Richard John Lacey

Assessment of silver and gold substrates for the detection of amphetamine sulfate by surface enhanced Raman scattering (SERS)

Methods of detection of amphetamine sulfate using surface enhanced Raman scattering (SERS) from colloidal suspensions and vapour deposited films of both silver and gold are compared. Different aggregating agents are required to produce effective SERS from silver and gold colloidal suspensions. Gold colloid and vapour deposited gold films give weaker scattering than the equivalent silver substrates when high concentrations of drug are analysed but they also give lower detection limits, suggesting a smaller surface enhancement but stronger surface adsorption. A 10(-5) mol dm(-3) solution (the final concentration after addition of colloid was 10(-6) mol dm(-3)) of amphetamine sulfate was detected from gold colloid with an RSD of 5.4%. 25 microl of the same solution could be detected on a roughened gold film. The intensities of the spectra varied across the film surface resulting in relatively high RSDs. The precision was improved by averaging the scattering from several points on the surface. An attempt to improve the detection limit and precision by concentrating a suspension of gold colloid and amphetamine sulfate in aluminium wells did not give effective quantitation. Thus, positive identification and semi-quantitative estimation of amphetamine sulfate can be made quickly and easily using SERS from suspended gold colloid with the appropriate aggregating agents.

The first controlled reduction of the high explosive RDX

The first reduction chemistry of the high explosive RDX that allows subsequent functionalization into a SERRS active species.

X-RAY-SCATTERING SIGNATURES FOR MATERIAL IDENTIFICATION

X-ray scattering at low angles demonstrates diffraction effects that can be used to characterize materials. The effects of overlying material are shown not to affect the usefulness of the data for the identification of explosives. The important features in the scattering signature are identified.

Remote Detection Using Surface-Enhanced Resonance Raman Scattering

Surface-enhanced resonance Raman scattering (SERRS) provides intense Raman signals that are shown here to be stable in a target and to be detectable at least 10 meters from the spectrometer. The results indicate that SERRS labeling of objects and their detection at a distance with a low-power laser is feasible. Rhodamine and a dye specifically designed to give good surface adhesion, [4(5′-azobenzotriazyl)-3,5-dimethoxyphenylamine] (ABT DMOPA), were adsorbed onto silver particles and the particles dispersed in poly(vinyl acetate) (PVA) and varnish. SERRS from rhodamine was not detected from colloid dispersed either in PVA or varnish, presumably due to displacement of the dye from the silver surface. ABT DMOPA gave good SERRS. Maps of the SERRS intensity of films indicated variability of 10–20% if ultrasound was applied to improve dispersion during mixing. Scattering performance was evaluated using a system with the sample held up to one meter from the probe head. The intensity of the scattering from samples kept in the dark showed little change over a period of up to one year. However, when the samples were left in direct sunlight, the scattering intensity dropped significantly over the same period but could still be determined after eight months. An optical system was designed and constructed to detect scattering at longer distances. It consisted of a probe head based on a telephoto or CCTV lens that was fiber-optically coupled to the spectrometer. Effective detection of SERRS was obtained 10 m from the spectrometer using 3.6 mW of power and a 20 s accumulation time.

Characterization and identification of contraband using UV resonant Raman spectroscopy

A range of explosives and narcotics have been examined using Raman spectroscopy with 244 nm excitation. This wavelength of excitation eliminates the fluorescence problems associated with excitation at visible wavelengths. Comparison with spectra obtained using visible excitation reveals that resonance Raman scattering is occurring. This results in simplified spectra, and enhanced Raman scattering efficiencies.

Optimization of a low-angle x-ray scatter system for explosive detection

Coherent scatter measurements have been shown to be a potentially useful tool in the detection of energetic materials. The relationship between explosive volume, method of concealment, environment, and resulting threat has been considered in the design of our energy dispersive low angle x-ray scatter system. The principle application of the system is for the detection of explosives concealed within passenger luggage in sheet form. The effects of parameters such as scattering angle, beam collimation, explosive material geometry, overlying materials and counting statistics have been measured experimentally and comparison made with theoretical prediction. It has been found that: 1) scatter signature analysis dictates optimum scattering angles for different explosives, and 2) partial volume effects must be combined with scatter angles to give total system optimization.

Computational Design and Fabrication of Optical Fibre Fluorescent Chemical Probes for the Detection of Cocaine

A rationally designed fluorophore has been developed and has been incorporated into molecularly imprinted polymers, as the basis of the design of a sensor. Its use has allowed the fabrication of two different designs of fibre-optic chemical probes using an approach based on the change of the emitted fluorescence being related to the concentration of the desired species that was present. A high sensitivity to the drug Cocaine was achieved with each of the probes, showing positive changes in the fluorescence signal achieved in response to 1-100 μM solutions of the drug, in solution in aqueous acetonitrile. High sensitivity for Cocaine over a range of compounds was demonstrated for one of the probes (probe X) and detection of the drug is possible even in the presence of strong fluorescence interference. The work has also shown that probes of this type do not need to be discarded when used: re-use of probe X is possible using a straightforward washing procedure and the calibration performance was maintained.

Real time analysis of scattered x-ray spectra for sheet explosives detection

The use of multivariate calibration for the real time analysis of energy dispersive x-ray scatter profiles is being investigated. The requirements of a practical baggage scanner necessitate rapid interrogation and an analysis procedure is required that can differentiate between spectral structure in diffraction profiles in very noisy data. Multivariate analysis has been successfully used to identify sheet explosives in cases with acquisitions as low as several hundred counts. Two detector systems, a high resolution HPGe detector and a room temperature CdZnTe detector, have been used. The precision of the model predictions are highly dependent upon the detector system used producing a significantly smaller error with the high resolution detector.

Is the holy grail plastic? Radiation Identification from plastic scintillators

Radiation monitoring at national borders is becoming more common place and so efforts to reduce the burden of false positives (or nuisance alarms) at checkpoint operations without reducing the ability to detect potential threats is now a key objective for many nations. Plastic scintillators are relatively cheap to deploy in large volumes, are rugged and sensitive to a range of gamma energies. However, at present, plastic detectors that are available for deployment for security applications provide only minimal or no energy discrimination as the response to gamma radiation is primarily via Compton scattering so photopeaks are usually not visible. Thousands of shipping containers containing Naturally Occurring Radioactive Materials (NORM) made from ceramics, stoneware and other natural products are transported worldwide on a daily basis. Some of these NORM loads are sufficiently radioactive to trigger alarms from plastic scintillator detectors which have limited ability to also identify the radionuclides present thus necessitating secondary inspection which increases the operational overhead. Previous studies have been carried out to ascertain if radionuclide discrimination using plastic scintillators is possible with a variety of approaches including deconvolution and computer learning. In this paper, a two stage algorithm is described. An example implementation of the algorithm is presented, applied to operational data, and has been installed in real time operation on a polyvinyltoluene (PVT) detector.

Design and synthesis of a fluorescent molecular imprinted polymer for use in an optical fibre-based cocaine sensor

Previously, we have developed chemical sensors using fibre optic-based techniques for the detection of Cocaine, utilising molecularly imprinted polymers (MIPs) containing fluorescein moieties as the signalling groups. Here, we report the computational design of a fluorophore which was incorporated into a MIP for the generation of a novel sensor that offers improved sensitivity for Cocaine with a detection range of 1-100μM. High selectivity for Cocaine over a suite of known Cocaine interferants (25μM) was also demonstrated by measuring changes in the intensity of fluorescence signals received from the sensor.