Towards fine-tuning the surface corona of inorganic and organic nanomaterials to control their properties at nano-bio interface

Designing nanomaterials for biological applications has become an emerging interdisciplinary area of science; however that raises the need to understand the materials interaction with different biological components at the nano-bio interface. Such basic understanding is required for the development of nanomaterials-based diagnosis, therapy and medicine. In this perspective, this thesis investigated development of new synthetic methodologies to control the surface corona and composition of nanoparticles in a single step. Specifically, tryptophan and tyrosine amino acids were employed to synthesize gold, silver and their bimetallic nanoparticles. These materials can be viewed as amino acid functional groups anchored onto nanoparticles corona, which can render these surfaces like artificial enzymes. Captivatingly, these nanomaterials exhibited peroxidise-like behaviour and this property was found to be composition, temperature and surface functionalization dependent. Furthermore, antibacterial studies demonstrated that toxicity against Gram positive bacteria ( Staphylococcus albus ) originated from the amino acid corona whereas the composition of nanoparticles didn’t play a significant role. Conversely, antibacterial activity against Gram negative bacterium ( Escherichia coli ) was found to be composition dependent and capping of amino acids had little influence. These findings established a strong correlation between the surface corona and metal composition of nanoparticles and their antibacterial activities against two different bacterial strains. Moreover, in order to demarcate how this surface functionalization plays a critical role in biological action; non-toxic Au nanoparticles were further chosen to reveal the significant influence of surface functionalization. Tyrosine reduced Au nanoparticles turn out to be a potential antibacterial agent after they were sequentially functionalized using polyoxometalates and lysine. Functional polyoxometalates imparted antibacterial potential on the surface of nanoparticles and the cationic nature of lysine worked as guide to target negatively charged bacterial cells. These nanoparticle-based functional antibacterial agents are seen to employ a physical mode of action against bacteria by causing pore formation, cell wall cleavage and cell lysis. The above-discussed inorganic nanoparticles are not suitable for DNA delivery applications due to their inherent toxicity as well as the long residence time of the inorganic nanomaterials within the living system. Therefore, DNA delivery vector requires an organic nanomaterial that could encapsulate the DNA. Another reason to choose organic nanostructures is they can be broken down by enzymatic reactions within the bacterial cells. In this context, organic materials based nanostructures were employed for DNA delivery applications and to understand their interaction with DNA. Tri-block copolymer (PEO 20- PPO 69- PEO 20 ) was used as the organic material and when pDNA was mixed along with the polymer, they formed self-assembled nanostructures that could be used as non-viral DNA delivery vehicles. The electrostatic interaction between the phosphate group (PO 4 3- ) of pDNA and the hydrophilic segments (PEO) of the polymer chains drive the self-assembly process. At 1:10 weight ratio of pDNA and polymer the bacterial transformation was found to be the maximum, leading to over six folds higher transformation efficiency. Furthermore, during transformation studies, the integrity and functionality of the green fluorescent protein (GFP) pDNA in nanostructures were also demonstrated within the cellular environment by the expression of GFP gene