Fluorescent Probes for Sensing and Imaging within Specific Cellular Organelles

Abstract

Fluorescent probes have become powerful tools in biosensing and bioimaging because of their high sensitivity, specificity, fast response, and technical simplicity. In the last decades, researchers have made remarkable progress in developing fluorescent probes that respond to changes in microenvironments (e.g., pH, viscosity, and polarity) or quantities of biomolecules of interest (e.g., ions, reactive oxygen species, and enzymes). All of these analytes are specialized to carry out vital functions and are linked to serious disorders in distinct subcellular organelles. Each of these organelles plays a specific and indispensable role in cellular processes. For example, the nucleus regulates gene expression, mitochondria are responsible for aerobic metabolism, and lysosomes digest macromolecules for cell recycling. A certain organelle requires specific biological species and the appropriate microenvironment to perform its cellular functions, while breakdown of the homeostasis of biomolecules or microenvironmental mutations leads to organelle malfunctions, which further cause disorders or diseases. Fluorescent probes that can be targeted to both specific organelles and biochemicals/microenvironmental factors are capable of reporting localized bioinformation and are potentially useful for gaining insight into the contributions of analytes to both healthy and diseased states. In this Account, we review our recent work on the development of fluorescent probes for sensing and imaging within specific organelles. We present an overview of the design, photophysical properties, and biological applications of the probes, which can localize to mitochondria, lysosomes, the nucleus, the Golgi apparatus, and the endoplasmic reticulum. Although a diversity of organelle-specific fluorescent stains have been commercially available, our efforts place an emphasis on improvements in terms of low cytotoxicity, high photostability, near-infrared (NIR) emission, two-photon excitation, and long fluorescence lifetimes, which are crucial for long-time tracking of biological processes, tissue and body imaging with deep penetration and low autofluorescence, and time-resolved fluorescence imaging. Research on fluorescent probes with both analyte responsiveness and organelle targetability is a new and emerging area that has attracted increasing attention over the past few years. We have extended the diversity by developing organelle-specific responsive probes capable of detecting changes in biomolecular levels (reactive oxygen species, fluoride ion, hydrogen sulfide, zinc cation, thiol-containing amino acids, and cyclooxygenase-2) and the microenvironment (viscosity, polarity, and pH). Future research should give more considerations of the "low-concern" organelles, such as the Golgi apparatus, the endoplasmic reticulum, and ribosomes. In addition, given the tiny sizes of subcellular organelles (20-1000 nm), we anticipate that clearer visulization of the cellular events within specific organelles will rely on super-resolution optical microscopy wi...

Applications of vibrational tags in biological imaging by Raman microscopy

“…Many fluorescent organelle probes have been developed by covalently incorporating an organelle-anchoring motif. 63, 64 However, the cytotoxicity, cell membrane permeability, non-specific interaction and photo-stability are the major issues in fluorescent organelle imaging.…”

An NIR-emitting lysosome-targeting probe with large Stokes shift via coupling cyanine and excited-state intramolecular proton transfer

“…1,2 Because of the importance of lysosomes to cell function and human health, there are strong interests in developing fluorescent probes for visualization of subcellular organelles. 3 Most lysosome probes include organic amines to facilitate their selectivity, which induce an increase in lysosomal pH (an alkalinizing effect), 4 causing adverse effect on cell activity. It remains a challenge to develop a fluorophore which can target lysosome without perturbing the pH.…”

Rapid relaxation pathway of the excited state of linear merocyanines in solutions

“…The autofluorescence wavelength range in the human body is mainly at 300–500 nm; hence, when merocyanine is used as a probe, the autofluorescence interference can be avoided, and the background noise can be reduced. Besides, conventional dyes such as rhodamine and cyanine, with a nitrogen end resulting in a positive charge in the organism, are easily combined with proteins or DNA in the plasma and living environment, making the testing of a specific substance deficient when used as a fluorescent probe . Merocyanine (structure shown in Figure ) consists of three parts, a push‐electron substituent (indole, D ); a conjugated, linear, long‐carbon chain (polymethine chain); and a pull‐electron substituent (indandione, A ).…”