N-alkyl functionalized squaraine dyes as fluorescent probes for the detection of serum albumins

Abstract

Here we synthesize a series of benzoindolium squaraine dyes with N-substituents (SQ) and examine these dyes as fluorescent probes to detect serum albumins. Methods. Organic synthesis, fluorescent spectroscopy, absorption spectroscopy, fluorescent microscopy. Results. The spectralluminescent properties of SQ dyes in the aqueous solution were investigated in the presence of bovine serum albumin (BSA), human serum albumin (HSA), equine serum albumin (ESA), ovalbumin (OVA), beta-lactoglobulin (BLG) and lysozyme (LYS), as well as in the presence of nucleic acid. The maxima of excitation spectra of the studied dyes in the buffer solution ranged within 623-673 nm, with the fluorescence emission maxima lying between 635 and 690 nm. All these dyes showed a similar increase in the fluorescence intensity with serum albumins and at the same time with the red shift up to 12 nm, which could point out the binding of the dyes to proteins. These dyes demonstrate a noticeably lower fluorescence intensity in the presence of OVA, BLG, and LYS, which structurally differ from serum albumins. The studied dyes gave no significant fluorescent response to the addition of nucleic acids. The equilibrium constants of dyes binding to BSA (K) were estimated as 3.0 ± 0.3x10 5 M -1 for SL-2411 and 2.4 ± 0.6x10 5 M -1 for SL-2412. Based on the relative values of K, we could suppose that the mechanism of dye-BSA binding is the interaction of the chromophore of the dye with the protein globule. It was shown that SL-2411 penetrates the cell membrane and distri bu tes in the cytoplasm without co-localization with MitoTracker Green. Conclusion. These dyes could apply fluorescent spectroscopy for protein detection and potentially visualize cell components with minimum to no autofluorescence.

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“…At the same time, the shape of the dye 2412 absorption spectrum broadens (520-750 nm) with a new peak in the short wavelength regions and a low extinction coefficient value, which probably indicates the dye aggregation in water. In our previous work, we showed that no evidence of the aggregate destruction was observed after a change in concentration of dye 2412 [27]. However, the destruction of the aggregates was observed after the dissolving of dye 2412 in the BSA solution.…”

“…In our previous work [27], we reported the spectral-luminescent properties of N-substituents benzoindoliumsquaraine dyes and their interaction with albumins of different structures. All studied dyes in complexes with serum albumins demonstrated an increase in fluorescence emission intensity compared to the free state in an aqueous solution.…”

The squaraine derivatives as potential photosensitizers in photodynamic therapy of cancer

“…At the same time, the shape of the dye 2412 absorption spectrum broadens (520-750 nm) with a new peak in the short wavelength regions and a low extinction coefficient value, which probably indicates the dye aggregation in water. In our previous work, we showed that no evidence of the aggregate destruction was observed after a change in concentration of dye 2412 [27]. However, the destruction of the aggregates was observed after the dissolving of dye 2412 in the BSA solution.…”

“…In our previous work [27], we reported the spectral-luminescent properties of N-substituents benzoindoliumsquaraine dyes and their interaction with albumins of different structures. All studied dyes in complexes with serum albumins demonstrated an increase in fluorescence emission intensity compared to the free state in an aqueous solution.…”

Вплив Агрегації Бензоіндосквараїнів На Генерацію Синглетного Кисню

“…і здатність проникати крізь клітинну мембрану розглянуто в роботі [10]. Вибір бензоіндоленінової кінцевої групи зумовлений тим, що барвники на її основі малотоксичні, зокрема широковживаний у медицині індоціанін зелений (indocyanine green (ICG)) [11], задовільно розчинні у фізіологічному розчині і мають високі квантові виходи флуоресценції.…”