A quantitative description for optical mass measurement of single biomolecules

Abstract

Label-free detection of single biomolecules in solution has been achieved using a variety of experimental approaches over the past decade. Yet, our understanding of the magnitude of the optical contrast and its relationship to the underlying atomic structure, as well as the achievable measurement sensitivity and precision remain poorly defined. Here, we use a Fourier optics approach combined with an atomic structure-based molecular polarizability model to simulate mass photometry experiments from first principles. We find excellent agreement between several key experimentally-determined parameters such as optical contrast-to-mass conversion, achievable mass accuracy and molecular shape/orientation dependence. This allows us to determine detection sensitivity and measurement precision that is mostly independent of the optical detection approach chosen, resulting in a general framework for light-based single molecule detection and quantification.