In this Review article, we systematically summarize the design and applications of various kinds of long-lived emissive probes for bioimaging and biosensing via time-resolved photoluminescence techniques. The probes reviewed, including lanthanides, transition-metal complexes, organic dyes, carbon and silicon nanoparticles, metal clusters, and persistent phosphores, exhibit longer luminescence lifetimes than that of autofluorescence from biological tissue and organs. When these probes are internalized into living cells or animals, time-gated photoluminescence imaging selectively collects long-lived signals for intensity analysis, while photoluminescence lifetime imaging reports the decay details of each pixel. Since the long-lived signals are differentiated from autofluorescence in the time domain, the imaging contrast and sensing sensitivity are remarkably improved. The future prospects and challenges in this rapidly growing field are addressed.

A type I Ru(ii) photosensitizer retained an excellent PDT effect under hypoxia through the formation of highly-oxidative hydroxyl radicals under light irradiation.

Photothermal therapy (PTT) as a kind of noninvasive tumor treatment has attracted increasing research interest. However, the efficiency of existing PTT agents in the near-infrared (NIR) region is the major problem that has hindered further development of PTT. Herein, we present an effective strategy to construct the efficient photothermal agent by utilizing an intramolecular photoinduced electron transfer (PeT) mechanism, which is able to dramatically improve photothermal conversion efficiency in the NIR region. Specifically, an NIR dye (A1) constructed with dimethylamine moiety as the electron donor and the aza-BODIPY core as the electron acceptor is designed and synthesized, which can be used as a class of imaging-guided PTT agents via intramolecular PeT. After encapsulation with biodegradable polymer DSPE-mPEG, nanophotothermal agents with a small size exhibit excellent water solubility, photostability, and long-time retention in tumor. Importantly, such nanoparticles exhibit excellent photothermal conversion efficiency of ∼35.0%, and the PTT effect in vivo still remains very well even with a low dosage of 0.05 mg kg upon 808 nm NIR laser irradiation (0.5 W cm). Therefore, this reasonable design via intramolecular PeT offers guidance to construct excellent photothermal agents and subsequently may provide a novel opportunity for future clinical cancer treatment.

It is very meaningful to develop bifunctional therapeutic agents which can monitor the tumor hypoxia in real time as well as maintain good photodynamic therapy (PDT) effect under hypoxia. To achieve it, herein, a series of hydrophilic phosphorescent starburst Pt(II) porphyrins as bifunctional therapeutic agents for simultaneous tumor hypoxia imaging and highly efficient PDT have been rationally designed and synthesized. They have been obtained by using Pt(II) porphyrins as the functional core and cationic oligofluorenes as the arms. Such a three-dimensional structural feature ensures their hydrophilicity, ultrasensitive oxygen-sensing performance, and high O quantum yields. Furthermore, the O-sensitive phosphorescence lifetimes of starburst Pt(II) porphyrins are beneficial to eliminate the interference from background fluorescence remarkably and enhance the signal-to-noise ratio of hypoxia imaging by using phosphorescence lifetime imaging microscopy. Their PDT effects were also evaluated both in vitro (under both hypoxia and normoxia) and in vivo. As a result, tumor hypoxia can be significantly differentiated and tumor growth can be inhibited effectively, while the systemic toxicity is not observed. All of these results demonstrate that starburst Pt(II) porphyrins could be used as the promising bifunctional therapeutic agents for early diagnosis and treatment of cancer.