, can adsorb probe 1 through electrostatic interactions, which causes fluorescence quenching of probe 1. Histone can control the interactions between the perylene probe and BPs, which can be further regulated by the introduction of a protease. Thus, the protease activity can be monitored by detecting the fluorescence intensity changes of probe 1. The method is label free, sensitive and selective. As low as 1 ng/mL trypsin can be easily detected. Graphical abstract fx1 Highlights • Black phosphorus nanosheets were used as the quencher for a fluorometric assay. • A label-free method for protease detection and inhibitor screening. • Histone controlled interactions between a perylene probe and black phosphorus nanosheets were used for signal transduction. • No covalent modifications were needed, and the assay is simple, sensitive and selective. [ABSTRACT FROM AUTHOR]

In this work, a fluorescence turn-on method for copper(II) detection is reported. A molecular beacon (MB) was designed as a template. Cu 2+ was reduced to Cu + in the presence of a reductant (ascorbic acid). Two short single-stranded oligonucleotides one was labeled with a 5′-alkyne and the other with 3′-azide group, proceeded a template-dependent chemical ligation through the Cu(I)-catalyzed azide-alkyne cycloaddition. The newly generated click-ligated long chain oligonucleotide, which was complementary to the MB, opened the MB hairpin structure and resulted in a turn on fluorescence. The increase in fluorescence intensity is directly proportional to the amount of Cu 2+ added to the assay solution. The present assay is quite sensitive and allows the detection of 2 nM Cu 2+ . The described assay also exhibits high selectivity over other metal ions. [ABSTRACT FROM AUTHOR]

Abstract: Single-stranded deoxyribonucleic acid (ssDNA)-wrapped single-walled carbon nanotubes (SWNTs) were modified on the surface of glassy carbon electrode (GCE) by covalent modification technique. Field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectrum (XPS), electrochemical impedance spectroscopy (EIS), and cyclic voltammetric (CV) were used to characterize the properties of this modified electrode. The results showed that SWNTs–ssDNA composites were successfully immobilized onto the surface of GCE. Moreover, this modified electrode exhibited high stability, largely active areas, and efficiently electrocatalytic activities. It had been used for the analysis of various biomolecules, such as dopamine (DA), uric acid (UA), and ascorbic acid (AA), and the results were satisfactory. [Copyright &y& Elsevier]

Abstract: A novel electrochemical sensor has been constructed by use of a glassy carbon electrode (GCE) coated with a gold nanoparticle/choline (GNP/Ch). Electrochemical impedance spectroscopy (EIS), field emission scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the properties of this modified electrode. It was demonstrated that choline was covalently bounded on the surface of glassy carbon electrode, and deposited gold nanoparticles with average size of about 100nm uniformly distributed on the surface of Ch. Moreover, the modified electrode exhibits strong electrochemical catalytic activity toward the oxidation of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with obviously reduction of overpotentials. For the ternary mixture containing DA, AA and UA, these three compounds can be well separated from each other, allowing simultaneously determination of DA and UA under coexistence of AA. The proposed method can be applied to detect DA and UA in real samples with satisfactory results. [Copyright &y& Elsevier]

A simple and efficient fluorometric sensing method is developed for the rapid detection of nitroaromatic explosives, based on the quenching of monomer and excimer emission of benzo[ghi]perylene and coronene. The ratiometric method (I E /I M) offers a linear response as a function of the concentration of picric acid (PA, i.e. 2,4,6-trinitrophenol), which is used as a model example of the nitroaromatic compounds (NOCs). The detection range is observed to be 0.1–120 μM of PA (22.9 ppb–27.5 ppm). The bright emission of the stable probe excimer and monomer can be easily distinguished under UV lamp from the quenched solution with nitro-aromatic molecules that enables naked-eye detection of nitro-aromatic explosives. The fluorescent paper strips prepared by embedding the probes on the surface of the paper are used for fast, portable and selective detection of NOCs. Our optimized methods can easily detect and quantify NOCs down to 0.1 μM. The sensing process is free of commonly encountered interferences such as volatile organic compounds (VOCs), acids, bases, oxygen, and salt solutions. Nitroaromatic explosives sensing via probe fluorometric assay and fluorescent paper strips visual detection. Image 1 • A simple and efficient fluorometric sensing method was developed for the rapid detection of nitro-aromatic explosives. • Fluorescence quenching of monomer and excimer emission of benzo[ghi]perylene and coronene was used as probe. • Ratiometric method (I E /I M) offered a linear response of detection in the range of 0.1–120 μM. • The quenching of bright emission of probe excimer and monomer enabled naked-eye detection of explosives. • The fluorescent paper strips were prepared for the fast, portable and selective detection of NOCs. [ABSTRACT FROM AUTHOR]

