Amino acid-functionalized polyampholytes as natural broad-spectrum antimicrobial agents for high-efficient personal protection†
Airborne pollutants including particulate matter (PM) and microorganisms threaten public health. Fibrous filters in personal protection equipment have shown good PM removal ability but a poor biocidal effect. Herein, a series of highly biocompatible amino acid-grafted enzymatic hydrolysis lignin derivatives (EHL-AA-x) with both cationic/anionic groups were synthesized by nucleophilic substitution. The structures of EHL-AA-x were characterized by NMR, FT-IR, GPC, DLS, potentiometric titration, surface charge and elemental analysis. In vitro biological assays showed that the inhibition efficiency of EHL-AA-x against Gram-negative bacteria increased from 10 to 57% when the grafting amount of amino acids varied from 0 to 0.62 mmol g−1 at a concentration of 10 mg mL−1, while that against Gram-positive bacteria reached 99%. It is not only 4 times higher than that of birch wood hydrotropic lignin, but also comparable to that of lignin/nanosilver composites. The morphological changes observed by SEM indicated that EHL-AA-x damaged the cell membrane of bacteria, suggesting a membrane disruption mechanism. QCM-D and AFM analysis showed that the increase of electrostatic and hydrophobic interactions between EHL-AA-x and bacteria is the key factor for the improvement of the antimicrobial activity. Subsequently, a mask fabricated from the optimal EHL-AA-x-coated non-woven fabrics could inhibit >95% bacteria in 30 min, while a number of living bacteria were detected on the inner layer of the control commercial mask. In addition, the mask with EHL-AA-x could prevent the adhesion of bacteria by the formation of anionic and cationic hydration layers. Using this strategy, ideal lignin-based antimicrobial materials with good bacteriostatic activity and anti-bio-adhesion properties could be designed and used in personal protection equipment.