Next-generation molecular diagnostic sensing systems seek to meet the needs of high-risk patients for portable, convenient, low-cost detection that is also reliable with a sufficient sensitivity and dynamic range for the chosen target. Optical micro- and nanosensors have incredible potential for early stage detection of cancer biomarkers in human serum samples for applications such as treatment monitoring and recurrence diagnosis due to their reliability for measuring protein-protein interactions. Plasmonic sensors are appealing for biosensing applications due to the high sensitivity of the generated evanescent fields to local refractive index changes. However, widespread applications of these sensors are limited due to bulky, high-cost instrumentation requirements and insufficient limit of detection for pertinent cancer biomarker proteins. These sensors are currently based on surface plasmon resonance, extraordinary optical transmission, localized surface plasmon resonance, or a combination of these mechanisms. In this thesis, a new type of plasmonic sensor and sensing method are developed and studied for the detection of the cancer biomarker carcinoembryonic antigen. The optical properties of this device are studied in detail and its distinct spectral properties simultaneously reduce instrumentation requirements and improve the limit of detection to a suitable level for cancer biomarker screening.First, a gold plasmonic nanocup array, which operates based on a combination of extraordinary optical transmission and localized surface plasmon resonance, is studied for two biosensing applications. The first is a drug binding study to cytochrome P450 proteins and the second is a cell adhesion imaging study. From these studies, the advantages and disadvantages of the plasmonic nanocup array are identified and a new plasmonic sensor is developed. This sensor design begins with the plasmonic nanocup array and adds an insulator layer followed by a second gold layer, such that the final device consists of a metal-insulator-metal cavity embedded in the 3D nanocup array. The spectral properties of this device include a sensitive, on-resonance, relative change in transmission intensity with a refractive index change without a spectral shift and spectral locations with no intensity change with refractive index change. Therefore, this device shows a great potential for spectrometer-free plasmonic sensing, which greatly reduces instrumentation costs for portable diagnostic systems and also enables imaging-mode detection. The limit of detection for the cancer biomarker carcinoembryonic antigen is 1 ng/mL with the metal-insulator-metal plasmonic nanocup array, 1 µg/mL for the plasmonic nanocup array without any multilayered nanocavity structure, and 100 ng/mL for a commercialized conventional surface plasmon resonance sensor. Therefore, this new type of plasmonic sensor makes relevant limits of detection possible for cancer biomarker proteins. Several different multilayered nanostructured cavity devices are studied in this dissertation, including a metal-insulator-metal nanopillar device for surface enhanced Raman spectroscopy sensing. In each case, the sensing method is critically studied and the device is optimized. The plasmon-photon interaction in the multilayered system is examined in detail and it is shown that the plasmonic mode and cavity mode can be engineered to optimally couple. Overall, the multilayered plasmonic sensors developed in this dissertation are promising for future portable sensing systems to fill the gap for low-cost, high performing molecular diagnostics.
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Development of nanoplasmonic devices for biosensing applications
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