fluorochrome

A fluorochrome is a fluorescent chemical compound used to label biological molecules in fluorescence-based detection methods. It typically absorbs light at a shorter wavelength and emits light at a longer wavelength. Fluorochromes are often conjugated to antibodies, nucleic acids, or other biomolecules to enable visualization or quantification of targets in cells and tissues. They may be dyes or other fluorescent entities and are sometimes distinguished from the underlying fluorophore by emphasizing their role as labeling reagents.

Common families include fluorescein derivatives (for example FITC), rhodamine and tetramethylrhodamine derivatives, and cyanine dyes such as Cy3 and Cy5, as well as commercially available dye kits like Alexa Fluor dyes. Properties of fluorochromes vary in brightness, defined by the product of the extinction coefficient and quantum yield, and in photostability, spectral profile, and pH sensitivity. Selection depends on the available excitation sources (lasers, LEDs) and detectors, as well as concerns about spectral overlap in multiplex assays.

In practice, fluorochromes are used in immunofluorescence microscopy, flow cytometry, fluorescence in situ hybridization (FISH), and various labeling assays. They can be attached via reactive groups (for example NHS esters, amines, sulfhydryls) to antibodies, oligonucleotides, or proteins. Modern multiplexing often relies on panels of fluorochromes with distinct emission spectra, necessitating compensation for spectral overlap. Overall, fluorochromes are central tools in optical detection and imaging of biological processes.