In Situ Deposition of Silver Nanoparticles on Polydopamine Nanospheres for an Ultrasensitive Electrochemical Aptasensor of Ochratoxin A

Abstract

This work proposed a novel and facile strategy for in-situ deposition of silver nanoparticles (AgNPs) on polydopamine nanospheres (PDANSs), and used the as-synthesized nanocomposite (AgNPs/PDANSs) as electrochemical tracer for an ultrasensitive aptasensor of ochratoxin A (OTA). The morphology and composition of PDANSs and AgNPs/PDANSs were characterized by electron microscopies and energy dispersive X-ray spectroscopy, and the results showed that AgNPs uniformly on PDANSs surface. AgNPs/PDANSs were combined with streptavidin (SA) to obtain signal probe for constructing of OTA aptasensor. Sequentially, the thiolated capture DNA (cDNA) was firstly immobilized on the gold electrode (GE) to capture the OTA aptamer, and then SA/AgNPs/PDANSs nanoprobes could bind with the end biotin of the aptamer through biotin-streptavidin biorecognition. The monitoring of the proposed OTA aptasensor was realized by the electrochemical stripping signal of AgNPs on PDANSs, and PDANSs was used for signal amplification. In the presence of OTA, the aptamer was preferentially bonded with OTA because of their high affinity, and resulted in the decrease of signal tags on the aptasensor surface, which reduced the electrochemical response signal of AgNPs. Under optimal experimental conditions, the proposed aptasensor offered a wide linear range from 1.0 × 10−6 μM to 1.0 × 10−2 μM and a low detection limit of 0.57 pM (S/N = 3). Meanwhile, This AgNPs/PDANSs-based OTA aptasensor had excellent specificity, stability and reproducibility, and was successfully employed for OTA detection in red wine samples, which showed promising application in electrochemical analysis of other toxic molecules.