Electrochemical sensing of fipronil in fruit and vegetable based on gold nanocrystal and target-induced DNA cycle signal amplification

Development of a high-performance electrochemical aptasensor that can detect fipronil in fruits and vegetables is important for human health improvement. This paper presents a method for synthesising Rubus Corchorifolius–like gold (RC-Au) nano-crystals using a type of 21 peptide as a shape inducer. The synthesis process involves the concurrent growth of nano-crystals and their asymmetric development, resulting in the formation of RC-Au nano-particles with increased exposure of their high-index facets, which enhances their catalytic activity. The RC-Au nano-crystals were then combined with an aptamer/auxiliary DNA hybrid to fabricate an electrochemical aptasensor that can sense fipronil via the release of the free auxiliary DNA strand, triggering target-induced DNA cycling. One fipronil molecule was found to transfer many RC-Au–thionine probes to the aptasensor surface, with the resulting oxidation and reduction of the probes leading to signal amplification. Increasing the concentration of fipronil from 1 × 10−17 to 1 × 10−12 M led to a linear increase in the amperometric current. A limit of detection of 3.7 × 10−18 M (S/N = 3) was obtained. The developed sensor exhibits higher sensitivity than other electrochemical fipronil sensors and was satisfactorily used to detect fipronil in fruits and vegetables.