Communication—Selective Electrochemical Detection of Catechin Compounds in Herbal Medicines

Most electrochemical sensors reported for catechin determination in herbal medicines actually involve the detection of not only catechins but also other flavonoids. This work proposes a strategy to selectively detect and quantify flavan-3-ol, known as catechins, in the presence of other flavonoids by complexation with AlCl3. Flavonoids (e.g.,rutin, quercetin) form stable complex with AlCl3 which affect the electrooxidation of these molecules. Hence, the electrochemical oxidation of catechin is free from the interference of other flavonoids as shown by differential-pulse voltammetry using glassy-carbon electrode. The approach was applied to herbal medicines and mass-spectrometry confirmed the presence of catechins in such samples.

Electrochemical detection of adrenaline and hydrogen peroxide on carbon nanotube electrodes

Adrenaline and hydrogen peroxide have neuromodulatory functions in the brain and peroxide is also formed during reaction of adrenaline. Considerable interest exists in developing electrochemical sensors that can detect their levels in vivo due to their important biochemical roles. Challenges associated with electrochemical detection of hydrogen peroxide and adrenaline are that the oxidation of these molecules usually requires highly oxidising potentials (beyond 1.4 V vs Ag/AgCl) where electrode damage and biofouling are likely and the signals of adrenaline, hydrogen peroxide and adenosine overlap on most electrode materials. To address these issues we fabricated pyrolysed carbon electrodes coated with oxidised carbon nanotubes (CNTs). Using these electrodes for fast-scan cyclic voltammetric (FSCV) measurements showed that the electrode offers reduced overpotentials compared with graphite and improved resistance to biofouling. Adrenaline oxidises on this electrode at 0.75(±0.1) V and reduces back at −0.2(±0.1) V while hydrogen peroxide oxidation is detected at 0.85(±0.1) V on this electrode. The electrodes are highly sensitive with a sensitivity of 16 nA µM−1 for Adrenaline and 11 nA µM−1 for hydrogen peroxide on an 80 µm2 electrode. They are also suitable to distinguish between adrenaline, hydrogen peroxide and adenosine thus these probes can be used for multimodal detection of analytes.

Electrochemical Detection of Waterborne Bacteria Using Bi-Functional Magnetic Nanoparticle Conjugates

Detection of microbial contamination in water is imperative to ensure water quality. We have developed an electrochemical method for the detection of E. coli using bi-functional magnetic nanoparticle (MNP) conjugates. The bi-functional MNP conjugates were prepared by terminal-specific conjugation of anti-E. coli IgG antibody and the electroactive marker ferrocene. The bi-functional MNP conjugate possesses both E. coli-specific binding and electroactive properties, which were studied in detail. The conjugation efficiency of ferrocene and IgG antibodies with amine-functionalized MNPs was investigated. Square-wave voltammetry enabled the detection of E. coli concentrations ranging from 101–107 cells/mL in a dose-dependent manner, as ferrocene-specific current signals were inversely dependent on E. coli concentrations, completely suppressed at concentrations higher than 107 cells/mL. The developed electrochemical method is highly sensitive (10 cells/mL) and, coupled to magnetic separation, provides specific signals within 1h. Overall, the bi-functional conjugates serve as ideal candidates for electrochemical detection of waterborne bacteria. This approach can be applied for the detection of other bacteria and viruses.

Two new bis(pyridine)-bis(amide)-based copper(II) coordination compounds for the electrochemical detection of trace Cr(VI) and efficient electrocatalytic oxygen evolution

Two new metal-organic compounds (MOCs) [Cu(L)0.5(3-nba)2] (1) and [Cu(L)(2,5-tdc)] (2) have been hydrothermally synthesized by employing the ligand N,N′-di(3-pyridyl)adipoamide (L) and two carboxylic acids (3-Hnba = 3-nitrobenzoic acid, 2,5-H2tdc = 2,5-thiophenedicarboxylic acid) as ligands. Compound 1 displays a metal-organic chain-like structure formed by the {Cu2(3-nba)4} double-paddle wheel units and the µ 2-bridging L ligands. The adjacent polymeric chains form a supramolecular layered structure through hydrogen bonding. Compound 2 shows a 3D metal-organic polymeric framework derived from Cu-L layers and µ 2-bridging 2,5-tdc ligands, which presents a 3,5-connected {4.62}{4.66.83} topology. The electrochemical and electrocatalytic behavior of the two compounds has been studied in detail. Carbon paste working electrodes modified with compounds 1 and 2 can be used as highly selective sensors for detecting traces Cr(VI). Both electrodes show also electrocatalytic performance in oxygen evolution reactions (OERs).