Multiplexed electrochemical aptasensor based on mixed valence Ce(III, IV)-MOF for simultaneous determination of malathion and chlorpyrifos.

In this work, a multiplexed electrochemical aptasensor based on mixed valence Ce-MOF was constructed for the simultaneous determination of malathion and chlorpyrifos. Firstly, Ce(III, IV)-MOF materials with many catalytic sites were synthesized and characterized by SEM, TEM, XPS, FT-IR, XRD, and UV-Vis. Then, the chlorpyrifos and malathion signal markers based on Ce(III, IV)-MOF were prepared using thionine (Thi) and ferrocene (Fc) used as the electrochemical probe. The electrochemical signal was amplified by the reduction of thionine catalyzed by the spontaneous cycle of Ce(III, IV) in Ce(III, IV)-MOF skeleton and the reduction of ferrocene catalyzed by ascorbic acid (AA) in solution. The detection of the two targets did not interfere with each other, and the quantitative detection was realized with high sensitivity. The detection range of chlorpyrifos and malathion were 1.0 µM ∼ 0.1 pM, and the detection limits of chlorpyrifos and malathion were 0.038 and 0.045 pM (S/N = 3), respectively. The sensor provided a new idea for the simultaneous determination of multi-component and had a high application prospect in the field of food safety in the future.

A label-free electrochemical aptasensor based on 3D porous CS/rGO/GCE for acetamiprid residue detection.

A novel label-free electrochemical aptasensor was fabricated based on a three-dimensional porous electrode (3D-CS/rGO/GCE) for the detection of acetamiprid residues. The sensing signal was generated by the DNA itself. The porous electrode was prepared by electrodeposition in situ and characterized by scanning electron microscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). These results indicated that the porous electrode has a uniform nanoporous structure, high active area, and excellent conductivity, leading to improve the transmission efficiency of current signals. The 3D-CS/rGO/GCE was used to increase a load of acetamiprid aptamer on the electrode. Meanwhile, DNA self-assembly strategy was used to further increase the DNA amounts. Thus the electrochemical current was amplified significantly due to increased phosphate group amounts by the above synergistic effect. The determination of acetamiprid residues using square wave voltammetry (SWV) showed good sensitivity, with the linear range from 0.1 pM to 0.1 µM and the detection limit was 71.2 fM. The label-free electrochemical aptasensor was also used to detect acetamiprid residues in tea samples with satisfactory results.

High-Performance Sm-Doped Pb(Mg1/3Nb2/3)O3-PbZrO3-PbTiO3-Based Piezoceramics.

High-performance piezoelectric materials are pivotal to many electromechanical applications including piezoelectric actuators, sensors, and transducers. However, the general approach to achieve high piezoelectric properties by establishing morphotropic phase boundary (MPB) has limitation due to the weak anisotropy of the Gibbs free energy profile at the MPB region. Here, aliovalent Sm3+-doped 0.4Pb(Mg1/3Nb2/3)O3-(0.6-x)PbZrO3-xPbTiO3 piezoelectric ceramics were fabricated by a solid-state method, where the optimized piezoelectric coefficient d33 = 910 pC/N, dielectric constant εr = 4090, and Curie temperature TC = 184 °C were obtained at x = 0.352, being attributed to the synergistic contributions from the MPB and enhanced local structural heterogeneity. Rayleigh analysis was adopted to study the intrinsic and extrinsic contributions in Sm-doped PMN-PZ-PT ceramics, where the extrinsic contribution was found to be on the order of 25-67% at 4 kV/cm. Of particular significance is that a large signal d33* = 820 pm/V (at 20 kV/cm) with a minimal strain variation of 5% was achieved for a composition of x = 0.372 over the temperature range of 20-160 °C, being superior to those previously reported piezoelectric ceramic materials. This work offers a good paradigm to simultaneously achieve high piezoelectric properties with good temperature stability in ferroelectric ceramics, which have great potential for piezoelectric application at elevated temperatures.

Dual-Signaling Amplification Electrochemical Aptasensor Based on Hollow Polymeric Nanospheres for Acetamiprid Detection.

In this work, we first reported a dual-signaling electrochemical aptasensor based on layer-by-layer template technology and catalytic amplification for acetamiprid detection. Herein, the signal probe of the ferrocene (Fc)-based hollow polymeric nanospheres (Fc-HPNs) were prepared with repeated electrostatic adsorption between anionic poly(acrylic acid) and hyperbranched cationic polyethylenimine. In addition, ascorbic acid (AA) as an enhancer can catalyze the reduction of Fc-HPNs, which results in significant enhancement of the oxidation peak current of Fc-HPNs. Remarkably, the Fc-HPNs played dual roles: as nanocarriers to significantly increase the load amount of Fc and as nanoreducers to effectively catalyze reduction by AA for further signal amplification. Therefore, because of the special nanostructures of Fc-HPNs and the effective catalytic effect of AA, a dual-signaling electrochemical aptasensor was proposed. Surprisingly, this proposed assay for trace amounts of target detection exhibits excellent sensitivity with a linear range from 10 nM to 1 fM and a limit of detection down to 0.33 fM (S/N = 3), which opened a novel avenue and versatile strategy for monitoring of acetamiprid.

