Planet earth has been experiencing droughts of devastating proportions. With these droughts becoming more frequent and widespread, many areas of the world are unequipped to deal with the economic and agricultural impacts. About 44 percent of the world’s population resides in and around coastal regions. Thus, resorting to the oceans for clean drinking water is an obvious solution. Zwitterions are environmentally friendly molecules that maintain a positive and negative charge simultaneously. Research has shown that these types of molecules possess non-fouling or fouling release capabilities in a variety of marine applications due to their hydrophilic properties. Therefore, using zwitterionic polymer coatings in an effort to eliminate the membrane fouling issue that plagues ocean water reverse osmosis (RO) desalination plants is promising. Currently, harmful chemicals are added to the water to reduce membrane fouling, but this approach merely suppresses the issue. RO membrane fouling has prevented ocean desalination from emerging as a viable source of fresh water due to high maintenance and operation costs. Most commercially available RO membranes are comprised of either cellulose acetate or aromatic polyamide, and both are susceptible to fouling. I will synthesize two zwitterionic polymers, poly(sulfobetaine methacrylate) (pSBMA) and poly(carboxybetaine methacrylate) (pCBMA), that will be grafted to the membrane surface. I will then expose the coated membranes to solutions of fluorescently tagged protein and compare the non-fouling performance to an uncoated membrane by measuring the fluorescent light intensity of the surface binding proteins. In addition, enzyme-linked immunosorbent assays (ELISA) will be used to quantify the surface protein binding. Utilizing the zwitterionic coatings to eliminate the fouling issues experienced by desalination plants will reduce the monetary and environmental costs. This action will further prevent the addition of harmful chemicals that are released into the environment.

Cancer diagnostic immunoassays are widely used for the detection of disease in vitro, but low antigen concentrations may not be detected in an early stage or confused for baseline noise, leading to false negative or positive diagnoses. Poly(carboxybetaine methacrylate) (PCB) is a zwitterionic polymer that strongly resists biofouling while allowing simple functionalization and effective bioconjugation to proteins. Coating this polymer on iron oxide nanoparticles via a DOPA attachment group allows for easy antibody immobilization, to realize low nonspecific binding and high signal-to-noise ratio in one platform. Methods for nanoparticle construction include synthesis of MNPs (magnetic nanoparticles) coated with PCB-DOPA and PCB-DOPA2. The coated particles are functionalized with FITC-BSA and FITC-streptavidin using EDC/NHS chemistry to optimize conjugation parameters. A model antibody (ALCAM antibody) is then conjugated to test the platform’s sensitivity for immunoassays. The functionalized nanoparticles are characterized with Dynamic Light Scattering (DLS), fluorescence spectroscopy, flow cytometry, and Surface Plasmon Resonance (SPR). Control groups with bare beads, functionalized beads with no polymer coating, or no functionalization are also processed in the experiment to compare with experimental groups. In preliminary tests, the functionalized magnetic nanoparticles have a high level of immobilization of each tested protein or antibody (FITC-BSA, FITC-streptavidin, and ALCAM antibody). In the plasma stability test, the PCB-coated and beads show low nonspecific binding even with high levels of functionalization. The experimental immunoassay can detect a low concentration of the ALCAM cancer biomarker in bovine serum, with less baseline noise than a commercial immunoassay (Luminex MagPlex®). The functionalized magnetic nanoparticles have a low detection limit to an early-stage cancer biomarker and a high signal-to-noise ratio due to reduced nonspecific binding. This platform could be extended to many clinical immunoassays in which either false negative or false positive diagnostic readings are problem.