Electrochemical Functionalization of <i>N</i>‑Methyl-2-pyrrolidone-Exfoliated Graphene Nanosheets as Highly Sensitive Analytical Platform for Phenols

Graphene nanosheets (GS) were easily prepared from graphite via a one-step ultrasonic exfoliation approach using <i>N</i>-methyl-2-pyrrolidone (NMP) as the solvent. Compared with the widely used graphene oxide (GO) obtained by multistep chemical oxidation, the NMP-exfoliated GS exhibited apparently better electrochemical activity toward the oxidation of a series of phenols like hydroquinone, catechol, 4-chlorophenol, and 4-nitrophenol. Interestingly, the electrochemical activity of GS toward these phenols can be further enhanced by simply anodizing at 1.8 V for 2 min (denoted as EGS), reflected by the apparently enlarged oxidation peak currents in voltammograms and the obviously reduced charge transfer resistance in electrochemical impedance spectra (EIS). Characterizations by techniques like X-ray photoelectron spectra (XPS), Raman spectra, and atomic force microscopy (AFM) demonstrated that the introduction of new oxygen-containing groups or edge-plane defects and the enhanced surface roughness were responsible for the enhanced activity of EGS. Thereafter, a simple electrochemical method for the highly sensitive detection of phenols was established and the detection limits were 0.012 μM, 0.015 μM, 0.01 μM, and 0.04 μM for hydroquinone, catechol, 4-chlorophenol, and 4-nitrophenol, respectively. The facile synthesis of EGS, together with its high electrochemical activity, thus created a novel platform for developing highly sensitive electrochemical sensing systems

Mesoporous-TiO2 nanoparticles based carbon paste electrodes exhibit enhanced electrochemical sensitivity for phenols

Mesoporous-TiO2 nanoparticles (meso-TiO2) and nano-TiO2 particles (nano-TiO2) were synthesized and characterized using scanning electron microscopy. The electrochemical behaviours of carbon paste electrodes (CPE), nano-TiO2/CPE and meso-TiO2/CPE were investigated using K3[Fe(CN)6] as the electrochemical probe. It was observed that the peak potential separation was remarkably decreased at the meso-TiO2/CPE with higher peak currents in comparison with the other two CPEs. Moreover, the electrochemical performance towards phenol and p-substituted phenol detection was studied with remarkably enhanced oxidation signals at meso-TiO2/CPE. The meso-TiO2 shows considerable surface enhancement effects towards phenols which increase linearly with Hammett’s constants. Additionally at higher NaCl concentrations, the oxidation peak currents of phenols notably increases at meso-TiO2/CPE, while remaining unchanged at CPE and nano-TiO2/CPE. In summary meso-TiO2 nanoparticles are superior electrode materials for electrocatalysis

Portable, Self-Powered, and Light-Addressable Photoelectrochemical Sensing Platforms Using pH Meter Readouts for High-Throughput Screening of Thrombin Inhibitor Drugs

In this work, a self-powered, portable, and light-addressable photoelectrochemical sensor (P-LAPECS) is developed for efficient drug screening using a handheld pH meter readout. The sensor, which employs thrombin inhibitors as the drug model, is constructed by evenly immobilizing biotin-labeled and thrombin-cleavable peptides on eight separated sensing zones of a single gold film electrode. The incubation of each peptide sensing zone with thrombin leads to the reduction of binding sites for streptavidin-labeled fullerene (C₆₀) PEC bioprobes, which directly reflects the activity of thrombin by the variation of both photocurrent and photovoltage, and therefore allows the screening of thrombin inhibitors using either a single-channel electrochemical analyzer or a portable pH meter. Consequenty, the inhibition efficiency evaluation of multiple thrombin inhibitors can be achieved by just one electrode, and the screening result obtained by the pH meter is very close to that acquired by the electrochemical analyzer. Moreover, P-LAPECS can realize the light-addressable detection of thrombin with a detection limit as low as 0.05 pM. The present work thus demonstrates the possibility of constructing portable, inexpensive, sensitive, and high-throughput biosensing platforms using ubiquitous pH meters for laboratories all over the world

4‑Amino-1-(3-mercapto-propyl)-pyridine Hexafluorophosphate Ionic Liquid Functionalized Gold Nanoparticles for IgG Immunosensing Enhancement

A novel ionic liquid, 4-amino-1-(3-mercapto-propyl)-pyridine hexafluorophosphate (AMPPH), was successfully synthesized and characterized. Subsequently, AMPPH was used as a functional monomer to fabricate AMPPH-modified gold nanoparticles (AMPPH–AuNPs) via a one-pot synthesis method. The as-prepared AMPPH–AuNPs were confirmed with transmission electron microscopy and X-ray photoelectron spectroscopy. AMPPH–AuNPs were used to construct a biocompatible interface to immobilize rabbit anti-human IgG (anti-HIgG) onto a glassy carbon electrode (GCE) surface, followed by a cross-linking step with glutaraldehyde to fabricate an anti-HIgG–AMPPH–AuNPs/GCE. The nonspecific binding sites were enclosed with bovine serum albumin (BSA) to develop an immunosensor for human IgG. Electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical properties of the developed immunosensor. The results indicate that AMPPH–AuNPs can improve the immunosensing performance. The current response of the immunosensor was found linearly related to human IgG concentration in the range of 0.1–5.0 ng mL^–1 and 5.0–100.0 ng mL^–1. The detection limit is estimated to be 0.08 ng mL^–1 (<i>S</i>/<i>N</i> = 3). The obtained immunosensor was successfully applied to the analysis human IgG immunoglobulin in human serum, and the results were well consistent with ELISA method

White-Light-Exciting, Layer-by-Layer-Assembled ZnCdHgSe Quantum Dots/Polymerized Ionic Liquid Hybrid Film for Highly Sensitive Photoelectrochemical Immunosensing of Neuron Specific Enolase

ZnCdHgSe quantum dots (QDs) functionalized with <i>N</i>-acetyl-l-cysteine were synthesized and characterized. Through layer-by-layer assembling, the ZnCdHgSe QDs was integrated with a polymerized 1-decyl-3-[3-pyrrole-1-yl-propyl]­imidazolium tetrafluoroborate (PDPIT) ionic liquid film modified indium tin oxide (ITO) electrode to fabricated a photoelectrochemical interface for the immobilization of rabbit antihuman neuron specific enolase (anti-NSE). After being treated with glutaraldehyde vapor and bovine serum albumin successively, an anti-NSE/ZnCdHgSe QDs/PDPIT/ITO sensing platform was established. Simplely using a white-light LED as an excitation source, the immunoassay of neuron specific enolase (NSE) was achieved through monitoring the photocurrent variation. The polymerized ionic liquid film was demonstrated to be an important element to enhance the photocurrent response of ZnCdHgSe QDs. The anti-NSE/ZnCdHgSe QDs/PDPIT/ITO based immunosensor presents excellent performances in neuron specific enolase determination. The photocurrent variation before and after being interacted with NSE exhibits a good linear relationship with the logarithm of its concentration (log <i>c</i>_NSE) in the range from 1.0 pg mL^–1 to 100 ng mL^–1. The limit of detection of this immunosensor is able to reach 0.2 pg mL^–1 (<i>S</i>/<i>N</i> = 3). The determination of NSE in clinical human sera was also demonstrated using anti-NSE/ZnCdHgSe QDs/PDPIT/ITO electrode. The results were found comparable with those obtained by using enzyme-linked immunosorbent assay method