DNA condensation induced by plasmonic heating from array of silver domains

Different molecules in mixed solutions can be separated from each other along a temperature gradient. This phenomenon, so-called Soret effect, is quite important for molecular manipulation in various research fields. Typically, infrared laser has been utilized to obtain a temperature gradient in a certain area, but no large temperature gradient is made with this method. In contrast, plasmonic heating from a periodic array of metal domains is one of the effective ways to obtain a large local temperature gradient. In this work, we utilized the plasmonic heating from the array of silver (Ag) domains to attempt creation of such a large gradient for local periodic condensation (Soret effect) of DNA. In fact, a large, periodic temperature gradient with a magnitude of ~0.5K/µm was achieved through the excitation of the Ag array with blue light (400-440nm). In this temperature field, DNA molecules (5.6kbp), being labeled with fluorescent dyes (SYBR Gold) and mixed in a polyethylene glycol (PEG) solution, was found to be condensed at the edge of the heating domains: namely, a positive Soret effect was observed. Details of this experimental results will be discussed on site.