Effect of Photon Counting Shot Noise on Total Internal Reflection Microscopy

TL;DR

This paper models how photon counting shot noise affects the spatial resolution of total internal reflection microscopy (TIRM) in measuring particle-substrate interactions, highlighting the importance of photon statistics and integration time.

Contribution

The study develops and validates a model linking photon shot noise to TIRM resolution, emphasizing the role of photon-counting statistics and integration time in measurement accuracy.

Findings

Photon shot noise limits TIRM spatial resolution.

Optimal integration time balances noise reduction and temporal accuracy.

Model validated with simulations and experiments.

Abstract

Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal particle and a transparent substrate by measuring the intensity of light scattered by the particle when it is illuminated by the evanescent field that is created from light totally internally reflected at the substrate interface. From these measurements, the height-dependent effective potential $\varphi(z)$ between the colloidal particle and the substrate can be measured. The spatial resolution with which TIRM can resolve the height $z$ and effective potential $\varphi(z)$ is limited by the intrinsic shot noise of the photon counting process used to measure the scattered light intensity. We develop a model to determine the spatial resolution with which TIRM can measure $\varphi(z)$ and verify its validity with simulations and experiments. We further establish the critical role of photon-counting statistics and the intensity integration time $\tau$ in TIRM measurements, which is a trade-off between narrowing the width of the photon counting distribution and capturing the instantaneous position of the probe particle.