Jian-Bo He

Thin layer-based spectral and electrophoretic study of electro-oxidation of solid ellagic acid.

Acquisition of data from both in situ spectroscopy detection and online chromatography-like separation is important for studying complex electrochemical reactions. The present work provides an example of combination of thin-layer spectral and electrophoretic electrochemistry, both based on thin-layer electrolysis. Two thin-layer electrochemical cells were used to investigate the electro-oxidation of solid ellagic acid at different potentials, in acidic, physiological, and alkaline buffer media. UV-vis spectra and cyclic voltabsorptograms of the oxidation products were recorded in situ without interference from the solid reactant. Four oxidation products, depending upon the buffer pH and the applied potential, were separated and detected by electrophoretic electrochemistry. The major products possess redox stability, possibly with a diquinonemethide structure. The minor product is considered as an o-quinone derivative with a lactone-ring-opening, which can be reduced or further oxidized at appropriate potentials. A consecutive-parallel reaction mechanism is proposed for the formation of four products of ellagic acid in different pH media, which enriches the knowledge about the oxidation pathway and antioxidant property of this biologically active polyphenol compound.

Luminol, horseradish peroxidase and antibody ternary codified gold nanoparticles for a label-free homogenous chemiluminescent immunoassay

In this work, the chemiluminescence (CL) reagent luminol, the CL catalyst horseradish peroxidase (HRP) and antibody ternary codified gold nanoparticles (AuNPs) were assembled for an amplified CL immunoassay. Firstly, luminol and HRP bifunctionalized AuNPs (HRP–luminol–AuNPs) with good CL activity and catalytic properties were synthesized via a simple and facile strategy. Then, luminol, HRP and antibody ternary codified AuNPs (HRP/Ab–luminol–AuNPs) with good CL activity, catalytic properties, and antigen-specificity were further assembled. In the presence of the corresponding antigen, crosslinking aggregation of the HRP/Ab–luminol–AuNPs occurred due to the highly specific antigen–antibody immunoreactions, resulting in a great increase in CL intensity. Then, a label-free homogeneous CL immunoassay was developed by virtue of the HRP/Ab–luminol–AuNPs acting as an amplifying sensing probe. The fabricated immunosensor exhibited a wide linear range from 0.1 ng mL−1 to 1 μg mL−1 with a detection limit of 0.03 ng mL−1 for human IgG determination. Furthermore, the sensing strategy was extended to the detection of the cancer biomarker alpha-fetoprotein (AFP) with a detection limit of 5 pg mL−1, which is more sensitive than the conventional enzyme-linked immunosorbent assay (ELISA). The proposed sensing strategy is simple, sensitive, selective, low-cost and convenient, and could be used for the detection of antigen in real samples, so it holds great application potential in clinical diagnosis and biomedical applications. Moreover, this sensing strategy can serve as a general detection platform for the immunoassay of other biomolecules by using the respective antibodies and corresponding antigens.

An ultrasensitive label-free colorimetric assay for glutathione based on Ag + regulated autocatalytic oxidation of o-phenylenediamine

The discriminative determination of glutathione (GSH) over cysteine (Cys) and homocysteine (Hcy) is still challenging in bioassays due to their similar functional groups. Herein, a novel, simple, rapid, sensitive and cost-effective label-free colorimetric method for the selective determination of GSH over Cys and Hcy was proposed. In this assay, firstly, o-phenylenediamine (OPD) could be oxidized by silver ions (Ag+) to produce silver nanoparticles (AgNPs) and pale yellow colored 2,3-diaminophenazine (shorted as OPDox) with absorbance peak center at 429 nm. The as-formed AgNPs could further catalyze the redox reaction between OPD and Ag+. In the presence of GSH, GSH could chelate with Ag+, inhibiting the oxidation ability of Ag+, and link with AgNPs, influence the catalytic ability of AgNPs. Furthermore, GSH possesses strong reducibility to reduce OPDox, resulting in color fading of the detection solution and decrease in absorbance intensity. The proposed Ag+-OPD based sensing system exhibited a wide linear range from 2 nM to 1 µM for GSH detection, with the limit of detection as low as 1.7 nM. Moreover, this developed method was successfully applied to GSH detection in plasma and urine samples with satisfied results.

A catechin-modified carbon paste electrode for electrocatalytic determination of neurotransmitters

Catechin is a polyphenol antioxidant which can be found in great abundance in the leaves of tea plants. In this study, catechin was electrodeposited on an activated carbon paste electrode for electrocatalytic determination of two neurotransmitters, dopamine (DA) and serotonin (ST). The voltammetric conditions for electrode preparation in catechin solution were optimized as follows: phosphate buffer at pH 7.4, catechin concentration of 1.0 mM, potential window of 0.2–1.6 V (vs. Ag/AgCl/KClsat), scan rate of 50 mV s−1 and cycle number of 15. The prepared electrode showed high electrocatalytic activity for the oxidation of both DA and ST. The highest electrocatalytic activity for DA oxidation was observed in the physiological pH (7.4) buffer solution. Amperometric detection under stirring achieved a current sensitivity of 10.29 nA nM−1 cm−2 to DA in the linear concentration range of 10–780 nM, and 4.81 nA nM−1 cm−2 to ST in the range of 30–2340 nM, with the lowest detection limits of 0.5 and 3 nM for DA and ST, respectively. The resulting biosensor was successfully used to quantify DA and ST in commercial samples with high sensitivity and good stability. In addition, the fact that the oxidized catechin can effectively promote the electron transfer processes of DA and ST may help in understanding the role of catechin in nervous excitement.