Keith T. Carron

Surface-Enhanced Raman Scattering Detection of Amphetamine and Methamphetamine by Modification with 2-Mercaptonicotinic Acid

We have demonstrated the use of surface-enhanced Raman scattering (SERS) spectroscopy for the detection of the phenylalkylamines amphetamine and methamphetamine. This work can be viewed as the first phase of development toward a one-step drug detection method with a selective reactive coating on a SERS substrate. This work involves a fairly complicated coupling reaction prior to surface derivatization. Future efforts will be directed at creating a reactive coating directly on the surface. The amines were derivatized by a coupling reaction with 2-mercaptonicotinic acid (2-MNA) with the use of dicyclohexylcarbodiimide (DCC) as the coupling reagent to form the amide compounds AMNA [N-(1-methyl-2-phenylethyl)-2-mercaptopyridine-3-carboxamide] and MMNA [N-methyl-N-(1-methyl-2-phenylethyl)-2-mercaptopyridine-3-carboxamide]. The amides were qualitatively identified from SERS spectra. Quantification of the amides was accomplished by adding the internal standard pentachlorothiophenol (PCTP) and measuring the intensity of Raman bands of the analyte relative to a Raman band of the internal standard. Calibration curves were plotted of the relative peak intensity ratios as a function of analyte concentration. Detection limits of 19 ppm and 17 ppm were found for amphetamine/2-MNA (AMNA) amide and methamphetamine/2-MNA (MMNA) amide, respectively.

Qualitative analysis and the answer box: a perspective on portable Raman spectroscopy.

Miniaturization of Raman instruments has created a new genre of devices for qualitative analysis of materials. These new devices are introducing Raman spectroscopy to a diverse range of applications.

Stability and Surface Uniformity of Selected Thiol-Coated SERS Surfaces:

The use of surface-enhanced Raman scattering (SERS) as an analytical technique continues to grow, but questions about its viability remain. This paper addresses the concern about the long-term stability of the surfaces used with the SERS technique. We have studied the long-term stability of Ag surfaces coated with three different thiol compounds. For this study, we have used 1-propanethiol, 1-do-decanethiol, and p-cresolthiol to coat the Ag surfaces. These surfaces showed long-term stabilities of over a month with minimal surface degradation. In order to mimic a realistic application of SERS, we stored the coated surfaces in a solution of water. Sodium dodecylsulfate (SDS) was added to maintain consistent surface wetting conditions so that reproducible results were obtainable on a day-to-day basis. Spatial heterogeneity of the surfaces and coating was analyzed with a fiber-optic Raman system. The spatial heterogeneity of the surfaces explains the day-to-day variations observed in the detection when the same portion of the surface used for analysis varies from day to day.

Lab-on-a-Bubble Surface Enhanced Raman Indirect Immunoassay for Cholera

We describe a novel sandwich assay based on surface enhanced Raman scattering (SERS) comprised of buoyant silica microspheres coated with antibodies against the β subunit of the cholera toxin (CT), and gold nanoparticles tagged with a Raman reporter, shelled with silica and coated with antibodies against the β subunit of the CT. Together these components couple to form a sandwich which, after incubation, floats on the surface of the sample. The buoyant silica microparticle/nanoparticle reporter combination has been coined a lab on a bubble (LoB). LoB materials may provide a platform for rapid detection of antigen in solution and offers advantages over lateral flow or magnetic pull-down assays. The Raman reporter provides a unique and intense signal to indicate a positive analysis. Our limit of detection for the β subunit of the CT in a buffer based system is 1100 ng.

SERS and XPS studies of the molecular orientation of thiophenols from the gaseous state onto silver

Abstract Formation of monolayer films by the spontaneous assembly of thiophenol and 4-chlorothiophenol adsorbed from their gaseous states was monitored by surface-enhanced Raman scattering (SERS) and X-ray photoelectron spectroscopy (XPS). SERS, XPS, and contact-angle measurements indicate that the films adsorbed from gaseous thiols are well oriented.

