Conjugation of Quantum Dots to 3-Mercaptophenylboronic Acid for Analysis of Sialic Acids on Erythrocyte Surfaces.

Phenylboronic acid derivatives (PBAs) are mimetic lectins that interact with 1,2- or 1,3-diols, groups commonly found in carbohydrates, including sialic acid (SA), a molecule involved in various biological processes, such as cell adhesion and signaling. SA is also responsible for the negative Zeta potential (ζ) of erythrocytes. What makes PBAs special, compared to other carbohydrate-recognizing molecules, is that their recognition properties can be modulated not only by environmental conditions, such as pH, but also by the addition of substituents to their structure. As a result, this organoborane has been applied for carbohydrate sensing and fundamental research in glycobiology. In addition, some PBAs, such as 3-mercaptophenylboronic acid (MPBA), contain thiol groups in their molecular structure, enabling their conjugation with nanostructures, such as quantum dots (QDs). QDs, when conjugated with MPBA, give rise to versatile fluorescent probes with advantageous properties capable of interacting with carbohydrates. Therefore, in this chapter, we present a protocol for the conjugation of hydrophilic QDs with MPBA via dative bonding and its application for studying the SA content in freshly collected and stored erythrocytes using fluorescence-based techniques. We hope that this chapter will be useful in guiding future work involving the application of QDs-MPBA conjugates in life sciences.