•A novel method to prepare TiO2/Ag nanoparticles (AgNPs) complex has been developed.•The unique self-clean properties of the TiO2-Ag NPs structures can be used as reclycable SERS substrate.•The TiO2-Ag NPs SERS substrates show high sensitivity in detecting thiram molecules, which is a kind of pesticides.A multifunctional TiO2/Ag nanoparticles (AgNPs) complex substrate was prepared via a three-step approach, which included the hydrothermal route on a Ti substrate, the deposition of Ag by photo-reducing method and the annealing treatment under high temperature. The effect of the annealing process on the morphology, structure and surface-enhanced Raman scattering (SERS) performance of the substrate was systematically investigated, and the optimal substrate was obtained. Herein, 4-aminothiophenol (4-ATP), methylene blue (MB) and crystal violet (CV) were employed as probe molecules to test the sensitivity and UV-cleanable property of the hybrid SERS substrate. The results suggested that the substrate exhibited relatively high enhancement ability, good stability, reproducibility, and recyclability. The synthesised SERS-active substrate was further used to detect thiram molecules, a kind of pesticides, and the limitation of detection in ethanol, apple juice and apple peel reached 10−7 M, 10−6 M and 240 ng/cm2, respectively. The detection limit of thiram in the apple juice was below than the maximal residue limit of 7 ppm (2.9 × 10−5 M) in fruit prescribed by the U.S. Environmental Protection Agency (EPA). These results demonstrated that TiO2/AgNPs complex substrate exhibited promising application with respect to its potential use for on-site detection of residual pesticides.

•A novel fluorescent assay for AChE and its inhibitor detection has been developed.•This novel assay is based on the fluorescent copper nanoparticles.•This assay shows high sensitivity and selectivity for AChE activity detection.The poly(thymine) (poly T) can effectively template the in situ formation of copper nanoparticles (CuNPs) within several minutes under ambient conditions, offering great potential as fluorescence probe for biochemical analysis without complicated modifications. However, the exploration of poly T-templated CuNPs (poly T-CuNPs) for biochemical applications is still at its very early stage. Herein, a novel fluorescent assay has been developed for acetylcholinesterase (AChE) and its inhibitor detection based on poly T-CuNPs. In the absence of AChE, the high affinity between Cu2+ and thymine leads to the formation of fluorescent CuNPs. In the presence of AChE, the fluorescence of poly T-CuNPs is quenched based on the reaction between Cu2+ and thiocholine generating from the hydrolysis of ATCh by AChE. This detection assay is simple without the requirement for complex labeling of probe DNA and the multiple preparation procedure of fluorescent compounds. The detection assay is highly sensitive for sensing AChE in the concentration ranging from 0.11 to 2.78 mU mL−1 with a detection limit of 0.05 mU mL−1 and is feasible for screening AChE inhibitor. This method paves a new way for exploring the biosensing applications of the poly T-CuNPs.A novel fluorometric assay for acetylcholinesterase and its inhibitor detection based on the in situ formation of fluorescent copper nanoparticles is proposed.Download high-res image (92KB)Download full-size image

A facile, low cost and time-saving method to synthesize porous NiCo2O4 nanoplatelet and nanorod structures is developed via a simple two-step route. A flakes assembled precursor containing Ni-Co hydroxides is firstly prepared via a facile, low-cost chemical bath coprecipitation process only using diluted ammonia solution as a precipitant to govern over the nucleation, growth, and agglomeration processes.Then, porous NiCo2O4 nanoplatelet and nanorod structures are successfully obtained through pyrolyzing the above precursor. The influence of the calcination temperature is mainly studied on the pyrolysis reaction. The calcination temperature has statistically significant effects on the morphology and structure evolution, crystallinity, electronic conductivity and the electrochemical performances of the products. The optimized, nanoplatelet predominated NiCo2O4 spinel, calcinated at 300 ∘C for 6 h (denoted as NC300), has excellent crystallinity and electric conductivity. It shows a superior-specific capacitance of 1362F g−1 at a current density of 1 A g−1.When the current density increases to 16 A g−1, the specific capacity still retains 964 F g−1 (70.8% capacity retention). Ragone plot indicates maximum energy density of our porous NC300 electrode is 75.67 W h kg−1 at a power density of 499.82 W kg−1. Cycle-life tests show that the specific capacitance of NC300 is nearly stable between 300 and 1500 cycles, indicating its potential use in energy-storage field.The simplicity and practicability of the modified pyrolysis process may facilitate the successful commercial applications in electrochemical capacitors for nanostructured NiCo2O4 spinel.

We demonstrated here the crosslinked N-doped graphene (NG) can be rapidly prepared through a one-step burning process of graphene oxide. The doping process completed within 3 minutes and the N content in the obtained NG reached to 5.6%. The obtained crosslinked NG shows mesoporous structure with relatively high specific area, large pore volume and various N types. As a supercapacitor, the resultant NG exhibits rapid diffusion of electrolyte ions and shows superior capacitive performance, excellent specific capacitance (317.5 F/g at the current density of 1 A/g) and high cycling stability (93% retention after 5000 cycles). The obtained results indicate that the crosslinked NG is a promising candidate for creating supercapacitors with high performance and relatively low cost.

