Electrochemical biosensor based on Au5Ir@graphene quantum dot nanocomposite and DNA walker for detection of atrazine in environmental water with extremely high sensitivity and selectivity

Existing electrochemical sensors are inadequate for detecting pesticides at extremely low level. This study presents an electrochemical biosensor based on gold-iridium alloy (Au₅Ir) and DNA walker for detection of atrazine. Au₅Ir@RFBP-GQD nanocomposite was synthesized via the reduction of chloroauric acid and iridium trichloride using arginine and folic acid-functionalized boron and phosphorus-doped graphene quantum dot (RFBP-GQD). The synergy between Au and Ir, along with the formation of Schottky heterojunction, enhances the catalytic activity. The Au₅Ir was covalently conjugated with hairpin DNA and thionine forming a redox probe that was used to construct the electrochemical biosensor for atrazine detection, coupled with a DNA walker mechanism. Atrazine triggers the DNA walker, leading to the introduction of multiple redox probes onto the gold electrode surface. The oxidation and reduction of thionine molecules within these redox probes elicit highly sensitive electrochemical response. The integration of Au₅Ir@RFBP-GQD catalysis with the DNA walker results in significant signal amplification. The biosensor exhibits superior sensitivity and selectivity compared to other atrazine sensors, with a linear detection range from 1×10^-18 to 1×10^-12 M and a low detection limit of 3.4×10^-19 M (S/N=3). The proposed analytical method was successfully used for detection of atrazine in environmental water.