Bifunctional carbon dots for cell imaging and inhibition of human insulin fibrillation in the whole aggregation process

Abstract

Due to the favorable stability, water solubility and good biocompatibility, carbon dots have attracted much attention. Herein, a novel nitrogen-doping bifunctional carbon dots (N-BCDs) with ultra-highly quantum yield (QYabs = 70.4%) is prepared through microwave-assisted method. 50 μg/mL of N-BCDs emit intense fluorescence in HeLa and GES-1 cells with negligible cytotoxicity. In addition, effective inhibition of N-BCDs to human insulin (HI) fibrillation is observed even at 10:1 (mass ratio of HI: N-BCDs) by ThT fluorescence, CD assay and TEM. N-BCDs prevent HI from fibrillation with prolonged lag time and reduced fluorescent intensity at equilibrium, regardless of the addition time of N-BCDs (HI: N-BCDs = 1:1, mass ratio), which has been rarely reported before. Furthermore, the morphology of final HI fibrils is shorter and thinner in the presence of N-BCDs. Mechanism studies reveal that the enhanced hydrogen bond between HI monomers and N-BCDs inhibits nucleation during the lag stage (Ka: 1.54 × 104 L·mol−1, 298 K), while the accumulation of N-BCDs blocks the growth of profibrils in the elongation stage. To the best of our knowledge, it's the first time to observe the accumulation of N-BCDs around HI profibrils with TEM. Our study provides a new strategy for developing efficient nanoparticle inhibitors for protein fibrillation.