Green biomass carbon points with efficient broad-spectrum antibacterial activity and widespread application.

With low toxicity and good biocompatibility, carbon dots (CDs) are widely used in the fields of biosensing and drug delivery. In recent years, they have demonstrated excellent antimicrobial properties, thus becoming another research hotspot in the antimicrobial field. However, most of the studies showed that CDs were effective in inhibiting Gram-positive bacteria but ineffective against Gram-negative bacteria. In this study, macadamia nutshell (MNS)-CDs were prepared from the hard shells of macadamia nuts by a one-step hydrothermal method, and their appearance, morphology, structural composition, antimicrobial properties, and toxicity were investigated. The results showed that the MNS-CDs were spherical particles with an average diameter of about 4.25 nm, with hydrophilic groups, a hemolysis rate of less than 2%, good biocompatibility, and excellent antimicrobial properties against both Gram-negative and Gram-positive bacteria. The antimicrobial mechanism of these materials was also investigated. The inhibition of Gram-negative bacteria by MNS-CDs was mainly due to electrostatic interactions, while the inhibition of Gram-positive bacteria was mainly based on activated oxygen sterilization. Furthermore, MNS-CDs achieved good antimicrobial effects when applied in the fields of water purification, plates, fabrics, and food packaging, indicating that the prospects of their broad application are good.