Zhimin Liu

Studies on electrochemical organophosphate pesticide (OP) biosensor design based on ionic liquid functionalized graphene and a Co3O4 nanoparticle modified electrode

In this study, a new type of organophosphate pesticide (OP) biosensor was successfully fabricated based on the immobilization of acetylcholinesterase (AChE) by cross-linking on a glassy carbon electrode (GCE) modified with ionic liquid functionalized graphene (IL-GR), Co3O4 nanoparticles and chitosan (CHI). The introduction of IL-GR and Co3O4 nanoparticles not only enhanced the surface area of the modified electrode for enzyme immobilization but also facilitated the electron transfer, resulting in a high sensitivity of the biosensor. The fabrication process of the sensing surface was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). For the oxidation of thiocholine, a hydrolysis product of acetylthiocholine, the peak current at the AChE/IL-GR/Co3O4/CHI/GCE electrode is larger than those at AChE/IL-GR/CHI/GCE and AChE/Co3O4/CHI/GCE electrodes. A linear relationship between the inhibition percentage (I%) and logarithm of the concentration of dimethoate was found in the range from 5.0 × 10−12 to 1.0 × 10−7 M, with a detection limit of 1.0 × 10−13 M (S/N = 3). The proposed biosensor provided an efficient and promising platform for the immobilization of AChE and exhibited higher sensitivity and acceptable stability for the detection of organophosphate pesticides.

Development of a sensitive acetylcholinesterase biosensor based on a functionalized graphene–polyvinyl alcohol nanocomposite for organophosphorous pesticide detection

A highly sensitive and stable acetylcholinesterase (AChE) biosensor was successfully developed based on ionic liquid functionalized graphene (IL-GR) and polyvinyl alcohol (PVA) to detect organophosphorous pesticides (OPs). IL-GR was firstly synthesized through the epoxide ring-opening reaction between 1-aminoethyl-2,3-dimethylimidazolium bromide (IL) and graphite oxide, and then was homogeneously dispersed in PVA to form an IL-GR–PVA nanocomposite in order to modify a glassy carbon electrode (GCE) for AChE immobilization. The IL-GR–PVA nanocomposite with excellent conductivity and biocompatibility offered an extremely hydrophilic surface for AChE adhesion. It effectively promoted the electron transfer rate of the electrode interface and facilitated the access of substrates to the active centers. Using phorate as a model compound, the conditions for OP detection were optimized. Under optimum conditions, a linear relationship between the inhibition percentage (I%) and logarithm of concentration of phorate was found in the range from 1.0 × 10−14 to 1.0 × 10−9 M and from 1.0 × 10−9 to 1.0 × 10−6 M, with a detection limit of 8.0 × 10−15 M (S/N = 3). The easily prepared electrochemical sensor had favorable stability and sensitivity, thus providing a new pesticide detection method.

A highly sensitive electrochemical OP biosensor based on electrodeposition of Au–Pd bimetallic nanoparticles onto a functionalized graphene modified glassy carbon electrode

A fast and stable organophosphate pesticide (OP) biosensor with enhanced sensitivity has been developed for the detection of OPs by using Au–Pd bimetallic nanoparticles and ionic liquid functionalized graphene–chitosan nanocomposites (Au–Pd/IL-GR–CHI). An electrodeposition method was first applied to form Au–Pd nanoparticles on the surface of IL-GR–CHI, which were characterized by scanning electron microscopy and electrochemical methods. The electron transfer resistance of the Au–Pd/IL-GR–CHI modified electrode was smaller than that of the Au/IL-GR–CHI (or Pd/IL-GR–CHI) modified electrode, indicating that the presence of Au–Pd/IL-GR–CHI hybrid nanocomposites on the electrode surface could improve the reactive sites, reduce the interfacial resistance, and make the electron transfer easier. The Au–Pd/IL-GR–CHI hybrid nanocomposites with excellent conductivity, catalytic activity and biocompatibility offered an extremely hydrophilic surface for AChE adhesion. Under optimal conditions, based on the inhibition of organophosphate pesticides (OPs) on the AChE activity, using phorate as a model compound, the biosensor detected phorate in the linear range from 5.0 × 10−16 to 2.5 × 10−13 M and from 4.9 × 10−13 to 9.5 × 10−6 M, with a detection limit of 2.5 × 10−16 M (S/N = 3). The developed biosensor exhibited many advantages such as high sensitivity, acceptable stability and low cost, thus providing a promising tool for the analysis of OPs.

