Development of various carbon nanoparticles and albumin complexes for potential theranostics applications

Carbon quantum dots (CQDs) are promising materials for many biomedical applications. However, their unique properties may be much enhanced by heteroatom doping and albumin decorating, which leads to improved functionality as reliable CQD-based simultaneous diagnosis and drug delivery systems, respectively. Therefore, in this study, three types of CQDs, with various doping conditions, namely pure carbon dot (CDs), N-doped CQD (NCDs), and S–N doped CQD (SNCDs), were functionalized over bovine serum albumin (BSA), a type of serum protein that is commonly used in drug delivery systems, and their binding was systematically optimized using the central composite design algorithm, by response surface methodology. Therefore three types of CQD-BSA complexes were obtained, namely CD-BSA, NCD-BSA, and SNCD-BSA. The statistical system was set to achieve the best results for both the absorbance of BSA, as well as the emission strength for each CQD-BSA complex. The structural changes of BSA have been investigated by the FTIR spectrum for various CQD-BSA complexes, indicating that the secondary structure and biological activity of BSA have not been influenced significantly, after incubation with different CQDs, except for a slight change in the case of SNCDs-BSA complex, inferring non-covalent interaction in some binding sites. The fluorescence intensity results also show that the formation of the complex did not reduce the emission of CQDs very much. Based on the results, the synthesized complexes can serve as suitable carriers for simultaneous drug delivery and diagnosis applications.