Based on the controlled aggregation of quantum dots (QDs), a valid, reliable, and label-free fluorescence turn-on strategy is established for the detection of alkaline phosphatase activity. The aqueous solution of anionic QDs exhibits intense fluorescence. However, the addition of cationic polymer (poly-1) significantly quenched the fluorescence of the QDs via their induced aggregation. While short 3′-phosphorylated DNA (DNA-P) could not be extended by terminal deoxynucleotidyl transferase (TdT) and therefore, fluorescence of the QDs was recovered negligibly. The effective elimination of phosphate group of DNA-P in the presence of alkaline phosphatase (ALP) produced 3′-OH termini and the resulting DNA could be sufficiently extended by TdT. The presence of greater binding strength between the elongated DNA and poly-1 is very crucial to compete with the poly-1/QDs aggregates and release the QDs. Turned-on fluorescence emission is observed due to the efficient release of the QDs. A novel strategy for alkaline phosphatase detection is therefore established. Our method is quite sensitive and selective, as low as 0.1 mU/mL ALP can be easily detected. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2) is a common oxidant that plays an important role in many biological processes and is also an important medium analysis in various fields. In this work, a new electrochemical nanosensor capable of detecting and quantifying hydrogen peroxide was introduced. This nanosensor was fabricated by electrodepositing prussian blue (PB)/graphene quantum dots (GQDs)/polypyrrole (PPy) on single nanopore electrode etched from single gold nanoelectrode. This prepapred nanosensor exhibits good electrochemical response to hydrogen peroxide with high sensitivity and stability, with a linear response in the 2.0 and 80 μM by using amperometric method and differential pulse voltammetry (DPV) method. The limit of detections are 0.33 μM (S/N = 3) for amperometric method and 0.67 μM (S/N = 3) for differential pulse voltammetry (DPV) method, respectively. This nanosensor can be used for the determination of hydrogen peroxide in human urine, and can serve as a new electrochemical platform to monitor H 2 O 2 release from single living cells due to its small overal dimension and high sensitivity. [Display omitted] • Nanosensor was fabricated on single nanopore electrode filled with Prussian blue and graphene quantum dots coated by Polypyrrole. • New nanosensor shows good electrocatalytic activity towards H2O2 oxidation. • This nanosensor can serve as a new electrochemical platform to monitor H2O2 release from single living cells due to its small overal dimension. [ABSTRACT FROM AUTHOR]

A new nanozyme (CuGaa) with switchable enzyme-like activity of peroxidase and polyphenol oxidase was successfully prepared based on guanidinoacetic acid and copper. The two enzyme-like activities can be easily switched by changing temperature or adding MnCl 2. At 4 °C, polyphenol oxidase-like activity decreased to nearly 1%, and the material is mainly characterized by peroxidase-like activity at this point. However, at 60 °C in the presence of 20 mM MnCl 2 , the peroxidase-like activity decreased to nearly 10%, and the polyphenol oxidase-like activity of the materials increased to 140%. Based on the switchable enzyme-like activity of CuGaa, detection methods for thymol and hydrogen peroxide were developed. In addition, a rapid combination strategy was further established combined with logic gate technology for the facile identification of complex contamination in honey, which provided new ideas for low-cost and rapid honey identification. The graphic descriptives that CuGaa has polyphenol oxidase-like and peroxidase-like activities, and that under different conditions, CuGaa can be made to exhibit only one enzyme activity. [Display omitted] • Nanozyme with switchable enzyme-like activity. • Thymol detection at high temperature based on the nanozyme. • A sensing strategy combined with logic gate technology. • A facile identification of complex contamination in honey. [ABSTRACT FROM AUTHOR]

