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This paper examines infrared spectroscopic effects for the standoff detection of an explosive material, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), inkjet printed on an aluminum surface. Results of a spectroscopic study are described, using multiple optical setups. These setups were selected to explore how variations in the angles of incidence and collection from the surface of the material result in corresponding variations in the spectral signatures. The goal of these studies is to provide an understanding of these spectral changes since it affects standoff detection of hazardous materials on a reflective substrate. We demonstrate that variations in spectral effects are dependent on the relative surface concentration of the deposited RDX. We also show that it is reasonable to use spectroscopic data collected in a standard laboratory infrared spectrometer outfitted with a variable angle reflectometer set at 0° as reference spectra for data collected in a standoff configuration. These results are important to provide a systematic approach to understanding infrared (IR) spectra collection using standoff systems in the field, and to allow for comparison between such data, and data collected in the laboratory. Although the precise results are constrained to a specific material system (thin layers on a reflective substrate), the approach and general discussion provided are applicable to a broad range of IR standoff sensing techniques and applications.

Approaches to provide chip-scale aqueous chemical sensing for environmental and health monitoring via a photonic integrated circuit (PIC) technology are showing promise. To meet future U.S. Army demand, we have investigated waveguide structures compatible with feature sizes offered by modern mass-manufacturing PIC foundries. We have found that wide subwavelength grating (SWG) waveguide structures can maximally interact with an encapsulating analyte capture material with low propagation loss. We describe the analyte/light interaction component of our general integrated photonics chemical detector sensitivity model and use it to compare the effectiveness of waveguide geometries for sensing. The structures we have investigated afford superior detection to strip and slot waveguides. Finally, we introduce a novel tapered SWG waveguide geometry with improved transmission and similar sensitivity to nontapered SWG designs.

Color vision results from the interaction of retinal photopigments with reflected or transmitted visible light. The International Commission on Illumination (CIE) developed the CIE color-matching chart, which separates colors on the basis of the interaction of their spectral profiles with three retinal photopigments in the human eye. We report the development of an infrared chromaticity (CIE-IR) chart, which mimics the CIE chart, in order to discriminate between different chemicals on the basis of the interactions of their IR signatures with three different IR optical filters, instead of the retinal photopigments in the human eye. Our results demonstrate that the CIE-IR chart enables separation of different classes of chemicals, as the visible CIE chart does with color, except for those in the IR spectral region. Such results clearly show that the biomimetic sensing method based on human color vision is in fact a true analogue to color vision and that the proposed CIE-IR chart can be used as a classification method unique to this biomimetic sensing modality.

Infrared spectroscopy is a powerful laboratory technique for detection of and discrimination between hazardous chemical threats, such as explosive materials, and non-hazardous background chemicals. Transitioning this method to the field however has significant challenges, especially when being deployed as a standoff, or proximate standoff technique. The main issue for proximate standoff detection lies in the ability of a system to collect enough reflected light from a source illuminating a surface to provide chemical information for the target material. This issue is further exacerbated when trying to detect highly scattering materials on surfaces, such as particulates or powders, which are typical forms for explosive materials. While diffuse reflectance from such materials provides good chemical vibrational absorption band information, when being collected at some distance away from the sample, this scattering provides a significant detection challenge. We present detection results for highly scattering inkjet printed explosive standards, collected at proximate standoff distances (~ 0.5 m) in a laboratory environment. Discrimination between these standards using both conventional infrared spectroscopy, as well as NRL’s unique optical filter based biomimetic sensing approach are discussed. This work is meant to inform the rational development of portable infrared optical sensors for detection of explosives at proximate distances in operational environments.

