Waveguide-enhanced Raman spectroscopy (WERS) enables the detection and identification of trace concentrations of vapor-phase analytes using a functionalized chip-scale photonic circuit. Here, we show that WERS signal can be collected from part-per-billion levels of targeted analytes in a backscatter geometry, which, compared to forward-scatter, simplifies component integration and is more tolerant of waveguide loss and modal interference. In addition, we discuss our progress towards a compact Raman sensing system that incorporates a handheld spectrometer and chip-scale optical filters. We demonstrate that a handheld, thermo-electrically cooled spectrometer can be used for backscatter WERS with a comparable signal-to-noise to that of a liquid-nitrogen cooled benchtop spectrometer. Finally, we describe efforts to integrate the dichroic Raman filter on-chip using arrays of unbalanced Mach-Zehnder interferometers. Measurements show filter performance sufficient for integration with WERS: Transmission of >80% of the laser in the cross port and Stokes signal in the through port; and extinction of the laser by >20 dB in the though port and of Stokes signal by >8 dB in the cross port.
The detection of chemical hazards on surfaces continues to be a challenge for the sensing community. In order to minimize risk to users, a desirable configuration is a non-contact (standoff) system, which can operate a safe distance from the hazard. A conceptual solution to this challenge is the Wide-Area Mapping and Identification (WAMId) system. The WAMId prototype breadboard combines two distinct technologies, hyperspectral imaging and standoff Raman spectroscopy, operating in tandem to locate and identify anomalous areas of interest and then presumptively identify surface contaminates. In the developed configuration, a single short to mid wave infrared (SWIR/MWIR) hyperspectral camera images a scene of interest, data is processed to locate anomalous materials and the resulting coordinates from the scene are uploaded to a gimbal control which then slews an 830 nm Raman system to perform presumptive identification measurements. In this work, we present the results of the program, to include system development, and sample testing data for three chemicals.
The US Army Research, Development and Engineering Command – Chem Bio center is leading an inter-agency working group, to expand chemical inkjet printing techniques, and to fabricate surface standards in a controlled, uniform and quantifiable fashion, for the evaluation of stand-off active and passive optical systems. A CommercialOff-the-Shelf (COTS) standard inkjet printer was redesigned to deposit precise amounts of chemicals and explosive material on defense relevant surfaces, allowing for the generation of calibration test standards. RDECOM-CB is currently utilizing the inkjet techniques to support an Army forensics detection program where inkjet samples are used for detection of trace energetic materials and illicit drugs of abuse within residual latent fingerprints, as well as leading a North Atlantic Treaty Organization (NATO) Task Group (TG) to develop and recommend to NATO a reference standard methodology (or methodologies) for fabricating quantifiable surface standards for the evaluation of stand-off active and passive optical systems. QA/QC were performed on printed materials to determine accuracy and precision. Raman imaging and the Image-J software package was used to calculate particle statistics such as size distribution, average particle size, and fill factor. The software algorithm finds individual particles and calculates their area from a brightfield image montage. An approximate diameter of each particle, and the total fractional area of the surface covered are also calculated. For qualitative analysis Raman Chemical Imaging is performed to confirm the chemical make-up of the deposited samples. For the quantitative analysis, printed samples were analyzed by either Ion Chromatography with Conductivity Detection (IC-CD) for potassium chlorate based explosives analysis or LC-MS/MS for RDX analysis. We will present the results of inkjet samples produced for the Army forensics program as well as NATO benchmark exercise that consisted of printing trace amounts of inkjet explosive samples and performing QA/QC procedures to determine accuracy, precision and mass transport efficiency.
