Preparation of Dawson heteropolyacid-embedded silver nanoparticles/graphene oxide nanocomposite thin film used to modify pencil graphite electrode as a sensor for trace electrochemical sensing of levodopa.

Abstract

Measurement of levodopa (LD) as the most efficient treatment accessible for controlling the symptoms of Parkinson's disease was investigated. The electrocatalytic measurement of LD was performed at the surface of pencil graphite electrode (PGE) modified with graphene oxide (GO) and silver nanoparticle@Dawson heteropolyacid (AgNPs@DHPA). For this purpose, GO and the intermediate (AgNPs@DHPA) were first synthesized using a simple, cost-effective and straightforward method. The synthetic compounds, morphology, and surface characteristics of the modified sensor were evaluated. The results demonstrated that AgNPs@DHPA well-dispersed on the GO/PGE surface with a mean size of 6.27nm and thickness of 42nm. The electrochemical behavior of the modified PGE was also investigated. The heterogeneous charge transfer rate constant (ks) and transfer coefficient (α) for the electron transfer between AgNPs@DHPA/GO and PGE were obtained as 16.44s-1 and 0.59, respectively. Also, the diffusion coefficient of LD for AgNPs@DHPA/GO/PGE thin film was calculated using chronoamperometric experiments (D=9.05×10-6cm2s-1). Optimal parameters were obtained to access the best response for the measurement of LD. The results revealed that the modified PGE was able to measure the trace amounts of LD in phosphate buffer solution (pH=6.0) in the concentration ranges from 3.0×10-9 to 1.0×10-7M and 1.0×10-7 to 1.0×10-5M. The calculated limit of detection was obtained 7.6×10-10M which was much better than the previously reported electrochemical sensors. The modified electrode was used to measure LD in tablet, blood serum and urine.