Sweat provides direct information of the real-time emotional and cognitive state of the subject, with applications ranging from situational awareness and mission effectiveness of armed forces to disease diagnosis for clinicians. Development of a broad class of human performance monitoring devices to quantify sweat biomarkers necessitates non-invasive, real-time monitoring of ultra-low concentrations (μM to fM) of hormones, proteins, and neurotransmitters. Field effect transistors are the predominant sensor approach whereby the gate electrode is modified with a selective bio-recognition element (BRE). However, FETs have diminished sensitivity in high ionic strength environments associated with sweat. Alternatively, BRE-modified photonic integrated circuits (PICs) have high sensitivity in high ionic strength fluids, low cost at the manufacturing scale, and enable a number of novel device concepts to achieve ultra-low levels of detection. One major technological challenge is to predict the limit of detection (LoD), or sensor response function, for a particular PIC geometry in a microfluidic chamber. LoD is highly dependent on analytic capture efficiency, fluid dynamics and affinity, analyte/light interaction, and analyte concentration. This work presents finite element simulations to emulate microfluidic BRE sweat sensors and provide a predictive limit of detection for different sensing structures or elements. Specifically, the optimum mass transfer and kinetics for sensing approaching single molecule detection is discussed, including flow characteristics, biomarker size, adsorption and desorption kinetics, and sensor geometry. Key metrics include capture efficiency (molecules being captured over molecules entering channel ), time to reach steady state, and temporal adsorption site occupancy to predict PIC system LoD. It is found that these systems are kinetically controlled, with capture efficiencies remaining below 1% even for kads/kdes ratios of 1010 . The need for adsorption kinetics measured for flow systems instead of stationary fluid systems is stressed, as these parameters are what need to be optimized to greatly increase analyte capture.

Wearable biosensors have emerged as an advancement in the field of performance and threat monitoring in part due to the potential to overcome the limits of conventional soldier health monitoring and environmental sensing technologies. However, to transition these devices to universal use, several challenges like selectivity, sensitivity, stability, level of invasivity, and efficient sample handling must be overcome. Additionally, discovery of novel biomarker and correlation to performance for current and emerging threats should continue. We introduce the integration of a synthetic and biomimetic xerogel layer onto a photonic chip, for the stable and selective monitoring of targeted soldier performance biomarkers. The molecularly imprinted polymer (MIP) material has been optimized for selection and capture of the human stress hormone cortisol, and a proof-of-principle experiments will be discussed. This sensor can be integrated onto a wearable diagnostics platform, thus potentially providing real-time monitoring of stress, and other biomarkers, in commonly accessed fluids like sweat.

Laser-Based Optical Detection of Explosives offers a comprehensive review of past, present, and emerging laser-based methods for the detection of a variety of explosives. This book: Considers laser propagation safety and explains standard test material preparation for standoff optical-based detection system evaluation Explores explosives detection using deep ultraviolet native fluorescence, Raman spectroscopy, laser-induced breakdown spectroscopy, reflectometry, and hyperspectral imaging Examines photodissociation followed by laser-induced fluorescence, photothermal methods, cavity-enhanced absorption spectrometry, and short-pulse laser-based techniques Describes the detection and recognition of explosives using terahertz-frequency spectroscopic techniques Each chapter is authored by a leading expert on the respective technology, and is structured to supply historical perspective, address current advantages and challenges, and discuss novel research and applications. Readers are left with an in-depth understanding and appreciation of each technology’s capabilities and potential for standoff hazard detection.

Grating waveguide structures have the opportunity to greatly improve photonic integrated circuit sensor sensitivity. We have examined the impact of wide subwavelength grating waveguide geometries on sensor performance. We present the progress of our design exploration and compare performance to existing slot and strip waveguide structures.

Development of a sensor consisting of a molecularly imprinted polymer integrated onto a photonic chip is discussed. This sensor has applications for threat detection, including current known and emerging hazards, and chemical and biological material via target specific sensing, concentrating and filtering. The photonic device that the MIP is integrated onto allows for the measurement of small quantities of target material, thus demonstrating potential application to materials like acute toxic chemicals or even low-incidence high-consequene pathogens. This paper highlights the recent early work to progress this capability focusing on MIP development for deposition onto a photonic sensing chip.

Field detection of chemical, biological, radiological, nuclear and explosive (CBRNE) threats requires the development of highly selective sensors with low size, weight, power and cost (SWaP-c). Recent developments have demonstrated that an optical biomimetic sensing approach, based on human-eye color detection can provide high-confidence discrimination of target chemicals while rejecting potential interferents with similar chemical structures. This biomimetic sensing method operates by identifying differences in the overlap between target and interferent chemical infrared absorption bands utilizing three, overlapping, optical bandpass filters. This method is non-spectroscopic and requires only the use of commercially available, off-the-shelf optical components. This approach has been demonstrated for volatile chemical vapors in the mid-wave-infrared (3 – 5 μm). Based on this success, experimental studies of this biomimetic sensing approach have been expanded further into the long wave infrared spectral region (6 – 12 μm) and for detection of explosives on surfaces, including aluminum and plastics. We present discrimination results using this biomimetic sensing approach for explosive samples on surfaces in both the mid- and long- wave infrared. Numerical data, along with experimentally collected data, are discussed. We demonstrate that this method is capable of discriminating between similar explosives on surfaces as well as between these explosives and potential environmental interferents. We present the results of these experiments and discuss potential transition of this approach to future field-ready stand-off devices and applications.

