FP relies upon a measurable difference in polarized emission after excitation. The change in polarized emission is caused by a difference in speed of rotation which is a function of the size ratio of the bound to unbound probe. This can eliminate the traditional assay washing steps, and may eliminate the need for isolation of the sample from a more complex fluid.
Excitation is achieved by a series of short laser pulses.
Photon counting is done in the intervals between pulses. The pulse from the diode decays very rapidly, unlike the decay from a lamp, and thus the scattered light is not registered. The TSPF1 software is designed also to reduce the noise contribution from autofluorescence, further increasing sensitivity. Transient-State does not share these restrictions and limitations.