What is the difference between extrinsic fluorescence and intrinsic fluorescence?

Extrinsic fluorescence involves the use of external fluorescent probes or dyes that are added to a sample, allowing for specific labeling of molecules or structures, which enhances contrast and sensitivity. In contrast, intrinsic fluorescence arises from naturally occurring fluorescent molecules within a sample, such as certain amino acids (e.g., tryptophan) or co-factors (e.g., NADH), without any external labeling. While extrinsic fluorescence can be tailored for specific applications, intrinsic fluorescence provides information about the native state of biomolecules.