10780
J. Phys. Chem. C 2007, 111, 10780-10784
Electrochemical Preparation of Silver Nanostructure on the Planar Surface for Application in Metal-Enhanced Fluorescence Li Shang, Hongjun Chen, and Shaojun Dong* State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Changchun, 130022, P. R. China ReceiVed: December 19, 2006; In Final Form: April 26, 2007
We introduce a fast and simple method, named the potentiostatic electrodeposition technique, to deposit metal particles on the planar surface for application in metal-enhanced fluorescence. The as-prepared metallic surfaces were comprised of silver nanostructures and displayed a relatively homogeneous morphology. Atomic force microscopy and UV-visible absorption spectroscopy were used to characterize the growth process of the silver nanostructures on the indium tin oxide (ITO) surfaces. A typical 20-fold enhancement in the intensity of a nearby fluorophore, [Ru(bpy)3]2+, could be achieved on the silvered surfaces. In addition, the photostability of [Ru(bpy)3]2+ was found to be greatly increased due to the modification of the radiative decay rate of the fluorophore. It is expected that this electrochemical approach to fabricating nanostructured metallic surfaces can be further utilized in enhanced fluorescence-based applications.
Introduction Fluorescence spectroscopy is widely used in biochemical research and has become the dominant method enabling the revolution in medical diagnostics, DNA sequencing, and genomics. Although fluorescence is a highly sensitive technique, there is still a need for increased detection sensitivity. Recent studies showed that the interactions of fluorophores with metallic particles and surfaces could be used to obtain increased fluorescence intensities.1-3 Such fluorescence enhancement by metallic particles or surfaces has been termed metal-enhanced fluorescence (MEF) and has already been applied to increase the sensitivity of detection in biological assays.4-7 MEF is believed to occur due to a coupling of the oscillating dipole of the fluorophore with the plasmon resonance from a metal particle which results in increased emission intensities and better photostabilities of the fluorophore.8,9 For medical and biotechnology applications, such as in diagnostic or sensing devices, it would be useful to obtain MEF at desired locations in the measurement device.10 In this regard, several methods have been developed recently, such as self-assembly of metal colloids,11,12 vapor deposition,13 or chemical reduction.14-16 However, efforts to pursue a more convenient and controllable avenue is still of great interest for the application in metal-enhanced fluorescence. Meanwhile, it seemed biologically valuable to devise methods for fabricating metallic surfaces without harsh reagents. Electrochemical deposition is very useful for the preparation of new materials with specific characteristics (thin layers, dispersed materials, and nanostructures), especially the transition elements and semiconductor compounds.17-19 Compared with other methods such as vapor deposition and self-assembly, electrochemical deposition has proven to be especially economical, highly productive, and readily adoptable.20 Therefore, it is meaningful and appealing to make use of the advantages of the electrodeposition method for the preparation of a MEF active surface. Here, in this work, we report our studies of employing * Corresponding
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a potentiostatic electrodeposition technique to electrochemically prepare the MEF surface. As will be shown in this paper, a nanostructured silver film can be readily fabricated by the electrochemical deposition of silver from halide-free solutions under precisely controlled electrochemical conditions. This preparation of the nanostructured silver film is fast and requires less silver. Meanwhile, this technique enables one to control the size/density of the silver deposited on the surface by simply controlling experimental parameters such as the applied voltage, the deposition time, and the silver concentration. Therefore, we expect that this electrochemical technique can be further developed to deposit silver on diagnostic or sensing devices for applications of MEF. Experimental Section Tris(2,2′-bipyridyl)dichlororuthenium(II) (Ru(bpy)3Cl2) and polyvinyl alcohol (PVA) were purchased from Sigma-Aldrich (USA). Silver nitrate (AR) was purchased from Beijing Chemical Co. (China). Indium tin oxide (ITO)-covered glass slides were obtained from Shenzhen Hivac Vacuum Photoelectronics Co. Ltd. (China, resistivity
