OPTIMIZING POLYMERS FOR USE IN ELECTRONIC ENVIRONMENTAL SENSORS
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Date
2018-04-10
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Johns Hopkins University
Abstract
Electronic sensors are often an ideal choice for vapor and liquid environmental monitoring due to their highly adaptable structures, rapid testing time, and simplicity of use. Biomolecule sensors achieve selectivity to a particular analyte of interest through attachment of a specific antibody to a portion of the active device substrate. Sensors for gases such as ammonia do not have the option of a selective antibody, but must instead rely on monitored molecular interactions between the active surface and the atmosphere. In both of these cases, it is of utmost importance to design the recognition layer in such a way to allow for both high specificity and high sensor output response. We can modify these films in numerous ways to achieve optimum device performance. In the following projects, I investigated some chemical and physical attachment layer optimization methods that may be used to meet specific device requirements including flexibility, portability, and rapid speed.
This dissertation is broadly divided into two sections: vapor sensing (Chapter 2) and biomolecule sensing (Chapters 3 and 4).
For vapor sensors, many different methods allow for increased sensitivity to target gases. The addition of metal particles and controlled porosity to a conductive film provides for increased sensitivity to ethylene, which is typically poorly reactive due to its simple chemical structure. In a separate project, two electronic devices are used in tandem with an inverter geometry to increase selectivity for ammonia sensing. This device is fabricated entirely on a plastic, flexible substrate which can be conveniently worn by an individual at risk for ammonia exposure.
The biomolecular sensors presented in this work can detect the small electronic shift that occurs from protein binding to a corresponding antibody in the sensing layer. However, this attachment produces a limited voltage or current change alone. While it is common to use secondary labels and additives to increase this signal, in the case of measuring antibiotic-resistant bacteria in the field, the design is required to be as simple and portable as possible, thus limiting the possibility of complicated additives or processing. For this reason, I developed a binding polymer layer with acid-labile side chains that deprotect in the presence of pH changes. When measuring this film with electrochemical impedance spectroscopy, it is possible to see the decrease in impedance that occurs upon complementary protein binding, as the hydrophobic polymer layer degrades and allows infiltration with water.
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Keywords
polymer chemistry, chemical sensor, biosensor, MRSA