Mitochondrial STED Imaging and Membrane Potential Monitoring with a Cationic Molecular Probe

Perylene diimide based fluorescent sensors for aqueous detection of perfluorooctane sulfonate (PFOS)

BACKGROUND

Perfluorooctane sulfonate (PFOS), one of the most harmful members of the large group of per- and poly-fluoroalkyl substances (PFAS), is notorious for its environmental persistence, bioaccumulation, and toxic effects, raising serious environmental and health concerns. Developing rapid and sensitive methods to detect PFOS in water is critical for effective monitoring and protection against this hazardous chemical.

RESULTS

In this study, we developed rapid and highly sensitive fluorometric sensors (PDI-2+ , PDI-6+ ) for detecting PFOS. We also investigated the influence of the sensor's molecular structure on its performance. Our findings reveal that the formation of a supramolecular complex between PFOS and the cationic fluorophores, facilitated by the synergistic interplay of electrostatic, hydrophobic and π-π stacking interactions, enables a quick and efficient fluorometric sensing response for the detection of PFOS in aqueous systems. Remarkably, the detection limit for PFOS was found to be as low as 3.5 nM (1.9 ppb) for PDI-2+ and 2.7 nM (1.4 ppb) for PDI-6+ , showcasing the high sensitivity of the sensor. The PDI sensors also demonstrate a high level of selectivity for PFOS against PFOA (another top two PFAS designated as hazardous substances by the U.S. EPA), other PFAS like GenX, structurally similar detergents, and inorganic salts typically found in water. Furthermore, the sensor's successful detection of PFOS in real water samples underscores its potential for environmental monitoring.

SIGNIFICANCE

The development of novel, water-soluble fluorometric sensors offers a promising solution for the rapid and sensitive detection of PFOS in water. Their high selectivity and low detection limits make them valuable tools for environmental monitoring and pollution control. The findings of this study contribute to the advancement of analytical techniques for PFAS detection and support ongoing efforts to mitigate the environmental and health risks posed by PFOS contamination.

Mitochondria-Activated Wash-Free Fluorescent Probe for Visualizing Single-Cell Photodamage

Cell viability assessment is essential in biological and medical research. There is a growing demand for fluorescent probes that can rapidly, reliably, and wash-free evaluate cell viability in complex scenarios. Electron transport chain (ETC) is one of the earliest indicators of cellular distress and holds great potential for assessing cell viability. In this study, we introduce Rhodalive, a mitochondria-targeted ETC-activated fluorescence turn-on probe for single-cell viability assessment. Rhodalive is specifically activated by free electrons leaked from the ETC and localized to the mitochondria, enabling wash-free, spatiotemporal, and super-resolution fluorescence imaging of active mitochondria. Moreover, Rhodalive can effectively distinguish live cells from fixed cells, quantify H2O2-induced cell damage, and visualize single-cell photodamage induced by localized blue light exposure and photodynamic therapy. Rhodalive provides a convenient and reliable tool for dynamically assessing single-cell viability with promising applications in evaluating early mitochondrial dysfunction and advancing drug discovery.

Harnessing an MMP-Independent NIR Probe Unveiling the Different Mitochondrial Cristae Changes during Mitophagy and Ferroptosis under STED Microscopy

Mitochondrial cristae remain dynamic structures in order to adapt various physiopathologic processes (e.g., mitophagy and ferroptosis); thus, visualizing and tracking different changes of cristae are crucial for a deeper understanding of these processes. Fluorescent probes that can realize long-term visualization of mitochondrial cristae under stimulated emission depletion (STED) microscopy are powerful tools for their in-depth research. However, there are few reports on such probes, and their constructions remain challenging. Here, we reported a robust squaraine probe (CSN) for visualizing and tracking the changes of mitochondrial cristae in various physiological and pathological processes using STED microscopy. The lipophilic unit of CSN enabled it to firmly immobilize in mitochondria via a hydrophobic interaction, which let the labeling ability of CSN independent of mitochondrial membrane potential (MMP). Using CSN, the mitochondrial cristae were clearly observed at a resolution of 52 nm under STED microscopy. Furthermore, CSN was successfully applied to track the destruction processes of mitochondrial cristae during autophagy and ferroptosis. Interestingly, we found that during mitophagy, mitochondria first underwent swelling and cristae rupture, and then partial vacuolization, and finally complete vacuolization, whereas during ferroptosis, mitochondria first underwent a gradual reduction in the number of cristae, and then partial fracture, and finally vacuolization. This work revealed the difference in mitochondrial cristae changes during mitophagy and ferroptosis, which provided insights into the two physiological and pathological processes. We believed that CSN could serve as a desirable tool to track cristae changes of intracellular activity processes.