Fluorescence enhancement of near infrared cell membrane probe by β-cyclodextrin supramolecular interaction
Graphical abstract
Introduction
Host-guest supramolecular system had been proved to be an ideal strategy to change the fluorescence properties of dyes [1]. Among the macrocyclic host molecules, β-cyclodextrin (β-CD) was commonly used in construction of host-guest system due to its merits of simple production, availability, cavity diameter and low price [2,3]. β-CD is a hollow cone-shaped oligosaccharide with hydrophilic outer surface and lipophilic inner cavity [4]. The special structure of β-CD enabled it to spontaneously form inclusion complexes with many hydrophobic guest molecules, and ultimately improve the solubility in water and fluorescence intensity of guest molecules [5]. Fluorescence enhancement was the most obvious property observed during the formation of the host-guest complexes [6,7], and fluorescence quenching was very rare [8].
In addition, the reported dyes generally emitted in the UV–visible region [9]. The fluorescence emission in this region was affected by the limited tissue penetration ability [10]and low signal-to-noise ratio, so their application in biological imaging was limited [11]. On the contrary, near infrared (NIR) fluorescent dyes (650–900 nm) had the advantages of strong tissue permeability, small damage to biological samples and low interference of bioautofluorescence [12,13], which were suitable for biological imaging [[14], [15], [16]]. Unfortunately, the quantum yields of most NIR dyes in water were very low, which greatly limited the biological application of NIR dyes [12]. Therefore, it was urgent to improve the fluorescence quantum yield of near-infrared fluorescent dyes in water. Researchers were also trying to solve this problem. Therefore, structural modification was a common strategy [17], but this method was usually complex and inefficient. In recent years, supramolecular systems based on β-CD had been widely used in modifying dyes [18]. Generally speaking, dyes and recognized host molecules were bound by noncovalent bonds [19]. On the one hand, complex organic synthesis was avoided; on the other hand, the combination of host molecules and dyes could improve the optical properties of dyes. Fluorescent sensors based on the host-guest interaction were extensively used in the detection of ions, explosives and bioactive molecules [20]. However, the application of fluorescent probes based on host-guest design in fluorescence imaging of living cells and organelles was rarely reported.
Cell membrane is located in the outer layer of the cell, which is a phospholipid bilayer that separates the internal and external environment of the cell [21]. The structure and properties of cell membrane provide the basis for its driving physiological function [22]. Meanwhile, it can ensure the communication of materials and information between cells and external environment. In view of the vital role and physiological function of cell membrane, the design of cell membrane fluorescent probe is essential. Inspired by the excellent properties of β-CD, a novel near-infrared fluorescence probe with high fluorescence quantum yield was designed by combining β-CD with near-infrared fluorescence emission.
Section snippets
Materials and characterization methods
1-iododectane was purchased from TCI (Tokyo-) Chemical Industry Co., Ltd., and other chemicals involved in the experiment were purchased from Shanghai bide Pharmaceutical Technology Co., Ltd. and Energy Chemical Co., Ltd. All organic solvents were purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd.
The analytical test instruments used in this experiment refer to the published literature of our lab [23].
Synthesis of 2-((1E,3E)-4-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)buta-1,3-dien-1-yl)-4-octadecyloxazolo [4,5-b]pyridin-4-ium (probe PM-A)
The mixture of compound 3 (514.0 mg, 1.0 mmol), compound 4 (3-(7-(diethylamino)-2-oxo-2
Design and synthesis
Probe PM-A was efficiently prepared as outlined in Scheme 1. 2-Methyloxazole [4,5-b]pyridine (1) [26] and 3-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)acrylaldehyde (4) were synthesized according to the reported method [27]. 2-Methyl-4-octadecyloxazolo [4,5-b]pyridin-4-ium iodide (3) was synthesized by alkylation of compound 1 with 1-iododectane in 95% yield. In the presence of trimethylchlorosilane (TMSCl), compound 3 with good biological activity [28] and compound 4 with good optical properties [
Conclusion
In conclusion, a near-infrared fluorescent probe PM-A for cell membrane was designed. The probe owned the merits of simple synthesis, long emission wavelength, large Stokes shift and high photo-stability. Moreover, the probe showed low cytotoxicity and high-performance cell membrane staining. Importantly, PM-A with β-cyclodextrin could greatly reduce the concentration required for cell staining, and stained all cells uniformly and highly specifically even at a low concentration. This discovery
CRediT authorship contribution statement
Qing Yu: Conceptualization, Methodology, Investigation. Ya-Nan Wang: Investigation, Writing – original draft. Hao-Chi Hao: Investigation. Ru Sun: Investigation, Methodology, Writing – review & editing. Jian-Feng Ge: Conceptualization, Data curation, Formal analysis, Writing – review & editing, Funding acquisition.
Declaration of competing interest
The authors declare that they have no known competitive financial interests or personal relationships that may affect the work reported in this article.
Acknowledgments
Thanks to the National Natural Science Foundation of China (21977078) for supporting this work.
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These authors contributed equally to this work.