Fluorescent Probes for Lipid Membranes: From the Cell Surface to Organelles

Abstract

Conspectus Biomembranes are ubiquitous lipid structures that delimit the cell surface and organelles and operate as platforms for a multitude of biomolecular processes. The development of chemical toolsfluorescent probesfor the sensing and imaging of biomembranes is a rapidly growing research direction, stimulated by a high demand from cell biologists and biophysicists. This Account focuses on advances in these smart molecules, providing a voyage from the cell frontierplasma membranes (PM)toward intracellular membrane compartmentsorganelles. General classification of the membrane probes can be based on targeting principles, sensing profile, and optical response. Probes for PM and organelle membranes are designed based on multiple targeting principles: conjugation with natural lipids or synthetic targeting ligands and in situ cell labeling by bio-orthogonal chemistry, conjugation to protein tags, and receptor–ligand interactions. Thus, to obtain membrane probes targeting PM with selectivity to one leaflet, we designed membrane anchor ligands based on a charged group and an alkyl chain. According to the sensing profile, we define basic membrane markers with constant emission and probes for biophysical and chemical sensing. The markers are built from classical fluorophores, exemplified by a series of bright cyanines and BODIPY dyes bearing the PM anchors (MemBright). Membrane probes for biophysical sensing are based on environment-sensitive fluorophores: (1) polarity-sensitive solvatochromic dyes; (2) viscosity-sensitive fluorescent molecular rotors; (3) mechanosensitive fluorescent flippers; and (4) voltage-sensitive electrochromic dyes. Our solvatochromic probes based on Nile Red (NR12S, NR12A, NR4A), Laurdan (Pro12A), and 3-hydroxyflavone (F2N12S) through polarity-sensing can visualize liquid ordered and disordered phases of lipid membranes, sense lipid order and its heterogeneity in cell PM, detect apoptosis, etc. Chemically sensitive probes, combining a dye, membrane-targeting ligand, and molecular recognition unit, enable the detection of pH, ions, redox species, lipids, and proteins at the biomembrane surface. In terms of the optical response profile, we can identify (1) fluorogenic (turn-on) probes, allowing background-free imaging; (2) ratiometric probes, e.g., solvatochromic probes, which enable ratiometric imaging by changing their emission/excitation color; (3) fluorescence lifetime-responsive probes, e.g., fluorescence molecular rotors and flippers, suitable for fluorescence lifetime imaging (FLIM); and (4) switchable probes, important for single-molecule localization microscopy. We showed that combining solvatochromic probes with on–off switching through a reversible binding specifically to cell PM enables the mapping of their biophysical properties with superior resolution. While the majority of efforts have been focused on PM, the probes for cellular organelles, such as endoplasmic reticulum, mitochondria, Golgi apparatus, etc., emerge rapidly. Thus, nontargeted solvatochromic probes can disting...

Lysosomes Targeting pH Activable Imaging‐Guided Photodynamic Agents

“…[28][29][30][31] The synthetic versatility of BODIPYs also allows to increase the selectivity towards the targeted tissues by conjugation to biomolecules for selective system delivery, [32][33][34][35][36][37][38] or by specific stimuli-responsive activation of the PS. [14][15][16] Indeed, the BODIPY molecular structure can be engineered with functional groups turning on or off specific spectroscopic signatures of molecules under specific physiological conditions and upon reaction with specific analytes allowing accumulation in targeted subcellular compartments, e. g., lysosomes, [39][40][41][42][43] lipidic membrane, [44][45][46][47][48] mitochondria, [43,[49][50][51][52][53][54][55][56][57] endoplasmic reticulum [43,58] and nucleus. [59][60][61] More specifically, targeting the lysosomes is a known strategy to develop efficient anticancer therapeutics, including PDT agents, fluorescent probes and theranostic agents.…”

Lipophilic Anchors that Embed Bioconjugates in Bilayer Membranes: A Review

“…Small-molecule fluorescent probes are used often to stain cell plasma membranes for imaging, tracking, and sensing experiments and the broad topic has recently been summarized in excellent review articles. ,, The focus of this present article is on the structural features that promote membrane anchoring of the dye conjugates.…”

Editorial: Specialty grand challenge: Structure, spectroscopy, and imaging

“…Fluorescence has been used for many decades to detect organelles or specific molecules intracellularly. A wide range of label compounds were designed and prepared, according to different requirements by biologists and biophysicists (Klymchenko, 2023). Such studies included redox-active transition metal-based probes, containing essential metal ions such as iron, manganese, and copper, some of them approved as optical and magnetic resonance imaging agents [Xue et al, 2022].…”