Chromophores in biological tissue

Chromophores in biological tissue refer to light-absorbing molecules or molecular moieties that contribute to the optical properties of tissues by absorbing specific wavelengths of visible and near-infrared light, primarily through electronic or vibrational transitions.[2][4][5][6] Major chromophores include hemoglobin (oxygenated HbO2 and deoxygenated Hb), water, lipids, and melanin, which dominate tissue absorption spectra and enable diffuse optical spectroscopy (DOS) for non-invasive assessment of oxygenation, hydration, and composition.[5] Minor chromophores such as methemoglobin, myoglobin, bilirubin, collagen, and cytochromes (e.g., cytochrome c oxidase) provide additional spectral contributions, often linked to specific physiological states like oxidative stress or muscle metabolism.[5] These molecules play essential roles in oxygen transport (heme-based proteins like hemoglobin), pigmentation (melanin), structural integrity (collagen), and cellular respiration (cytochromes).[5][6] In disease contexts, alterations in chromophore concentrations signal hypoxia, tumors, ischemia, or inflammation; for instance, elevated methemoglobin indicates oxidative damage, while shifts in hemoglobin oxygenation monitor tumor angiogenesis or therapy response.[5] Examples include porphyrin-based structures like heme in hemoglobin and chlorophyll, which feature conjugated double bonds for photon capture.[2][4][6] DOS exploits these properties for clinical applications, distinguishing healthy from pathological tissues via absorption peaks (e.g., HbO2 at 542/576 nm, water at 972 nm).[5] Overall, chromophores underpin tissue optics but are not a singular therapeutic target like a receptor or enzyme.[2][5]

Other names

ChromophoreBiological chromophoresTissue chromophoresEndogenous chromophores