A dual amplification electrochemical immunosensor based on HRP-Au@Ag NPs for carcinoembryonic antigen detection.

A sensitive sandwich-type electrochemical immunosensor based on dual amplification strategy was constructed. The dual amplification strategy has been used secondary antibody(Ab2)-horseradish peroxidase(HRP)-Au@Ag nanoparticles (Au@Ag NPs) for carcinoembryonic antigen(CEA) detection. Ab2-HRP-Au@Ag NPs as dual amplification markers triggered the disproportionation of H2O2, which could facilitate the catalytic oxidation of hydroquinone to quinone(BQ). In addition, due to their large surface area and excellent conductivity, nitrogen-doped graphene were used as a platform to firmly assemble primary antibody (Ab1). Above mentioned generated amout of BQ are corresponding to trace CEA, resulting in the highly electrochemical reduction signal. Under the optimal conditions, the linear range of CEA concentration was 0.0001-100 ng mL-1, and the limit of detection (LOD) could be as low as 0.05 pg mL-1. Importantly, the immunosensor also showed acceptable stability, reproducibility and selectivity.

Ultrasensitive "signal-on" electrochemical aptasensor for assay of acetamiprid residues based on copper-centered metal-organic frameworks.

In present work, a versatile "signal-on" electrochemical aptasensor with ultra-sensitivity and high selectivity for detecting acetamiprid residues has been successfully constructed. Electrochemistry behaviors of as-synthesized copper-centered metal-organic frameworks (CuMOF) on various electrodes were investigated in details. The results indicated that CuMOF exhibited well-behaved redox events. Thus, we used Au-CuMOF as signaling element to label probe DNA (pDNA). The gold nanoparticles-reduced graphene oxide (Au-rGO) has a high specific surface area and excellent conductivity, which was utilized to immobilize complementary strand (cDNA). In the presence of acetamiprid, Au-CuMOF-labeled pDNA would hybridize with the exposed cDNA, allowing CuMOF to approach the electrode and produce a sensitive signaling current. Such a "signal-on" method does not suffer from the drawbacks of "signal-off" methods. The linear range of this proposed electrochemical aptasensor was 0.1 pM-10.0 nM and the detection limit was as low as 2.9 fM. This platform exhibited wonderful selectivity, stability, and repeatability, and was successfully applied to detect acetamiprid residues in tea samples exhibiting enormous practical application potential.

Simultaneous determination of copper, lead, and cadmium at hexagonal mesoporous silica immobilized quercetin modified carbon paste electrode.

A new method was developed for simultaneous determination of copper, lead, and cadmium, based on their voltammetric response at a carbon paste electrode modified with hexagonal mesoporous silica (HMS) immobilized quercetin (HMS-Qu/CPE). Compared with quercetin modified carbon paste electrode (Qu/CPE) and quercetin ionic liquid modified carbon paste electrode (Qu-IL/CPE), the HMS-Qu/CPE exhibited improved selectivity and high sensitivity toward the detection of copper, lead, and cadmium. The properties of the HMS-Qu/CPE in 0.1 M HCOONa-HCl buffer solution (pH 4.7) were investigated by adsorptive stripping voltammetry (ASV) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of copper, lead, and cadmium at the modified electrodes and factors affecting the preconcentration procedures were also investigated. Detection limits of 5.0, 0.8, 1.0 nM for copper, lead, and cadmium were obtained, respectively. The method is simple, fast, sensitive, and selective, and is successfully applied to soil sample.

Single-cell analysis by electrochemical detection with a microfluidic device.

A novel electrochemical method with a microfluidic device was developed for analysis of single cells. In this method, cell injection, loading and cell lysis, and electrokinetic transportation and detection of intracellular species were integrated in a microfluidic chip with a double-T injector coupled with an end-channel amperometric detector. A single cell was loaded at the double-T injector on the microfluidic chip by using electric field. Then, the docked cell was lysed by a direct current electric field strength of 220 V/cm. The analyte of interest inside the cell was electrokinetically transported to the detection end of separation channel and was electrochemically detected. External standardization was used to quantify the analyte of interest in individual cells. Ascorbic acid (AA) in single wheat callus cells was chosen as the model compound. AA could be directly detected at a carbon fiber disk bundle electrode. The selectivity of electrochemical detection made the electropherogram simple. The technique described here could, in principle, be applied to a variety of electroactive species within single cells.

Measurement of histamine in individual rat peritoneal mast cells by capillary zone electrophoresis with electrochemical detection.

Capillary zone electrophoresis was employed for the analysis of histamine in single rat peritoneal mast cells using an amperometric detector with a carbon fiber microdisk bundle electrode. In this method, individual mast cells and then 0.02 mol/l NaOH as a lysing solution are injected into the front end of the separation capillary by electromigration with an aid of a inverted microscope. A cell injector was constructed. Using it, the cell suspension was static, when a voltage for injecting single cells was applied. Histamine in single rat peritoneal mast cells have been identified. Quantitation has been accomplished through the use of calibration curves. The mean amount of histamine for nine cells is 95.8 fmol, which is consistent with the literature value.