Nanoscale Environment Sensing Scheme with Brownian Nanorod and Plasmon Resonator

Abstract

Tracking a Brownian particle’s motion allows localized parameters at its immediate vicinity to be measured. In this, the introduction of a rod that is drawn by a tunable attractive force to a cylindrical pillar overcomes the problems of the particle drifting away from the venue of measurement as well as colliding with other particles. With nanoscale particles, fluorescence labeling suffers from photobleaching and erratic signal due to blinking, while monitoring the polarization of scattered light is limited by the accuracy of correlating the rotational state of the rod to intensity changes. Here, we advance having the cylindrical pillar operate as a surface plasmon-based optical resonator to sense the contacts of nanorods. Simulations with a one-dimensional summed difference expression developed to reduce the difficulty of analyzing a three-dimensional dataset comprising wavelength, rod orientation, and gap distance allowed us to confirm distinct changes in transmission at 600 nm across all orientation angles with contact to noncontact or vice versa. This allows application of a cutoff transmission threshold. The metric f, which defines the proportion of incidences when the nanorod moves freely under Brownian motion influence, showed reduction with normalized charge increase. Good linear sensitivity responses were found at specific ranges in the f versus normalized charge relationship, which when correlated with temperature T, showed df/dT to be maximal when the normalized charge product value was −200. From an uncertainty estimation conducted, a restriction to 1 standard deviation variation necessitated only O(10−2) seconds of sampling using standard photodetectors. This portends significant advantages when sensing environments that are changing temporally rapidly.