Job M. Bello

Silver-coated alumina as a new medium for surfaced-enhanced Raman scattering analysis

A new and simple substrate for inducing surface-enhanced Raman scattering (SERS) was investigated. This new SERS substrate consists of a solid support, such as a microscope slide, coated with alumina and then covered with silver. The alumina used in this work is an agglomerate-free type available in several submicron nominal particle diameters and is widely used as polishing powders. Several substrate conditions, such as the silver thickness used to coat the alumina, the amount of alumina deposited on the glass support, and the particle size of the alumina, were investigated extensively to determine the optimal experimental conditions for obtaining the SERS enhancement. In addition, it was also shown that the SERS enhancement obtained from the silver-coated alumina substrate was comparable to—or even better than—that obtained with previously used substrates. The analytical figures of merit, such as spectral features, signal reproducibility, linear dynamic range, and limits of detection, were investigated to demonstrate the analytical potential of this new substrate.

Surface-Enhanced Raman Scattering Fiber-Optic Sensor

A fiber-optic system was developed for exciting and collecting surface-enhanced Raman scattering (SERS) signals generated from a sensing plate tip having silver-coated microparticles deposited on a glass support. Various fiber parameters, such as fiber type, fiber-substrate geometry, and other experimental parameters, were investigated to obtain the optimum conditions for the SERS fiber-optic device. In addition, analytical figures of merit relevant to the performance of the SERS fiber-optic sensor, such as SERS spectral characteristics, reproducibility, linear dynamic range, and limit of detection, were also investigated.

Surface-active substrates for Raman and luminescence analysis.

This paper describes the development of active materials for optically enhanced Raman and fluorescence spectroscopy. The substrates for surface-enhanced Raman scattering investigated in this study involved silver-coated microspheres on glass plates. The effect of various experimental parameters, such as angle of incidence and excitation wavelength, were investigated. The substrate used for surface luminescence analysis consisted of a cellulose membrane coated with fumed silica microparticles, to enhance the sensitivity of analysis. Examples of analysis of benzo[a]pyrene and its derivatives are used to illustrate the efficacy of the analytical techniques.

Surface-enhanced Raman scattering interaction of p-aminobenzoic acid on a silver-coated alumina substrate

Abstract The adsorption behavior of p -aminobenzoic acid (PABA) molecules on a silver-coated alumina surface-enhanced Raman scattering (SERS) substrate was investigated. For spotted PABA and PABA in non-polar solvents, the PABA molecule is adsorbed flat on the surface of the SERS substrate. In this orientation, the benzene ring is π-bonded to the substrate, and the molecule is further anchored to the substrate by the binding of the lone pairs of NH 2 and COO − groups onto the metal surface. On the other hand, the adsorption behavior of PABA in a polar solvent is greatly influenced by the hydrogen bonding of the amine group with the polar solvent. In this orientation, the molecule is preferentially adsorbed through the COO ± and assumes a non-flat orientation on the metal surface.

Optically Transparent Thin-Film Electrode Chip for Spectroelectrochemical Sensing

A novel microfabricated optically transparent thin-film electrode chip for fluorescence and absorption spectroelectrochemistry has been developed. The working electrode was composed of indium tin oxide (ITO); the quasi-reference and auxiliary electrodes were composed of platinum. The stability of the platinum quasi-reference electrode was improved by coating it with a planar, solid state Ag/AgCl layer. The Ag/AgCl reference was characterized with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cyclic voltammetry measurements showed that the electrode chip was comparable to a standard electrochemical cell. Randles-Sevcik analysis of 10 mM K3[Fe(CN)6] in 0.1 M KCl using the electrode chip gave a diffusion coefficient of 1.59 × 10-6 cm2/s, in comparison to the value of 2.38 × 10-6 cm2/s using a standard electrochemical cell. By using the electrode chip in an optically transparent thin-layer electrode (OTTLE), the absorption based spectroelectrochemical modulation of [Fe(CN)6]3-/4- was demonstrated, as well as the fluorescence based modulation of [Ru(bpy)3]2+/3+. For the fluorescence spectroelectrochemical determination of [Ru(bpy)3]2+, a detection limit of 36 nM was observed.

Multivariate Analysis To Quantify Species in the Presence of Direct Interferents: Micro-Raman Analysis of HNO3 in Microfluidic Devices

Microfluidic devices are a growing field with significant potential for applications to small scale processing of solutions. Much like large scale processing, fast, reliable, and cost-effective means of monitoring streams during processing are needed. Here we apply a novel micro-Raman probe to the online monitoring of streams within a microfluidic device. For either macro- or microscale process monitoring via spectroscopic response, interfering or confounded bands can obfuscate results. By utilizing chemometric analysis, a form of multivariate analysis, species can be accurately quantified in solution despite the presence of overlapping or confounding spectroscopic bands. This is demonstrated on solutions of HNO3 and NaNO3 within microflow and microfluidic devices.

Surface-enhanced Raman spectroscopy for remote sensing

Conventional Raman spectroscopy is often limited by its low sensitivity due to the inherently weak Raman cross section of organic chemicals. A relatively new detection technique, Surface-Enhanced Raman Scattering (SERS) spectroscopy is based on recent experimental observations, which have indicated enhancement of the Raman scattering efficiency by factors of up to 106 when a compound is adsorbed on rough metallic surfaces that have submicron-scale protrusions. In this report we discuss the development of the SERS technique as a tool for monitoring hazardous chemical emissions and its application to in situ remote sensing.