Gram‐Typing Using Conjugated Oligoelectrolytes

Abstract

It is shown that Gram-type differentiation, an essential tool in microbiology, can now be easily accomplished by using the chain-elongated conjugated oligoelectrolyte COE-S6. Specifically, COE-S6 can be used as a fluorescent membrane probe that distinguishes between Gram-negative and Gram-positive bacteria in a single step. Confocal microscopy of labeled microorganisms and differential scanning calorimetry with phospholipidand lipopolysaccharide-containing model membranes suggest that lipopolysaccharides impede COE-S6 membrane intercalation in Gramnegative bacteria. Both Gram-types within a mixture are discretely labeled by counterstaining COE-S6 with the nonspecific and lipophilic membrane probe FM 4-64. This single-step procedure allows for the in situ visualization of individual Gram-types in complex polymicrobial biofilms. Given that COE-S6 fluorescence intensity increases considerably post intercalation, it can be used for the detection of Gram-positive bacteria by the naked eye. COE-S6 does not inhibit bacterial growth and is simple to use, making it a promising membrane-specific fluorescent probe.

Recent Progress in Identifying Bacteria with Fluorescent Probes

“…Zhou et al synthetically conjugated an oligoelectrolyte probe ( 50 ) in Figure 21 to specifically identify Gram-positive bacteria. Although probe 50 carries a large positive charge, the presence of an outer membrane on the surface of Gram-negative bacteria makes it difficult to insert [ 118 ]. Bai et al synthesized a cationic polyfluorene derivative probe, PFP−NMe 3 + /CB[7] ( Figure 22 ), which could form a supramolecular complex with cucurbit[7]uril (CB[7]) that could be reversibly decomposed by amantadine (AD) to form a more stable CB[7]/AD complex and release the probe.…”

Polarity-Sensitive and Membrane-Specific Probe Quantitatively Monitoring Ferroptosis through Fluorescence Lifetime Imaging

“…To quantitatively detect polarity changes of plasma membranes during ferroptosis, it is necessary to develop novel effective plasma membrane-targeted polarity probes. Although many previously reported probes have succeeded in demonstrating the morphology of the plasma membrane, their environmental sensitivity has not been optimized, or remains unknown. − Only a very few membrane probes have displayed the polarity responsiveness by changing the intensity of a single emission band, the accuracy of which was very likely interfered by various uncertain factors such as the uneven local concentration of the probe in the highly heterogeneous intracellular environment. − Based on previous experiences, several international research teams, − including our group, − have recommended the applications of fluorescence lifetime imaging (FLIM) for quantitative analyses of microenvironment in various subcellular organelles. For example, FLIM imaging using targetable molecular rotors have been applied for quantitation of microviscosity of plasma membranes, , lysosomes, mitochondria, ,, endoplasmic reticulum, nuclei, and so forth.…”

Membrane-intercalating conjugated oligoelectrolytes

“…diagnostic tools). 15,16 Through intentional chemical design, MICOEs can also be manipulated in their conversion pathway of captured photon energy, and be repurposed as photodynamic or photothermal agents for therapy. 17,18…”