John W. Haas

Determination of nicotine by surface-enhanced Raman scattering (SERS)

The analytical application of surface-enhanced Raman spectroscopy (SERS) to the determination of nicotine is demonstrated. A simple spectroelectrochemical method using a copper or silver electrode as the SERS substrate has been developed, consisting of three steps: polishing a working electrode to a mirror finish; roughening the electrode in an electrolyte solution; and, finally, depositing the nicotine analyte onto the roughened electrode after immersion in a sample solution. During the reduction cycle, a large enhancement in nicotine Raman scattering is observed at the electrode surface. The intensity of the SERS signal on a silver electrode is linear with concentration from 10 to 900 ppb, with an estimated detection limit of 7 ppb. The total analysis time per sample is approximately five minutes. This procedure has been used to analyze the extract from a cigarette side-stream smoke sample (environmental tobacco smoke); the SERS results agree well with those of conventional gas chromatographic analysis.

Surface-Enhanced Raman Detection of Aqueous Cyanide

Cyanide ion (CN−) has been the subject of numerous studies probing the mechanisms underlying the surface-enhanced Raman scattering (SERS) phenomenon. This work examines various aspects critical to application of SERS for direct detection of trace cyanide in groundwater and in wastewater streams. A new method for direct quantitation of cyanide in aqueous electrolyte has been developed that uses an ex situ oxidation-reduction cycle to precondition a planar silver electrode. Cyanide ion can be detected in 0.1 M KCl with a linear response between 100 ppm and 10 ppb. The estimated limit of detection is approximately 8 ppb. The effects of pH, electrolyte level, and two common background ions, nitrate (NO3−) and sulfate (SO42–), have been characterized. Cyanide response was found to be sensitive to pH, with optimal performance observed at neutral to basic pH. Electrolyte concentrations of 0.001 M reduced response to cyanide by a factor of five, while levels above 0.1 M had no significant effect. The addition of 10-ppm sulfate ion decreased response approximately 40%, while the presence of nitrate ion at concentrations up to 100 ppm had a negligible effect on SERS response. These results suggest that cyanide ion can be detected directly in high-ionic-strength aqueous solutions, such as groundwater.

SURFACE ENHANCED RAMAN-SCATTERING FROM MILDLY ROUGHENED SURFACES - VARIATION OF SIGNAL WITH METAL GRAIN-SIZE

Abstract The intensity of surface enhanced Raman scattering from benzoic acid derivatives on mildly roughened, thermally evaporated Ag films shows a remarkably strong dependence on metal grain size. Large grained (slowly deposited) films give a superior response, by up to a factor of 10, to small grained (quickly deposited) films, with films of intermediate grain size yielding intermediate results. The optical field amplification underlying the enhancement mechanism is due to the excitation of surface plasmon polaritons (SPPs). Since surface roughness characteristics, as determined by STM, remain relatively constant as a function of deposition rate, it is arged that the contrast in Raman scattering is due to differences in elastic grain boundary scattering of SPPs (leading to different degrees of internal SPP damping), rather than differences in the interaction of SPPs with surface inhomogeneities.

Spectroelectrochemical technologies and instrumentation for environmental and process monitoring

The importance of techniques to sense and monitor the environment are becoming increasingly more important with the intensifying presence of groundwater and soil contaminations. Our research and development effort is aimed at producing a commercial, low cost, field portable instrument for the field screening/in situ monitoring of contamination from organic solvents based on the principle of combining spectroscopic, electrochemical, and fiber optic techniques. Some of the advantages of this technique for monitoring a contamination site are cost, small size of sampling probe, real-time analysis, the capability of sensing in adverse environments, and the ability of using a central detection facility. The technique has an advantage over current integrating fiber optic chemical sensing methods in that the sensing only takes place when the electrochemical device is turned on. This should enable long-term monitoring of a site to be accomplished with only one probe/instrument system.

Surface-enhanced Raman sensor for nitroexplosive vapors

Surface-enhanced Raman scattering has been measured for solutions of 2,4-dinitrotoluene (2,4-DNT), trinitrotoluene (TNT), and hexahydro-1,3,5-trinitro-s-triazine (RDX) adsorbed onto metal foils, island films, coated microspheres, and colloids. The wavelength selectivity of the method was also investigated for lasers which potentially may be used in a field instrument. Preliminary room temperature vapor-phase SERS detection of 2,4-DNT adsorbed on gold foil has been achieved. The results demonstrate the potential of SERS as a detector of buried landmines when coupled to compact man- portable Raman instrumentation.

Multimode ionization cell for gas chromatographic detection

A user‐selectable, multimode, beta‐ionization cell has been developed for gas chromatographic (GC) detection. The system consists of a modified dc current (nonpulsed) electron capture cell enclosed in a stainless‐steel vacuum chamber. A gas mixing manifold connected to the input of the detector enables various reagent gases to be mixed with the GC effluent prior to entering the detector cell. Simply by varying the pressure of the reagent gas inside the detector from atmospheric to as low as 50 mTorr, one of four different modes of operation can be achieved. These include (1) conventional electron capture detection (atmospheric pressure), (2) cross‐section ionization electron emission (<1 Torr), (3) low‐pressure argon ionization electron emission (1–10 Torr), and (4) mixed electron capture/electron emission (100–300 Torr). One advantage of this detector is the ability to switch between selective detection (electron capture) and universal detection (argon ionization) by only changing the operating pressure ...