Recent advances in subwavelength grating (SWG) structures have shown promise in sensing applications. Though prior sensors have obtained high index sensitivities, their designs have not focused on providing strong analyte/light interaction efficiency for low analyte concentration flows. We have explored high-contrast grating “fish-bone” and segmented SWG structures in the hopes of improving this aspect. We present below the progress of our design exploration of these structures and compare their performance to a typical slot waveguide to understand their impact on spectral transmission and analyte interaction. The best performing structures will be experimentally functionalized with label-free analyte capture materials to sense specific threat molecules via index change. We envision building manyanalyte multiplexed sensor arrays from these devices to enable simultaneous monitoring of multiple chemical and biological threats or human biomarkers with high sensitivity, specificity, and low probabilities of false alarm.

We are studying the viability of a chip-scale integrated photonics based sensor assay array for wearable soldier health monitoring and environmental hazard warning applications. We propose using label-free analyte capture material clad wide subwavelength grating (SWG) waveguides as the sensor elements in a multiplexed array to probe the myriad variety and concentration ranges of chemical hazards and biomarker health molecules expected in these applications. We present here the simulated behavior of both rectangular and tapered wide SWG geometries. We discuss their transmission spectra, effective index, bulk sensitivity, and cladding dependence on waveguide width alongside strip and slot waveguide geometries. Experimental transmission and effective index measurements validating our simulation techniques are also given.

Hazard detection systems must be evaluated with appropriate test material concentrations under controlled conditions in order to accurately identify and quantify unknown residues commonly utilized in theater. The existing assortment of hazard reference sample preparation methods/techniques presents a range of variability and reproducibility concerns, making it increasingly difficult to accurately assess optically- based detection technologies. To overcome these challenges, we examined the optimization, characterization, and calibration of microdroplets from a drop-on-demand microdispenser that has a proven capability for the preparation of energetic reference materials. Research presented herein focuses on the development of a simplistic instrument calibration technique and sample preparation protocol for explosive materials testing based on drop-on-demand technology. Droplet mass and reproducibility were measured using ultraviolet-visible (UV-Vis) absorption spectroscopy. The results presented here demonstrate the operational factors that influence droplet dispensing for specific materials (e.g., energetic and interferents). Understanding these parameters permits the determination of droplet and sample uniformity and reproducibility (typical R2 values of 0.991, relative standard deviation or RSD ≤ 5%), and thus the demonstrated maturation of a successful and robust methodology for energetic sample preparation.

The utility of peptide-based molecular sensing for the development of novel biosensors has resulted in a significant increase in their development and usage for sensing targets like chemical, biological, energetic and toxic materials. Using peptides as a molecular recognition element is particularly advantageous because there are several mature peptide synthesis protocols that already exist, peptide structures can be tailored, selected and manipulated to be highly discerning towards desired targets, peptides can be modified to be very stable in a host of environments and stable under many different conditions, and through the development of bifunctionalized peptides can be synthesized to also bind onto desired sensing platforms (various metal materials, glass, etc.). Two examples of the several Army relevant biological targets for peptide-based sensing platforms include Ricin and Abrin. Ricin and Abrin are alarming threats because both can be weaponized and there is no antidote for exposure. Combining the sensitivity of SERS with the selectivity of a bifunctional peptide allows for the emergence of dynamic hazard sensor for Army application.

Peptides have emerged as viable alternatives to antibodies for molecular-based sensing due to their similarity in recognition ability despite their relative structural simplicity. Various methods for peptide capture reagent discovery exist, including phage display, yeast display, and bacterial display. One of the primary advantages of peptide discovery by bacterial display technology is the speed to candidate peptide capture agent, due to both rapid growth of bacteria and direct utilization of the sorted cells displaying each individual peptide for the subsequent round of biopanning. We have previously isolated peptide affinity reagents towards protective antigen of Bacillus anthracis using a commercially available automated magnetic sorting platform with improved enrichment as compared to manual magnetic sorting. In this work, we focus on adapting our automated biopanning method to a more challenging sort, to demonstrate the specificity possible with peptide capture agents. This was achieved using non-toxic, recombinant variants of ricin and abrin, RiVax and abrax, respectively, which are structurally similar Type II ribosomal inactivating proteins with significant sequence homology. After only two rounds of biopanning, enrichment of peptide capture candidates binding abrax but not RiVax was achieved as demonstrated by Fluorescence Activated Cell Sorting (FACS) studies. Further sorting optimization included negative sorting against RiVax, proper selection of autoMACS programs for specific sorting rounds, and using freshly made buffer and freshly thawed protein target for each round of biopanning for continued enrichment over all four rounds. Most of the resulting candidates from biopanning for abrax binding peptides were able to bind abrax but not RiVax, demonstrating that short peptide sequences can be highly specific even at this early discovery stage.

