Detection of chemicals and biomaterials using aluminium gallium nitride/gallium nitride high electron mobility transistors and hydrogen detection by epitaxial graphene

• Main Author: Chu, Byung Hwan
• Format: Dissertation
• Language: English
• Subjects: chemical engineering
• ISBN: 9781267169419; 1267169419

There has been growing interests in the use of field-effect based semiconductors with functionalized surfaces for applications in homeland security, medical diagnosis, and environmental monitoring. In this work, AlGaN/GaN high electron mobility transistors (HEMTs) with functionalized gate areas were used for selectively detecting target analytes. The two-dimensional electron gas channel at the AlGaN/GaN interface of the HEMT structure is extremely sensitive to the change of surface potential that occurs due to adsorption of analytes on the surface of the gate area. The HEMT sensor produces an electrical signal that can be directly interpreted with a response time of several seconds.
InN films can provide surface sites for reversible anion adsorption. The InN thin film was successfully integrated on the gate area of the HEMT for the detection of Cl- ions. The drain current of the HEMT sensor increased as a function of chloride ion concentration contrary to cations such as Na+, Mg2+, and H+ that showed no effect. The sensor was tested over a range of chloride ion concentrations from 100 nM to 100 muM. The chloride ion HEMT sensors could be used to monitor the dilution factor of exhaled breath condensate.
Lactic acid detection was demonstrated using HEMT sensors by functionalizing the gate area with ZnO nanorods. The ZnO nanorod array, grown with a low temperature hydrothermal method, provided a large effective surface area while functioning as immobilization sites for the enzyme, lactate oxidase. Decomposition of lactic acid via enzymatic reactions induced drain current change within several seconds upon exposure to lactic acid. Lactic acid concentrations ranging from 167 nM to 139 muM were tested.
Highly specific protein detection with HEMT sensors have been achieved by utilizing antigen-antibody binding. Thioglycolic acid was used as a chemical anchor that immobilizes antibodies to the gold-coated gate area of the HEMT. Successful detection of vitellogenin (Vtg), a protein that could indicate an egg producing organism's exposure to endocrine disrupters, was demonstrated in both phosphate buffer saline and diluted largemouth bass serum. The lowest Vtg concentration tested in diluted largemouth bass serum was 3.95 mug/ml. Antibody-gated-HEMTs can also be used for toxin detection. The functionalization process used to immobilize the antibody for protective antigen, a component of Anthrax toxin, was enhanced by crosslinking chemicals ethyl-(dimethylaminopropyl) carbodiimide and sulfo-N-Hydroxysuccinimide.
Graphene, a sheet of carbon atoms arranged in a honeycomb lattice, has excellent electrical properties that suggest it will function as an excellent sensor. Graphene formed by chemical vapor deposition on silicon carbide (SiC) was integrated with a catalytic platinum film to detect hydrogen gas. The graphene/platinum structure 17 showed fast response to hydrogen and effects of platinum thickness, background temperature, and polarity of the SiC to hydrogen sensitivity were investigated. Also, the detection selectivity of hydrogen was found to be high compared to gases such as oxygen, nitrogen oxide, and methane.