Molecular interaction and temperature-induced structural alteration of hydrophilic CdSe:CdS:ZnS quantum dots-apoferritin composite

Abstract The encapsulation of core-shell quantum dots (QDs) on apoferritin protein and the thermal stability of these composites have been sparingly reported. In this study, we created a quantum dot-apoferritin composite and investigated its interaction and temperature-induced structural changes. The encapsulation of mercaptopropionic acid functionalized CdSe:CdS:ZnS core-shell QDs in apoferritin was validated using a high-resolution transmission electron microscope. The increasing concentrations (0-250 ng/mL) of QDs in composite (using 0.1 mg/mL apoferritin) showed an increase in absorbance, a decrease in tryptophan fluorescence intensity, and a change in circular dichroism characteristic peaks with increasing temperatures (25 °C, 37 °C and 55 °C). HR-TEM image supports these findings, showing an increase in size (12.0±1.0 nm at 25 °C, 12.5±1.0 nm at 37 °C, and 15±1.3 nm at 55 °C) and gradual release of QDs from the core showing 6±1% (37 °C) and 68±5% (55 °C) hollow composite particles. The single particle analysis for molecular structural elucidation using the negative stain sample confirmed the encapsulation of four QD particles at 25 °C. However, it showed multiple 2D class averages at 37 °C and 55 °C. This heterogeneity in 2D class averages confirms the destabilization of this composite at 37 °C and 55 °C. The single particle analysis revealed the molten globule-like structure of the QD-apoferritin composite at 55 °C. This study revealed that QDs induced significant structural alteration in the apoferritin at a much lower temperature than its melting temperature (80 °C).