Highly selective and sensitive biosensor for cysteine detection based on in situ synthesis of gold nanoparticles/graphene nanocomposites

A novel electrochemical biosensor for highly sensitive and selective detection of cysteine based on in situ synthesis of gold nanoparticles (AuNPs)/reduced graphene oxide (RGO) nanocomposites is proposed. Graphene oxide (GO) was reduced by dopamine, and then in situ synthesis of AuNPs by the phenolic hydroxyl groups of dopamine on the RGO surface. The sulphydryl group of cysteine could bind not only with AuNPs through AuS bond but also with polydopamine on the RGO surface through Michael addition reaction. The combining of cysteine with the AuNPs/RGO leads to the decrease in the peak currents of electrochemical probe [Ru(NH3)6]3+, which could be used for indirect electrochemical sensing of cysteine. The change of the peak currents value of [Ru(NH3)6]3+ was linear with the concentration of cysteine in the range from 1.0 × 10−9 to 3.0 × 10−8 M with a linear coefficiency of 0.991. The detection limit was 1.0 × 10−10 M (S/N = 3). The proposed electrochemical biosensor is rapid, convenient and low-cost for effective sensing of cysteine.