Donor manipulation for constructing a pH sensing thermally activated delayed fluorescent probe to detect alkaliphiles

Synthesis, optical properties, and application of novel chalcone skeleton as pH fluorescent probe: Based AIE + ESIPT strategy

A series of "turn off" pH fluorescence probes with chalcone skeleton for basic system have been developed. The molecules emitted bright yellow fluorescence under acidic condition, resulting AIE coupled ESIPT characteristic and ICT process. What's more, the compounds exhibited excellent sensitivity and selectivity for detecting pH as a facile "On-Off" fluorescence probe, and the fluorescence of them were quenched with the ESIPT process interrupted under alkaline condition. Theoretical calculation for the related compounds also performed to verify the electron effect on photophysical properties and confirm the rational speculation on the mechanism.

Unravelling Immune-Inflammatory Responses and Lysosomal Adaptation: Insights from Two-Photon Excited Delayed Fluorescence Imaging

Two-photon excitation (TPE) microscopy with near-infrared (NIR) emission has emerged as a promising technique for deep-tissue optical imaging. Recent developments in fluorescence lifetime imaging with long-lived emission probes have further enhanced the spatial resolution and precision of fluorescence imaging, especially in complex systems with short-lived background signals. In this study, two innovative lysosome-targeting probes, Cz-NA and tCz-NA, are introduced. These probes offer a combination of advantages, including TPE (λex = 880 nm), NIR emission (λem = 650 nm), and thermally activated delayed fluorescence (TADF) with long-lived lifetimes (1.05 and 1.71 µs, respectively). These characteristics significantly improve the resolution and signal-to-noise ratio in deep-tissue imaging. By integrating an acousto-optic modulator (AOM) device with TPE microscopy, the authors successfully applied Cz-NA in two-photon excited delayed fluorescence (TPEDF) imaging to track lysosomal adaptation and immune responses to inflammation in mice. This study sheds light on the relationship between lysosome tubulation, innate immune responses, and inflammation in vivo, providing valuable insights for the development of autofluorescence-free molecular probes in the future.

A novel ratiometric fluorescent sensor from modified coumarin-grafted cellulose for precise pH detection in strongly alkaline conditions

Accurate and convenient monitoring of pH under extreme alkaline conditions is still a challenge. In this work, 4-(3-(7-hydroxy-2-oxo-2H-chromen-3-yl)-3-oxoprop-1-en-1-yl)benzamide (HCB), a coumarin derivative, was grafted onto dialdehyde cellulose (DAC) to obtain a sensor DAC-HCB, which exhibited a ratiometric fluorescent response to the pH of alkaline solutions, resulting in a significant fluorescent color change from yellow to blue (FI459 nm/FI577 nm) at pH 7.5-14. The structure of DAC-HCB was characterized through FT-IR, XRD, XPS, SEM. The pKa of sensor DAC-HCB was 13.16, and the fluorescent intensity ratio FI459 nm/FI577 nm possessed an excellent linear characteristic with pH in the scope of 9.0-13.0. Meanwhile, sensor DAC-HCB showed good selectivity, anti-interference, and fast response time to basic pH, which is an effective fluorescent sensor for examination of pH in alkali circumstance. The recognition mechanism of DAC-HCB to OH- was elucidated with HRMS and density-functional theory (DFT) computational analyses. Sensor DAC-HCB was successfully used for precise detection of environmental water samples pH. This work furnished a new protocol for test strips as a convenient and highly efficient pH detection tool for the high pH environment, and it has great potential for application in environmental monitoring.

Real-time visualization the pH fluctuations of living cells with a ratiometric near-infrared fluorescent probe

In situ real-time quantitative monitoring pH fluctuation in complex living systems is vitally significant. In the current work, a ratiometric near-infrared (NIR) probe (MCyOH) was developed to confront this challenge. MCyOH exhibited good sensitivity, photostability, reversibility, and an ideal pKa (pKa = 6.65). Ratiometric character of MCyOH is beneficial to accuracy detect the pH fluctuations in living cells under different stimulation. The observations showed that intracellular pH was decreased when HepG2 cells under oxidative stress or starvation conditions. In particular, HepG2 cells was acidulated after addition of ethanol, however, the acidification phenomenon was attenuated or disappeared when HepG2 cells preincubated with disulfiram or fomepizole. Finally, MCyOH was successfully applied to observe the increasement of intracellular pH when HepG2 cells treated with fomepizole individually. Overall, MCyOH would be a practical candidate to explore pH-associated physiological and pathological varieties.

A triphenylamine-based fluorescence probe for detection of hypochlorite in mitochondria

The level of HClO/ClO^- in mitochondria is essential to keep the normal function of mitochondria. Therefore, it is meaningful to accurately and quickly monitor ClO^- in mitochondria. In this work, a new triphenylamine-based fluorescence probe PDTPA was designed and synthesized, in which pyridinium salt and dicyano-vinyl group were introduced as mitochondria targeting site and reaction site for ClO^-. The probe showed high sensitivity and fast fluorescence response (<10 s) in the detection of ClO^-. Moreover, the probe PDTPA had good linearity in a wide concentration range of ClO^- and its detection limit was calculated as 10.5 μM. Confocal fluorescence images demonstrated that the probe could target mitochondria and track the fluctuations of endogenous/exogenous ClO^- levels in the mitochondria of living cells.

Analyte-Triggered Excited-State Intramolecular Proton Transfer- Delayed Fluorescence: A General Approach for Time-Resolved Turn-On Fluorescence Imaging

The research of delayed fluorescence (DF) has been a hot topic in biological imaging. However, the development of analyte-triggered small molecule DF probes remains a considerable challenge. Herein a novel excited-state intramolecular proton transfer-delayed fluorescence (ESIPT-DF) approach to construct analyte-stimulated DF probes was reported. These new classes of ESIPT-DF luminophores were strategically designed and synthesized by incorporating 2-(2'-hydroxyphenyl)benzothiazole (HBT), a known ESIPT-based fluorophore, as acceptor with a series of classic donor moieties, which formed a correspondingly twisted donor-acceptor pair within each molecule. Thereinto, HBT-PXZ and HBT-PTZ exhibited significant ESIPT and DF characters with lifetimes of 5.37 and 3.65 μs in the solid state, respectively. Furthermore, a caged probe HBT-PXZ-Ga was developed by introducing a hydrophilic d-galactose group as the recognition unit specific for β-galactosidase (β-gal) and ESIPT-DF blocking agent and applied to investigate the influence of metal ions on β-gal activity on the surface of Streptococcus pneumoniae as a convenient tool. This ESIPT-DF "turn-on" approach is easily adaptable for the measurement of many different analytes using only a predictable modification on the caged group without modification of the core structure.