The steady-state reactions covered in the last chapter last for many minutes and can be followed with common laboratory equipment. However, when \(\mathsf {E}\) and \(\mathsf {S}\) are mixed, the initial formation of \(\mathsf {ES}\) happens in milliseconds and can be followed only with specialized equipment. Flow techniques, pressure or temperature jumps, and caged compounds may be used. Modern sensors like surface plasmon resonance and quartz crystal microbalances can measure binding events without the need for labelling. Isotope effects occur when an enzyme prefers one isotope over another.