Production of nanoparticles using several materials for labeling of biological molecules

Various size-controlled metal nanoparticles (NPs) coated with probe DNAs have been developed. Gold, silver, germanium, copper, or nickel was thermally deposited as the inner layer on the surface of a polystyrene bead, and gold was coated as the outer layer for immobilizing thiolated probe DNAs by Au-S covalent bonding. The ultraviolet-visible (UV-vis) spectra of NPs showed that an outer gold layer thickness of 2 nm was sufficient for the immobilization of probe DNAs having a signal/noise (S/N) ratio of specific attachment of NP probes on the DNA chips eight-times higher than that of fluorescent probes. The size distributions of NPs were within the 6.7% coefficient of variation regardless of the type of metal and size. The different metal layers of NPs were also discriminated successfully by measuring backscattered electron intensity by scanning electron microscopy (SEM). The results indicate that NPs can be used for a two-dimensional probe set for SEM observation of size differences and differences in the type of metal used.