Article: Schein, P; O’Dell, D; Erickson, D; (2016) “Dynamics of an Optically Confined Nanoparticle Diffusing Normal to a Surface”, Physical Review E, 93 (6)
Abstract: Here we measure the hindered diffusion of an optically confined nanoparticle in the direction normal to a surface, and we use this to determine the particle-surface interaction profile in terms of the absolute height. These studies are performed using the evanescent field of an optically excited single-mode silicon nitride waveguide, where the particle is confined in a height-dependent potential energy well generated from the balance of optical gradient and surface forces. Using a high-speed CMOS camera, we demonstrate the ability to capture the short time-scale diffusion dominated motion for 800-nm-diam polystyrene particles, with measurement times of only a few seconds per particle.
Using established theory, we show how this information can be used to estimate the equilibrium separation of the particle from the surface. As this measurement can be made simultaneously with equilibrium statistical mechanical measurements of the particle-surface interaction energy landscape, we demonstrate the ability to determine these in terms of the absolute rather than relative separation height. This enables the comparison of potential energy landscapes of particle-surface interactions measured under different experimental conditions, enhancing the utility of this technique.
Funding Acknowledgement: US National Institutes of Health [1R01GM106420-01]
Funding Text: This work was supported by the US National Institutes of Health under Grant No. 1R01GM106420-01. Experiments were performed in the Nanobiotechnology Center Shared Research Facilities at Cornell.