Recent progress of fluorescence lifetime imaging microscopy technology and its application

In the past decade, fluorescence lifetime imaging microscopy (FLIM) has been widely used in biomedical research and other fields. As the fluorescence lifetime is unaffected by probe concentration, excitation intensity and photobleaching, the FLIM has the advantages of high specificity, high sensitivity and capability of quantitative measurement in monitoring microenvironment changes and reflecting the intermolecular interactions. Despite decades of technical development, the FLIM technology still faces some challenges in practical applications. For example, its resolution is still difficult to overcome the diffraction limit and the trade-off among imaging speed, image quality and lifetime accuracy needs to be considered. In recent years, a great advance in FLIM and its application has been made due to the rapid development of hardware and software and their integration with other optical technologies. In this review, we first introduce the principle and characteristics of FLIM technology based on time domain and frequency domain. We then summarize the latest progress of FLIM technology: 1) imaging speed enhancement based on hardware improvement such as optimized time-correlated single photon counting module, single photon avalanche diode array detector, and acoustooptic deflector scanner; 2) lifetime measurement accuracy improvement by the proposed algorithms such as maximum likelihood estimate, Bayesian analysis and compressed sensing; 3) imaging quality enhancement and spatial resolution improvement by integrating FLIM with other optical technologies such as adaptive optics for correcting the aberration generated in the optical path, special illumination for equipping wide-field FLIM with optical sectioning ability, and super-resolution techniques for exceeding the resolution limit. We then highlight some recent applications in biomedical studies such as signal transduction or plant cell growth, disease diagnosis and treatment in cancers, Alzheimer's disease and skin diseases, assessment for toxicity and treatment efficiency of nanomaterials developed in the past few years. Finally, we present a short discussion on the current challenges and provide an outlook of the future development of enhanced imaging performance for FLIM technology. We hope that our summary on the state-of-the-art FLIM, our commentary on future challenges, and some proposed avenues for further advances will contribute to the development of FLIM technology and its applications in relevant fields.