The Phos-4 has 2 key features that are useful for fluorescence sensing.:-
- Selectable Filtering
- Multi-Wavelength Excitation
LED’s have two disadvantages when used as light sources for measuring fluorescent:-
- “Substrate fluorescence” – small amounts of light generated at wavelengths much greater than the peak;
- Spectrum width, limiting measurements to fluorophores with large Stoke’s shifts.
Simply adding a filter into the light path substantially reduces the optical power.
However the Phos-4 P provides an adjustable lens to allow the light to be focused through the filter and maximise the optical output.
Some fluorophores respond differently to different excitation wavelengths. For example, see Wencel et al, 2009; (Sensors and Actuators B 139, 2009; 208–213). By alternately exciting these fluorophores at two wavelengths, the ratio of the fluorescence can be used to measure pH. The P4-VCGB-U00 LED module has 4 LED dies, two of which (405nm & 450nm) can be used to make ratiometric fluorescence-based pH measurements.