Solution-based carbon quantum dots as electrochemical “on–off” switch in aqueous medium: Engineering of a sustainable green sensor and its computational investigation

Abstract

It is crucial to establish sensitive electroanalysis of pollutants in water environments, but this is difficult due to their redox inertness and uncertain detection methods. We herein report an electrochemical switch ‘on–off sensor for the selective detection of Hg(II) and amoxicillin (AMX) based on a switch platform system. Our design used a carbon quantum dot (CQD)-based sensing probe (SP) to intensify the electrochemical signal due to its excellent conductivity. The “switch-on” state was attained by introducing the Hg(II) ions and sensing probe (SP) onto the electrode surface to facilitate electron transfer. The modified electrode signifies an excellent electrocatalytic activity of Hg (II), giving sharp anodic and cathodic peaks at 0.53 and 0.42 (V vs. SCE), respectively. Upon addition of AMX, it cleaves the SP into fragments from the sensing interface, hindering the electrochemical signal to create a “switch-off” state. As expected, the SP displayed a desirable linear response range from 0.0 to 100 nM and the detection limit down to 15.0 nM. Density functional theory (DFT) calculations confirm that the binding energy of the AMX with the Hg(II) ion is greater than that of SP and Hg(II). Moreover, the probe showed excellent stability and reproducibility with Hg(II) selectively; thus, it confines great scope for application in environmental water sciences. Further, the switch “on–off” sensing behavior of SP providing two chemical inputs (Hg (II) and AMX) helps to set up an INHIBIT logic gate. A series of experiments, including DFT and electrochemistry, demonstrate the detection mechanism and enhanced electrochemical sensitivity. This sustainable engineering approach creates a perfect sensor using a carbon quantum dots-based sensing probe from waste paper.