Multimodal Fluorescent-Magnetic Nanoprobe Based on Mannose-Binding Lectin

Fluorescent-magnetic bimodal nanoparticles (BNPs) can be produced through the conjugation of quantum dots (QDs) and superparamagnetic iron oxide nanoparticles (SPIONs). The versatility and applicability of BNPs can be enhanced by conjugating them with biomolecules, like the mannose-binding lectin (MBL). MBL is a protein that binds to mannose and N-acetyl-D-glucosamine, present on the surfaces of microorganisms, in the presence of calcium. Herein, we developed a multimodal nanoprobe based on QDs, SPIONs, and MBL (BNPs-MBL) for investigating the glycobiology of microorganisms, their detection and magnetic isolation. Carboxyl coated QDs and silane-functionalized SPIONs were synthesized and covalently conjugated via carbodiimide chemistry. Subsequently, MBL was added to the BNPs. The supernatant of the BNPs was analyzed by UV-Vis absorption spectroscopy to confirm the binding of QDs to the SPIONs. Additionally, to confirm conjugation and verify the preservation of the physicochemical properties of the nanoparticles, BNPs MBL were characterized by emission spectroscopy, Fourier-transformed infrared spectroscopy (FTIR), Zeta potential () analysis, and magnetization measurements. To evaluate the biological application of BNPs-MBL, Candida albicans yeasts were used as proof-of-concept due to their mannose-rich surfaces. Cells were incubated with BNPs-MBL in the presence or absence of calcium, and the labeling efficiency was evaluated by fluorescence microplate reader (FMR) and flow cytometry. UV–Vis analysis of the BNP supernatant revealed that ~71% of QDs were efficiently bound to SPIONs. A redshift of 25 nm was observed after QDs-SPION conjugation, with no significant change following MBL addition. FTIR and  analysis confirmed the MBL conjugation to BNPs, evidenced by molecular signatures of both components and a surface charge alteration of ~6 mV (in modulus). Magnetization analysis confirmed the preservation of the superparamagnetic behavior of BNPs-MBL. The FMR analysis of yeasts in the presence of calcium showed a fluorescence intensity of about 80% higher than in its absence. Flow cytometry showed that, with calcium, BNPs-MBL labeled ca. 76% of the cells, whereas only 16% were labeled without calcium. Both results indicated that the cell interaction was mediated by MBL. Thus, a fluorescent-magnetic multimodal nanoprobe (BNPs-MBL) was developed with the capacity to specifically interact with biological systems, showing potential for applications in glycobiology studies.