Room-Temperature Detection of a Single Molecule’s Absorption by Photothermal Contrast

Abstract

Hot Enough to See: Over the last decade, detection of fluorescence from individual molecules has allowed for increasingly detailed probing of biochemical reaction mechanisms. The key advantage of fluorescence detection is the absence of background; the signal appears as a glowing point in a void. However, not all molecules fluoresce, and so alternative detection methods are needed. Gaiduk et al. (p. 353 ) now show that a photothermal detection scheme can resolve absorption events by individual molecular dyes that exhibit poor fluorescence efficiency. The technique relies on each molecule's release of heat to the surrounding solvent after light absorption, an energy dissipation mechanism that is enhanced as fluorescence efficiency declines. The solvent heating alters the local refractive index just enough to scatter a portion of a probe beam backwards, revealing the absorption.