A novel sensor array was developed based on the enzyme/nanozyme hybridization for the identification of tea polyphenols (TPs) and Chinese teas. The enzyme/nanozyme with polyphenol oxidase activity can catalyze the reaction between TPs and 4-aminoantipyrine (4-AAP) to produce differences in color, and the sensor array was thus constructed to accurately identify TPs mixed in different species, concentrations, or ratios. In addition, a machine learning based dual output model was further used to effectively predict the classes and concentrations of unknown samples. Therefore, the qualitative and quantitative detection of TPs can be realized continuously and quickly. Furthermore, the sensor array combining the machine learning based dual output model was also utilized for the identification of Chinese teas. The method can distinguish the six teas series in China, and then precisely differentiate the more specific tea varieties. This study provides an efficient and facile strategy for the identification of teas and tea products. [Display omitted] • A novel sensor array was developed based on the enzyme/nanozyme hybridization. • Six TPs in Chinese tea were successfully distinguished. • Effective identification of six major teas series and more specific 17 tea varieties. • Machine learning based dual output model for TPs' qualitation and quantitation. • Machine learning based dual output model for identifying tea samples. [ABSTRACT FROM AUTHOR]

Abstract: Based on the enhancement of chemiluminescence (CL) of luminol-hydrogen peroxide-gold nanoparticles system by fluoroquinolones (FQs), a novel and rapid CL method is reported for the determination of FQs derivatives. Under the optimum conditions, the CL intensity is proportional to the concentration of FQs derivative in solution. The corresponding linear regression equations are established over the range of 0.08–1.28μg/mL for norfloxacin, 0.013–1.32μg/mL for ciprofloxacin, 0.014–1.4μg/mL for lomefloxacin, 0.029–1.46μg/mL for fleroxacin, 0.02–1.0μg/mL for ofloxacin and 0.01–1.44μg/mL for levofloxacin, respectively. The limits of detection (S/N =3) are 3.2, 9.5, 7.0, 9.0, 8.0, and 8.0ng/mL with the relative standard deviation (n =11) 4.3, 1.5, 1.9, 1.3, 1.6 and 2.1% for norfloxacin, ciprofloxacin, lomefloxacin, fleroxacin, ofloxacin and levofloxacin, respectively. This proposed method has been applied to detect FQs derivatives in human urine successfully. [Copyright &y& Elsevier]

Abstract: A novel flow-injection chemiluminescence (FI-CL) method for the determination of estrogens is proposed, based upon its enhancing effect on the CL reaction of luminol with hydrogen peroxide catalyzed by tetrasulfonated manganese phthalocyanine (MnTSPc) in alkaline solution. Under the selected experimental conditions, a linear relationship was obtained between the CL intensity and the concentration of estrone in the range of 1.0×10−7 to 1.0×10−6 mol/l, estradiol in the range of 9.0×10−8 to 1.0×10−6 mol/l and estriol in the range of 3.0×10−7 to 2.0×10−6 mol/l, respectively. The detection limits were 5.1×10−8 mol/l for estrone, 7.2×10−9 mol/l for estradiol and 6.5×10−8 mol/l for estriol with a relative standard deviation of 2.8% for 5.0×10−7 mol/l estrone, 2.4% for 1.0×10−7 mol/l estradiol, and 3.1% for 7.0×10−7 mol/l estriol (n =11). This method has been applied to the determination of estrogen in pharmaceutical injections and tap water with satisfactory results. [Copyright &y& Elsevier]

