Long-wavelength (λex/em, red or near-infrared) fluorophores have significant advantages over the conventional blue and green light excitable fluorophores because long-wavelength lights scatter less, can penetrate deeper into tissues, are disturbed minimally by the autofluorescence of endogenous chromophores in biological systems, and cause less disturbance and photodamage to cells and living organisms. To date, several long-wavelength fluorophores have been designed, published, as well as commercialized for various applications. Whereas each fluorophore has advantages over one another, general limitations of many fluorophores are that they are minimally water soluble and thus aggregate extensively in water. Moreover, tailoring a fluorophore to long-wavelength absorption and emission regime and maintaining sufficient water solubility for biological applications require many challenging synthesis steps. In this project we have designed, synthesized and characterized two long-wavelength water-soluble fluorophores. We have studied photophysical properties and assessed the efficacy of these fluorophores for potential applications in aqueous environments. In both fluorophores, polar functional groups were attached to increase water solubility. Comparison of their photophysical properties in different environments provided various structure-optical property relationships of the fluorophores. Fluorophores without a polar functional group were non-luminescent both in water and in presence of protein (human serum albumin, HSA) due to extensive self-aggregation. Emission of the water-soluble fluorophores were undetectable in aqueous buffer (quantum yield&lt;0.01) solution. However, addition of human serum albumin greatly enhanced the emission for both fluorophores, indicating binding of fluorophore with the protein, which led to detection of as low as ten nano-molar of the protein in phosphate buffer. Initial binding assay analysis indicates binding of the fluorophores within the protein’s hydrophobic pocket which leads to many fold enhancements of fluorescence and consequential facile quantitative detection of HSA in buffer solution.

Water-soluble red fluorophores: Synthesis, spectral properties, and protein association study

255th National Meeting (2018)

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