(415b) N-Isopropylacrylamide (NIPAAM)-Modified Ultrafiltration Membranes with Bacterial Sensing Abilities

The presence of microorganisms in feed water can further exacerbate fouling due to the accumulation of microorganisms onto the membrane surface and on the feed spacer between the envelopes, or biofouling. Microorganisms transported to the membrane element can attach to the feed side of the membrane and the spacer. Attachment depends on Van der Waals forces, hydrophobic interactions and electrostatic interactions between the microorganisms and the surface. Biofouling control has been attempted via biocide additions; however, while a biocide may kill the biofilm organisms, it usually will not remove the biofouling layer, and may cause bacteria that survive disinfection to potentially become more resistant. Therefore, bacterial detection is essential in determining biofouling potential.

In situ detection of bacteria in membrane-based water treatment systems is critical since biofouling can significantly impact membrane efficiency. Moreover, there is a keen interest in tracking and eliminating potential pathogens in these systems. With very few exceptions, techniques for specific detection of bacteria in aqueous systems are based on membrane filtration followed by culturing and phylogenetic or functional analysis. Direct detection strategies, which eliminate the bias introduced in culture-based methods, are gaining in popularity. Biorecognition molecules have been designed to label characteristic artifacts (e.g., exocellular proteins, fatty acids) and genomic material (e.g., nucleic acids). Methods based on the detection of antibodies against microbial specific exocellular proteins (antigens) are characterized by their simplicity, rapid response, and financial viability. For specific detection, antibodies (Ab) can be immobilized on surfaces for immunocapture of target bacterial species and subsequent separation of the target species from complex matrices. Antibodies have been applied to target a wide range of bacteria in various sample types including natural waters and sediments. Support media for antibody-based sensors have included the surfaces of magnetic beads, microplates, and glass slides.

We propose to produce 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. The phase change arises from the existence of a lower critical solution temperature (LCST) such that the polymer precipitates from solution as the temperature is increased. This temperature is determined to be where the mass is changing the fastest. This capability can be exploited to control adsorption/desorption. We then will use the polymer film to act as the support medium for bacterial sensing. To our knowledge, this is the first application of conjugated polymers attached to membranes for bacterial sensing.

While this project will focus on developing fouling resistant membranes with in-situ bacterial sensing, this technology can easily be translated to small membrane coupons. The method of immunocapture uses antibodies and we attach those antibodies using a carbodiimide acting as a zero-length linker to connect the NIPAAM to the antibody. The polymers being studied for this application are Hydroxypropyl Cellulose and N-Isopropylacrylamide and have LCSTs in a usable temperature range. Prior work involved building the nanostructured surface with HPC, current research involves NIPAAM polymerization on the membrane surface using cerium ammonium nitrate as the initiator. The benefits of each polymer and their filtration performance will be compared using various methods. Wetcell Atomic Force Microscopy allows us the image the surface and do roughness analysis while under different temperatures in an aqueous environment. This means we can detect how rough the surface is at the low temperatures, where the film should be extended; and at high temperatures, where the film should be collapsed. FTIR was used to find surface chemistries, flux measurements showed whether the polymer surface had an effect on fouling, and bacterial detection via fluorescent tags showed sensing capabilites.