Silver-enhanced imaging of DNA hybridization at DNA microarrays with scanning electrochemical microscopy

The use of scanning electrochemical microscopy (SECM) to image oligodeoxynucleotide (ODN) hybridization at spots on microarrays has been demonstrated. ODN probes at a microarray surface were hybridized with a biotinylated target, and the regions where sequence-specific hybridization had occurred were developed by the silver staining process (adsorption of streptavidin-gold nanoparticles followed by silver particle deposition). As a consequence of the staining process, the surface conductivity of the region where hybridization had taken place increased. Such an increase in conductivity was sensitively detected by a SECM tip. The SECM detection level for a 17mer target was found to be at 30 amol per spot (or 3.0 fmol per slide). These values compare well with those from other detection methods (e.g., fluorescence and colorimetric detections). Coupled with the alteration of the hybridization temperature, sequence-specific (single-base mismatch) DNA analysis can be accomplished. A reasonable sample throughput (imaging an area of 0.24 cm x 0.24 cm in about 38 min at a tip scanning speed of 50 mum/s) was obtained.