•We report a facile and simple assay for AChE and its inhibitor screening.•The proposed method shows high sensitivity.•The developed assay is simple without the use of nanomaterials.•The assay paves the way for the sensing of other enzymes.A novel colorimetric method for the detection of acetylcholinesterase (AChE) and its inhibitor by taking utilization of Ag [I] ion–3,3′,5,5′-tetramethylbenzidine (TMB) detection system has been proposed. Ag [I] ion could oxidize TMB to induce a blue color and an absorption peak centered at 652 nm. In the presence of AChE, acetylthiocholine (ACh) was hydrolyzed to thiocholine. Ag [I] ion could interact with thiocholine and thiocholine can reduce the oxidized TMB (oxTMB) to TMB, both of which suppressed the oxidation capacity of Ag [I] ion, resulting in a blue color fading and a decrease of the absorbance at 652 nm. The developed assay is highly sensitive with a low detection limit of 4.3 μU/mL. Moreover, the method was also applied in AChE inhibitor sensing. The obtained assay is fairly simple, inexpensive and sensitive without the utilization of nanomaterials, which may be not only used for the sensing of other hydrolytic enzyme activities with properly selected substrates, but also used for the screening of potential inhibitor drugs.A facile and simple colorimetric method for acetylcholinesterase and its inhibitor detection is proposed.

We describe a sensitive and selective colorimetric method for the determination of the activity of the enzyme acetylcholinesterase (AChE) and its inhibitors. Detection is based on the fact that acetylthiocholine iodide (ATCI) catalyzes the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 to form a blue product (ox-TMB) with an absorption peak at 652 nm, but that oxidation is suppressed if ACTI previously is hydrolyzed by AChE to form thiocholine which decolorizes ox-TMB. In the presence of inhibitor, the activity of AChE is inhibited, thereby inducing the recovery of the blue coloration. Based on these findings, a highly sensitive method is developed for the determination of AChE and its inhibitors. The assay only requires mixing of buffer, solutions of ATCI, TMB, H2O2 and a sample containing AChE and photometric measurement. It works in the 0.05 to 5 mU•mL−1 enzyme activity range and has a detection limit as low as 30 μU•mL−1. The inhibitor neostigmine causes 50 % enzyme inhibition in 14.5 nM concentration. This analytical system has a wide scope in that it may be applied to the determination of the activity of various other hydrolases with proper substrates.

A novel colorimetric biosensor for the determination of tetracyclines (TCs) based on the Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) is presented in this paper. TCs are known to have a strong tendency to complex with metal ions such as Fe(II) and Fe(III) on the surface of Fe3O4 MNPs. Experiments results show that the complexation of Fe3O4 MNPs and TCs could lead to the accelerated catalysing H2O2-mediated oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by Fenton chemistry. The reaction starts with oxidation of Fe3O4 MNPs-TCs complex by dissolved oxygen to generate reactive oxygen species (ROS), primarily ·OH, leading to deepen the color of the solution. Analysis results can be seen with the naked eye and monitored by UV–vis spectra. Under the optimal conditions, the detection limits are 26 nM for oxytetracycline (OTC), 45 nM for tetracycline (TC) and 48 nM for doxycycline (DOX). Moreover, this method has been applied for the determination of OTC content in drugs with satisfactory results. The proposed colorimetric biosensor is advantageous over other conventional methods in terms of convenient operation without any complicated chemical synthesis, modification, or tedious experimental procedures and its simple signal generation and detection by the naked eye. To the best of our knowledge, this is the first report on the enhancement effect of TCs on Fe3O4 MNPs-TMB-H2O2 reaction and its application in colorimetric TCs analysis. The designed colorimetric strategy may provide a promising alternative detection for TCs in clinical samples.A novel colorimetric biosensor for the determination of tetracyclines based on the Fe3O4 magnetic nanoparticles is presented.

In this study, we successfully, for the first time, prepared nitrogen and fluorine dual-doped mesoporous graphene (NF–MG) via the thermal treatment of graphene oxide/polyaniline composites (GO/PANI) and NH4F. Benefiting from the synergistic effect of N and F co-doping into the G framework, the oxygen reduction reaction performance of the optimal catalyst (NF–MG3) is comparable with the-state-of-the-art Pt/C catalyst in an alkaline medium, which makes it an ideal candidate as an efficient metal-free ORR electrocatalyst in fuel cells.

