Engineering tools at the nano-bio interface have enabled transformative advances in molecular diagnostics, therapeutic monitoring, and cellular manipulation. However, challenges remain in achieving continuous real-time sensing, intracellular probing, and controlled actuation within an integrated, multifunctional platform. Nanotechnology, particularly through localized surface plasmons (LSPs), addresses these challenges by leveraging radiative decay for enhanced optical sensing (e.g., SERS) and non-radiative decay for nanoscale actuation (e.g., photothermal effects and vapor nanobubbles). Conventional plasmonic systems, however, are limited in wavelength multiplexing, versatility, and spatial mode overlap. To overcome these shortcomings, this dissertation presents a wavelength-multiplexed multimodal optical nano-bio interfaces enabled by multiresonant plasmonic architectures. These systems combine advanced plasmonic designs with intimate bio-nano interfaces, achieving multifunctionality across a broad spectral range for biochemical sensing and nanoscale actuation. The core platform is built on metal-insulator-metal (MIM) plasmonic nanolaminate nanopillar arrays (NLNPAs), which provide tunable multiresonant responses, nanoscale mode overlap, and an intimate bio-nano interface. For biochemical sensing, the multiband plasmonic resonances enable broadband surface-enhanced Raman scattering (SERS), offering high sensitivity and molecular specificity across a wide spectral range. This capability facilitates high-dimensional molecular fingerprinting, providing insights into spatial-temporal biochemical processes. Additionally, the platform enhances nonlinear optical processes, such as second- and third-harmonic generation (SHG/THG), enabling broadband, label-free sensing and bio-actuation with tunable performance. Beyond sensing, the multiresonant plasmonic interface supports precise nanoscale actuation through femtosecond laser-induced vapor nanobubbles. This approach enables highly localized, minimally invasive membrane permeabilization—optoporation—facilitating intracellular biochemical sensing and molecular delivery with nanoscale precision. Such capabilities hold significant promise for applications in bio-nanophotonics, targeted drug delivery, and cellular biochemical analysis, offering a pathway for advancing molecular diagnostics, minimally invasive therapies, and precise nanosurgery. As a proof-of-concept, a vapor nanobubble-enabled regenerative SERS sensing platform is demonstrated for continuous, wavelength-multiplexed biochemical monitoring. By combining photothermal nanocavitation with plasmonic SERS hotspots, the system achieves ultrasensitive molecular detection in protein-rich biofluids, such as bacterial biofilms associated with chronic wounds. This platform allows real-time monitoring of biochemical evolution in complex biointerfaces, offering a robust tool for continuous molecular fingerprinting in dynamic biological systems. Collectively, these advancements establish the wavelength-multiplexed multimodal optical nano-bio interface as a versatile platform that bridges the gap between nanoscale optical engineering and biological applications. By enabling simultaneous spatial-temporal sensing and actuation with nanoscale precision, this work paves the way for transformative applications in molecular diagnostics, real-time therapeutic monitoring, and cellular biochemical analysis. Future efforts toward portable instrumentation and integration with wearable or implantable technologies will further enhance the platform's potential for non-invasive, real-time monitoring in clinical and healthcare settings, driving forward the future of bio-nanophotonics. / Doctor of Philosophy / The ability to observe, analyze, and control biological processes at the tiniest scales—down to individual cells and molecules— has the potential to transform our understanding of life and revolutionize medicine, diagnostics, and healthcare. Imagine tools that can simultaneously detect disease-related molecules, deliver medicine with pinpoint accuracy, and monitor changes happening inside cells in real time. Achieving this, however, is no small feat. Existing tools often lack the ability to perform multiple tasks at once or adapt to the dynamic nature of living systems. To address this, we developed a new type of nano-bio interface that uses specialized nanostructures to interact with light in unique ways. These tiny structures can trap and amplify light across a wide range of colors, allowing us to achieve multifunctional capabilities at different colors: detecting molecules, probing inside cells, and even triggering specific biological responses using short bursts of laser light. For sensing, the system enhances Raman spectroscopy, a technique that reads the molecular "fingerprints" of chemicals, helping us detect and identify molecules with high precision. For cellular manipulation, we use short laser pulses to generate tiny bubbles that can temporarily open cell membranes—optoporation—enabling drug delivery or accessing the cell's biochemical content without causing harm. Additionally, the system can monitor changes over time, such as the molecular activity within bacterial biofilms, which are responsible for chronic infections. This work opens exciting new possibilities for medicine and biology: detecting diseases earlier, delivering therapies more precisely, and analyzing biological processes in real time. In the future, these nano-tools could be incorporated into portable devices, wearables, or implants, enabling doctors and scientists to monitor health and treat diseases in ways that are faster, safer, and more effective.