The development of a simple and effective method for the highly sensitive and selective discrimination of proteins is a subject of enormous interest. Herein, we report the construction of a novel fluorescence detection method based on a perylene probe for the highly efficient discrimination of multiple proteins. Single-stranded DNA (ssDNA) could induce aggregation of the perylene probe which caused quenching of probe fluorescence. After the addition of a protein, the protein could interact with the ssDNA-probe assembly complex with "turn-on" or further "turn-off" fluorescence response. A sensor array was designed based on the above phenomena which could realize the successful discrimination of proteins with 100% accuracy of cross validation. Nine representative proteins were successfully recognized. Moreover, it was observed that a protein could induce characteristic effect on the DNA-probe assembly with varying pH of assay buffer. Thus, different proteins showed unique fluorescence response towards assay buffers having different pH values. The assay buffer pH was then utilized as a sensing channel. Based on Linear Discriminant Analysis (LDA) nine proteins were successfully discriminated at the nanomolar concentration with 100% accuracy of cross validation. Furthermore, the sensor array also demonstrated differentiation of the nine proteins regardless of their concentration. The developed sensor array could also detect the proteins with great precision in human urine sample at a quite low concentration, which suggests its practical applicability for analysis of biological fluids. Fluorescence sensor array based on DNA induced PeryProbe self-assembly. Image 1 • A fluorescence sensor array is developed for the discrimination of proteins. • Negatively charged ssDNA induced self-assembly of the perylene probe. • The array was based on the different interactions between the protein and the ssDNA-PeryProbe assembly complex. • The array could discriminate proteins regardless of their concentration. • The array was applied to discriminate proteins in human urine samples. [ABSTRACT FROM AUTHOR]

Nano-sized electrodes have their special advantages for sensing applications, such as small overall dimension, fast response and low background current. In this work, single gold nanoclusters (AuNCs) were controllably prepared on single Pt nanoelectrode surface by electrodeposition method. The AuNCs covered Pt nanoelectrode (AuNCs/PtNE) had steady-state voltammetric response in redox species solution, which was similar to micro-/nano-sized electrodes. It was interesting to find isonicotinic acid hydrazide (INH, also known as isoniazid) showed good electrochemical response on AuNCs/PtNE surface, which had investigated carefully by square wave voltammetry (SWV) and chronoamperometry. Moreover, the prepared single AuNCs/PtNEs showed the capability for INH sensing with good sensitivity, reproducibility and selectivity, which was demonstrated for INH detection in human urine samples. Image 1 • Single gold nanoclusters (AuNCs) were controllably prepared on single Pt nanoelectrode surface by electrodeposition method. • The single AuNCs/PtNE showed excellent electrochemical responses for isonicotinic acid hydrazide (INH) oxidation. • A single AuNCs-based nanosensor was developed for INH sensing with good sensitivity, reproducibility and selectivity. [ABSTRACT FROM AUTHOR]

Solid-nanopores/nanopipettes have the exquisite ability to reveal the changes in molecular volume due to the advantages of adjustable size, good rigidity and low noise. Herein, a new platform for sensing application was established based on G-quadruplex-hemin DNAzyme (GQH) functionalized gold-coated nanopipettes. In this method, GQH was immobilized on gold-coated nanopipette, which could be used as a catalyst for the reaction of H 2 O 2 with 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) to promote the conversion of ABTS to ABTS+ ions inside gold-coated nanopipette, and the change of transmembrane ion current could be monitored in real time. At the optimal conditions, there was a correlation between the ion current and the concentration of H 2 O 2 in a certain range, which could be used for the hydrogen peroxide sensing. The GQH immobilized nanopipette provides a useful platform to investigate enzymatic catalysis in confined environment, which can be used in electrocatalysis, sensing and fundamental electrochemistry. [Display omitted] • GQH-functionalized gold-coated nanopipettes was fabricated successfully. • GQH-functionalized nanopipettes was used as a catalyst for H 2 O 2 and ABTS reaction. • The conversion of ABTS to ABTS + ions resulted the change of ICR. • A H 2 O 2 sensor was established using the GQH-functionalized nanopipettes platform. [ABSTRACT FROM AUTHOR]

