Near-infrared fluorophores for biomedical imaging

In vivo near-infrared (NIR) fluorescence imaging is an emerging biomedical imaging modality for use in both fundamental scientific research and clinical practice. Owing to advances in reducing photon scattering, light absorption and autofluorescence through innovations in the broad 700-1,700 nm NIR window, NIR fluorescence affords high imaging resolution with increasing tissue penetration depths. In this Review, we cover recent progress made on NIR fluorescence imaging in both the 700-900 nm NIR-I and the 1,000-1,700 nm NIR-II windows by highlighting an increasingly developing palette of biocompatible NIR fluorophores that span the entire NIR window and include inorganic nanoparticles, organic macromolecules and small molecules with tunable emission wavelengths. Together with advances in imaging instrumentation allowing for the efficient detection of long-wavelength NIR photons, recently developed NIR fluorophores have fuelled biomedical imaging from contrast-enhanced imaging of anatomical structures and molecular imaging of specific biomarkers to functional imaging of physiological activities, both for preclinical animal studies and clinical diagnostics and interventions.