Development of Smart Membrane Filters for Microbial Sensing

Recent efforts aimed at minimizing membrane fouling have emphasized an increasing demand for on-line monitoring in an effort to accurately predict membrane performance. The development of an in-situ bacterial monitoring system that is integrated within the membrane can meet that need. Because the target is bacterial monitoring, organic matter fouling must be controlled to avoid interference/masking of bacterial sensing as well as to prevent permeability loses. Combining bacterial monitoring with a membrane designed for fouling control is a novel and unique concept. We have produced a fouling-resistant membrane by attaching a stimuli-responsive polymer film on the surface, which offers the potential to collapse or expand the polymer film. A temperature decrease can cause the film to expand into a hydrophilic state while a temperature increase causes a collapse into a hydrophobic state. By continuously triggering the phase transition, the non-equilibrium movement of the polymer film may offer better protection of the surface than at equilibrium. Increasing temperature to collapse the film and immediately decreasing temperature to expand it would create a sweeping motion at the molecular (nanometer) level along the surface. The surface of a cellulose acetate membrane was grafted with a thermally responsive hydroxypropyl cellulose (HPC) film layer. Aqueous solutions of HPC possess a lower critical solution temperature of approximately 40°C (while cross-linked structures had an LCST of 46°C): above this temperature the solution phase separates. When attached to the membrane surface, the film layer collapses upon increasing the temperature above the phase transition temperature and expands away from the surface when cooled. Biorecognition molecules targeting selected bacteria were covalently bound to specific moities originating from the polymer film for in situ detection. Typically, the biological recognition component consists of enzymes, receptors, nucleic acids, or antibodies specific to biological markers. In this proof-of-concept study, antibodies were used due to their simplicity, proven efficacy, and rapid response.