Fluorescence studies of single biomolecules.

Single-molecule fluorescence has the capability to detect properties buried in ensemble measurements and, hence, provides new insights about biological processes. Ratiometric methods are normally used to reduce the effects of excitation beam inhomogeneity. Fluorescence resonance energy transfer is widely used but there are problems in inserting the fluorophores in the correct position on the biomolecule, particularly if the structure is not known. We have recently developed two-colour coincidence single-molecule fluorescence that addresses this problem. This method can be used to determine quantitatively the multimerization states of biomolecules, in solution without separation. The future prospects of single-molecule fluorescence as applied to biological molecules are discussed.