UC Davis

Enzyme-linked Immunosorbent Assay (ELISA) serves as a fundamental tool for the selective and sensitive detection of various analytes, including antibodies, pesticides, antibiotics, proteins, and pathogens, playing a crucial role in biomedical diagnosis, chemical quality control, and the detection of hazardous chemicals in foods and environments. Despite its widespread use, conventional ELISA faces limitations such as high costs, limited scalability and flexibility for personal use, challenges in simultaneously examining multi-target chemicals at low concentrations, and reliance on specialized instrumentation and trained personnel. In response to these challenges, paper-based ELISA (p-ELISA) emerged as an alternative, using fibrous and microporous platforms to offer increased surface area, reduced cost, and ease of use. However, the inherent heterogeneous structure of paper and fibrous membranes, particularly in the vertical direction, impedes the penetration of large biomolecules, leading to less biomolecule incorporation and, consequently, reduced sensitivity and inhomogeneous colorimetric signals. Addressing these deficiencies, this dissertation introduces a novel biosensing platform based on chemically modified melamine foam (MF) with a three-dimensional (3D) reticulated macroporous structure. Our study has proven that this foam-based ELISA (f-ELISA) platform to be rapid, sensitive, additive, and volume-responsive, showcasing its versatility across various ELISA methodologies, including direct, competitive, and sandwich ELISA. Moreover, the platform's adaptability to varied ligands, such as antibodies, nanobodies, and peptides, alongside its capability to accurately detect a wide range of targets, including biomarkers, antibiotics, environmental toxicants, pathogens, etc., underscores a substantial improvement upon conventional and paper-based ELISA techniques. Specifically, Chapter 1 summarizes the background information on current detection techniques and applications of melamine foam in varied fields. In Chapter 2, a novel, highly sensitive, naked-eye detectable colorimetric biosensor was developed based on chemically modified melamine foam (MF). This platform is designed for the rapid, on-site detection of various environmental hazards and toxicants in fluid systems. Using the unique three-dimensional reticulated macroporous structure of MF, this platform enables the fast and efficient transfer of biomolecules, ensuring enhanced sensitivity and broad applicability across multiple detection methods, including direct, competitive, and sandwich ELISA. This advancement of f-ELISA technology demonstrates significant improvements over traditional and paper-based ELISA methods, offering an alternative solution for environmental monitoring and potential healthcare applications. In Chapter 3, the application of f-ELISA in the detection of bacterial cells could further demonstrate the advantages of the macroporous features offered by the chemically modified MF as mentioned in Chapter 2. In essence, this study paves the way for a rapid, sensitive, and volume-flexible biosensing platform, using E. coli O157:H7 as a proof of concept, which holds promise for the rapid and ultrasensitive detection of various pathogenic bacteria in real-world applications. In Chapter 4, the study elaborates on refining the foam-based ELISA (f-ELISA) platform developed in Chapter 2 and Chapter 3, showcasing its expanded versatility and efficacy for onsite detection applications. Through different chemical modifications to melamine foam, the research developed a macroporous 3D substrate that effectively binds various ligands, including antibodies, nanobodies, and peptides. This study highlights the platform's adaptability, affordability, and user-friendly design, making it a versatile and effective tool in diagnostics, offering broader applications, and improving detection processes in various fields. Lastly, Chapter 5 summarizes the invention of the f-ELISA system and its applications under different scenarios.