Biology, one molecule at a time

Single-molecule techniques have moved from being a fascinating curiosity to a highlight of life science research. The single-molecule approach to biology offers distinct advantages over the conventional approach of taking bulk measurements; this additional information content usually comes at the cost of the additional complexity. Popular single-molecule methods include optical and magnetic tweezers, atomic force microscopy, tethered particle motion and single-molecule fluorescence spectroscopy; the complement of these methods offers a wide range of spatial and temporal capabilities. These approaches have been instrumental in addressing important biological questions in diverse areas such as protein–DNA interactions, protein folding and the function(s) of membrane proteins.