Single-molecule optical absorption imaging by nanomechanical photothermal sensing

Significance Absorption microscopy is a promising technique that can detect single nonfluorescent molecules. However, fundamental limitations of existing optical absorption methods result in noisy detection signals for single molecules, which has hindered many anticipated applications. A promising method is to optically measure the photothermal heating of single molecules. In this paper, we present a photothermal microscopy technique where we detect the photothermal heating of single molecules mechanically with a temperature-sensitive nanomechanical drum. With our method, we achieve an unprecedented optical absorption sensitivity, enabling the detection of single molecules with large signal-to-noise ratios. This enables interesting applications such as the accurate localization of naturally occurring marker molecules or the identification of single molecules by measuring their absorption spectrum.