Probing the interaction of 3-mercaptophenylboronic acid with carbohydrates using quantum dots

Abstract

A fluorescent probe based on quantum dots (QDs) and 3-mercaptophenylboronic acid (MPBA) was applied to study the interaction of MPBA with different carbohydrates. Cadmium telluride (CdTe) QDs functionalized/stabilized with mercaptosuccinic acid (MSA) were conjugated to MPBA using a direct strategy based on the affinity of thiol groups for the nanocrystal semiconductor surface. The conjugation was confirmed through flow cytometry by analyzing the nanosystem interaction with sialic acid (SA) from erythrocyte membranes. The ability of the conjugate to distinguish SA levels was also evaluated using erythrocytes freshly collected (0 days) and stored for different periods (8, 15, and 21 days). Then, the interaction of the QDs-MPBA conjugate, at various pHs, with carbohydrates (glucose, sucrose, xylose, and galactose) was investigated using emission spectroscopy. The capacity of the nanosystem to detect galactose using a fluorescence microplate reader (FMR) was also evaluated. The QDs-MPBA conjugate was able to quantitatively recognize and differentiate SA levels from erythrocyte membranes. Galactose resulted in the highest conjugate fluorescence suppression, enabling its detection. According to the Stern–Volmer model, the quenching was primarily dynamic. Using the FMR, limit of detection (LOD) and limit of quantification (LOQ) for galactose were estimated as 51 and 170 mM, respectively. The conjugate was also able to detect galactose in spiked plasma samples. Therefore, this study demonstrates the potential of the QDs-MPBA nanosystem for optical detection of galactose and for distinguishing SA content in erythrocyte membranes.