Luminescent probes for luminescence lifetime sensing and imaging in live cells: A narrative review

Abstract

Luminescence (mostly fluorescence and phosphorescence) probes are a powerful tool widely used in the life sciences research. They can be used, for example, in the quantitative analysis of physiological parameters, visualization of different cell organelles, and measurement of drug transportation. The luminescence intensity and lifetime of these probes are among the main signals recorded and evaluated in these applications. Other reviews have discussed optical probes from the perspective of their luminescence intensity. However, the luminescence lifetime, which depends on the molecular microenvironment but not the probe concentration, is another promising metric for biological sensing and imaging applications. In this review, we aim to introduce the basic strategies of FLIM probe design. We also present applications of these probes, including sensing of intracellular pH, cation/anion concentrations, oxygen levels, biomolecule contents, and physiological parameters, as well as live-cell imaging based on luminescence lifetime. Studies based on FLIM imaging of cells or tissues with endogenous organic molecules are not included in this mini review. With the rapid development of microscopy technology for fluorescence lifetime imaging, fluorescence lifetime-based probes have shown great potential in a variety of biological applications.