A MULTIPLEX NANOPLATFORM BASED ON QUANTUM DOTS AND MERCAPTOPHENYLBORONIC ACIDS FOR OPTICAL SENSING OF SACCHARIDES

Quantum dots (QDs) are semiconductor nanocrystals that exhibit unique photophysical properties. Due to their semiconductor surface, QDs can be functionalized by thiolated compounds, including the 3- mercaptophenylboronic acid (MPBA), a molecule capable of binding to different saccharides depending on the sample pH. Herein, in this study, the surface of QDs was modified by MPBA, and the affinity of this nanoprobe for different saccharides was evaluated. QDs and QDs-MPBA were characterized by absorption and emission spectroscopies. The interactions of the QDs-MPBA with the different saccharides (glucose, galactose, xylose, and sucrose) were evaluated by emission spectroscopy. In addition to these saccharides, the affinity of the nanosystem for sialic acid (SA), a carbohydrate present on the surface of erythrocytes, was analyzed by flow cytometry. For both cases, different pH conditions were tested. Absorption and emission spectra of the QDs were not significantly altered after their functionalization by MPBA. In the presence of the saccharides, at pH 7.4 the emission intensity of the nanosystem was significantly reduced only in the presence of galactose, enabling the differentiation of this saccharide from the others. QDs-MPBA at pH 7.0 also interacted with SA presented in the membranes of erythrocytes collected and stored in EDTA tubes for 0, 7, 14, and 21 days. As the storage time increased, the cell labeling profile progressively decreased, indicating a loss of SA. Therefore, the QDs-MPBA nanosystem showed versatility and great potential as an optical sensor for the detection of galactose and SA in suspension or associated with cell membranes.