The FP.3 accessory employs Chirascan’s photoelastic modulator (PEM) and a single photomultiplier detector for fluorescence polarisation/anisotropy measurements. This configuration provides greater sensitivity and a simpler instrument configuration than conventional fluorescence polarisation instrumentation. Conventional fluorescence polarisation measurements are made using a T-format design featuring two detectors and three polarisers; one for generating the polarised excitation light and two for collection of the horizontal and vertical components of the fluorescence signal from which the fluorescence polarisation (or anisotropy) value is derived. The sensitivity of this technique is limited by the use of the emission polarisers and differences in sensitivity between the fluorescence detectors. Option FP.3 utilises Chirascan’s PEM to generate vertical and horizontal polarised light eliminating the requirement for two detectors. Operating with a 100kHz modulation cycle, the single fluorescence detector detects both the horizontal and the vertical components of the emission. In addition, the absence of emission polarisers allows for the simultaneous collection of the total fluorescence signal. This approach also simplifies instrument configuration: the fluorescence polarisation detector mounts in side observation port of the sample chamber in the same way as for conventional total fluorescence measurements.
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