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

Abstract

The thermal stability of core–shell quantum dots (QDs) encapsulated apoferritin has been sparingly reported. In this study, we reported the spontaneous encapsulation of mercaptopropionic acid functionalized CdSe:CdS:ZnS core–shell QDs and temperature-induced structural changes of QDs-apoferritin composite using biophysical techniques and negative stain single particle analysis. An increase in absorbance and decrease in tryptophan fluorescence intensity was observed by increasing QDs concentration (0–250 ng/mL). A change in circular dichroism characteristic peaks was observed with increasing temperatures (25 °C, 37 °C, and 55 °C). HR-TEM image also showed 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) along with 6 ± 1% and 68 ± 5% release of QDs (than 25 °C) from the composite at 37 °C and 55 °C, respectively. The single particle analysis confirmed the encapsulation of four QD particles at 25 °C but showed multiple 2D class averages at 37 °C, confirming the destabilization and molten globule-like structure at 55 °C. This study revealed that QDs induced significant structural alteration in the apoferritin at a much lower temperature than its normal melting temperature (80 °C).