DNA nanostructure-based magnetic beads for potentiometric aptasensing

In this work, a simple, general, and sensitive potentiometric platform is presented, which allows potentiometric sensing to be applied to any class of molecule irrespective of the analyte charge. DNA nanostructures are self-assembled on magnetic beads via the incorporation of an aptamer into a hybridization chain reaction. The aptamer target binding event leads to the disassembly of the DNA nanostructures, which results in a dramatic change in the surface charge of the magnetic beads. Such a surface charge change can be sensitively detected by a polycation-sensitive membrane electrode using protamine as an indicator. With an endocrine disruptor bisphenol A as a model, the proposed potentiometric method shows a wide linear range from 0.1 to 100 nM with a low detection limit of 80 pM (3 sigma). The proposed sensing strategy will lay a foundation for the development of potentiometric sensors for highly sensitive and selective detection of various targets

Electrochemical Evaluation of the Mechanism of Acetylcholinesterase Inhibition Based on an Electrodeposited Thin Film

An interface embedded gold nanoparticles in sol-gel thin film was constructed by one-step electrochemical deposition. Acetylcholinesterase (AChE) was physically absorbed onto to the interface to form a thin enzymatic layer. The proposed thin enzymatic layer, having kinetics similar to that of the enzyme in solution, provides an ideal sensing platform to electrochemically evaluate the chemical mechanism of enzyme inhibition. Lineweaver-Burk plot and surface plasmon resonance confirmed that the inhibition of AChE by malathion followed an irreversible mechanism and was a mixed type of competitive and noncompetitive. On the contrary, the degrees of inhibition by Pb2+ and Fe3+ were independent of the incubation time and the AChE concentrations, showing the reversibility of the inhibition. Furthermore, UV-vis absorption spectra indicated that the AChE mediated the hydrolysis of acetylthiocholine to yield a reducing agent thiocholine that reduced Fe3+ to Fe2+ and Fe2+ presented an effect of activation. To meet the demand of the biosensor design, we further investigated the relationship between inhibition percentage and both incubation time and inhibitor concentration. The enzyme's sensitivity to solvent effects and reactivation of the biosensor were also evaluated. It is anticipated that a rapid evaluation of the chemical mechanism of AChE inhibition could paves the way to rationally design biosensors and new compounds, as candidates for the treatment of Alzheimer's disease and pesticides.An interface embedded gold nanoparticles in sol-gel thin film was constructed by one-step electrochemical deposition. Acetylcholinesterase (AChE) was physically absorbed onto to the interface to form a thin enzymatic layer. The proposed thin enzymatic layer, having kinetics similar to that of the enzyme in solution, provides an ideal sensing platform to electrochemically evaluate the chemical mechanism of enzyme inhibition. Lineweaver-Burk plot and surface plasmon resonance confirmed that the inhibition of AChE by malathion followed an irreversible mechanism and was a mixed type of competitive and noncompetitive. On the contrary, the degrees of inhibition by Pb2+ and Fe3+ were independent of the incubation time and the AChE concentrations, showing the reversibility of the inhibition. Furthermore, UV-vis absorption spectra indicated that the AChE mediated the hydrolysis of acetylthiocholine to yield a reducing agent thiocholine that reduced Fe3+ to Fe2+ and Fe2+ presented an effect of activation. To meet the demand of the biosensor design, we further investigated the relationship between inhibition percentage and both incubation time and inhibitor concentration. The enzyme's sensitivity to solvent effects and reactivation of the biosensor were also evaluated. It is anticipated that a rapid evaluation of the chemical mechanism of AChE inhibition could paves the way to rationally design biosensors and new compounds, as candidates for the treatment of Alzheimer's disease and pesticides

A Three-Dimensional Origami Paper-Based Device for Potentiometric Biosensing

Current paper-based potentiometric ion-sensing platforms are planar devices used for clinically relevant ions. These devices, however, have not been designed for the potentiometric biosensing of proteins or small molecule analytes. A three-dimensional origami paper-based device, in which a solid-contact ion-selective electrode is integrated with an all-solid-state reference electrode, is described for the first time. The device is made by impregnation of paper with appropriate bioreceptors and reporting reagents on different zones. By folding and unfolding the paper structures, versatile potentiometric bioassays can be performed. A USB-controlled miniaturized electrochemical detector can be used for simple and in situ measurements. Using butyrylcholinesterase as a model enzyme, the device has been successfully applied to the detection of enzyme activities and organophosphate pesticides involved in the enzymatic system as inhibitors. The proposed 3D origami paper device allows the potentiometric biosensing of proteins and small molecules in a simple, portable, and cost-effective way

Pulsed galvanostatic control of a solid-contact ion-selective electrode for potentiometric biosensing of microcystin-LR

We report here on the development of a chronopotentiometric assay for microcystin-LR based on enzymatic inhibition. The inhibition of protein phosphatase by microcystin-LR can be sensed potentiometrically by using 4-nitrophenyl phosphate as an enzyme substrate. A solid-contact ion-selective electrode (ISE) with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) as a transduction layer has been designed for potentiometric biosensing using the pulsed galvanastatic technique. By applying an anodic current, the enzymatic generated p-nitrophenol can be extracted into the polymeric membrane with tetradodecylammonium tetrakis(4-chlorophenyl)-borate to produce the chronopotentiometric signal. Meanwhile, a controlled voltage was applied to refresh the membrane for multiple consecutive measurements. The proposed potentiometric assay showed a linear response for microcystin-LR in the range 1-100 mu g/L with a detection limit of 0.5 mu g/L (3 sigma). We believe that the proposed method can be employed for sensitive, rapid and reliable determination of analytes involved in enzyme inhibition. (C) 2016 Elsevier B.V. All rights reserved