PLASMON EXCITON INTERACTION IN GOLD NANOSTRUCTURES AND QUANTUM DOT CONJUGATE AND ITS APPLICATION IN BIOSENSOR ZHANG TAO (B. Eng.) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 Declaration I Acknowledgements I would like to express my gratitude to all of those who have helped and inspired me during my four year doctoral study. My utmost thankfulness goes to my advisor, Prof. Chen Shing Bor for his patient guidance and selfless encouragement in my research and study at National University of Singapore. His exceptional intuition in physics and persistent desire for high quality research has motivated all his advisees, including me. I would like to thank my co-supervisor Prof. Lanry Yung Lin Yue for his guidance. I would like to thank my thesis committee, Prof. Zeng Huachun and Prof. Lu Xianmao for taking their precious time attending my thesis defense. My thanks also go to my previous and current labmates, Dr. Chieng Yuyuan, Dr. Ma Ying, MS Ang Yan Shan for their help during my study. My deepest gratitude goes to my family for their unflagging love and support throughout my life, especially my wife Wei Xiaowei whose fully support enables me to complete the work. In the last, I would like to thank all the funding agencies. This work is supported Ministry of Education, Singapore. II Table of Contents Declaration ................................................................................................................. I Acknowledgements .................................................................................................. II Table of Contents .................................................................................................... III Summary ................................................................................................................. VI List of Tables .......................................................................................................... IX List of Figures .......................................................................................................... X List of Symbols ...................................................................................................XVII Chapter 1 Introduction .............................................................................................. 1 Chapter 2 Literature Review ..................................................................................... 9 2.1 Plasmon-enhanced luminescence near noble metal nanostructures ........................ 9 2.2 Biosensing with plasmonic nanosensors. .............................................................. 12 2.3 Surface-enhanced Raman Scattering (SERS) based on plasmonic materials ....... 15 Chapter 3 Material Synthesis and Characterization ................................................ 20 3.1. Introduction .......................................................................................................... 20 3.2. Experimental Section ........................................................................................... 23 3.2.1 Synthesis of SAuNP with diameter of 11 nm, 25 nm, and 45 nm ..................... 23 3.2.2 Preparation of gold nanorod (AuNR) with aspect ratio of 3.5 ........................... 24 3.2.3 Synthesis of popcorn-shaped gold nanoparticles (PS-AuNP) ............................ 26 3.2.4 Functionalizing SAuNP with thiol and carboxyl-modified polyethelyene glycol (SH-PEG-COOH) via ligand exchange ...................................................................... 27 3.2.5 Two phase ligand exchange for AuNR and PS-AuNP....................................... 27 3.2.6 Conjugation of AuNP with QD to form AuNP-QD Nanoconjugates ................ 29 3.2.7 Characterization methods ................................................................................... 29 III 3.3 Results and Discussion ......................................................................................... 30 3.3.1. Spherical Gold nanoparticle and quantum dots conjugate (SAuNP-QD) ......... 30 3.3.2. Gold nanorod (AuNR) and quantum dot (QD) conjugate (AuNR-QD) ........... 35 3.3.3. Popcorn-shaped Gold Nanoparticles (PS-AuNP) and quantum dots (QDs) conjugate. .................................................................................................................... 40 3.4. Conclusion ........................................................................................................... 44 Chapter 4 Plasmon-Exciton Interactions in Single AuNP-QD conjugate: Correlating Modeling with Experiments................................................................. 46 4.1. Introduction .......................................................................................................... 46 4.2 Experiment section................................................................................................ 49 4.2.1 Characterization methods ................................................................................... 49 4.2.2. Finite-Difference Time-Domain (FDTD) modeling ......................................... 50 4.3 Results and Discussion ......................................................................................... 51 4.3.1 Steady-state photoluminescence properties of AuNP-QDs ............................... 51 4.3.2 FDTD simulation and electrodynamics calculation of PS-AuNP-QD system ... 57 4.3.3 Scattering properties of single SAuNP-QDs, AuNR-QDs and PS-AuNP-QD system ......................................................................................................................... 62 4.4 Conclusion ............................................................................................................ 81 Chapter 5 Protein Detection Based on PS-AuNP-QD Conjugate ........................... 85 5.1 Introduction ........................................................................................................... 85 5.2 Experiment Section ............................................................................................... 88 5.2.1 Synthesis of Biotinylated PS-AuNP-QD ........................................................... 88 5.2.2 Avidin Detection Based on Biotinylated PS-AuNP-QD .................................... 89 5.2.3 Attachment of Immunoglobulin G (IgG) onto the Surface of PS-AuNP-QD .... 89 5.2.4 E. Coli Bacteria Detection Based on PS-AuNP-QD-IgG .................................. 90 IV 5.3 Results and Discussions ........................................................................................ 90 5.3.1 Avidin Detection Based on Biotinylated PS-AuNP-QD .................................... 90 5.3.2 E. Coli Bacteria Detection Based on PS-AuNP-QD-IgG .................................. 95 5.4 Conclusion ............................................................................................................ 99 Chapter 6 Strong Surface-Enhanced Raman Scattering Signals of Analytes Attached on PS-AuNP-QD and the Application in Protein Structure Studies ...... 101 6.1 Introduction ......................................................................................................... 101 6.2 Experiment Section ............................................................................................. 104 6.2.1 Functionalizing PS-AuNPs with Thiotic Acid (TA) and 4-Mercaptobenzonic Acid (4-MBA) via Ligand Exchange ........................................................................ 104 6.2.2 Surface-enhanced Raman spectroscopy for 4-MBA attached on PS-AuNP-QD .................................................................................................................................. 104 6.2.3 Characterization Methods ................................................................................ 105 6.3 Results and Discussions ...................................................................................... 106 6.3.1 SERS spectrum of 4-MBA attached on PS-AuNP-QD.................................... 106 6.3.2 The application of PS-AuNP-QD in avidin structure study ............................. 109 6.4 Conclusion .......................................................................................................... 112 Chapter 7 Conclusion and Future Work ............................................................... 115 V Summary Plasmon Exciton Interaction in Gold Nanostructure and Quantum Dot Conjugate and its Applications in Biosensor By Zhang Tao By synthesizing gold nanostructure (AuNP) and quantum dot (QD) conjugates, we investigated the optical properties of this type of conjugates both experimentally and theoretically. Also, the potential applications of the conjugates in protein detection and surface-enhanced Raman scattering (SERS) were also explored. We synthesized three different sizes of spherical AuNPs (SAuNPs) (11 nm, 25 nm and 45 nm), and then functionalized them with carboxyl groups via ligand exchange. The amine-functionalized QDs can be reacted with SAuNPs and form amide bond between them. Dark field microscopy was employed to examine the single particle optical properties of this SAuNP-QD conjugate. The scattering spectra of SAuNP-QDs shows coupled modes between exciton and plasmon. According to our numerical simulation using finite-difference time-domain (FDTD) method, we also found that the interaction between SAuNP and QD depends on the polarization of the excitation light. Besides, the interaction between exciton and plasmon also affects the