Coordination coupling enhanced two-photon absorption of a ZnS-based microhybrid for two-photon microscopy imaging in HepG2

Ratiometrically pH-Insensitive Upconversion Nanoprobe: Toward Simultaneously Quantifying Organellar Calcium and Chloride and Understanding the Interaction of the Two Ions in Lysosome Function

Calcium and chloride levels are closely related to lysosome dysfunction. However, the simultaneous measurement of calcium (Ca²⁺) and chloride (Cl^-) in acidic subcellular organelles, which is conducive to a deep understanding of lysosome-related biological events, remains a challenge. In this study, we developed a pH-insensitive, ratiometric NIR nanoprobe for the simultaneous detection of Ca²⁺ and Cl^- in acidic lysosomes and determined the roles of the two ions in lysosome function. The upconversion nanoprobe with blue, green, and red emissions was modified with a Ca²⁺-sensitive dye (Rhod-5N) and Cl^--responsive fluorophore (10,10'-bis[3-carboxypropyl]-9,9'-biacridinium dinitrate, BAC). As a result of a dual-luminescence resonance energy transfer between upconversion nanoparticles (UCNPs) and Rhod-5N/BAC, the blue and green upconversion luminescence (UCL) of UCNPs were quenched and the red UCL was used as the reference signal. The ratiometric upconversion nanoprobe possesses a specific ability for the concurrent recognition of Ca²⁺ and Cl^- ions independent of the influence of the environmental pH. To locate the probe in the lysosome, dextran was further modified with upconversion nanoparticles. Then, the nanoprobe with a high spatial resolution was constructed for the simultaneous monitoring of Ca²⁺ and Cl^- in acidic lysosomes. Moreover, it was found that the reduction of lysosomal Cl^- affects the release of lysosomal Ca²⁺, which further blocks the activities of specific lysosomal enzymes. The ratiometric NIR nanoprobe has great potential for decoding and evaluating lysosomal diseases.

Rational Synthesis of Imine-Linked Fluorescent Covalent Organic Frameworks with Different pKa for pH Sensing In Vitro and In Vivo

Precise modulation of pH in living cells plays a vital role in the study of many diseases, such as cancer and rheumatoid arthritis. Here, a series of imine-linked covalent organic frameworks (COFs) were rationally designed and developed for pH sensing in tumor cells and zebrafish. Four monomers were chosen to synthesize COFs (COF₁-COF₄) with different pK_a by a simple orthogonal combination through condensation reaction. The as-obtained COFs exhibited a sensitive pH-dependent fluorescence response compared to their building blocks. Among them, COF₂ possessed a high crystallinity, excellent fluorescence, and suitable pK_a for biosensing. For bioimaging applications, COF₂ was modified with poly-d-lysine (PDL) to improve its biocompatibility and endocytosis efficiency. After that, PDL-modified COF₂ (PDL@COF₂) was used as a novel fluorescence probe with a superior linear pH response over the range from 5.0 to 8.0 due to its fully reversible protonation and deprotonation. The fluorescent PDL@COF₂ was further employed as a good candidate for pH imaging in tumor cells and zebrafish. The as-constructed environment-sensitive fluorescent COFs have greatly expanded the applications of COFs in the biological area.

A specific HeLa cell-labelled and lysosome-targeted upconversion fluorescent probe: PEG-modified Sr2YbF7:Tm3+

In this study, water-soluble PEG-modified Sr₂YbF₇:Tm³⁺ was prepared conveniently by a one-pot solvothermal method, where the molar ratio of Sr²⁺ to Yb³⁺ was controlled between 3 : 2 and 1 : 1. The optimum red-light emission at 677-699 nm was modulated via 0.7% Tm³⁺ doped under irradiation at 980 nm. Interestingly, biological experimental results showed that the PEG-modified Sr₂YbF₇:Tm³⁺ with low toxicity, excellent cell membrane permeability and high photostability can not only distinguish HeLa cells from mouse embryonic fibroblasts but also target the subcellular organelle lysosome in HeLa cells; therefore it can be anticipated that the as-prepared material would be a potential tool for cancer diagnosis.