Single cytosine-based electrochemical biosensor for low-cost detection of silver ions

Abstract

The development of Ag+ detection system with high sensitivity, selectivity and quantitatively accurate analysis is crucial because of the potential risk of Ag ion increasingly applied in various fields. As synthetic oligodeoxyribonucleotides are available to use, there have been few studies reported in the literature regarding techniques for electrochemical biosensors based on cytosine-enriched DNA used as the capture material of Ag ion. The high price and complex process for connecting NH2-terminal to DNA make it expensive to fabricate the Ag detecting system. In this study, we investigated the Ag ion detection system with single-cytosine (SC) used in the place of DNA with a functional group. The proposed system can guarantee the effect of span increase, price reduction of detection system, and lower detection limit due to the increase of immobilization efficiency by using SC as a capture probe.Three-electrode system was microfabricated on a glass wafer. SC was immobilized on the working electrode surface, and then this electrode was exposed to a solution with Ag ions and other SC for mismatching cytosine-Ag+-cytosine. Before detecting Ag ion, cyclic voltammetry and energy-dispersive X-ray spectroscopy were used for the identification of stable immobilization of SC on the surface of the functionalized Au electrode. The electrochemical analysis for increasing Ag ion concentration and the Ag+ selectivity of the SC probe were performed by square wave voltammetry. The resulted current increase is linear with the logarithmic concentration of Ag ion from 0.5nM to 1mM with ∼20pM of detection limit. The slope of in a target concentration range mentioned above are 9.14×10−2 per concentration decade with R2 value of 0.9814. The reason why our system has a lower detection limit than the previous studies is because the bound each single Ag ion performs a path role for electron transfer. Moreover, the proposed electrochemical assay has good selectivity to other environmentally relevant metal ions.