Why should the cut-off depth of fluorescence filter set be above OD5

In recent years, with the emergence of biomedical detection technologies such as life science technology fluorescent probe technology, fluorescence microscope, polarization fluorescence detection technology, multi-photon fluorescence detection technology, PCR gene amplification fluorescence quantitative detection, etc., higher technical requirements are put forward for the steepness and background depth of fluorescence filters.

We all know that the fluorescence filter is one of the important detection means in the field of biomedicine, and the fluorescence filter set is the key optical element for excitation light selection and fluorescence extraction, and the corresponding filter spectrum should be designed according to the excitation and emission characteristics of the selected reagent. In general, we require that the background depth of the filter be above OD5 (English: Optical Density is short for optical density) in order to have a better fluorescence imaging effect.

The duration of excited fluorescence emission of fluorescent reagent is very short: the brightness of emitted fluorescence is equivalent to 1‰ to 1/10000 of the energy of excitation light. Compared with excitation light, fluorescence is very weak, and both coexist in the test sample. And the wavelength interval between the excitation spectrum and the emission spectrum of fluorescence is very small (about 15nm-30nm), so we need to detect the fluorescence signal, the excitation light and the emission light in the fluorescence system should be separated from each other deeply in the spectrum. The fluorescence signal emitted by the sample can be detected only when the isolation degree reaches above OD4. In order to improve the accuracy of fluorescence detection, it is necessary to increase the isolation above OD5. Moreover, the higher the isolation of the filter, the stronger the detection ability of trace fluorescence, and the higher the detection accuracy of fluorescence microscope.