Molecular investigation on interfacial behaviors between carbon dots and dopamine: The highly pH-dependent self-assembly dynamics of nanocarriers

This work devotes to provide insights into the synthesis of nanosystems based on carbon dots (CDs) and dopamine (DPA) by molecular dynamics (MD) simulations, helping to guide the development of carbon-based nanocarriers for advanced cancer therapies. The solution pH is proved to be crucial for the self-assembly of CDs-DPA, and the hydrogen bonding (H-bonding) between the carboxyl groups on CDs and the polar groups in DPA is the driving force for the interfacial interaction. The affinity of CDs to DPA is strengthened with the pH rising under acidic conditions, due to the increasement of ionized carboxyl groups on CDs, whereas the trend reverses under alkaline conditions as the dominant DPA species transforms from cationic to anionic. Desirable self-assembly performances of CDs-DPA can be achieved under different conditions. CDs obtain the greatest compaction of DPA coating in the acidic condition of pH< 6.5, but the highest adsorption strength to DPA in weakly alkaline condition due to the most active H-bonding interaction. At pH∼10, DPA is more inclined to aggregate and adsorb on CDs in the form of clusters. Sodium ions are found to be capable of mediating anionic DPA adsorbed onto CDs by means of electrostatic attraction under strongly alkaline conditions.