Signal-on impedimetric electrochemical DNA sensor using dithiothreitol modified gold nanoparticle tag for highly sensitive DNA detection

Abstract

A signal-on impedimetric electrochemical DNA (E-DNA) sensor using gold nanoparticles (AuNPs) as tag was developed for highly sensitive detection of DNA hybridization. A probe ssDNA (PDNA) was immobilized by forming an amide between the NH2 moiety at the 5′-terminus of PDNA and the COOH group at self-assembled 11-mercaptoundecanoic acid on a gold electrode. Subsequently, AuNPs were attached to the SH moiety at the 3′-terminus of the immobilized PDNA by S–Au interaction, and then functionalized with OH by immersing the electrode in dithiothreitol solution. In the absence of the target DNA, the flexible single-stranded PDNA supports efficient contact between AuNP tag and electrode, ensuring a low electron transfer resistance (Ret) of the E-DNA sensor using the [Fe(CN)6]3−/4− redox probe. Upon hybridization, a rigid probe-target duplex is formed, which pushes the AuNP tag away from the electrode and increases the distance between AuNP tag and the electrode, thereby increasing the Ret of the E-DNA sensor. Based on hybridization-induced conformational changes, the E-DNA sensor shows an increased Ret response when the target DNA concentration is increased from 5fM to 500pM. Furthermore, the E-DNA sensor showed differentiation abilities for single-base mismatch.