To achieve these properties, several strategies have been developed: 1) TADF emitters capped with human serum albumin (HSA) or bovine serum albumin (BSA). Xiong et al. were the first to report a TADF emitter, DCF-MPYM (Figure ), that was used in conjunction with BSA. This adduct was employed as the contrast agent in the TRLI of MCF-7 cells, and showed long-lived luminescence (τd = 22.11 μs in deaerated ethanol) at λPL of 649 nm. The BSA protein provides a hydrophobic cavity and a reductive environment that shields the emitter from oxygen, thus permitting the long-lived delayed emission of DCF-MPYM to persist in the cells. 2) Self-assembled nanoparticles. Self-assembled water-dispersible nanostructures (NPs) based on three known TADF emitters (2CzPN, 4CzIPN, and 4CzIPN-Ph, Figure ) were reported by Lee et al. that relied on the limited water solubility of these compounds to form the NPs with sizes ranging from 80 to 200 nm. All three NPs showed a slight red-shift in their λPL compared to those in toluene, coupled with a slight decrease of their respective photoluminescence quantum yield (ΦPL) (19.4% for 2CzPN NPs, λPL = 503 nm; 11.9% for 4CzIPN NPs, λPL = 518 nm; and 3.6% for 4CzTPN-Ph NPs, λPL = 588 nm). Oneand two-photon fluorescence images using these NPs in an A549 cell were obtained using fluorescence microscopy and laser scanning confocal fluorescence, respectively. Although these self-assembled NPs show good biocompatibility, photostability, and water dispersibility, the authors did not demonstrate their TADF properties nor provide any TRFI studies. 3) Aggregation-induced delayed fluorescence (AIDF). The quenching of the emission by oxygen can be suppressed due to its limited ability to make physical contact with the emitter in the aggregated state. Qi et al. reported the use of three AIDF emitters, PXZ-NI, PTZ-NI and lysosome-targeting Lyso-PXZ-NI, each containing a 1,8naphthalimide (NI) acceptor. In aqueous solutions that produced the aggregated form, all three TADF materials demonstrated markedly enhanced delayed fluorescence when concentrations were increased. Subsequently, confocal fluorescence and lifetime imaging studies were performed using laser scanning microscopy and TRFI. This work demonstrated that these long-lived and biocompatible AIDF materials show great potential for high-contrast fluorescence lifetime imaging in living cells. 4) Organic dots (Odots) formed by encapsulating organic emitters in an amphiphilic polymer. Li et al.