Electrochemical sensing of biotin-avidin interaction on gold electrode modified by silver nanoparticles through covalent co-assembling

Electrochemical sensing of biotin-avidin interaction was investigated on gold electrode modified with 3-mercaptopropanoic acid (MPA) successively co-assembled with cysteamine functionalized silver nanoparticles and biotin or avidin. The stable aqueous colloid of cysteamine functionalized silver nanoparticles was synthesized successfully by well-known citric acid reduction method. Gold electrode was first modified with a monolayer of MPA by self-assembly technique. Then, cysteamine functionalized silver nanoparticles and biotin or avidin was co-assembled on the MPA modified gold electrode through an amide linkage. The stepwise modification process was optimized in terms of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurement in [Fe (CN)6]3−/4− redox system by varying the ratio of functionalized silver nanoparticles and biotin or avidin, viz., 1:2, 1:1, 2:1. Based on obtained results, the electrochemical sensing performances of 1:1 silver nanoparticle and biotin or avidin co-assembled gold electrode was performed by CV and EIS for varying concentration of complementary bio-affinity molecules in the same redox system. Both the CV and EIS measurements were found to have good response by resistive and capacitive changes due to coupling with a complementary biomolecule on co-assembled gold electrode. The use of avidin assembled gold electrode had led to much better response towards varying concentration of biotin over that of the biotin assembled gold electrode towards avidin.