Design Of Carbon Dot-and Polydopamine-based Novel Nanomaterials And Their Antibacterialapplications

Microbial infections pose a growing threat to human health.In particular,bacterial multidrug resistance,which is exacerbated by bacterial biofilm formation,is a major challenge for medical science.With the development of nanomedicine technology,novel nanomaterials have been widely applied to many microbial detection and treatment applications.Here,we developed two types of antibacterial nanomaterials(carbon dots(CDs)and polydopamine-based nanohybrids),studied their physicochemical properties,explored their antibacterial and antibiofilm performance,and investigated their antibacterial mechanisms.Quaternized CDs.The CDs prepared by the one-step solvothermal treatment of dimethyloctadecyl-[3-(trimethoxysilyl)propyl]ammonium chloride(abbreviated as Si-QAC)and glycerol possess ultrasmall size(ca.3.3±0.4 nm)and strong positively charged surfaces(zeta potential:+33.1±2.5 m V)with long alkyl chain-linked quaternary ammonium groups.Due to the different cell walls/membranes of Gram-positive and Gram-negative bacteria,the Si-QAC CDs exhibit selectively bactericidal activity(>99%inactivation efficiency)against Staphylococcus aureus(S.aureus)bacteria and distinguish Gram-positive bacteria from Gram-negative ones at a concentration of 5?g m L^–1.At a concentration of 1000 or 50?g m L^–1,the Si-QAC CDs can achieve>95%biofilm eradication or inhibition efficiencies against S.aureus biofilms.Interestingly,the quaternized Si-QAC CDs with ultrasmall sizes are able to penetrate into the biofilms formed by S.aureus and Escherichia coli(E.coli)bacteria and light up the whole biofilms at a concentration of 50?g m L^–1.Moreover,the experimental data confirmed that the Si-QAC CDs possess good biocompatibility.Besides,the mechanisms of the selective bacterial killing and imaging capabilities of Si-QAC CDs are discussed from the interactions(i.e.,electrostatic interaction and hydrophobic interaction)between CDs and bacteria.Polydopamine-based nanohybrids.The robust antibacterial nanohybrids(termed u-CPSs)are obtained by uniformly decorating the colistin-loaded polydopamine nanospheres(PDA NSs)with silver nanodots.The mussel-like PDA NSs,as an adhesive carrier,can bind to the bacterial surfaces where the drugs(colistin and silver ions)on the PDA surfaces can be released persistently via a near-infrared(NIR)laser-triggered manner.Besides,the u-CPSs possess excellent photothermal effect(photothermal conversion efficiency:?49.4%).The u-CPSs can realize synergistic bactericidal performance for combating bacteria-associated infections:inactivation of>6-log E.coli bacteria(the concentration of silver/colistin is 5/3.4?g m L^–1)and>95%eradication efficiency against E.coli biofilms under NIR laser irradiation.Moreover,the synergistic interaction mechanisms of the u-CPSs with bacteria and biofilms are explored in detail from membrane disruption and reactive oxygen species-induced DNA damage.In summary,in this thesis,we design two types of novel nanomaterials,CD-/PDA-based germicidal agents,study their physicochemical properties,evaluate their antibacterial and antibiofilm effects,and investigate their bactericidal mechanisms.We hope that our research can stimulate more researchers to develop more novel antibacterial agents against bacteria and their biofilms,and promote the wide use of the antibacterial nanomaterials in the treatment of microbial infections,and alleviate the medical dilemmas caused by the abuse of traditional antibiotics in the treatment of microbial infections.