Using dyes and filters in a fluorescent imaging system

The FluorImager fluorescence imaging system uses monochromatic 488-nm laser light to excite fluorochromes. It contains a built-in 515-nm long-pass filter that rejects excitation laser light, but allows emission light with wavelengths longer than 515 nm to pass through. A fluorochrome appropriate for use in the system is excitable by 488-nm light and emits at least some of its fluorescence at wavelengths longer than 515 nm. Two types of optical filters, long-pass and band-pass, are used in the system. Long-pass filters reject shorter wavelengths and transmit longer wavelengths. The number in the filter name denotes the cutoff wavelength (midpoint of the transition between rejected and transmitted light) for the filter. Band-pass filters transmit a band of wavelengths and reject both shorter and longer wavelengths. The numbers in the filter name denote the center wavelength of the passed band and the width of the band at half maximum transmission. Generally, when scanning for a single fluorochrome, only the built-in 515-nm long-pass filter is needed. An interchangeable filter can be added to decrease the contribution from a broad-spectrum background signal and to attenuate strong fluorochrome signals.