Metallogels from Silver Nanoparticles and Peptide Nanofibers as Antimicrobial Surfaces

Peptide amphiphiles (PAs) are elusive candidates to construct soft materials possessing various functionalities, including potent antimicrobial activity. It is imperative to look for a broad-spectrum antibiotic against which the genesis of drug resistance is difficult. Herein, a histidine-based PA is found to form a transparent metallohydrogel when AgNO3 is added to a hot solution of the PA in 2:1 (PA/AgNO3) molar ratio. Exposure to 365 nm UV lamp results in blue light-emitting silver nanocluster (NC) formation inside the hydrogel matrix. Interestingly, when the metallohydrogel is turned in solution through sheer thinning and rested for 12-14 h in ambient light, the gel reforms along with the formation of non-fluorescent silver nanoparticles (NPs). Thus, two different nanomaterials can be synthesized separately inside the gel matrix with modulation of the conditions. As the NC and NP formation takes place, ordered growth of these nanomaterials can be observed along the nanofibrous hydrogel network. Rheological measurements show enhancement of storage modulus in NC- and NP-containing hybrid hydrogels. This new nanohybrid system comprising peptide gel-based nanofibers and silver NC/NPs has potential applications against Gram-positive and Gram-negative bacteria. Furthermore, the plausible mechanism of the antimicrobial effects has been thoroughly investigated. The elevated levels of reactive oxygen species (ROS) found in the bacteria in the presence of the hybrid hydrogels establish that intra-cellular ROS generated in the cytosol of the bacteria is responsible for the death of bacteria. The current work indicates the hybrid hydrogel's utility as a potent antimicrobial agent.