Currently, there is keen interest in fabricating electronic devices based on metal nanoparticle arrays. We have been studying DNA sensing devices using gold nanoparticle arrays (particle diameter, 12-50 nm), which possess ~1-nm gaps between neighboring particles. Such gaps can be used as places for installation of a receptor molecule to perform molecular recognition. With this array arrangement, DNA sensing devices were fabricated to detect the complementarity of 12-24 mer oligonucleotides simply by monitoring the current flowing through the particle arrays. Single stranded DNA as a probe was bridged between the particles and resistance of the array was monitored on the addition of target DNA. In a series of experiments using different base sequences, complementary DNA molecules gave the largest responses (typically 250 mΩ ), while even with single base pair mismatches the responses decreased substantially (130 mΩ) for the array with a base resistance of 275 Ω.
There is much controversy about the conductivity of DNA, and recent data acquired for single double-stranded oligonucleotides by the scanning microprobe techniques have suggested large values ranging from 10 M to 1 G Ω. By using a particle array of 2 mm × 2 mm size we successfully detected such highly resistive DNA in a sensitive manner only with a standard equipment.
As an alternative approach, we also have fabricated optical devices based on gold nanoparticle arrays to monitor the shifts in the surface-plasmon band caused by the hybridization events. In these cases, a shift of 47 nm was observed for fully matched DNA (24 mer), while it reduced only by ~1 nm for a single base mismatched DNA. These devices are characterized comparatively to evaluate their applicability as high-throughput and miniaturized sensing techniques.
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