CONICET | Buscador de Institutos y Recursos Humanos

n the context of a main project to develop versatile near-infrared fluorescent probes for relevant biologic analytes we describe the synthesis and sensing performance of a boronolectin derived from a tricarbocyanine dye. Boronic acids have been widely used for saccharide recognition through the formation of a reversible complex with diols. The dynamic covalent nature of this interaction has inspired research on different kinds of molecular and supramolecular systems with a wide variety of applications1,2. A non-enzymatic, small and flexible saccharide binder is highly desirable for detection of simple carbohydrates as well as a methodology for biolabeling of glycoproteins, in vitro and in vivo. In addition, the use of fluorescence emission as the reporter signal would lead to high rated molecules as potential sensors. In the design of such probes, it is essential to consider some clue properties to enhance its biocompatibility. For example, excitation/ emission should be in the near-infrared (NIR) to achieve deep penetration in thick samples and reduced interference from auto-fluorescence of biomolecules and high water solubility is imperative to perform sensing in physiological conditions. Taking in mind these considerations, we synthesized boronolectin 1 as new fluorescent saccharide sensor by combining a versatile tricarbocyanine precursor with a convenient boronic acid residue. The synthesis of the chlorinated precursor was previously optimized by us and the coupling with the boronic acid fragment proceeds in mild conditions and good yields. Overall, the synthetic route is simpler than other available NIR dyes. Boronolectin 1 has an absorption maximum at 720 nm and an emission maximum at 820 nm and is completely soluble in water. The fluorescence emission is negligible in aqueous medium due to a photoinduced electron transfer (PET) process between the boronic residue and the amino base interaction. The fluorescence is significantly enhanced upon binding to the carbohydrate yielding an OFF-ON sensor. At physiological pH (buffer PBS 10 mM, pH 7.4) the probe has good selectivity toward fructose over other monosaccharides such as glucose, galactose, among others. The selectivity at pH 7.4 can be ascribed to the large difference between the pKa´s of the different complexes. The sensor has good reversibility, reproducibility and fast response to the saccharides in the range 0.1-200 mM at fixed pH. MCF7 cells incubated for 2 hours in Tyrode´s buffer containing 10mM of the probe showed no changes in cell morphology as compared to control cells. The image displayed an homogeneous staining of the cell surface with complete absence of background emission due to the nature of the NIR signal.