The requirement to detect hazardous materials (i.e., chemical, biological, and explosive) on a host of materials has led to the development of hazard detection systems. These new technologies and their capabilities could have immediate uses for the US military, national security agencies, and environmental response teams in efforts to keep people secure and safe. In particular, due to the increasing use by terrorists, the detection of common explosives and improvised explosive device (IED) materials have motivated research efforts toward detecting trace (i.e., particle level) quantities on multiple commonly encountered surfaces (e.g., textiles, metals, plastics, natural products, and even people). Non-destructive detection techniques can detect trace quantities of explosive materials; however, it can be challenging in the presence of a complex chemical background. One spectroscopic technique gaining increased attention for detection is Raman. One popular explosive precursor material is ammonium nitrate (AN). The material AN has many agricultural applications, however it can also be used in the fabrication of IEDs or homemade explosives (HMEs). In this paper, known amounts of AN will be deposited using an inkjet printer into several different common material surfaces (e.g., wood, human hair, textiles, metals, plastics). The materials are characterized with microscope images and by collecting Raman spectral data. In this report the detection and identification of AN will be demonstrated.

Generally the fabrication, assembly and evaluation of plasmonic nanostructures for surface enhanced Raman scattering (SERS) substrates has focused on static rigid substrates such as glass and silicon. However, these static substrates severely limit the application of plasmonic nanostructures as (i) they provide no means to alter the state of assembly of the nanostructures once they are formed or anchored on the surface i.e., not reconfigurable; and (ii) preclude applications which demand non-planar, flexible or conformal surfaces. The above considerations has led to the development of a novel class of SERS substrates based on flexible substrates such paper, polymer membranes and electrospun fibers. These flexible SERS media based on unconventional substrates such as paper offer distinct advantages compared to the conventional SERS substrates in that (i) flexible nature of the substrate enables conformal contact with the surfaces under investigation leading to efficient sample collection; (ii) porous nature of the SERS substrate (interstices between the fibers) provides efficient access to the analytes; (iii) high surface area of the 3D paper substrate results in large dynamic range of the chemical sensors; (iv) intricate network of fibers decorated with metal nanoparticles can provide potentially high density of electromagnetic hotspots; (v) intense light scattering caused by the fibrous structure of the substrate (e.g., paper) enables efficient light-metal interaction; and (vi) facile fabrication leads to efficient, robust, reliable, reusable and cost-effective SERS substrates. In this presentation, we will focus on the Army need for a more flexible (substrate surface and application) SERS substrate for universal sensing. This presentation will leverage from material presented at a flexible SERS (May 2014) workshop hosted by Dr. Srikanth Singamaneni at Washington University.

Regenerated surface-enhanced Raman scattering (SERS) substrates allow users the ability to not only reuse sensing surfaces, but also tailor them to the sensing application needs (wavelength of the available laser, plasmon band matching). In this review, we discuss the development of SERS substrates for response to emerging threats and some of our collaborative efforts to improve on the use of commercially available substrate surfaces. Thus, we are able to extend the use of these substrates to broader Army needs (like emerging threat response).

The synthesis of plasmonic nanorattles with accessible electromagnetic hotspots that facilitate highly sensitive detection of chemical analytes using surface enhanced Raman scattering (SERS) is demonstrated. Raman spectra obtained from individual nanorattles demonstrate the significantly higher SERS activity compared to solid plasmonic nanostructures.

We present the results of a three-year collaboration between the U.S. Army Edgewood Chemical Biological Center and the U.S. Army Research Laboratory-Aldelphi Laboratory Center on the evaluation of selected nanometallic surfaces developed for the Defense Advanced Research Projects Agency Surface-Enhanced Raman Scattering (SERS) Science and Technology Fundamentals program. The primary role of the two Army labs was to develop the analytical and spectroscopic figures of merit to unambiguously compare the sensitivity and reproducibility of various SERS substrates submitted by the program participants. We present the design and implementation of an evaluation protocol for SERS active surfaces enabling an enhancement value calculation from which different substrates can be directly compared. This method was established to: (1) collect physical and spectral characterization data from the small number of substrates (performer supplied) typically encountered, and (2) account for the complex fabrication technique and varying nature of the substrate platforms encountered within this program.

