BODIPY Fluorophores for Membrane Potential Imaging

Abstract

Fluorophores based on the BODIPY scaffold are prized for their tunable excitation and emission profiles, mild syntheses, and biological compatibility. Improving the water-solubility of BODIPY dyes remains an outstanding challenge. The development of water-soluble BODIPY dyes usually involves direct modification of the BODIPY fluorophore core with ionizable groups or substitution at the boron center. While these strategies are effective for the generation of water-soluble fluorophores, they are challenging to implement when developing BODIPY-based indicators: direct modification of BODIPY core can disrupt the electronics of the dye, complicating the design of functional indicators; and substitution at the boron center often renders the resultant BODIPY incompatible with the chemical transformations required to generate fluorescent sensors. In this study, we show that BODIPYs bearing a sulfonated aromatic group at the meso position provide a general solution for water-soluble BODIPYs. We outline the route to a suite of 5 new sulfonated BODIPYs with 2,6-disubstitution patterns spanning a range of electron-donating and -withdrawing propensities. To highlight the utility of these new, sulfonated BODIPYs, we further functionalize them to access 13 new, BODIPY-based, voltage-sensitive fluorophores (VF). The most sensitive of these BODIPY VF dyes displays a 48% ΔF/F per 100 mV in mammalian cells. Two additional BODIPY VFs show good voltage sensitivity (≥24% ΔF/F) and excellent brightness in cells. These compounds can report on action potential dynamics in both mammalian neurons and human stem cell-derived cardiomyocytes. Accessing a range of substituents in the context of a water-soluble BODIPY fluorophore provides opportunities to tune the electronic properties of water-soluble BODIPY dyes for functional indicators.

GlycoBODIPYs: Sugars Serving as a Natural Stock for Water‐soluble Fluorescent Probes of Complex Chiral Morphology

“…[15] Certain hydroxy functions or even complete sugar units can be redundant or derivatized, [16] as was also recently found in our group. [17] Although BODIPYs have already been transformed into water-soluble analogues by various approaches (Scheme 1) such as by sulfonation, [18] introduction of ammonium, [19] carboxylate, [20] multiple PEG residues, [21] or recently by a bistriflyl-substituted carbanion, [22] most of them suffer from a tedious synthetic route (sulfonated peptidyl linkers), [19] the incorporation of unnecessary structural ballast (PEG), or from the introduced charge, which can impair facile cell-uptake and further functionalizations in organic media. Furthermore, the native fluorescence of BODIPYs can often be substantially compromised after the derivatization process (PEG, peptidyl linkers, meso pyridinium [23] ).…”

Activity‐Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

“…Voltagefluors 2.1.Cl and 2.4.Cl (VF2.1.Cl/VF2.4.Cl) were the first‐generation ABS sensors for voltage imaging in living cells by this design strategy . From this starting point, a broad family of voltage sensors have been created with various excitation/emission profiles . This approach has enabled the tuning of molecular wires from styryl to fluorene, targeting of cells by bio‐orthogonal labeling, esterase cleavage, or light activation, as well as quantitative voltage measurements by fluorescence lifetime imaging microscopy (FLIM) .…”

Prevalent Bioimaging Scaffolds: Synthesis, Photophysical Properties and Applications

“…B) Selected examples show influence of alkyl substituents and π‐extension on photophysical properties in EtOH ( 33 ‐ 35 ) or MeOH ( 36 ‐ 37 ); [50,51c,60] ϵ unit: M −1 cm −1 . C) Selected examples for the application of BODIPY derivatives as bioimaging fluorophores [55b,56] …”

“…Compound 38 exemplifies bimodal imaging tags that can be used to label bioactive molecules (Figure 9C) [55b] . Further applications for bioimaging include staining of natural lipids ( e. g ., with commercial dye 34 ) and larger BODIPY derivatives such as 39 have recently been reported as fluorescent probes for membrane potential imaging [56] . In addition, BODIPYs have recently been used as fluorescent sensors for the detection of H 2 S, [57] thiols [58] and hypochlorite (ClO − ) [59] in vivo and/or in living cells.…”