LONG-TERM MONITORING SENSOR NETWORK

Long-term monitoring (LTM) associated with subsurface contamination sites is a key element of Long Term Stewardship and Legacy Management across the Department of Energy (DOE) complex. However, both within the DOE and elsewhere, LTM is an expensive endeavor, often exceeding the costs of the remediation phase of a clean-up project. The primary contributors to LTM costs are associated with labor. Sample collection, storage, preparation, analysis, and reporting can add a significant financial burden to project expense when extended over many years. Development of unattended, in situ monitoring networks capable of providing quantitative data satisfactory to regulatory concerns has the potential to significantly reduce LTM costs. But survival and dependable operation in a difficult environment is a common obstacle to widespread use across the DOE complex or elsewhere. Deploying almost any sensor in the subsurface for extended periods of time will expose it to chemical and microbial degradation. Over the time-scales required for in situ LTM, even the most advanced sensor systems may be rendered useless. Frequent replacement or servicing (cleaning) of sensors is expensive and labor intensive, offsetting most, if not all, of the cost savings realized with unattended, in situ sensors. To enable facile, remote monitoring of contaminants and other subsurface parameters over prolonged periods, Applied Research Associates, Inc has been working to develop an advanced LTM sensor network consisting of three key elements: (1) an anti-fouling sensor chamber that can accommodate a variety of chemical and physical measurement devices based on electrochemical, optical and other techniques; (2) two rapid, cost effective, and gentle means of emplacing sensor packages either at precise locations directly in the subsurface or in pre-existing monitoring wells; and (3) a web browser-based data acquisition and control system (WebDACS) utilizing field-networked microprocessor-controlled smart sensors housed in anti-fouling sensor chambers. The monitoring network is highly versatile and can be applied to a variety of subsurface sensing scenarios in different media. However, the current project focused on monitoring water quality parameters of pH, oxidation-reduction potential, conductivity, and temperature in groundwater.

Surface-enhanced Raman scattering from mildly roughened surfaces: influence of metal grain size on signal

The intensity of surface enhanced Raman scattering (SERS) from benzoic acid and benzoic acid derivatives on mildly roughened, thermally evaporated Ag films shows a strong dependence on the rate at which the Ag film was deposited. Slowly deposited Ag films give a superior SERS response, by up to a factor of 10, to quickly deposited films, with films deposited at an intermediate rate yielding intermediate results. Careful examination using STM indicates that little distinction can be made between the differently prepared films in terms of surface roughness. By contrast TEM measurements reveal that the average metal grain dimension in slowly deposited Ag films is about 3-4 times greater than that in their quickly deposited counterparts. On the premise that the fundamental excitation of importance to the enhancement mechanism is the surface plasmon polariton (SPP) it is argued that the contrast in Raman scattering efficiency is due to differences in elastic grain boundary scattering of SPPs (leading to different degrees of internal SPP damping), rather than differences in the interaction of SPPs with surface inhomogeneities. Corollary data on elastic SPP-photon scattering obtained in a related experiment are also presented.

Advances in surface-enhanced Raman spectroscopy for hazardous waste monitoring

Surface-enhanced Raman spectroscopy is being evaluated for use as an advanced method for detecting organic contaminants in groundwater during field-screening of environmental samples. The SERS technique offers attractive and unique capabilities for detecting a wide range of organic contaminants in aqueous environments at ppm to ppb levels. An inexpensive computer-controlled portable spectrometer system coupled to a fiberoptic probe has been developed for rapid on-site and in situ determination of organic contamination in groundwater. Applications of recent advances in substrate fabrication for use with environmental samples are discussed, and critical issues pertaining to substrate durability, repeatability, sensitivity, selectivity and universality are addressed.

Pedestrian dead reckoning using a novel sensor module that interfaces with modern smart devices

Tracking individuals in areas such as dense urban environments and building interiors is desirable for numerous critical applications, but has been problematic mainly because of the unreliability or unavailability of GPS in many locations of interest. To date, tracking applications that utilize inertial sensors within smart devices have had varied degrees of success: accuracy typically dips below that of standard GPS within minutes and depends strongly on the quality of the sensors in the device, as well as the location that the device is carried on the body. In this paper we present a sensor module that interfaces with modern smart devices and which utilizes a low-cost, commercial-off-the-shelf, 9-axis IMU and pressure sensor to provide an advanced pedestrian dead reckoning solution. The sensor module is designed to communicate with the smart device (e.g., iOS, Android or Windows) via the audio jack and is intended for use as a beltmounted pedestrian tracker. In addition to describing the device hardware and functionality, we present our approach to processing the sensor module data streams to determine a user’s position. Results using the prototype sensor module in operationally relevant scenarios is presented and discussed.