Synchronous coefficient of drag alteration
Synchronous coefficient of drag alteration (SCODA) is a biotechnology method for purifying, separating and/or concentrating bio-molecules. SCODA has the ability to separate molecules whose mobility (or drag) can be altered in sync with a driving field. This technique has been primarily used for concentrating and purifying DNA, where DNA mobility changes with an applied electrophoretic field. Electrophoretic SCODA has also been demonstrated with RNA and proteins. Theory As shown below, the SCODA principle applies to any particle driven by a force field in which the particle's mobility is altered in sync with the driving field. SCODA principle For explanatory purposes consider an electrophoretic particle moving (driven) in an electric field. Let: (1) and (2) denote an electric field and the velocity of the particle in such a field. If is constant the time average of . If is not constant as a function of time and if has a frequency component proportional to the time average of need not be zero. Consider the following example: (3) Substituting (3) in (2) and computing the time average, , we obtain: (4) Thus, it is possible to have the particle experience a non-zero time average velocity, in other words, a net electrophoretic drift,