Living cells as test tubes.

The combination of specific probes and advanced optical microscopy now allows quantitative probing of biochemical reactions in living cells. On selected systems, one can detect and track a particular protein with single-molecule sensitivity, nanometer spatial precision, and millisecond time resolution. Metabolites, usually difficult to detect, can be imaged and monitored in living cells with coherent anti-Stokes Raman scattering microscopy. Here, we describe the application of these techniques in studying gene expression, active transport, and lipid metabolism.