Mercury Detection with Gold Nanoparticles: Investigating Fundamental Phenomena and Expanding Applications By Jeffrey Scott Crosby A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Engineering - Mechanical Engineering in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Catherine P. Koshland, Co-Chair Professor Chris Dames, Co-Chair Professor Carlos Fernandez-Pello Professor Costas P. Grigoropoulos Professor S. Katharine Hammond Spring 2013 Abstract Mercury Detection with Gold Nanoparticles: Investigating Fundamental Phenomena and Expanding Applications by Jeffrey Scott Crosby Doctor of Philosophy in Engineering-Mechanical Engineering University of California, Berkeley Professor Catherine Koshland, Co-Chair Professor Chris Dames, Co-Chair Mercury is a pollutant of grave concern with well documented neurological and developmental health impacts. Better sensing methodology would improve detection and control of mercury and thus reduce its health burden. Gold nanoparticles provide a sensing medium with potential advantages in sensitivity, selectivity, robustness, and cost over established techniques. Mercury readily adsorbs onto the surface of the gold changing the localized surface plasmon resonance which is measured as a shift in the peak optical absorbance wavelength. This shift is dependent on the mercury concentration and predictable with classical electromagnetism. This work investigates some of the fundamental relationships driving sensor response. The effects of mass transfer and surface kinetics on mercury/gold nanoparticle adsorption are determined with analytical models and experimental results based on impinging flow geometry. To decouple mass transfer and surface kinetics adsorption, electrical analogy models are constructed and fit to the experimental data. The models can account for variations in flow conditions and surface coatings on the nanoparticles. These models are generalizable to other systems. Results from these fundamental investigations are used to improve and extend sensor performance. The time response or collection efficiency is optimized depending on system requirements. Using the knowledge gained, the applicability of gold nanoparticle mercury sensors is extended to a fiber optic based system and aqueous detection. Nanorods deposited on the surface of a fiber optic cable have a linear response with concentration and are able to detect mercury down to 1.0 μg/m3. The modification of an established oxidation/reduction scheme for use with the sensor allows for the detection of ionic and organic mercury from water samples which ordinarily would not be reactive with gold nanoparticles. The aqueous sensor was able to detect mercury below the EPA’s drinking water limit. 1 This work is dedicated to my mother and father. The best teachers I ever had. i Table of Contents 1. Introduction on mercury and noble metal nanoparticle sensors ........................................... 1 1.1 Health effects of mercury ..................................................................................................... 1 1.1.1Historical background of mercury toxicity ...................................................................... 1 1.1.2 Mercury’s physiological effects ...................................................................................... 2 1.1.3 Epidemiological basis for dose-response ....................................................................... 2 1.1.4 Mercury exposure assessment ....................................................................................... 5 1.2 Mercury cycle and fate and transport .................................................................................. 5 1.2.1 Mercury sources ............................................................................................................. 5 1.2.2 The mercury cycle ........................................................................................................... 7 1.2.3 Bioaccumulation of methylmercury ............................................................................... 9 1.3 Regulation and detection of mercury ................................................................................. 11 1.3.1 Regulatory background ................................................................................................ 11 1.3.2 Current mercury detection methods ........................................................................... 12 1.4 Gold nanoparticles as mercury sensors .............................................................................. 13 1.4.1 Noble metal nanoparticles background ....................................................................... 13 1.4.2 Noble metal nanoparticle synthesis and assembly ...................................................... 14 1.4.3 Nanoparticles as sensors .............................................................................................. 16 1.4.4 Interaction of mercury with gold nanoparticles ........................................................... 17 1.4.5 Prior gold nanoparticle mercury sensors ..................................................................... 21 2. Mass transfer, surface kinetics and thermodynamics of mercury adsorption on gold nanoparticles ................................................................................................................................ 24 2.1 Background .......................................................................................................................... 24 2.1.1 Mass transfer and gas sensors ..................................................................................... 24 2.1.2 Adsorption .................................................................................................................... 31 2.2 Adsorption of mercury on gold nanospheres ..................................................................... 42 2.2.1 Experimental methods ................................................................................................. 42 2.2.2 Results ........................................................................................................................... 45 2.2.3 Application of adsorption models to data .................................................................... 49 2.3 Combined mass transfer and surface kinetics model ......................................................... 52 2.3.1 Theoretical background (RC circuit analogy) ................................................................ 52 2.3.2 Applying the RC model to mercury-gold nanosphere data .......................................... 56 2.3.3 RC model results ........................................................................................................... 58 ii 2.3.4 Conclusion .................................................................................................................... 62 3. Detection of air borne elemental mercury concentration with gold nanorod decorated fiber optic sensors ................................................................................................................................. 65 3.1 Background .......................................................................................................................... 65 3.1.1 Fiber optic based sensing ............................................................................................. 65 3.1.2 Evanescent waves ......................................................................................................... 68 3.1.3 Application of the Mie and Gans solutions to gold nanoparticles ............................... 70 3.2 Experimental procedure ...................................................................................................... 75 3.2.1 Materials and methods: ............................................................................................... 75 3.2.2 Fiber optic sensor results ............................................................................................. 78 3.3 Discussion: temperature effects and selectivity of fiber optic sensors .............................. 82 3.4 Concluding remarks on fiber optic sensors ......................................................................... 83 4. Detection of mercury in aqueous samples with gold nanoparticles ..................................... 85 4.1 Introduction ......................................................................................................................... 85 4.1.1 Motivation .................................................................................................................... 85 4.1.2 Challenges of mercury measurement in aquatic environments .................................. 85 4.1.3 Current measurement techniques ............................................................................... 87 4.2 Aqueous mercury detection utilizing gold nanoparticles ................................................... 88 4.2.1 Experimental design ..................................................................................................... 88 4.2.2 Results ........................................................................................................................... 91 4.3 Discussion of aqueous mercury detection .......................................................................... 98 4.3.1 Sensor improvement via mass transfer optimization .................................................