The development of a sensing platform to detect and identify biological, chemical, and energetic hazards is a long-sought-after goal of the Army and other first responder communities. Surface enhanced Raman scatting (SERS) is a spectroscopic technique gaining popularity as it address many sensing needs. However, despite the many advantages of SERS, it remains a marginalized sensing technique primarily due to the challenges in fabricating a reliable, highly sensitive, reproducible nanoscale surface. In this work, we demonstrate that many of the substrate fabrication challenges have been overcome by a newly developed, commercially available, next generation Klarite SERS substrate. These substrates are fabricated similarly to the standard Klarite substrates, but due to variations in the size and spacing of the surface features, they have increased sensing capabilities. The sensitivity for detecting the model SERS analyte, trans-1,2-bi-(4-pyridyl) ethylene (BPE) using both a 633- and 785-nm laser system is demonstrated. For one of the next generation substrates, the detection limit improved by as much as 4 times for BPE (under some conditions). This improved performance may in part be attributed to physical changes to the substrate surface including an increased density of features and plasmon absorbance band locations.

There is an increasing need and challenge for early rapid and accurate detection, identification, and quantification of chemical, biological, and energetic hazards in many fields of interest (e.g., medical, environmental, industrial, and defense applications). Increasingly to meet these challenges, researchers are turning to interdisciplinary approaches combining spectroscopy with nanoscale platforms to create technologies that offer viable and novel solutions for today’s sensing needs. One technology that has gained increasing popularity to meet these needs is surface enhanced Raman scattering (SERS). SERS is particularly advantageous as it does not suffer from interferences from water, requires little to no sample preparation, is robust and can be used in numerous environments, is relatively insensitive to the wavelength of excitation employed and produces a narrow-band spectral signature unique to the molecular vibrations of the analyte. SERS enhancements (chemical and electromagnetic) are typically observed on metalized nanoscale roughened surfaces. For ideal SERS sensing, a commercially available uniform and reproducible nanoscale surface demonstrating high sensitivity are desirable. Additionally, if these surfaces can be modified for the selective sensing of hazard materials, an ideal sensor platform for dynamic in field measurements can be imagined. In this proceedings paper, preliminary efforts towards the characterization and application of commercially available next generation Klarite substrates will be demonstrated. Additionally, efforts toward chemical modification of these substrates, through peptide recognition elements, can be used for the targeted sensing of hazardous materials.

The United States Army and the first responder community are evaluating optical detection systems for the trace detection of hazardous energetic materials. Fielded detection systems must be evaluated with the appropriate material concentrations to accurately identify the residue in theater. Trace levels of energetic materials have been observed in mutable polymorphic phases and, therefore, the systems being evaluated must be able to detect and accurately identify variant sample phases observed in spectral data. In this work, we report on the novel application of drop-on-demand technology for the fabrication of standardized trace 1,3,5-trinitro-1,3,5-triazine (RDX) samples. The drop-on-demand sample fabrication technique is compared both visually and spectrally to the more commonly used drop-and-dry technique. As the drop-on-demand technique allows for the fabrication of trace level hazard materials, concerted efforts focused on characterization of the polymorphic phase changes observed with low concentrations of RDX commonly used in drop-on-demand processing. This information is important when evaluating optical detection technologies using samples prepared with a drop-on-demand inkjet system, as the technology may be “trained” to detect the common bulk α phase of the explosive based on its spectral features but fall short in positively detecting a trace quantity of RDX (β-phase). We report the polymorphic shifts observed between α- and β-phases of this energetic material and discuss the conditions leading to the favoring of one phase over the other.

The existing assortment of reference sample preparation methods presents a range of variability and reproducibility concerns, making it increasingly difficult to assess chemical detection technologies on a level playing field. We are investigating a drop-on-demand table-top printing platform which offers precise liquid sample deposition and is well suited for the preparation of effective reference materials. Current research includes the development of a sample preparation protocol for explosive materials testing based on drop-on-demand technology. A quartz crystal microbalance and Raman spectroscopy are used to investigate droplet and sample uniformity and reproducibility. Results are compared to samples prepared using a drop and dry method.

