The detection sensitivity obtained when combining electron-microscopy counting with gold-nanoparticle labeling of target nucleic acids complementary to probe DNA microarrays with the detection sensitivity obtained when using optical-microscopy measurement of conventional fluorescent labeling. Target DNAs were reacted with probe DNAs on DNA microarrays on which micro-columns had been etched so the target DNA could be agitated. The targets were reacted with the other probe DNA immobilized onto the surface of the nanoparticles. The labeled target DNAs were measured by using field-emission scanning electron microscopy (FE-SEM) imaging and counting the nanoparticles. The detection sensitivity of nanoparticle-labeling measurement was 1000 times that of fluorescent-labeling measurement, and the S/N ratio of nanoparticle-labeling measurement was 100 times that of fluorescent-labeling measurement. The results indicate that the nanoparticle-labeling method using FE-SEM counting is sensitive enough that it has a possibility for measuring targets expressed in a cell without amplification such as polymerase chain reaction (PCR).
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