Counting Constituents in Molecular Complexes by Fluorescence Photon Antibunching

Modern single molecule fluorescence microscopy offers new, highly quantitative ways for studying the systems biology of cells while keeping the cells healthy and alive in their natural environment. In this context, a quantum optical technique, photon antibunching, has found a small niche in the continuously growing applications of single molecule techniques to characterize small molecular complexes. Here, we review some of the most recent applications of photon antibunching in biophotonics research, and we provide a guide for how to conduct photon antibunching experiments at the single molecule level by applying techniques borrowed from time-correlated single photon counting (TCSPC). We provide a number of new examples for applications of photon antibunching to the study of multichromophoric molecules and small molecular complexes.