Formulation of resonant optical force based on the microscopic structure of chiral molecules

Optical manipulation, exemplified by Ashkin's optical tweezers, is a promising technique in the fields of bioscience and chemistry, as it enables the non-destructive and non-contact selective transport or manipulation of small particles. To realize the separation of chiral molecules, several researchers have reported on the use of light and discussed feasibility of selection. Although the separation of micrometer-sized chiral molecules has been experimentally demonstrated, the separation of nanometer-sized chiral molecules, which are considerably smaller than the wavelength of light, remains challenging. Therefore, we formulated an optical force under electronic resonance to enhance the optical force and enable selective manipulation. In particular, we incorporated the microscopic structures of molecular dipoles into the nonlocal optical response theory. The analytical expression of optical force could clarify the mechanism of selection exertion of the resonant optical force on chiral molecules. Furthermore, we quantitatively evaluated the light intensity and light exposure time required to separate a single molecule in a solvent. The results can facilitate the design of future schemes for the selective optical manipulation of chiral molecules.