Laser diffractometer for single-particle scattering measurements

A laser diffractometer (polar nephelometer) constructed for single-particle studies is described. It takes advantage of an array of optical fibres and a scanning disc to allow the use of a single photomultiplier tube for the detection of scattered light. A background subtraction scheme makes the instrument especially valuable in cases where background scattering exceeds the scattering from the observed particle, for example for living cells in aqueous media. The system can be easily integrated with particle trapping equipment such as laser tweezers or an electrodynamic balance.