The Pennsylvania State University The Graduate School Department of Chemistry DESIGN AND DEVELOPMENT OF NANOSTRUCTURED SURFACES FOR ENHANCED OPTICAL SENSING A Dissertation in Chemistry by Miguel A. Santiago Cordoba © 2017 Miguel A. Santiago Cordoba Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy May 2017 The dissertation of Miguel A. Santiago Cordoba was reviewed and approved* by the fol- lowing: Melik C. Demirel Professor of Engineering Science and Mechanics, Material Research Institute and Huck Institutes of Life Sciences Dissertation Advisor Co-chair of Committee Christine D. Keating Professor of Chemistry Co-chair of Committee John V. Badding Professor of Chemistry Benjamin J. Lear Associate Professor of Chemistry Darrell Velegol Distinguished Professor of Chemical Engineering Christopher E. Hamilton Research Scientist Material Scientist and Technology Division Los Alamos National Laboratory Los Alamos, NM 87545 Special Member Thomas E. Mallouk Evan Pugh Professor of Chemistry, Physics, Biochemistry and Molecular Biology Head of the Department of Chemistry *Signatures are on file in the Graduate School ABSTRACT At smaller size regimes, materials’ physicochemical properties change with respect to bulk analogs. In the case of metal nanoparticles like gold or silver, specific wave- lengths of light can induce a coherent oscillation of their conduction electrons, gener- ating an optical field confined to the nanoparticle surface. This phenomenon is termed surface plasmon, and has been used as an enhancing mechanism in optical sensing, allowing the detection of foreign materials at small concentrations. The goal of this dissertation is to develop nanostructured materials relying on surface plasmons that can be combined with different optical sensing platforms in order to enhance current detection limits. Initially, we focus on the development of surfactant free, stimuli responsive nanopar- ticle thin films, which undergo an active release when exposed to a stimulus such as a change in pH. These nanoparticle thin films provide faster analyte particle transport and direct electronic coupling with the analyte molecule, all without attenuating the evanescent wave from the optical transducer to the particle. These stimuli responsive nanostructured substrates are tested within a surface enhanced Raman platform for the detection of biomolecular probes at sub-nanomolar concentrations and µL sample iii sizes. Furthermore, the developed nanosubstrates can be patterned, providing a ver- satile nanoparticle thin film for multiplexing analysis, offering a substantial ad- vantage over conventional surface based nanoparticle detection methods. Our results encouraged further optimization of light-matter interactions in optical detection platforms. It is for that reason that this dissertation evolves towards con- fined optical systems. Particularly, whispering gallery microcavities confine electro- magnetic waves – at high volumes – at the boundary of a dielectric resonator. In this dissertation, we examined the sensitivity of whispering gallery modes combining op- tical microcavities with plasmonic nanoparticles in analogy to a “nanoantenna”. First, our hybrid methodology is tested by analyzing the resonant wavelength displacement of a whispering gallery mode cavity upon perturbation with a gold nanoparticle layer containing a model protein. Next, we developed a real-time optical sensing platform relying on whispering gallery microcavities and surface plasmons, and then tested it for the detection of a model protein at fM concentration (less than 1000 protein mol- ecules). Finally, this plasmonic-photonic coupling process involving whispering gallery modes is studied via a self-referenced methodology relying on the mode splitting of a whispering gallery resonance. Specifically, we studied the mode splitting evolution of a resonant whispering gallery microcavity as a function of gold nanoparticle adher- ence with varying diameters. Mode splitting increases as the localized surface plas- mon wavelength of the nanoparticle approaches the spectral line of the whispering iv gallery mode. Plasmonic-photonic coupling observed in this study provides a novel alternative to achieve single particle detection using mode splitting, as well as under- standing optimization of particle size for plasmonic-photonic coupling. The study described herein opens a new way to optimize current optical sensing tech- nology, enabling not only the detection of an analyte, but also the execution of funda- mental studies of analyte interactions at ultralow concentrations. v TABLE OF CONTENTS LIST OF FIGURES .................................................................................................................. viii LIST OF TABLES ...................................................................................................................... xv ACKNOWLEDGMENTS ......................................................................................................... xvi Chapter 1 Introduction ......................................................................................................... 1 1.1 Light-matter InteraCtions ................................................................................................ 1 1.2 Light-matter InteraCtions at the NanosCale ............................................................... 6 1.3 Light-matter InteraCtions from a Sensing Viewpoint ............................................. 8 1.4 Scope of this Dissertation .............................................................................................. 12 Chapter 2 Material Synthesis of QuasiperiodiC PlasmoniC Nanoparticle Arrays .................................................................................................................. 17 2.1 PlasmoniC NanopartiCles ............................................................................................... 19 2.2 PlasmoniC NanopartiCle Synthesis .............................................................................. 22 2.3 Stimuli-responsive Substrates ..................................................................................... 26 2.4 Protein Biomarker DeteCtion ....................................................................................... 34 2.5 DeteCtion of Viral MoleCular Probes .......................................................................... 39 2.6 Summary .............................................................................................................................. 45 Chapter 3 OptiCal ResonanCes and Confined Systems: An IntroduCtion to Whispering Gallery Systems ........................................................................ 47 3.1 General DesCription of Resonator Systems .............................................................. 47 3.2 OptiCal MiCroCavities and Whispering Gallery ResonanCes ............................... 51 3.3 Hybrid PhotoniC-PlasmoniC MiCrocavity Whispering Gallery Resonators ... 59 3.4 Protein-PartiCle deteCtion with miCroCavity resonators .................................... 62 3.5 MiCroCavity-PartiCle Coupling ...................................................................................... 72 3.6 Summary .............................................................................................................................. 78 Chapter 4 Ultrasensitive Protein DeteCtion Studies in Real-Time ...................... 80 4.1 MoleCular DeteCtion in Real-Time .............................................................................. 80 4.2 Real-Time Protein DeteCtion Platforms Utilizing WG Modes ............................ 83 4.3 Results .................................................................................................................................. 87 4.4 OptiCal Trapping ............................................................................................................... 93 4.5 Summary ........................................................................................................................... 105 vi Chapter 5 Single PlasmoniC NanopartiCle DeteCtion in a Whispering Gallery Microcavity ....................................................................................... 107 5.1 Whispering Gallery Mode ResonanCes – An introduCtion to Mode Splitting ................................................................................................................. 107 5.2 Single PlasmoniC PartiCle Detection – Experimental Methodology .............. 112 5.3 Single PlasmoniC PartiCle Detection – Results and DisCussion ...................... 119 5.4 Summary ........................................................................................................................... 126 Chapter 6 ConClusion and Future Work ..................................................................... 128 6.1 Conclusion ........................................................................................................................ 128 6.2 Future Work .................................................................................................................... 133 Bibliography ......................................................................................................................... 136 vii LIST OF FIGURES Figure 2.1 The Lycurgus cup exhibiting (A)reflected and (B)transmitted light. The cup shows Lycurgus being enmeshed by Ambro- sia.ãDepartment of Prehistory and Europe, The British Mu- seum.