Interaction of cadmium sulfide quantum dots with jacalin for specific recognition of cancer cells

Surface functionalizations of quantum dots (QDs) are expected to improve their optoelectronic properties and advance their targeting nature, which is highly warranted for application in molecular imaging and biomedical diagnostics. Therefore, an understanding the interaction between surface functionalization agents and QDs is a prerequisite for their application. Herein, we investigated the interaction between cadmium sulfide (CdS) QDs and dietary T-antigen binding lectin (jacalin) isolated from Indian jack fruit seeds. Fluorescence spectroscopy study showed that CdS QDs effectively quenched the intrinsic fluorescence of jacalin. Analysis of fluorescence quenching at a different temperature indicated that the mechanism of interaction is static and a non-radiation energy transfer occurred within the molecules. The obtained binding constant, K_a value in the order of 10⁴ M⁻¹ at the tested temperature range suggested that the binding affinity between jacalin and CdS QDs is in the same range as those obtained for the interaction of lectin with carbohydrate. Thermodynamic analysis of the binding data, ΔH⁰=−44.24±1.21 kJ mol⁻¹, ΔS⁰=−60.92±4.10 J mol⁻¹ K⁻¹ and ΔG⁰=−26.21±0.1 kJ mol⁻¹ suggested that the binding reaction is enthalpy-driven spontaneous process. Hemagglutination activity of jacalin is well preserved even after binding to CdS QDs, indicating that the jacalin-CdS QDs complex can recognize T-antigens of the malignant tissues. To support the claim, we demonstrated selective fluorescence labeling of chronic myeloid leukemia cells, K562 with jacalin-CdS QDs complex.