In this work, 2-methylimidazole (MI) was doped into the Bpy-Cu nanozyme as a second ligand to form a novel laccase-mimicking enzyme (MI-Bpy-Cu). By comparison, MI-Bpy-Cu nanozyme was identified to have excellent laccase-mimicking activity, high stability and catalytic kinetic properties. It may be that the incorporation of 2-methylimidazole helped the nanozymes to build a structure closer to natural laccase and accelerate the electron transfer rate, thereby achieving the purpose of enhancing the activity. Furthermore, we observed that MI-Bpy-Cu nanozymes could oxidize the colorless (+)-Catechin to generate a yellow radical product, and a novel colorimetric sensing strategy for (+)-Catechin was successfully developed. The method had excellent selectivity and anti-interference properties, and also had good application in the analysis of (+)-Catechin in dairy products. [Display omitted] • The 2-methylimidazole was first incorporated as a second ligand to enhance the activity of laccase-mimicking enzymes. • The nanozyme was modified close to the natural laccase composition. • The colorimetric method was successfully established for the analysis of (+)-Catechin in dairy products. • The method has high selectivity and interference resistance. [ABSTRACT FROM AUTHOR]

Development of new hot spots for surface enhanced Raman scattering (SERS) technique is of great significance recently. Herein, we developed a single Au nanowire (NW)-based nanosensor for adenosine triphosphate (ATP) sensing by using in-situ SERS technique. Single Au NWs, fabricated by laser-assisted pulling method and hydrofluoric acid (HF) etching process, were linked with single-stranded HS-terminated DNA. After that, gold-silver bimetallic nanoparticles (Au/Ag NPs), attached with thiol-containing Raman dyes and ATP aptamer, were immobilized on DNA-modified single AuNW due to the designed affinity between ATP aptamer and single-stranded DNA. This single AuNW-based device exhibited strong SERS signals. In the presence of adenosine triphosphate (ATP), due to the strong specific affinity between the aptamer and the target, the Au/Ag NPs will be separated from the AuNW, resulting in the obvious decrease of the Raman signals, which can be used for ATP sensing with high sensitivity, selectivity and stability. This nanosensor can be used as an ideal platform for real applications, especially at some confined-space samples, such as trace detection, single cell and in vivo analysis. [Display omitted] • A single Au nanowire (NW)-based nanosensor for adenosine triphosphate (ATP) sensing was established. • The combination of nanoparticles and nanowires provides SERS with a strong electromagnetic field coupling. • This nanosensor can be used as an ideal platform for real applications, especially at some confined-space samples. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemical immunosensor for detection of Salmonella has been developed based on using high density gold nanoparticles (GNPs) well dispersed in chitosan hydrogel and modified glassy carbon electrode. The composite film has been oxidized in NaCl solution and used as a platform for the immobilization of capture antibody (Ab 1 ) for biorecognition. After incubation in Salmonella suspension and horseradish peroxidase (HRP) conjugated secondary antibody (Ab 2 ) solution, a sandwich electrochemical immunosensor has been constructed. The electrochemical signal was obtained and improved by comparing the composite film with chitosan film. The result has shown that the constructed sensor provides a wide linear range from 10 to 10 5 CFU/mL with a low detection limit of 5 CFU/mL (at the ratio of signal to noise, S/N=3:1). Furthermore, the proposed immunosensor has demonstrated good selectivity and reproducibility, which indicates its potential in the clinical diagnosis of Salmonella contaminations. [ABSTRACT FROM AUTHOR]

