Ultrasensitive DNA detection based on coulometric measurement of enzymatic silver deposition on gold nanoparticle-modified screen-printed carbon electrode

Abstract

An ultrasensitive DNA detection method based on coulometric measurement of enzymatic silver deposition on gold nanoparticle (AuNP)-modified screen-printed carbon electrode (SPCE) was developed. The DNA sensor was prepared by self-assembly of a hairpin probe DNA, dually labeled with thiol at its 5′ end and biotin at its 3′ end, on AuNPs on SPCEs. The immobilized probe can shielded the biotin from being approached by a bulky alkaline phosphatase-linked streptavidin (Sv-ALP) conjugate. In the presence of the target DNA, hybridization caused conformational change in the probe DNA and forced biotin away from the surface of the AuNPs. Sv-ALP was bound to the biotin and catalyzed the hydrolysis of ascorbic acid 2-phosphate to form ascorbic acid. The latter reduced the silver ions for the deposition of metallic silver on the electrode surface. The deposited silver was then measured by coulometric analysis in the H2SO4 solution. A considerable increase in signal was obtained because of the accumulation and near-exhaustive coulometric oxidation of metallic silver. Under optimal conditions, the dynamic detection range of the target DNA was from 3.0×10−17 to 1.0×10−14molL−1, and the detection limit was 1.5×10−17molL−1. Further, the DNA sensor exhibited selectivity against single-base mismatched DNA.