An electrochemiluminescence biosensing platform for Hg2+ determination based on host–guest interactions between β-cyclodextrin functionalized Pd nanoparticles and ferrocene

A solid-state electrochemiluminescence (ECL) switch biosensor using a Ru(bpy)32+/β-cyclodextrin–Pd nanoparticles (β-CY–PdNPs)/gelatin (Gel) complex and a ferrocene-labeled DNA probe (Fer-DNA) for the detection of Hg2+ was successfully developed. The ECL biosensor includes an ECL substrate and an ECL signal switch. The Ru(bpy)32+/β-CY–PdNPs/Gel composite modified on a glassy carbon electrode was used as the ECL substrate, which could bring about a clear and stable ECL signal by Ru(bpy)32+. Meantime, the hairpin-like Fer-DNA probe acted as the ECL signal switch, which was designed by a molecular recognition strategy and attached to β-CY–PdNPs through host–guest interactions between β-CY and ferrocene. Our investigation indicated that, when Hg2+ was absent, the Fer-DNA probe retained its hairpin structure and led to an obvious quenching effect of the Ru(bpy)32+ signal. However, when the biosensor was incubated with Hg2+, the specific T–Hg2+–T interaction brought about a change of the Fer-DNA conformation, and such conformation adjustment resulted in a clear signal recovery of Ru(bpy)32+ owing to the reduced quenching effect of ferrocene. The ECL switch biosensor offered good linear responses for Hg2+ in the range of 0.003–600 ng mL−1 with a detection limit of 0.0015 ng mL−1 at the 3sblank level.

A novel electrochemiluminescence sensor for bisphenol A determination based on graphene–palladium nanoparticles/polyvinyl alcohol hybrids

Herein, graphene–palladium nanoparticles (PdNP–GR) were synthesized and dispersed in polyvinyl alcohol (PVA) to obtain a PdNP–GR/PVA composite. The composite was used to establish a novel Ru(bpy)32+-based electrochemiluminescence (ECL) sensing platform for the sensitive detection of bisphenol A (BPA). The electrochemical and ECL responses of BPA on the PdNP–GR/PVA-modified glassy carbon electrode (GCE) were greatly enhanced as compared to those on PVA/GCE or bare GCE. It was found that PdNP–GR exhibited good electron transfer ability and catalytic activity. In addition, the ECL signal on the Ru(bpy)32+/PdNP–GR/PVA composite-modified electrode was greatly amplified by BPA. Under optimum conditions, a good linear relationship was obtained for the ECL intensity versus the logarithm of BPA concentration in the range of 1.0 × 10−10 to 1.0 × 10−5 M, with the detection limit of 2.5 × 10−11 M (S/N = 3). The fabricated sensing platform was successfully applied for the detection of BPA in baby bottle, and relatively satisfactory recoveries were obtained.

Fabrication of a highly sensitive electrochemiluminescence chlorpromazine sensor using a Ru(bpy)32+ incorporated carbon quantum dot–gelatin composite film

A novel electrochemiluminescence sensing platform for the sensitive detection of chlorpromazine (CPZ) was fabricated based on a Ru(bpy)32+/carbon quantum dots/gelatin composite film. Carbon quantum dots (CQDs) in the composite film which have the ability to enhance the ECL intensity were synthesized by a simple and cost-saving method. As Ru(bpy)32+ was entrapped in the gelatin (Gel), the efficient immobilization of Ru(bpy)32+ could be achieved, which resulted in a stable ECL signal. In addition, the ECL signal on the Ru(bpy)32+/CQDs/Gel composite modified electrode was greatly amplified by CPZ. The electrochemical and ECL behaviors of the proposed sensor were investigated. Under the optimum conditions, the ECL intensity was well-proportional to the logarithm of CPZ concentration in the range of 5.0 × 10−10 to 1.0 × 10−5 M, with the detection limit as low as 8.0 × 10−11 M (S/N = 3). Furthermore, the ECL sensor was successfully applied for the determination of CPZ in spiked urine samples and exhibited a desirable result, which indicated that this sensor has potential application in CPZ analysis in real samples.