Real-time imaging of viscosity in the mitochondrial matrix by a red-emissive molecular rotor

Mitochondrial Structure, Dynamics, and Physiology: Light Microscopy to Disentangle the Network

Mitochondria serve as energetic and signaling hubs of the cell: This function results from the complex interplay between their structure, function, dynamics, interactions, and molecular organization. The ability to observe and quantify these properties often represents the puzzle piece critical for deciphering the mechanisms behind mitochondrial function and dysfunction. Fluorescence microscopy addresses this critical need and has become increasingly powerful with the advent of superresolution methods and context-sensitive fluorescent probes. In this review, we delve into advanced light microscopy methods and analyses for studying mitochondrial ultrastructure, dynamics, and physiology, and highlight notable discoveries they enabled.

Design and Application of Fluorescent Probes to Detect Cellular Physical Microenvironments

The microenvironment is indispensable for functionality of various biomacromolecules, subcellular compartments, living cells, and organisms. In particular, physical properties within the biological microenvironment could exert profound effects on both the cellular physiology and pathology, with parameters including the polarity, viscosity, pH, and other relevant factors. There is a significant demand to directly visualize and quantitatively measure the fluctuation in the cellular microenvironment with spatiotemporal resolution. To satisfy this need, analytical methods based on fluorescence probes offer great opportunities due to the facile, sensitive, and dynamic detection that these molecules could enable in varying biological settings from in vitro samples to live animal models. Herein, we focus on various types of small molecule fluorescent probes for the detection and measurement of physical parameters of the microenvironment, including pH, polarity, viscosity, mechanical force, temperature, and electron potential. For each parameter, we primarily describe the chemical mechanisms underlying how physical properties are correlated with changes of various fluorescent signals. This review provides both an overview and a perspective for the development of small molecule fluorescent probes to visualize the dynamic changes in the cellular environment, to expand the knowledge for biological process, and to enrich diagnostic tools for human diseases.

A red-emitting mitochondria targetable fluorescent probe for detecting viscosity in HeLa, zebrafish, and mice

Viscosity, an essential parameter of the cellular microenvironment, has the ability to indicate the condition of living cells. It is closely linked to numerous diseases like Alzheimer's disease, diabetes, and cardiovascular disorders. Therefore, it is necessary to design tools to effectively monitor viscosity changes, which could provide promising avenues for therapeutic interventions in these diseases. Herein, we report a novel mitochondria-targeting fluorescent probe GX-VS which was suitable for the detection of viscosity changes in vivo and in vitro. The probe GX-VS had many advantages such as long emission wavelength (650 nm), large Stokes shift (105 nm), significant fluorescence enhancement (59-fold), high sensitivity, good biocompatibility and so on. Biological experiments showed that the probe could target mitochondria and detect viscosity alterations in HeLa cells. Moreover, it has been successfully utilized to monitor viscosity changes induced by lipopolysaccharides (LPS) in inflammatory zebrafishes and living mice, which further underscored the capacity of GX-VS to explore fluctuations in viscosity within living organisms.

Small-molecule fluorogenic probes for mitochondrial nanoscale imaging

Mitochondria are inextricably linked to the development of diseases and cell metabolism disorders. Super-resolution imaging (SRI) is crucial in enhancing our understanding of mitochondrial ultrafine structures and functions. In addition to high-precision instruments, super-resolution microscopy relies heavily on fluorescent materials with unique photophysical properties. Small-molecule fluorogenic probes (SMFPs) have excellent properties that make them ideal for mitochondrial SRI. This paper summarizes recent advances in the field of SMFPs, with a focus on the chemical and spectroscopic properties required for mitochondrial SRI. Finally, we discuss future challenges in this field, including the design principles of SMFPs and nanoscopic techniques.

A ratiometric fluorescence probe for selective and sensitive detection of leucine aminopeptidase in lysosome

We designed a novel ratiometric fluorescent probe P1-Leu with a donor-acceptor-donor fluorophore for the detection of leucine aminopeptidase in lysosomes. P1-Leu exhibits a lower detection limit than the ratiometric donor-π-acceptor probe, due to the low ratiometric background. Besides, P1-Leu has good lysosome-targeting ability and realizes the distinction of LAP levels in different cells.