Access to clean water has become a critical issue as the water resources became scarce. There are several filtration techniques used in water treatment facilities such as reverse osmosis, and sand and gravel filters. Slow sand filtration is an economical filtration step used to obtain drinking water in cities. It filters particles and bacteria as water flows through the sand. Studies revealed that bacteria could alter their shape and fit into structures that are narrower than their sizes. The effect of flow on bacterial morphology in pores is not well documented. Here, we are applying nanobiotechnology to investigate the bacterial behavior in narrow structures as they are exposed to fluid flow. Miniaturized systems are great tools to mimic pores, and observe bacterial cells at a single cell level. This study will provide a pressure profile for pathogenic bacteria to improve the filtration processes. We designed sub-microfluidic devices that have 950 nm tall constrictions with widths ranging from 1.5-3 µm. The constrictions connect the inlet channel, where the pressure is applied, to an outlet channel, which is open to atmosphere.
The microfluidic devices were fabricated in the clean room. Constrictions were patterned on a silicon wafer with electron beam lithography, and chromium metal was sputtered to determine the height of the constrictions. Inlet and outlet microchannels were aligned onto the constrictions with photolithography. The completed master wafer was used as a mold to obtain poly-dimethylsiloxane (PDMS) devices, which were then permanently bonded to glass cover slips. PDMS is a polymer that is widely used in microfluidics field to study cells. Here, we studied two microorganisms: Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa). E. coli is an indicator of contamination when detected in water. The bacteria were initially grown overnight in lysogeny broth at 37 °C. The cultures were diluted to avoid accumulation of bacterial cells at the entrance of the constrictions. The cells were flowed through the constrictions as the pressure was applied at increasing increments by using Fluigent microfluidics flow control system, which was connected to a house airline. The images were taken after each pressure application.
Our results show that filtration of species varies with the applied pressure. When the cells are exposed to the same applied pressure, the physiology of bacteria becomes a critical factor to determine their behavior in narrow structures. E. coli, which is larger in diameter and less motile than P. aeruginosa, entered the constrictions at higher pressure values. As the constriction size became narrower than the diameter of both bacteria, the pressure applied significantly increased. Further analysis is critical to determine optimum parameters for separating pathogens to improve the filtration processes.
See more of this Group/Topical: Topical Conference: Environmental Aspects, Applications, and Implications of Nanomaterials and Nanotechnology