FLIM and PLIM in biomedical research – An innovative way to combine autofluorescence and oxygen measurements

Abstract: Fluorescence lifetime imaging microcopy (FLIM) is successfully used to image the intracellular fluorescent coenzymes NAD(P)H and FAD+. The redox state of these coenzymes is a parameter which helps to reveal the metabolic status of living cells and tissues. However, metabolic reactions are strongly dependent on the intracellular oxygen level. One promising optical method to monitor oxygen in biomedical samples is phosphorescence lifetime imaging microscopy (PLIM). PLIM is based on oxygen-dependent quenching of the phosphorescence of so-called “phosphors”. In this way, PLIM enables measurement of the oxygen partial pressure (pO2) within living cells. This review describes the FLIM and PLIM approaches used in biomedical research, drawing particular attention to the techniques of simultaneous FLIM and PLIM, which provide correlative imaging of both the fluorescence lifetime of metabolic coenzymes and pO2-sensitive phosphorescence lifetime.