Electrochemical imaging of localized sandwich DNA hybridization using scanning electrochemical microscopy.

Imaging of localized hybridization of nucleic acids immobilized on gold-DNA chip was performed by means of the feedback mode of scanning electrochemical microscopy (SECM). Thiol-tethered oligodeoxynucleotide (HS-ODN) probes, spotted on a gold surface, were hybridized with unmodified target sequence via sandwich hybridization with a biotinylated signaling probe. Spots where sequence-specific hybridization had occurred were developed by adding a streptavidin-alkaline phosphatase conjugate and biocatalyzed precipitation of an insoluble and insulating product. As a consequence, the surface conductivity of the spotted region of the chip where hybridization had taken place changed. These changes in conductivity were sensitively detected by the SECM tip. The proposed method allows imaging of a DNA array in a straightforward way. Analysis of real samples was also performed coupling this method with polymerase chain reaction. The imaging of 60 nM PCR amplicon (255 bp) was demonstrated.