pH-Switchable Electrochemical Sensing Platform based on Chitosan-Reduced Graphene Oxide/Concanavalin A Layer for Assay of Glucose and Urea

Abstract

A facile and effective electrochemical sensing platform for the detection of glucose and urea in one sample without separation was developed using chitosan-reduced graphene oxide (CS-rGO)/concanavalin A (Con A) as a sensing layer. The CS-rGO/Con A with pH-dependent surface net charges exhibited pH-switchable response to negatively charged Fe(CN)6(3-). The principle for glucose and urea detection was essentially based on in situ pH-switchable enzyme-catalyzed reaction in which the oxidation of glucose catalyzed by glucose oxidase or the hydrolyzation of urea catalyzed by urease resulted in a pH change of electrolyte solution to give different electrochemical responses toward Fe(CN)6(3-). It was verified by cyclic voltammograms, differential pulse voltammograms, and electrochemical impedance spectroscopy. The resistance to charge transfer or amperometric current changed proportionally toward glucose concentration from 1.0 to 10.0 mM and urea concentration from 1.0 to 7.0 mM. On the basis of human serum experiments, the sensing platform was proved to be suitable for simultaneous assay of glucose and urea in a practical biosystem. This work not only gives a way to detect glucose and urea in one sample without separation but also provides a potential strategy for the detection of nonelectroactive species based on the enzyme-catalyzed reaction and pH-switchable biosensor.

The pH-switchable agglomeration and dispersion behavior of fluorescent Ag nanoclusters and its applications in urea and glucose biosensing

“…The effect of UA was mainly attributed to the high acidity of the aqueous UA solution and because UA donates H + , leading to a decrease in the pH of the reaction solution and interference in the detection of urea and Glu. 42 Moreover, the reversible pH-dependent signal response behavior of the Ag NCs is reproduced in the sensing system for urea and Glu detection. Figure 6a shows that the pH of the reaction system could alternate between 5 and 7 by adding urea and Glu to the solution and that the fluorescence signal turned on and off with the change in pH (Figure 6b and c), indicating that this Ag NCsbased sensing system was regenerative for urea and Glu detection and that the regenerability of this sensor makes it more applicable and meaningful.…”

pH-Controllable Bioelectrocatalysis Based on Surface Charge and Conformation Switching of Nonelectroactive Protein

“…Therefore, the "on" and "off" states of the Lys/L-Cys interface were obviously confirmed by CVs and EIS. This pH-dependent behavior cannot be attributed to the probe itself because Fe(CN) 6 3 is pH-independent [1], and thus, it results from the changes in charges on the Lys surface. 3 solution at pH 6.19 (inset) and 12.13, respectively.…”

“…Reversibly switchable biocatalysis has been applied into electroanalytical chemistry for developing controllable biosensors and amplifing signal [1]. For this researching objective, one of the major challenges is to realize the controllable or stimuli-responsive bioelectrocatalysis [2].…”

“…For this researching objective, one of the major challenges is to realize the controllable or stimuli-responsive bioelectrocatalysis [2]. Among various external stimuli such as pH [1], ionic strength [3], temperature [4], and electric field [5], pH has been frequently used due to the simplicity and accuracy [1,6]. At the same time, a lot of functional materials, electron-transfer mediators, redox enzymes, and proteins have been used to modify electrodes and amplify the electrical signal [710].…”

“…At the same time, a lot of functional materials, electron-transfer mediators, redox enzymes, and proteins have been used to modify electrodes and amplify the electrical signal [710]. For example, Song's group used chitosan-reduced graphene oxide/concanavalin A to construct pH-switchable sensor for the detections of glucose and urea in the same sample [1]. Katz's groups used the poly(4-vinyl pyridine) (P4VP)-brush-modified indium tin oxide (ITO) electrode to reversibly switch the interfacial activity, which was based on the pH-sensitive change in the structure of P4VP polymer brush [11].…”