Investigating the interaction patterns at nano-bio interface is a key challenge for safe use of nanoparticles (NPs) to any biological system. The study intends to explore the role of interaction pattern at the iron oxide nanoparticle (IONP)-bacteria interface affecting antimicrobial propensity of IONP. To this end, IONP with magnetite like atomic arrangement and negative surface potential (n-IONP) was synthesized by co-precipitation method. Positively charged chitosan molecule coating was used to reverse the surface potential of n-IONP, i.e. positive surface potential IONP (p-IONP). The comparative data from fourier transform infrared spectroscope, XRD and zeta potential analyzer indicated the successful coating of IONP surface with chitosan molecule. Additionally, the nanocrystals obtained were found to have spherical size with 10–20 nm diameter. The BacLight fluorescence assay, bacterial growth kinetic and colony forming unit studies indicated that n-IONP (<50 μM) has insignificant antimicrobial activity against Bacillus subtilis and Escherichia coli. However, coating with chitosan molecule resulted significant increase in antimicrobial propensity of IONP. Additionally, the assay to study reactive oxygen species (ROS) indicated relatively higher ROS production upon p-IONP treatment of the bacteria. The data, altogether, indicated that the chitosan coating of IONP result in interface that enhances ROS production, hence the antimicrobial activity.

The work investigates the role of interfacial potential in defining antimicrobial propensity of ZnO nanoparticle (ZnONP) against different Gram positive and Gram negative bacteria. ZnONPs with positive and negative surface potential are tested against different bacteria with varying surface potentials, ranging −14.7 to −23.6 mV. Chemically synthesized ZnONPs with positive surface potential show very high antimicrobial propensity with minimum inhibitory concentration of 50 and 100 μg/mL for Gram negative and positive bacterium, respectively. On other hand, ZnONPs of the same size but with negative surface potential show insignificant antimicrobial propensity against the studied bacteria. Unlike the positively charged nanoparticles, neither Zn²⁺ ion nor negatively charged ZnONP shows any significant inhibition in growth or morphology of the bacterium. Potential neutralization and colony forming unit studies together proved adverse effect of the resultant nano-bacterial interfacial potential on bacterial viability. Thus, ZnONP with positive surface potential upon interaction with negative surface potential of bacterial membrane enhances production of the reactive oxygen species and exerts mechanical stress on the membrane, resulting in the membrane depolarization. Our results show that the antimicrobial propensity of metal oxide nanoparticle mainly depends upon the interfacial potential, the potential resulting upon interaction of nanoparticle surface with bacterial membrane.

Metal oxide nanoparticles (NPs) have shown enhanced antibacterial effects against many bacteria.

Applying the principles of green chemistry for the synthesis of nanoparticles (NPs) is an emerging field in the current era. Continuous production of NPs, i.e. simultaneous bacterial growth and NP production, if possible, would be more effective for different NP mediated applications. Hence, our approach here is to optimize the method to produce and extract silver nanoparticles (AgNPs) during growth of the bacteria Bacillus thuringiensis. The fabricated AgNPs were obtained when the bacteria were grown at a minimum inhibitory concentration of AgNO₃ in culture medium. The microorganism produced elemental silver NPs with particular surface physico-chemical properties pertaining to the cellular moieties acting as a capping agent. Fabrication of the NPs was confirmed using UV-Vis absorbance spectra, attenuated total reflection Fourier transform infrared spectra, zeta analysis, and field emission scanning electron micrographs. The UV-Vis and IR studies together indicated the presence of proteins on the NP surface. The fabricated NPs were further purified using size exclusion chromatography (SEC), and the presence of the NPs in different elutions was further confirmed using UV-Vis, IR spectroscopes, and TEM. The yield, upon purification, was 98.75 μg of AgNPs from 500 mL of the culture, which is a relatively good yield. Additionally, the purified AgNPs were found to have a relatively stronger antibacterial activity against Escherichia coli than commercially available AgNPs. The work shows that a microorganism with resistance to significant concentrations of metal ions can be used for continuous production of metal NPs for industrial as well as biological applications.