Effect of photon counting shot noise on total internal reflection microscopy

Fan Cui, David J. Pine

Research output: Contribution to journalArticlepeer-review


Total internal reflection microscopy (TIRM) measures changes in the distance between a colloidal particle and a transparent substrate by measuring the scattering intensity of the particle illuminated by an evanescent wave. From the distribution of the recorded separation distances, the height-dependent effective potentialφ(z) between the colloidal particle and the substrate can be measured. In this work, we show that spatial resolution with which TIRM can measureφ(z) is limited by the photon counting statistics of the scattered laser light. We develop a model to evaluate the effect of photon counting statistics on different potential profiles using Brownian dynamics simulations and experiments. Our results show that the effect of photon counting statistics depends on spatial gradients ∂φ/∂zof the potential, with the result that sharp features tend to be significantly blurred. We further establish the critical role of photon counting statistics and the intensity integration timeτin 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.

Original languageEnglish (US)
Pages (from-to)162-171
Number of pages10
JournalSoft Matter
Issue number1
StatePublished - Jan 7 2022

ASJC Scopus subject areas

  • General Chemistry
  • Condensed Matter Physics


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