Electrostatically Directed Assembly of Silver Nanoparticles for Application to Metal Enhanced Fluorescence Biosensing
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0951-E12-02
Electrostatically Directed Assembly of Silver Nanoparticles for Application to Metal Enhanced Fluorescence Biosensing De-Hao Tsai1,2, Shy-Hauh Guo3, Ray J. Phaneuf3, and Michael R. Zachariah1,2 1 Departments of Mechanical Engineering and Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, 20740 2 Process Measurement Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899 3 Department of Materials Science and Engineering, Univeristy of Maryland, College Park, MD, 20740
ABSTRACT In this paper we demonstrate a gas-phase process to fabricate Ag nanoparticles-based biosensing devices. Ag nanoparticles, prepared from the gas phase through spray pyrolysis, are sizeselected via electrostatic classification. These size-selected nanoparticles are then successfully attracted and aligned onto an electrostatic-patterned biased P-N junction substrate to form highresolution nanoparticle patterns. Particles in the size range of 30-100 nm were evaluated. Our approach provides a promising tool for precise assembly of nanoparticles for future device applications.
1. INTRODUCTION Silver nanoparticles have been considered as a desired component to enhance the labeling signal in bio-sensing processes [1, 2]. Compared to Au nanoparticles, the advantages of Ag particles are that they have a higher-frequency surface plasmon band, which can be applied to higher-frequency spectra regime. In addition, the extinction coefficient of the surface plasmon band of Ag nanoparticles is ~ 4 times as large as that of Au nanoparticles [1], and a stronger metal-enhanced fluorescence (MEF) ratio could hence be expected theoretically. To successfully apply Ag nanoparticles in this bio-labeling process, three conditions are required: (1) high purity; (2) well-controlled particle size; (3) effectively depositing and precisely positioning nanoparticles onto the required region. The production of Ag nanoparticles using the gas phase method is very effective in achieving the required conditions described above. First, gas phase production of Ag nanoparticles is a clean, continuous process, which can be operated at atmospheric conditions without requiring any vacuum environment or solvent medium [3, 4]. Second, charges can be readily placed on nanoparticles in the gas phase, for use in size selection. By a gas-phase electrostatic classification, high purity, monodisperse particles with a narrow size distribution can be obtained [4].
In order to effectively deposit and precisely position nanoparticles onto a device from the gas phase, electrostatic-directed methods have been used previously with some success [6, 7] and suggest a good strategy for aligning size-selected nanoparticles. In our previous work [5], we directed the deposition of particles on a substrate having lateral and vertical tunable fields. This was achieved by using an array of biased p-n junctions to generate a pattern of tunable electric fields, which enabled us to form stable charge patterns on the substrate. Under the r
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