autofluorescens

Autofluorescence, sometimes referred to as autofluorescens, is the natural emission of light by biological materials after they absorb light, without the addition of external fluorophores. In most tissues, fluorescence arises from endogenous fluorophores such as NADH, NADPH, flavins (FAD, FMN), lipofuscin, collagen, elastin, and porphyrins. When excited by ultraviolet or visible light, these molecules emit light at characteristic wavelengths, creating intrinsic contrast.

The intensity and spectrum of autofluorescence depend on tissue type, metabolic state, age, and fixation. Because many biological tissues exhibit autofluorescence, it can complicate the use of fluorescent stains; conversely, it can be exploited as a label-free source of information.

Applications include in vivo and ex vivo imaging, histology, and ophthalmology. Fundus autofluorescence imaging in the retina visualizes lipofuscin and other retinal pigment epithelium fluorophores to assess retinal health. Autofluorescence is also used to delineate tissue types and identify pathologies in dermatology, dentistry, and cancer research, often by comparing spectra or lifetimes with exogenous probes.

To improve specificity, researchers use spectral imaging, unmixing algorithms, and fluorescence lifetime imaging (FLIM) to separate autofluorescent signals from targeted labels. Two-photon excitation and optimized detectors can reduce background and enhance depth discrimination.

Limitations include variable autofluorescence across tissues and individuals, age-related changes, and the potential for autofluorescence to obscure weak signals from dyes. Proper calibration and appropriate excitation/emission settings are essential for reliable interpretation.