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Biosensors are highly selective and sensitive towards target molecules and should be convenient for on-site toxicant detection. However, the conventional biosensors, including enzyme-linked immunoassay (ELISA), are lacking high sensitivity and hard to reveal a significant colorimetric signal for detecting a trace amount of toxicant. Thus, the detection requires analytical instruments, which limit the application of biosensors for on-site detection. In this dissertation, highly sensitive and portable colorimetric biosensors for the detection of trace amounts of toxicants were designed and fabricated by covalently immobilizing antibodies onto controlled microporous and nanofibrous membranes. The high specific surface of the nanofibers significantly increased the number of immobilized antibodies and the binding capacity with the target toxicant. Thus, the sensitivity of the nanofibrous membrane biosensor was dramatically increased, and a trace number of toxicants could reveal a naked-eye detectable color. Additionally, the diffusion of large biomolecules inside nanofibrous membranes was investigated, revealing the heterogeneous structures of electrospun nanofibrous membranes significantly hinder the diffusion of antibodies into the membrane and dramatically limit the sensitivity of nanofibrous membrane biosensors. Such structural drawbacks of regular electrospun nanofibrous membranes could be overcome by increasing hydrophilicity and controlling microporous structure. Moreover, an ultra-highly sensitive and portable biosensor was fabricated after optimization.Specifically, chapter 1 summarizes the background information of biosensor and toxicant detection. Chapter 2 reviews the conventional toxicant detection methods, the technique of fabricating electrospun nanofibrous membrane, and the development of biosensors. In chapter 3, the nanofibrous membrane ELISA biosensors were fabricated for the detection of residual antibiotics in foods. The biosensors exhibited a signif

Biosensors are highly selective and sensitive towards target molecules and should be convenient for on-site toxicant detection. However, the conventional biosensors, including enzyme-linked immunoassay (ELISA), are lacking high sensitivity and hard to reveal a significant colorimetric signal for detecting a trace amount of toxicant. Thus, the detection requires analytical instruments, which limit the application of biosensors for on-site detection. In this dissertation, highly sensitive and portable colorimetric biosensors for the detection of trace amounts of toxicants were designed and fabricated by covalently immobilizing antibodies onto controlled microporous and nanofibrous membranes. The high specific surface of the nanofibers significantly increased the number of immobilized antibodies and the binding capacity with the target toxicant. Thus, the sensitivity of the nanofibrous membrane biosensor was dramatically increased, and a trace number of toxicants could reveal a naked-eye detectable color. Additionally, the diffusion of large biomolecules inside nanofibrous membranes was investigated, revealing the heterogeneous structures of electrospun nanofibrous membranes significantly hinder the diffusion of antibodies into the membrane and dramatically limit the sensitivity of nanofibrous membrane biosensors. Such structural drawbacks of regular electrospun nanofibrous membranes could be overcome by increasing hydrophilicity and controlling microporous structure. Moreover, an ultra-highly sensitive and portable biosensor was fabricated after optimization.Specifically, chapter 1 summarizes the background information of biosensor and toxicant detection. Chapter 2 reviews the conventional toxicant detection methods, the technique of fabricating electrospun nanofibrous membrane, and the development of biosensors. In chapter 3, the nanofibrous membrane ELISA biosensors were fabricated for the detection of residual antibiotics in foods. The biosensors exhibited a signif

Porous nanofibrous membranes have ultrahigh specific surface areas and could be broadly employed in protein purification, enzyme immobilization, and biosensors with enhanced selectivity, sensitivity, and efficiency. However, large biomolecules, such as proteins, have hindered diffusion behavior in the micro-porous media, significantly reducing the benefits provided by the nanofibrous membranes. The study of protein diffusion in polyacrylonitrile (PAN) nanofibrous membranes produced under varied humidity and polymer concentration of electrospinning revealed that heterogeneous structures of the nanofibrous membranes possess much smaller effective pore sizes than the measured pore sizes, which significantly affects the diffusion of large molecules through the system though sizes of proteins and pH conditions also have great impacts. Only when the measured membrane pore size is at least 1000 times higher than the protein size, the diffusion behavior of the protein is predictable in the system. The results provide insights into the design and applications of proper nanofibrous materials for improved applications in protein purification and immobilizations.

Enzyme-linked immunoassay (ELISA) is highly specific and selective towards target molecules and is convenient for on-site detection. However, in many cases, lack of high sensitivity makes it hard to reveal a significant colorimetric signal for detecting a trace amount of target molecules. Thus, analytical instruments are required for detection, which limits the application of ELISA for on-site detection. In the present study, a highly sensitive and naked-eyed detectable colorimetric biosensor for chloramphenicol (CAP) was prepared by incorporating ELISA onto surfaces of microporous and nanofibrous membranes. The high specific surface areas of the nanofibers significantly increased the number of antibodies covalently linked onto the fiber surfaces and binding capacity of the sensor with antigens present in a sample. With such an integration, the sensitivity of the ELISA sensor was dramatically increased, and a trace number of targets could reveal a naked-eye detectable color. The immunoassay sensor exhibited a significant naked-eye distinguishable color to chloramphenicol (CAP) at 0.3 ng/mL. The successful design and fabrication of the nanofibrous membrane immunoassay sensor provide new paths towards the development of on-site inspection sensors without the assistance from any instrument.

Enzyme-linked immunoassay (ELISA) is highly specific and selective towards target molecules and is convenient for on-site detection. However, in many cases, lack of high sensitivity makes it hard to reveal a significant colorimetric signal for detecting a trace amount of target molecules. Thus, analytical instruments are required for detection, which limits the application of ELISA for on-site detection. In the present study, a highly sensitive and naked-eyed detectable colorimetric biosensor for chloramphenicol (CAP) was prepared by incorporating ELISA onto surfaces of microporous and nanofibrous membranes. The high specific surface areas of the nanofibers significantly increased the number of antibodies covalently linked onto the fiber surfaces and binding capacity of the sensor with antigens present in a sample. With such an integration, the sensitivity of the ELISA sensor was dramatically increased, and a trace number of targets could reveal a naked-eye detectable color. The immunoassay sensor exhibited a significant naked-eye distinguishable color to chloramphenicol (CAP) at 0.3 ng/mL. The successful design and fabrication of the nanofibrous membrane immunoassay sensor provide new paths towards the development of on-site inspection sensors without the assistance from any instrument.