Exploring the interactions between polyethyleneimine modified fluorescent carbon dots and bovine serum albumin by spectroscopic methods

Firstly polyethyleneimine modified fluorescent carbon dots (PEI-CDs) were successfully fabricated in water-ethanol medium using ascorbic acid as carbon source. It was found that the prepared PEI-CDs were approximately spherical and monodispersed with an average diameter of 10 nm and the corresponding photoluminescence (PL) intensity was greatly enhanced compared to the bare CDs. And then the interactions between the obtained PEI-CDs and bovine serum albumin (BSA) were investigated by fluorescence quenching, UV-vis absorption and circular dichroism (CD) spectroscopies under the simulative physiological conditions. The analysis of BSA fluorescence quenching spectra at 300 K revealed that the probable quenching mechanism of BSA fluorescence by PEI-CDs was a static quenching process via forming a 1:1 complex with a binding constant of 1.773×104 M−1. In addition, the displacement experiments confirmed that the binding of PEI-CDs primarily occurred in site I of BSA. And the binding distance r was calculated to be 5.3 nm, indicating that the non-radiation energy transfer from BSA to PEI-CDs took place. Finally, the synchronous fluorescence and CD spectra of BSA were used to examine whether the binding of PEI-CDs disturbed the microenviroment around amino acid residues and the secondary structure of BSA.