Abstract
We report here a simple and innovative method to prepare large-scale silver nanoparticle films based on the controlled coffee ring effect. It is demonstrated that the films can be used as surface-enhanced Raman scattering probes to detect low-concentration medicines. Silver nanoparticles with the average size about 70 nm were prepared by reduction of silver nitride. In our experiment, the coffee ring effect was controlled by tilting the substrates during the deposition of silver nanoparticle films. Silver nanoparticle films were spontaneously formed on the surface of silicon substrates at the temperatures about 50°C based on the solvent evaporation and the coffee ring effect. The microstructure of the films was investigated using the scanning electron microscope and atomic force microscope. The surface roughness of the films is found as small as 20 nm. Then, the films were exposed to aqueous solutions of medicine at different concentrations. A comparison with a Raman spectra measured with a conventional Raman spectrometer showed that the Raman signal can be detected in the solution with concentrations as low as 1 × 10−5 M, and the enhancement factor achieved by the silver nanoparticle film can at least reach to 1.08 × 104. Our experimental results indicate that this technique is promising in the production of large-scale silver nanoparticle films for the surface-enhanced Raman scattering. These may be utilized in biochemical and trace analytical applications.
Highlights
Raman spectroscopy is an important analytical technique for chemical and biological analysis due to the wealth of information on molecular structures, surface processes, and interface reactions that can be extracted from Raman spectra [1]
An innovative concept of preparing silver nanoparticle films based on the coffee ring effect using the surfaceenhanced Raman spectroscopy for the detection of the low-concentration medicine is demonstrated
The silver nanoparticles were spontaneously formed on the surface of the silicon substrate at the temperatures about 50°C based on the coffee ring effect
Summary
Raman spectroscopy is an important analytical technique for chemical and biological analysis due to the wealth of information on molecular structures, surface processes, and interface reactions that can be extracted from Raman spectra [1]. For the last three decades, Raman techniques have experienced increasing application in many fields due to the observations of the enormous Raman enhancement of molecules adsorbed on special metallic surfaces. In 1974, it was first reported that an unusually strong enhanced Raman scattering signal occurred with pyridine molecules adsorbed on silver electrode surfaces that had been roughened electrochemically by oxidation-reduction cycles [2]. It was discovered that this process may enhance Raman activities at a 106-fold at an appropriately prepared coinage metal surface. The original substrates for SERS were electrochemically roughened metal electrodes [2]. The SERS probes can be arbitrarily classified in three categories: (1) metallic nanoparticles in suspension, (2) metallic nanoparticles immobilized on solid substrates, and (3) nanostructures fabricated directly on solid substrates, which include nanolithography, template synthesis of nanostructures, pulsed laser deposition, and laser lithography [5,6,7,8]
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