Surface-enhanced Raman scattering and cyclic voltammetry studies of synergetic effects in the corrosion inhibition of copper by polybenzimidazole and mercaptobenzimidazole at high temperature

The inhibition of copper corrosion by polybenzimidazole and mercaptobenzimidazole at room and high temperature was assessed by in situ surface-enhanced Raman scattering (SERS) and cyclic voltammetry (CV). It was found that a very compact protective layer, produced by immersion in polybenzimidazole and mercaptobenzimidazole mixture solutions, showed better anticorrosive performance than each single inhibitor component even at high temperatures. This synergetic effect of the two components was explained by the physico-chemical mechanism of corrosion inhibition of polymeric coatings. Meanwhile, the results implied that the SERS active substrate prepared by the HNO3 etching method was particularly useful for in situ characterization of many problems in high-temperature surface chemistry which otherwise could not be accomplished by the usual SERS active substrates.

Surface-enhanced Raman assays (SERA): measurement of bilirubin and salicylate

Results of a study to detect bilirubin and salicylate using SERS and a reactive coating are presented. The motivation for this work was to devel to develop an assay that would simplify an analysis by detecting the analyte in a whole blood sample. This would remove the risks and time associated with preparing a serum sample. Quantitative analysis was performed using partial least-squares. The results are that one can detect bilirubin and salicylate in whole blood at levels below the normal or therapeutic levels using a coating based on an argentiphilic diazonium molecule. The sharp Raman bands associated with the analyte–coating adduct are sufficiently resolved to allow the analyte to be detected in the presence of a complex matrix such as whole blood. Copyright

Selective-Ultratrace Detection of Metal Ions with SERS

We report the results from experiments involving the detection of metal ions with a Surface-Enhanced Raman Spectroscopic indicator (SERS indicator). Comparisons of metals showed that the SERS effect can be used to selectively detect metal ions according to their ionic radius. We determined a resolving power for separating the alkaline earth series. The results indicate that the resolving power of the SERS approach is superior to that of absorption spectroscopy. Quantitatively, under our experimental conditions, we found a detection limit of 270 ppb for Pb2+ and 85 ppb for Cu2+ with the indicator Eriochrome Black T.

From portable Raman to mobile Raman: the progression of Raman spectroscopy

Over the past 15, Raman systems have evolved from benchtop analyzers interfaced with a laptop computer to a smart phone based sensor. The journey from the first handheld system to newly developed smartphone-based Raman sensors is presented. Combining a Raman sensor with a smartphone enables advanced processors and cloud computing, greatly expanding Raman capabilities. We will discuss a range of applications, from process to security.

New designs for portable Raman instrumentation in defense applications

The realization of global terrorism after the September 11 attacks led immediately to a need for rapid field analysis of materials. Colorimetric test kits existed, but they are very subjective to interpret and they require contact with the sample. A push for handheld spectrometers quickly led to FTIR systems with ATR sampling, handheld IMS systems, and handheld Raman spectrometers. No single technique solves all of the problems of field detection. We will discuss the development of Raman instrumentation and, in particular, cover the advantages and the problems that are inherent in Raman portability. Portable Raman instrumentation began with a limited number of accessories: a point-and-shoot and some sort of vial adaptor. Currently this has expanded to stand-off attachments for measurements at a distance, air sampling to look for toxic gasses or aerosols, Orbital Raster Scan (ORS) to spatially average over samples, SERS attachments for trace detection, and fiber optic probes.The realization of global terrorism after the September 11 attacks led immediately to a need for rapid field analysis of materials. Colorimetric test kits existed, but they are very subjective to interpret and they require contact with the sample. A push for handheld spectrometers quickly led to FTIR systems with ATR sampling, handheld IMS systems, and handheld Raman spectrometers. No single technique solves all of the problems of field detection. We will discuss the development of Raman instrumentation and, in particular, cover the advantages and the problems that are inherent in Raman portability. Portable Raman instrumentation began with a limited number of accessories: a point-and-shoot and some sort of vial adaptor. Currently this has expanded to stand-off attachments for measurements at a distance, air sampling to look for toxic gasses or aerosols, Orbital Raster Scan (ORS) to spatially average over samples, SERS attachments for trace detection, and fiber optic probes.