(473j) Study of Bacterial Motion in Presence of Metallic Nanoparticles Using Microfluidics: A Microscale Approach for Developing Water Disinfection Device

Water borne diseases cause several local outbreaks around the world every year. As per WHO Drinking-water report of 2023, 0.5 million people deaths are caused annually, by drinking water sources contaminated with bacteria like faecal coliforms. Metallic nanoparticles and their composites in a packed bed form as a disinfection unit has been used in various commercial devices to tackle such. However, these devices have not been able to achieve flowrates comparable to RO or UV systems, which unlike the nanoparticle composite packed bed unit, are non-sustainable and accumulate non-biodegradable waste. Therefore, studying bacterial motion in presence of metallic nanoparticles from a microscale approach that mimics the flow in a packed bed is a novel approach that will aid the development of principles for designing enhanced water disinfection rates in these devices.

We have developed our own metallic nanoparticle impregnated activated carbon composite and studied its disinfection capabilities in a gravity-driven device containing the composite packed column as the main unit for purification. Four-dimensional X-ray microscopy has been used to analyse a control volume of the packed column which was further image processed to obtain the intergranular pore-network. Six parameters, namely- pore diameter, throat diameter, tortuosity, coordination number, fractal dimension, and porosity were determined to characterize the pore network. Based on these parameters, PDMS microfluidic channels were fabricated using soft lithography to study the effect of metallic nanoparticles on the bacterial motion mimicking the bacteria-nanoparticle interaction in the packed column.

GFP tagged- E.coli bacterial cells have been used as a representative bacteria for the experiments at a concentration of 10⁴ CFU/mL. Bacterial cells have been tracked, and their motion has been studied in the presence and absence of metallic nanoparticles impregnated on the internal walls of the PDMS microfluidic channel in the no-flow regime.

Quantities like diffusivity, anomalous diffusion coefficient, cell speed and turn angle have been calculated from 50 trajectories of the cells in both presence and absence of nanoparticles, each. Diffusivity has decreased by a factor of 17 indicating decline in cells’ ability to spread and proliferate and similarly cell speed has reduced by a factor of 4 which represents decreased in ability to move in a directed motion. Anomalous diffusion coefficient and turn angle has not shown significant change. This decrease in diffusivity and cell speed follows Dahlquist model of diffusivity based on run and tumble model predicting that bacteria still move in randomized motion with decreased motility but cannot figure out a directed motion.

The mentioned experiments have been performed in no-flow regime and currently on-going experiments in our designed microfluidic channels, are being used to understand how the motion of bacteria is affected in flow regime, in presence and absence of metallic nanoparticles, simulating the practical use of these nanoparticles in the substrate of several water disinfection devices.

This study is the first step to understand how spatial presence of antibacterial materials like metallic nanoparticles affect the motion of bacteria which could be further used to gain fundamental insights. These insights can drive the next generation of sustainable, high-efficiency and high-throughput water disinfection technologies from a microscale understanding.