Optical measurement of torsional spring modulus of a double-stranded DNA using half-coated nanoparticles

A technique of detecting the rolling and spinning of half-coated nanoparticles using interference ring patterns of the fluorescence has been applied to the measurement of torsional spring modulus of a double-stranded DNA. Using the unique ability to measure nanoparticle rotations in multiple degrees of freedom, we were able to determine the spinning of a nanoparticle tethered on the DNA and thereby the twisting of the DNA in real time. The detailed knowledge of the spinning as well as rolling behaviors of half-coated nanoparticles provides information about torsional elastic properties of the DNA under investigation.