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

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 single bondNH2 moiety at the 5′-terminus of PDNA and the single bondCOOH group at self-assembled 11-mercaptoundecanoic acid on a gold electrode. Subsequently, AuNPs were attached to the single bondSH moiety at the 3′-terminus of the immobilized PDNA by S–Au interaction, and then functionalized with single bondOH 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 5 fM to 500 pM. Furthermore, the E-DNA sensor showed differentiation abilities for single-base mismatch.