A deep-red emission fluorescent probe with long wavelength absorption for viscosity detection and live cell imaging.

Intracellular viscosity is closely related to a series of biological processes and could be a biomarker for various diseases. Herein, we reported a deep-red emission viscosity probe ACI, which showed a turn-on fluorescence effect with excellent selectivity encountering high viscous medium. To assure the practical biological application, ACI demonstrated not only a long wavelength emission at 634 nm but also a long wavelength excitation at 566 nm, which were crucial to afford deeper penetration depth and higher sensitivity in bioimaging. The photophysical properties and viscosity recognition mechanism of the probe were carefully discussed here. Theoretical calculations furtherly confirmed that high viscous medium could inhibit the twisted intramolecular charge transfer (TICT) process of the probe which quenched the fluorescence in low viscous media, and restore the emission. More importantly, it was successfully applied to visualize the viscosity in living cells. Graphical abstract.

A novel fluorescent probe with red emission and a large Stokes shift for selective imaging of endogenous cysteine in living cells.

Cysteine (Cys) plays crucial roles in physiological and pathological processes, and is related to many diseases. Selective monitoring of Cys over its analogues homocysteine (Hcy) and glutathione (GSH) is of great significance. A probe named ANT with an acrylate group as a recognizing moiety and a red-emission dye with a large Stokes shift (160 nm) as a fluorophore was designed and synthesized. The acrylate group can quench the fluorescence of ANT by a photoinduced electron transfer (PET) process. However, in the presence of Cys, the emission was switched on by the cleavage of the quencher through a concerted reaction including Michael addition and intramolecular cyclization. Furthermore, solution experiments showed that ANT exhibited high sensitivity and selectivity towards Cys with the maximum emission at 640 nm. Besides, ANT was successfully applied to specifically map endogenous Cys in living MCF-7 cells with low toxicity, despite the interference of Hcy and GSH. We hope that such a prepared novel probe will bring advancement in specifically differentiating Cys, Hcy and GSH.

Highly Efficient Near-Infrared Photosensitizers with Aggregation-Induced Emission Characteristics: Rational Molecular Design and Photodynamic Cancer Cell Ablation.

Photosensitizers (PSs) that play a decisive role in effective photodynamic therapy (PDT) have attracted great research interest. PSs with aggregation-induced emission (AIE) characteristics could overcome the deficiencies of traditional PSs that usually suffer from the aggregation-caused fluorescence quenching (ACQ) effect in applications and show enhanced emission and high singlet oxygen (1O2) generation efficiency in aggregates; therefore, they are outstanding candidates for imaging-guided PDT, and the development of AIE PSs with both excellent photophysical properties and 1O2 generation ability is highly desirable. Herein, three AIE fluorogens (AIEgens), BtM, ThM, and NaM, with a donor-π-acceptor (D-π-A) structure were designed and synthesized, and the photosensitizing ability was adjusted by π-linker engineering. All of the three AIEgens showed excellent photostability and high molar absorption coefficients, and their emission edges were extended to the near-infrared (NIR) region, with peaks at 681, 678, and 638 nm, respectively. NaM demonstrated the smallest ΔES1-T1, which was ascribed to its better separation degree of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The AIEgens were fabricated into nanoparticles (NPs) by amphipathic mPEG3000-DSPE encapsulating, and thus the obtained NaM NPs exhibited the best 1O2 generation efficiency under white light irradiation, which was almost 3 times that of the renowned PS rose bengal (RB). Furthermore, under white light irradiation, the cell killing efficiency of NaM NPs was also much better than those of the other two AIE PSs and RB. Therefore, NaM NPs revealed great potential to treat superficial diseases as a PS for PDT.

An ultralow concentration of two-photon fluorescent probe for rapid and selective detection of lysosomal cysteine in living cells.

Herein we reported a two-photon (TP) fluorescence "turn-on" probe MNPO, exhibiting high selectivity and sensitivity towards intracellular cysteine (Cys) with excellent lysosomal localization. The probe displayed fast response towards Cys over homocysteine (Hcy), glutathione (GSH), and other various analytes under physiological conditions. Low cytotoxicity made it successful for TP imaging of Cys in HeLa cells with an ultralow probe concentration of 250 nM, and a rapid response of only 10 min. Simultaneously, colocalization experiments in lysosome demonstrated its ability for specific in situ detection of lysosomal Cys in living cells, which shed light on its potential applications in biomedical applications. Beyond that MNPO was successfully applied for TP imaging of Cys in mice organ tissues such as heart, liver, and spleen, and the penetration depth of mice heart tissue was up to 184 µm, which disclosed the predominant TP characteristic. We believe that this study will provide some useful information toward diagnosis and treatment of pathogenesis associated with Cys or lysosomes in future.