Direct detection of single molecules by optical absorption

TL;DR

This paper demonstrates that standard absorption spectroscopy techniques can detect single molecules at room temperature, including those that do not fluoresce efficiently, expanding the scope of single-molecule analysis.

Contribution

It introduces a novel method for direct optical absorption detection of single molecules without fluorescence, applicable under ambient conditions.

Findings

Single molecules can be detected via absorption without fluorescence.

Absorption cross sections measured for single molecules in dark states.

Method applicable to non-fluorescent absorbing materials.

Abstract

The advent of single molecule optics has had a profound impact in fields ranging from biophysics to material science, photophysics, and quantum optics. However, all existing room-temperature single molecule methods have been based on fluorescence detection of highly efficient emitters. Here we demonstrate that standard, modulation-free measurements known from conventional absorption spectrometers can indeed detect single molecules. We report on quantitative measurements of the absorption cross section of single molecules under ambient condition even in their dark state, for example during photoblinking or strong quenching. Our work extends single-molecule microscopy and spectroscopy to a huge class of materials that absorb light but do not fluoresce efficiently.