A Novel Fe₃O₄/CdTe Fluorescence Probe For Sialic Acid Detection Based On Phenylboronic Acid-sialic Acid Recognition System

Sialic acid (SA) known as "N-acetyl lysine", is a natural derivative of 9-carbon monosaccharide. SA usually exist in the form of oligosaccharides, glycoproteins or glycolipid. Its main food source is milk powder, breast milk and milk. There are animal models confirming that insufficiency of SA intake influences mental development and learning ability. However, excessive SA intake leads to occurrence of inflammation in body. Some methods including HPLC and enzymatic assays are powerful for SA detection. But these methods need sophisticated instruments, expensive reagents and professional operation. So, there is a practical need to develop a facile, rapid and low-costing approach for determination of SA.At present, quantum dots (QDs) have been widely applied in the field of biological analysis because of their excellent fluorescence properties. However, it is very difficult to separate QDs from the sample matrix. But when QDs are conjugated with modified Fe3O4 magnetic nanoparticles, the conjugate is easy to be separated from the sample matrix due to the magnetism of the nanoparticles. The magnetic fluorescence nanoparticles have no selectivity, so it is necessary to be modified with some specific small molecules or macromolecules. Then, the functionalized Fe3O4/dTe magnetic fluorescence nano probe has high selectivity and rapid separation ability.A novel fluorescence method was established for detecting sialic acid (SA) by using 3-amino phenylboronic acid (PBA)-functionalized Fe3O4/CdTe magnetic nanoparticles as fluorescence probe. Initially, Fe3O4 nanoparticles were modified with amino groups, and then 3-mercapto propionic acid-stabilized CdTe quantum dots (QDs) were covalently linked to the amino-modified Fe3O4 nanoparticles to form Fe3OCdTe magnetic fluorescence nanoparticles. Finally, PBA was introduced on the surface of Fe3O4/CdTe to form PBA-functionalized Fe3O4/CdTe magnetic fluorescence nanoparticles. PBA has special binding affinity with SA in physiological environment of pH 7.4 compared to other saccharide. So this kind of nanoparticles can specifically recognize SA and its fluorescence intensity is quenched by SA. In addition, the conjugate of the nanoparticles and SA is easy to separate from the sample matrix due to its magnetism. Therefore, this nanoparticle can be used as a fluorescence probe to detect SA. Under the optimal conditions, the fluorescence intensity of the nano probe was found to be inversely linear with the concentration of SA in a wide range of 50 μg/mL-1.50 mg/mL, and the limit of detection was 16 μg/mL. PBA-functionalized Fe3O4/CdTe nano probe was applied to the determination of SA in infant formula, and the result showed high accuracy and precision: PBA-functionalized Fe3O4/CdTe nano probe has a potential to be used to monitor SA in food.