Abstract: In this work, we reported a sensitive chemiluminescent immunosensor for the detection of human leptin by using hemin/G-quadruplex DNAzymes to amplify detection signal. In this sensing system, the primary antibody (anti-human leptin) was firstly bound to the 96-well plates, and human leptin and biotinylated secondary antibody were successively combined to form sandwich-type immune complex through specific interactions. Then streptavidin labeled with hemin/G-quadruplex DNAzymes was assembled to the sandwich-type immunocomplex by streptavidin–biotin interaction. The DNAzymes exhibited an excellent catalytic activity to the chemiluminescent reaction of luminol with hydrogen peroxide in strong alkaline solution, leading to significant enhancement in response signal. Under the optimum conditions, the proposed immunosensor showed high sensitivity and selectivity with a low detection limit of 1.9pgmL−1 and a wide linear response range of human leptin from 10 to 1000pgmL−1. The immunosensor was used to detect human leptin in serum, and the results were in good agreement with the data obtained by conventional ELISA method. [Copyright &y& Elsevier]

A selective and sensitive colorimetric strategy for sulfide analysis was developed using GMP-Cu nanozymes with a laccase-like activity. This research discovered for the first time that sulfide could significantly enhance the catalytic activity of the GMP-Cu nanozymes by about 3.5 folds. The enhanced laccase activities duo to two reasons. First, Cu2+ in GMP-Cu nanozymes was reduced to Cu+. The other reason was the formation of Cu–S bond which was beneficial to accelerate the electron transfer rate to improve catalytic activity. Therefore, this method showed an excellent selectivity for sulfide. And it had a linear relationship in the sulfide concentration range of 0–220 μmol/L with a detection limit of 0.67 μmol/L. Furthermore, the proposed method was successfully applied to examine sulfide in the food systems. This new method may be used in sulfide detection to improve food quality and safety. [Display omitted] • A method of sulfide detection based on Cu-Nucleotide nanozymes with laccase-like activity is first constructed. • The catalytic activity of nanozymes is enhanced by bifunctional sulfide accelerating the electron transfer rate. • This study develops a facile sensing method for the detection of sulfide in food system. • The sensor detects sufide with good selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

The cancer diagnosis with single level of biomarkers suffers from limitation of insufficient accuracy. Hence, developing sensitive, rapid and adaptative analytical strategies for double-level biomarkers are essential for improving the accuracy of clinical cancer diagnosis at early stage. Herein, a DNA biosensor was established based on the catalytic hairpin assembly-mediated Y-junction nicking enzyme assisted signal amplification (CHA-YNEASA) circuits, where the two circuits were concatenated by molecular beacon (MB). In absence of target, both the CHA and YNEASA circuits were effectively hindered because of MB's outstanding ability to control signal background. In presence of target, the initiated CHA circuits made enzyme recognition sequences in close proximity to the assisted sequences to open MB, leading to further trigger the YNEASA circuits. Due to the unique design of dual signal amplification strategies, CHA-YNEASA circuits significantly shorten the reaction time, and improve signal-to-background ratio as well as facilitate the analysis process. It was demonstrated that a high sensitivity with limit of detection (LOD) of 0.9 pM for p53 gene detection was obtained just within 23 min by the proposed DNA biosensor. Moreover, mismatched p53 gene at nucleic acid level was effectively discriminated and strong anti-interference capability was achieved. Noticeably, the DNA biosensor was adaptative for designing a cytosensor at cell level using hairpin DNA, containing MUC1 aptamer and initiation strand of CHA-YNEASA circuits, as switch based on modularity principle. The cytosensor is able to measure MUC1 positive breast cancer cells (MCF-7) with the LOD as low as 100 cells/mL. Excellent specificity for MUC1 negative cells, and good anti-interference capability in 10% fetal bovine serum (FBS) were observed by the cytosensor. Therefore, the proposed DNA biosensor is a sensitive, rapid, adaptative platform for detection of double-level biomarkers, offering novel strategy applied for clinical cancer diagnosis. Image 1 1. DNA biosensor was developed based on catalytic hairpin assembly-mediated Y-junction nicking enzyme assisted signal amplification. 2. The DNA biosensor shows high efficiency of reaction leading to rapid analysis just in one-step. 3. High sensitivity, strong selectivity and anti-interference were achieved for p53 gene and cancer cell detection. 4. The DNA biosensor is adaptative for the detection of multilevel biomarkers using modularity principle. [ABSTRACT FROM AUTHOR]