A Gold/Zinc Oxide Thin Film-Based Surface Plasmon Resonance Biosensor for Disease and Environmental Applications

The purpose of this dissertation is to develop highly sensitive and selective assays for carbohydrate antigen 15-3 (CA15-3), mercury ion (Hg2+), silver ion (Ag+), cysteine (Cys) and interferon-gamma (INF-γ) using gold/zinc oxide (Au/ZnO) thin film-based surface plasmon resonance (SPR) sensors. First, Au/ZnO nanocomposite films were effectively employed to enhance the performance of SPR for the detection of CA15-3. Compared with the degree of the shift in SPR intensity induced by the specific binding event between antibody and antigen, the change of intensity on the Au/ZnO layers was increased by at least 2 fold over that on the gold/chromium (Au/Cr) layers. In addition, the Au/ZnO layers allowed for a detection limit 4 times lower than the Au/Cr layers, which are in widespread use as the sensing interfaces in current SPR-based detectors. Next, the “turn-on” reaction of a hairpin probe via coordination of Hg2+ by the thymine–thymine base pair results in a substantial increase in the SPR response, followed by specific hybridization with a gold nanoparticle probe to amplify the sensor performance. Meanwhile, the limit of detection is 1nM, which is lower than other recently developed techniques. An SPR sensor was then developed for the detection of Ag+ and Cys in aqueous solutions. This assay was based on the Ag+-induced conformational change of a cytosine-rich, single-stranded DNA. In the free state, single-stranded oligonucleotides fold into double-helical structures through the addition of Ag+ to cytosine-cytosine (C-C) mismatches. However, in the presence of Cys, which competitively binds to Ag+, the formation of the C-Ag+-C assembly is inhibited, resulting in free-state, single-stranded oligonucleotides. To enhance sensitivity, the DNA intercalator, daunorubicin, was employed to achieve signal enhancement. The detection limit for Ag+ was 10 nM with a measurement range of 50–2,000 nM, and the detection limit for Cys was 50 nM with a measurement range of 50–2,000 nM. Finally, the DNA aptamer with the hairpin structure was developed for the detection of IFN-γ with high sensitivity and selectivity. The streptavidin DNA aptamer was incorporated into the aptamer prober for the amplified detection of target molecules. Initially, the probe remains essentially in the inactive configuration. Addition of IFN-γ induced rearrangement of aptamer structure, allowing the self-assembly of the active streptavidin aptamer conformation for streptavidin molecular recognition. Under optimized conditions, the detection limit was determined as 33 pM and a dynamic range was up to 333 nM, which are even lower than those of the corresponding optical sensors. Since combined aptamers are composed of nucleic acids, this optical aptasensor provide advantages of high sensitivity, simplicity, reusability, and no further label or sample pretreatment. Given the disease and environmental applications, such biosensors have great potential to provide the targeted information in a direct, rapid, and simple manner. Thus, a gold/zinc oxide thin film surface plasmon resonance–based sensor will be an useful system for sensing applications.