Many bacteria have the capability to form a three-dimensional, strongly adherent network called ‘biofilm’. Biofilms provide adherence, resourcing nutrients and offer protection to bacterial cells. They are involved in pathogenesis, disease progression and resistance to almost all classical antibiotics. The need for new antimicrobial therapies has led to exploring applications of gold and silver nanoparticles against bacterial biofilms. These nanoparticles and their respective ions exert antimicrobial action by damaging the biofilm structure, biofilm components and hampering bacterial metabolism via various mechanisms. While exerting the antimicrobial activity, these nanoparticles approach the biofilm, penetrate it, migrate internally and interact with key components of biofilm such as polysaccharides, proteins, nucleic acids and lipids via electrostatic, hydrophobic, hydrogen-bonding, Van der Waals and ionic interactions. Few bacterial biofilms also show resistance to these nanoparticles through similar interactions. The nature of these interactions and overall antimicrobial effect depend on the physicochemical properties of biofilm and nanoparticles. Hence, study of these interactions and participating molecular players is of prime importance, with which one can modulate properties of nanoparticles to get maximal antibacterial effects against a wide spectrum of bacterial pathogens. This article provides a comprehensive review of research specifically directed to understand the molecular interactions of gold and silver nanoparticles with various bacterial biofilms.

Nisin is a naturally occurring bioactive small peptide produced by Lactococcus lactis subsp. lactis and belongs to the Type A (I) lantibiotics. Due to its potent antimicrobial activity, it has been broadly employed to preserve various food materials as well as to combat a variety of microbial pathogens. The present review discusses the antimicrobial properties of nisin and different types of their derivatives employed to treat microbial pathogens with a detailed underlying mechanism of action. Several alternative strategies such as combination, conjugation, and nanoformulations have been discussed in order to address several issues such as rapid degradation, instability, and reduced activity due to the various environmental factors that arise in the applications of nisin. Furthermore, the evolutionary relationship of many nisin genes from different nisin-producing bacterial species has been investigated. A detailed description of the natural and bioengineered nisin variants, as well as the underlying action mechanisms, has also been provided. The chemistry used to apply nisin in conjugation with natural or synthetic compounds as a synergetic mode of antimicrobial action has also been thoroughly discussed. The current review will be useful in learning about recent and past research that has been performed on nisin and its derivatives as antimicrobial agents.

Polysorbate 80 coated nanoparticles have been studied extensively for delivery of many bioactive molecules to the brain for diagnosis and treatment of different neurological disorders. The adsorption mechanism of polysorbate 80 on nanoparticles is not known due to a lack of suitable techniques for quantification at low concentrations. Here we report the probable mechanism of polysorbate 80 adsorption on poly-D,L-lactide-co-glycolide (PLGA) nanoparticles using a novel extraction procedure coupled with a highly sensitive attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopic method. Both methods facilitated the characterization and quantification of extracted surfactant at the nanogram level. Adsorption isotherm modeling reveals that polysorbate 80 follows a physisorption process (ΔG = 38 kJ Mol⁻¹) and forms a monolayer on the nanoparticle surface. Thermal analysis and X-ray photoelectron spectroscopy (XPS) further support polysorbate 80 coating and surface coverage on PLGA nanoparticles. Real-time ATR-FTIR analysis shows that polysorbate 80 interacts with nanoparticles through the ester group (–CO) and acyl chain (–CH₂) during the adsorption. The extent and direction of band shifts in real-time FTIR experiments suggest that the acyl chain of polysorbate 80 micelles loses its ordered structure and becomes flexible with a higher gauche/trans conformer ratio. Reduction in the degree of hydration of the ester group indicates an increase in hydrophobic interactions in the presence of PLGA nanoparticles. The results of FTIR analysis states that polysorbate 80 acquires a flat structure on the nanoparticle surface. This study on polysorbate 80 quantification and adsorption with ATR-FTIR spectroscopy can be extended to other non-ionic surfactants which will ultimately help in determination of biological fate of surfactant coated nanoparticles under in vivo conditions.