The U.S. Army Research Development Engineering Command Chemical Biological Center (RDECOM C&B) continues to develop technologies for the forensic detection of energetic materials and illicit drugs of abuse due to their recent confluence in counter terrorism operations. One specific technology developed here is the use of Raman Chemical imaging to detect these substances located concomitant with residual latent fingerprints. This study demonstrates the ability to identify threat materials non-destructively so that the fingerprint remains intact for further biometric analysis. Utilizing Raman spectroscopy, the Generation I Chemical Fingerprint Identification System (CFIS) semi-autonomously locates and identifies particles of interest found on the friction ridge of a given recovered fingerprint with minimal input from the operator. This work presents results from a collaborative effort between the U.S. Defense Forensic Science Center (DFSC) and RDECOM C&B in which two prototype CFIS systems were assessed with a variety of samples and examines additional practical considerations leading toward the development of the next generation of expeditionary systems for military forensic analysis.
Matrix assisted laser desorption ionization (MALDI) is a powerful technique that improved the mass spectrometry (MS) characterization of biological molecules. However this technique requires the mixing of matrix compound with the analyte of interest. The matrix compound used in MALDI process is not universal and usually depends heavily on the nature of analyte of interest being analyzed. As such there are many matrices that are used and without knowing the nature of your analyte it will be hard to predict which matrix is optimal for the most effective MALDI-MS analysis. Moreover, a high energy laser exposure is needed to initiate the ionization process through a charge transfer process between the matrix and analyte molecules. Recent advancement in the metalorganic framework (MOF) field introduced desirable surfaces that can be modified for various applications. Such MOFs can be synthesized with porous solid, and could have regular or predicted geometry. This project is introducing a novel idea of utilizing a modified MALDI substrate with MOF that can provide charge transfer between immobilized functionalized groups and analyte molecules that mimic the solvation process when a solution matrix is used. Begin the abstract two lines below author names and addresses.
We present the methodology and results of a standard assessment protocol to evaluate disparate SERS substrates that
were developed for the Defense Advanced Research Programs Agency (DARPA) SERS Science and Technology
Fundamentals Program. The results presented are a snapshot of a collaborative effort between the US Army Edgewood
Chemical Biological Center, and the US Army Research Laboratory-Aldelphi Laboratory Center to develop a
quantitative analytical method with spectroscopic figures of merit to unambiguously compare the sensitivity and
reproducibility of various SERS substrates submitted by the program participants. We present the design of a common
assessment protocol and the definition of a SERS enhancement value (SEV) in order to effectively compare SERS active
We are actively investigating the use of Raman spectroscopy for proximal standoff detection
of chemicals and explosive materials on surfaces. These studies include Raman Chemical Imaging of
contaminated fingerprints for forensic attribution and the assessments of commercial handheld or
portable Raman instruments operating with near-infrared (IR) as well as ultraviolet (UV) laser
excitation specifically developed for on-the-move reconnaissance of chemical contamination. As
part of these efforts, we have measured the Raman cross sections of chemical agents, toxic industrial
chemicals, and explosives from the UV to NIR. We have also measured and modeled the effect
interrogation angle has on the Raman return from droplets on man-made surfaces. Realistic droplet
distributions have been modeled and tested against variations in surface scan patterns and laser spot
size for determining the optimum scan characteristics for detection of relevant surface
Ultraviolet resonance Raman spectroscopy (UVRRS) has been used to examine a variety of different isomers of
nitroaromatic molecules. Due to the large cross section enhancements possible, UVRRS has the potential to be a
sensitive means for detecting trace quantities of explosives at standoff distances. Since it probes both the electronic and
vibrational states of the molecules, it can also be a selective means for differentiating between similar molecules.
Resonance Raman spectra will be discussed, along with the different trends that are observed, for the different positional
isomers of dinitrobenzene. In addition, spectra for the common explosive 2,4,6-trinitrotoluene will be presented.
Wide-field Raman chemical imaging (RCI) has been used to detect and identify the presence of trace
explosives in contaminated fingerprints. A background subtraction routine was developed to minimize the
Raman spectral features produced by surfaces on which the fingerprint was examined. The Raman image was
analyzed with a spectral angle mapping routine to detect and identify the explosives. This study shows the
potential capability to identify explosives non-destructively so that the fingerprint remains intact for further