Plasmonic nanostructures can enhance light-matter interactions in the subwavelength domain, which is useful for photodetection, light emission, optical biosensing, and spectroscopy. However, conventional plasmonic devices are optimized to operate in a single wavelength band, which is not efficient for wavelength-multiplexed operations and quantum optical applications involving multi-photon nonlinear processes at multiple wavelength bands. Overcoming the limitations of single-resonant plasmonics requires development of plasmonic devices that can enhance the optical interactions at the same locations but at different resonance wavelengths. This dissertation comprehensively studies the theory, design, and applications of such devices, called "multiresonant plasmonic systems with spatial mode overlap". We start by a literature review to elucidate the importance of this topic as well as its current and potential applications. Then, we briefly discuss the fundamentals of plasmonic resonances and mode hybridization to thoroughly explore, classify, and compare the different architectures of the multiresonant plasmonic systems with spatial mode overlap. Also, we establish the black-box coupled mode theory to quantify the coupling of optical modes and analyze the complicated dynamics of optical interactions in multiresonant plasmonic systems. Next, we introduce the nanolaminate plasmonic crystals (NPCs), wafer-scale metamaterials structures that support many (>10) highly-excitable plasmonic modes with spatial overlap across the visible and near-infrared optical bands. The enabling factors behind the NPC's superior performance as multiresonant systems are also theoretically and experimentally investigated. After that, we experimentally demonstrate the NPCs application in simultaneous second harmonic generation and anti-Stokes photoluminescence (ASPL) with controllable nonlinear emission properties. By designing specific non-linear optical experiments and developing advanced ASPL models, this work addresses some important but previously unresolved questions on the ASPL mechanism as well. Finally, we conclude the dissertation by discussing the potential applications of out-of-plane plasmonic systems with spatial mode overlap in wavelength-multiplexed devices and presenting some preliminary results. / Doctor of Philosophy / Emergence of electronic devices such as cellphones and computers has revolutionized our lifestyles over the past century. By manipulating the flow/storage of electrons at the nanometer scale, electronic components can be very compact, but their speed and energy performance is ultimately limited due to ohmic losses and finite velocity of the electrons. In parallel, photonic devices and circuits have been proposed that by molding the flow of light can overcome the mentioned limitations but are not as integrable as their electronic counterparts. Plasmonics is an emerging research field that combines electronics and photonics using nanostructures that can couple the light waves to the free electrons in metals. By confining the light at deep subwavelength scales, plasmonic devices can highly enhance the light-matter interactions, with applications in ultrafast optical communications, energy-harvesting, optical sensing, and biodetection. Conventionally, plasmonic devices are optimized to operate with a single light color, which limits their performance in wavelength-multiplexed operations and ultrafast non-linear optics. For such applications, it is far more efficient to use the more advanced "multiresonant plasmonic systems with spatial mode overlap" that can enhance the optical interactions at the same locations but for multiple light colors. This dissertation comprehensively studies these systems in terms of the fundamental concepts, design ideas, and applications. Our work advances the plasmonic field from both science and technology perspectives. In particular, we explore and classify the strategies of building multiresonant plasmonic systems with spatial mode overlap for the first time. Also, we establish the black-box coupled mode theory, a novel framework for analysis and design of complicated plasmonic structures with optimized performance. Furthermore, we introduce the "nanolaminate plasmonic crystals" (NPCs), large area and cost-effective devices that can enhance the optical processes for both visible and near-infrared lights. Finally, we demonstrate NPCs ability in simultaneous frequency-doubling and broadband emission of light and come up with advanced theoretical models that can explain the light generation and color conversion in plasmonic devices.