Sensitive, accurate and reliable methods are needed for the detection and identification of hazardous materials (chemical, biological, and energetic) in the field. Utilizing such a sensing capability incorporated into a portable detection system would have wide spread beneficial impact to the U.S. military and first responder communities. Surface enhanced Raman scattering (SERS) is increasingly becoming a reputable technique for the real-time, dynamic detection and identification of hazard materials. SERS is particularly advantageous as it does not suffer from interferences from water, requires little to no sample preparation, is robust and can be used in numerous environments, is relatively insensitive to the wavelength of excitation employed, and produces a narrow-band spectral signature unique to the molecular vibrations of the analyte. We will report on the characterization and sensing capabilities of these next generation SERS substrates for the detection of energetic materials (ammonium nitrate, TNT, PETN, and RDX). Additionally, new efforts producing highly uniform samples, with known concentrations of energetic materials inkjet printed onto the SERS sensing surface using a precisely calibrated MicroJet system will be shown.

There is an increasing need for rapid and accurate detection, identification, and quantification of chemical, biological, and energetic hazards in many fields of interest. To meet these challenges, researchers are combining spectroscopy with nanoscale platforms to create technologies that offer viable and novel solutions for today's sensing needs. One technology that has gained increasing popularity to meet these needs is surface enhanced Raman scattering (SERS). For ideal SERS sensing, commercially available uniform and reproducible nanoscale surface demonstrating high sensitivity are desirable. If these surfaces can be modified for the selective sensing of hazard materials, an ideal sensor platform for dynamic in field measurements can be imagined. In this proceedings paper, preliminary efforts towards the characterization and application of commercially available next generation Klarite substrates will be demonstrated and efforts towards selective sensing will be discussed.

Multiplexed surface enhanced Raman scattering (SERS) substrates, which enable chemically selective detection of two or more target analytes from a complex chemical mixture, are highly attractive for chemical detection in real-world settings. We introduce a new approach called plasmonic calligraphy that involves the formation of chemically selective test domains on paper substrates using functionalized plasmonic nanostructures as ink in a regular ballpoint pen. We demonstrate selective detection of positively and negatively charged analytes (rhodamine 6G and methyl orange) from complex chemical mixtures using polyelectrolyte-coated gold nanorods as SERS medium. The approach demonstrated here obviates the need for complex patterning techniques such as photolithography to create isolated test domains on paper substrates for multiplexed chemical detection. Plasmonic calligraphy can be easily extended to other shape-controlled nanostructures with different surface functionalities and potentially automated by implementation with a robotic arm.

Multiplex coherent anti-Stokes Raman scattering (MCARS) is used to detect several chemical warfare simulants, such as dimethyl methylphosphonate and 2-chloroethyl ethyl sulfide, with high specificity. The spectral bandwidth of the femtosecond laser pulse used in these studies is sufficient to coherently and simultaneously drive all the vibrational modes in the molecule of interest. Evidence shows that MCARS is capable of overcoming common sensitivity limitations of spontaneous Raman scattering, thus allowing for the detection of the target material in milliseconds with standard, uncooled universal serial bus spectrometers as opposed to seconds with cooled, intensified CCD-based spectrometers. In addition, the obtained MCARS spectrum of the investigated sample provides multiple unique signatures. These signatures are used in an off-line multivariate statistical analysis allowing for the material’s discrimination with high fidelity.

Surface enhanced Raman scattering (SERS) is rapidly emerging as a sensitive transduction platform for the trace detection of chemical and biological analytes. A critical challenge that needs to be addressed to propel this technique into real world applications is the poor chemical selectivity of the existing SERS substrates. In this communication, we demonstrate a novel biomimetic approach to enhance the selectivity of plasmonic nanostructures to target chemical analytes. In particular, we demonstrate that material-binding peptides, identified through phage-display, serve as recognition elements for selective capture of target chemical species from a complex chemical mixture. As a proof of concept, we show that a nitroaromatic explosive molecule, trinitrotoluene (TNT), can be detected down to 100 pM concentration even in a complex organic chemical mixture. This ultrasensitive and selective detection is enabled by TNT-binding peptides appended to gold nanorods, which serve as selective SERS media. To the best of our knowledge, this is the first demonstration of a biomimetic SERS substrate facilitating selective and sensitive detection of a target chemical analyte in the presence of numerous unknown interfering species.