fluoresceni

Fluoresceni, or fluorescence, is the emission of light by a material after it has absorbed electromagnetic radiation. The emitted light typically has a longer wavelength than the absorbed light, a difference known as the Stokes shift. Fluorescence occurs when a molecule absorbs a photon, promoting it to an excited electronic singlet state, and returns to the ground state by releasing one or more photons with lower energy. The process typically happens on a timescale of nanoseconds. If emission persists after excitation ceases, it is phosphorescence rather than fluorescence.

Fluorescent materials include organic dyes (such as fluorescein and rhodamine), fluorescent proteins (for example GFP and its derivatives), and inorganic systems (quantum dots, lanthanide complexes). Cells and tissues also show endogenous fluorescence from fluorophores like NADH and collagen.

Applications are widespread in science and medicine. Fluorescence is used in microscopy and imaging, flow cytometry, diagnostic assays, and chemical sensing. Fluorescence spectroscopy and imaging enable qualitative and quantitative analysis, including fluorescence lifetime imaging (FLIM) and Förster resonance energy transfer (FRET) studies.

Limitations and considerations include photobleaching, phototoxicity, spectral overlap between fluorophores, and environmental effects such as pH and ionic strength. Choice of fluorophore depends on brightness, stability, and compatibility with the assay.

History and naming: the phenomenon was described by Sir George Gabriel Stokes in 1852, who coined the term fluorescence.