Christa L. Brosseau

Portable Electrochemical Surface-Enhanced Raman Spectroscopy System for Routine Spectroelectrochemical Analysis

A simple, portable electrochemical surface-enhanced Raman spectroscopy (SERS) system is reported, consisting of a small benchtop Raman spectrometer, a laptop computer, and a portable USB potentiostat. Screen printed electrodes modified with silver colloidal nanoparticles are used as the SERS-active electrode, which exhibit long-term stability once prepared. Spectroelectrochemical analyses of para-aminothiophenol and melamine as model systems was conducted. In both cases, an increase in SERS signal is observed upon modulation of the applied voltage, indicating an inherent benefit of such a system wherein the surface charge can be easily tuned. Given the low cost, rapid analysis time, and good sensitivity of this system, this simple setup could be implemented for many on-site sensing applications, ranging from food and drug analysis to environmental monitoring and to chemical and biological warfare agent detection.

A simple complex on the verge of breakdown: Isolation of the elusive cyanoformate ion

Cyanide Hitches a Ride Cyanide is a by-product of the biosynthesis of ethylene in plants and it has been somewhat puzzling how the ion is safely removed before it can shut down enzymatic pathways by coordination to catalytic iron centers. A proposed mechanism has implicated the cyanoformate ion—essentially, a weak adduct of cyanide and carbon dioxide—as the initial product, although its lifetime was uncertain. Murphy et al. (p. 75; see the Perspective by Alabugin and Mohamed) crystallized this previously elusive adduct and found that its solution-phase stability varies inversely with the dielectric properties of the medium. The results bolster a picture in which the adduct shuttles the cyanide away from the hydrophobic confines of the enzyme before releasing the cyanide into the more polar aqueous surroundings. Characterization of a cyanide–carbon dioxide adduct bolsters its possible role in protecting a plant enzyme from cyanide inhibition. [Also see Perspective by Alabugin and Mohamed] Why does cyanide not react destructively with the proximal iron center at the active site of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, an enzyme central to the biosynthesis of ethylene in plants? It has long been postulated that the cyanoformate anion, [NCCO2]–, forms and then decomposes to carbon dioxide and cyanide during this process. We have now isolated and crystallographically characterized this elusive anion as its tetraphenylphosphonium salt. Theoretical calculations show that cyanoformate has a very weak C–C bond and that it is thermodynamically stable only in low dielectric media. Solution stability studies have substantiated the latter result. We propose that cyanoformate shuttles the potentially toxic cyanide away from the low dielectric active site of ACC oxidase before breaking down in the higher dielectric medium of the cell.

Development of a SERS-Based Rapid Vertical Flow Assay for Point-of-Care Diagnostics

Point-of-care (POC) diagnostic testing platforms are a growing sector of the healthcare industry as they offer the advantages of rapid provision of results, ease of use, reduced cost, and the ability to link patients to care. While many POC tests are based on chromatographic flow assay technology, this technology suffers from a lack of sensitivity along with limited capacity for multiplexing and quantitative analysis. Several recent reports have begun to investigate the feasibility of coupling chromatographic flow platforms to more advanced read-out technologies which in turn enable on-site acquisition, storage, and transmission of important healthcare metrics. One such technology being explored is surface-enhanced Raman spectroscopy or SERS. In this work, SERS is coupled for the first time to a rapid vertical flow (RVF) immunotechnology for detection of anti-HCV antibodies in an effort to extend the capabilities of this commercially available diagnostic platform. High-quality and reproducible SERS spectra were obtained using reporter-modified gold nanoparticles (AuNPs). Serial dilution studies indicate that the coupling of SERS with RVF technology shows enormous potential for next-generation POC diagnostics.

Surface-enhanced Raman spectroscopy analysis of house paint and wallpaper samples from an 18th century historic property

Conservation efforts for heritage buildings require a substantial knowledge of the chemical makeup of materials that were used throughout the lifetime of the property. In particular, conservators are often concerned with the identification of colorants used in both interior and exterior wall treatments (paint, wallpaper, etc.) in order to gain perspective into how the building may have appeared during a certain time period in its existence. Ideally, such an analysis requires a technique that provides molecular level information as to the identity of the colorant as well as other sample components (binders, fillers, etc.), which is useful for dating purposes. In addition, the technique should be easily applied to paint layer samples which can be extremely thin and fragile. Herein we report the surface-enhanced Raman spectroscopy (SERS) analysis of paint and wallpaper samples taken from exterior and interior surfaces of a historic building. Several pigments were identified in the samples, which ranged from early inorganic pigments (lead white, barium sulfate, calcium carbonate, anhydrous chromium(III) oxide) which have been used in house paints for centuries, to a more modern pigment (phthalocyanine blue), developed in the middle of the 20th century. This analysis highlights the usefulness of SERS in such a conservation effort, and demonstrates for the first time pigment identification in house paints and wallpaper using SERS, which has far-reaching implications not only in the field of conservation, but also in forensics, industrial process control, and environmental health and safety.

Electrochemical Surface-Enhanced Raman Spectroscopy as a Platform for Bacterial Detection and Identification

The field of bacterial screening is in need of a rapid, easy to use, sensitive, and selective platform for bacterial detection and identification. Current methods of bacterial identification lack time efficiency, resulting in problems for many sectors of society. Surface-enhanced Raman spectroscopy (SERS) has been investigated as a possible candidate for bacterial screening due to its demonstrated ability to detect biological molecules with a high degree of sensitivity. However, the field of bacterial screening using SERS is currently facing limitations such as signal irreproducibility, weak spectra, and difficulty differentiating between strains based on the SERS spectra of bacteria alone. The current study reports on the first ever use of electrochemical surface-enhanced Raman spectroscopy (EC-SERS) for bacterial screening. The results of this study demonstrate the ability of EC-SERS to greatly improve upon the SERS performance for the detection of Gram-positive and Gram-negative bacteria both in terms of improved peak intensities and spectral richness. EC-SERS shows great promise in its ability to advance SERS-based bacterial screening and could potentially be used for more efficient species discrimination at the point-of-need (PON).