Mercury Detection with Ag Nanoparticles Reduced on Si Thin Films
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1010-V09-06
Mercury Detection with Ag Nanoparticles Reduced on Si Thin Films A. Kaan Kalkan Functional Nanomaterials Laboratory, School of Mechanical and Aerospace Engineering, Oklahoma State University, Stillwater, OK, 74078 ABSTRACT A surface plasmon resonance mercury sensor was demonstrated by electroless reduction of silver nanoparticles on amorphous silicon thin films. Unlike the previous Ag/Au nanoparticle ñ Hg interaction investigations, which monitored the blue shift of the dipolar plasmon band of well-dispersed nanoparticles, the present work reveals and explores the red shift of the symmetric hybrid plasmon mode of the interacting nanoparticles in response to Hg vapor exposure. Sensitivity to Hg was explored with varying nanoparticle size, which could be controlled by the immersion time associated with the reduction process. The recovery of the hybrid plasmon band after the Hg exposure was also monitored which was observed to be slower than the recovery of the dipolar plasmon band for noninteracting particles. INTRODUCTION Mercury is a severe neurotoxin whose contamination in the environment has jumped threefold since the beginning of the industrial revolution. Coal-fired power plants are the major emitters of mercury, which enters the food chain via the air and water. With the emergence of surging economies around the globe and the resulting demands on coal usage, the potential for further mercury contamination is increasing. To monitor mercury levels, quick reliable means of mercury detection are needed. Nanostructured gold and silver offer the potential to detect trace levels of Hg by a fortunate combination of various attributes: 1) high affinity of Hg for Au and Ag; 2) high surface to volume at the nanoscale; 3) the presence of sharp and intense localized surface plasmon resonances in Ag and Au nanoparticles; 4) electron donation from Hg to Au/Hg leading to the energy shift of the surface plasmon resonance (SPR) that provides the basis for Hg detection. Previous work employing Au and Ag nanoparticles dispersed in water or immobilized on solid substrates, has shown the blue shift of the SPR peak in response to Hg saturated in air (15 ppm) and water (60 ppb), respectively [1-4]. These demonstrations employed a solution reduction technique resulting in surfactant stabilized nanoparticles, which otherwise are subject to complete aggregation in water. In the case of particle immobilization, the substrate surface had to be chemically modified by silanization with amine functional groups to which nanoparticles were subsequently chemisorbed [4]. On the other hand, direct synthesis of Au/Ag nanoparticles on a substrate is of interest for a number of reasons. First, the direct synthesis would be faster and more reproducible. Second, the absence of surfactant on the nanoparticles would enable faster response and higher sensitivity. Third, the surfactant-free Au/Ag surfaces can be easily modified with self-assembling monolayers as selective filters for mercury [5].
The present work demonstrates a surface plasm
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