Dynamics of DNA in periodic temperature gradient field created by plasmonic heating*

Different molecules in a solution can be separated from each other along a temperature gradient. This phenomenon, so-called Soret effect, offers an interesting method of molecular manipulation in various research fields. Plasmonic heating from periodic metal domains is one of the effective ways to create a periodic temperature gradient. In this work, we utilized the plasmonic heating from periodic silver (Ag) domains under emission of blue light (400 – 440 nm) to create the periodic temperature gradient (with a large amplitude of ~ 0.5 K/um), thereby attempting to observe the Soret effect on DNA molecules mixed in polyethylene glycol (PEG) solutions. The DNA molecules, labeled with fluorescent dyes, were concentrated in high temperature zones, confirming the positive Soret effect. In addition, for large DNA molecules (~ 166 Kbp), stretched conformations bridging two hot zones were occasionally observed and their diffusion appeared to deviate from the simple Fickian behavior, possibly because of the microscopic Soret effect within the molecule. Details of this observation will be discussed on site.