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Nanoparticles (NPs), when exposed to biofluids, become coated with proteins. As the protein is adsorbed on the surface, the extent of adsorption and the consequent effect on protein conformation and activity depend on the chemical nature, shape, and size of the nanoparticle. We have carried out a detailed study on the interaction of α-lactalbumin (a protein which forms the regulatory subunit of lactose synthase) with zinc oxide nanoparticles. The NPs were prepared by the sol-gel route and characterized by transmission electron microscopy, X-ray diffraction, UV-visible, and photoluminescence spectroscopy. ZnO particles were found to have a size of 4-7 nm with hexagonal structure. The interaction of protein with NP was examined using a combination of spectroscopic and computational methods. The binding was studied by ITC (isothermal calorimetry), and the result revealed that the complexation is mostly entropy driven and involves hydrophobic interaction. There is alteration in secondary structures in protein on binding ZnO nanoparticle, as revealed by circular dichroism (CD) and Fourier transform infrared spectroscopy (FITR). Finally, a comparison of structure, function, and stability of the α-lactalbumin-NP complex has been made by binding ZnO to other model proteins to get a better insight into the process of protein nanoparticle interaction. The present study thus provides useful insights into issues such as protein-nanoparticle recognition.

In this study mesoporous silica nanoparticles (MSPs) of different size and shape were developed, and their surface coatings altered to study their differential effect in enhancing the antibacterial activity. In brief, MSPs with three different aspect ratios 1, 2 and 4 were prepared, doped with silver ions and finally coated with the polymer chitosan. Both Gram-positive and Gram-negative bacteria were treated with the MSPs. Results indicated that silver ion doped and chitosan coated MSPs with the aspect ratio 4 (Cht/MSP4:Ag + ) has the highest antimicrobial activity among the prepared series. Further studies revealed that Cht/MSP4:Ag + was most effective against Escherichia coli (E.coli) and least effective against Vibrio cholerae (V.cholerae). To investigate the detailed inhibition mechanism of the MSPs, the interaction of the nanoparticles with E.coli membranes and its intracellular DNA was assessed using various spectroscopic and imaging-based techniques. Furthermore to increase the efficiency of the MSP combinatorial antibacterial strategy was also explored -nanoparticles in combination with kanamycin (antibiotic) was treated against Vibrio Cholerae (V. cholerae). Toxicity screening of these MSPs was conducted against Caco-2 cells, and the results show that the dose used for antibacterial screening is below the limit of toxicity threshold. Our findings show that both shape and surface engineering contributes positively towards bacteria killing, and the newly developed silver ion-doped and chitosan-coated MSP has good potential as an antimicrobial nanomaterial.

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