  The dielectrophoresis method for trapping and attaching nanoscale
double-stranded DNA between nanoelectrodes was developed. The method gives a
high yield of trapping single or a few molecules only which enables transport
measurements at the single molecule level. Electrical conductivity of
individual 140-nm-long DNA molecules was measured, showing insulating behavior
in dry conditions. In contrast, clear enhancement of conductivity was observed
in moist conditions, relating to the interplay between the conformation of DNA
molecules and their conductivity.
