Extrinsic Chiral Nanostructure Assembly for Force and Torque Modulation in Nanoscale

This research focused on numerical simulations of extrinsic chiral nanostructure assembly (ECNA) targeting optical manipulation of force and torque at the nanoscale. Finite-element-based simulations are performed for the quantitative estimation of optical force and torque upon the interaction of ECNA with left circularly polarized (LCP) and right circularly polarized (RCP) light. The ECNA is composed of a circular disk present in the center and six elliptical nanostructures surrounding the central disk. To explore the variation of optical force and torque on this ECNA, we varied parameters that include (i) semimajor and semiminor axes of the ellipse, (ii) orientation of the ellipse defined by an angle θ, (iii) radial distance of the position of the ellipse named as arc dimension, and (iv) aspect ratio (AR) of the ellipse. A host of design parameter variations alongside variations in incident light wavelength showcased that the generation of optical force and torque can be controlled by these design parameters. These kinds of ECNA have applications in biosensing, nanoscale flow manipulations, enhanced transport in nanoscale, drug delivery vehicles, active nanostructures, and more. The simulations revealed that not only torque and force can be controlled but also we can design ECNA such a way that it can produce torque for a range of wavelengths. The study also showcased a design wherein torque can be generated at the NIR light zone, and the same opens up possibilities of a range of biomedical applications.