Enhancement of electrocatalytic activity of DNA-conjugated gold nanoparticles and its application to DNA detection

Hydrazine electrooxidation readily occurs on bare Au nanoparticles (AuNPs), whereas it does not on DNA-conjugated AuNPs. Thus, when DNA-conjugated AuNPs are used as electrocatalytic labels in electrochemical DNA detection, anodic current of hydrazine is not easily observed within the potential window because of the high overpotential caused by the slow electron-transfer kinetics on DNA-conjugated AuNPs as well as the slow electron tunneling between the AuNP and the indium - tin oxide (ITO) electrode. NaBH₄ treatment significantly enhances the electrocatalytic activity of DNA-conjugated AuNPs. This enhancement substantially decreases the overpotential caused by the slow electron-transfer kinetics, and the anodic current of hydrazine can be measured within the potential window if the distance between the AuNP and the ITO electrode is not too large. The enhancement with NaBH₄ treatment allows high signal current, and the low intrinsic electrocatalytic activity of ITO electrodes allows low background current. The high signal-to-background ratio enables us to detect 1 fM target DNA without target amplification or enzymatic signal amplification. The ultrasensitive detection using versatile AuNP and simple chemical treatment is practically appealing.