In this work, a novel facile nanoparticle autocatalytic sensor based on the inhibition of the Ag autocatalytic reaction for the determination of Hg2+ was developed. o-Phenylenediamine (OPD) tended to be oxidized into 2,3-diaminophenazine (OPDox) by silver ions (Ag+) followed by the formation of silver nanoparticles (AgNPs). Employed as a catalyst, the thus-formed AgNPs would further promote the reaction between OPD and Ag+. When Hg2+ was introduced, Hg2+ adsorbed on the surface of the AgNPs, thus inhibiting the oxidation process mentioned above and achieving weakened fluorescence intensity. A linear relationship between fluorescence intensity and Hg2+ concentration (within the range from 10 nM to 2500 nM) was obtained and the detection limit reached as low as 8.2 nM. The proposed method was also applied for the determination of Hg2+ in real water samples with satisfactory results. The protocol showed excellent advantages of sensitivity and selectivity for Hg2+ over various metal ions and anions. Meanwhile, this method was simpler and more cost-effective compared with many reported nanomaterial- and DNA-based approaches. Furthermore, an “INHIBIT” logic gate based on the Ag+–Hg2+–OPD system has also been designed.

•A new colorimetric method for GSH detection is proposed.•This method could selectively detect GSH over Cys and Hcy.•This method is simple without the preparation of nanomaterials.•The proposed method is successfully applied to the detection of GSH in real samples.Glutathione (GSH) plays an important role in the biological system and serves many cellular functions. Since all of the biothiols possess similar functional groups, it is still challenging to selectively detect GSH over cysteine (Cys) and homocysteine (Hcy). In this work, a novel and simple colorimetric method for discriminative detection of glutathione (GSH) over Cys and Hcy is developed. The proposed method is based on the fact that Ag [I] ion could oxidize 3,3′,5,5′,-tetramethylbenzidine (TMB) to the oxidized TMB to induce a blue color and an absorption peak centered at 652 nm. However, the introduction of GSH could cause the reduction of oxidized TMB and it could also combine with Ag+, both of which result in a blue color fading and a decrease of the absorbance at 652 nm. Based on this finding, we propose a method to qualitatively and quantitatively detect GSH by naked eyes and UV–vis spectroscopy, respectively. The proposed method shows a low detection limit of 0.1 µM by naked eyes and 0.05 µM with the help of UV–vis spectroscopy. In addition, this method has great potential in discriminatively detecting GSH over other amino acid and biothiols. More importantly, this method is simple and fast without the preparation of nanomaterials and has also been successfully applied to the detection of GSH in biological fluids.

•Using C-dots for sensitive detection of H2Q is proposed for the first time.•The proposed method is simple without the use of enzyme.•The method is environment friendly.•This method can be expanded to detect other biomolecules.In this paper, a novel biosensor based on Carbon dots (C-dots) for sensitive detection of hydroquinone (H2Q) is reported. It is interesting to find that the fluorescence of the C-dots could be quenched by H2Q directly. The possible quenching mechanism is proposed, which shows that the quenching effect may be caused by the electron transfer from C-dots to oxidized H2Q-quinone. Based on the above principle, a novel C-dots based fluorescent probe has been successfully applied to detect H2Q. Under the optimal condition, detection limit down to 0.1 μM is obtained, which is far below U.S. Environmental Protection Agency estimated wastewater discharge limit of 0.5 mg/L. Moreover, the proposed method shows high selectivity for H2Q over a number of potential interfering species. Finally, several water samples spiked with H2Q are analyzed utilizing the sensing method with satisfactory recovery. The proposed method is simple with high sensitivity and excellent selectivity, which provides a new approach for the detection of various analytes that can be transformed into quinone.A facile method based on C-dots for sensitive detection of H2Q is proposed.

NiCo2O4 nanoflake composites were synthesized by using DNA molecules as templates via in-situ assembly and subsequent thermal treatment. The obtained NiCo2O4 composites were characterized by scanning electron microscopy, energy dispersive spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Cyclic voltammetry and chronopotentiometry tests were used to investigate the electrochemical properties of the as-prepared composites. Superior performances with a good specific capacitance (1468 F/g), an extraordinary rate capability (64.9% capacity retention at 16 A/g) and an excellent cycling stability (85.5% retention after 5000 cycles) were achieved. The DNA templates were introduced as the binder of NiCo2O4 and as the conductive matrix to facilitate the electron transmission between electroactive materials and outside current collectors, which resulted in the excellent electrochemical performances of the synthesized NiCo2O4 composites. It is believed that our NiCo2O4 nanocomposites could be used as effective electrode materials for supercapacitors.

•BSA-stabilized gold nanoclusters have been used for detecting melamine with a wide linear range and a low detection limit.•The method is verified by detecting melamine in milk powder and raw milk with satisfactory recoveries.•This method does not require any complicated modifications and expensive instrumentation.In this work, we proposed a facile, environmentally friendly and cost-effective assay for melamine with BSA-stabilized gold nanoclusters (AuNCs) as a fluorescence reader. Melamine, which has a multi-nitrogen heterocyclic ring, is prone to coordinate with Hg2+. This property causes the anti-quenching ability of Hg2+ to AuNCs through decreasing the metallophilic interaction between Hg2+ and Au+. By this method, detection limit down to 0.15 µM is obtained, which is approximately 130 times lower than that of the US food and Drug Administration estimated melamine safety limit of 20 µM. Furthermore, several real samples spiked with melamine, including raw milk and milk powder, are analyzed using the sensing system with excellent recoveries. This gold-nanocluster-based fluorescent method could find applications in highly sensitive detection of melamine in real samples.