Abstract
Vapor sensing via light reflected from photonic crystals has been increasingly studied as a means to rapidly identify analytes, though few studies have characterized vapor mixtures or chemical warfare agent simulants via this technique. In this work, light reflected from the natural photonic crystals found within the wing scales of the Morpho didius butterfly was analyzed after exposure to binary and tertiary mixtures containing dimethyl methylphosphonate, a nerve agent simulant, and dichloropentane, a mustard gas simulant. Distinguishable spectra were generated with concentrations tested as low as 30 ppm and 60 ppm for dimethyl methylphosphonate and dichloropentane, respectively. Individual vapors, as well as mixtures, yielded unique responses over a range of concentrations, though the response of binary and tertiary mixtures was not always found to be additive. Thus, while selective and sensitive to vapor mixtures containing chemical warfare agent simulants, this technique presents challenges to identifying these simulants at a sensitivity level appropriate for their toxicity.
Highlights
Positive identification of chemical warfare agents (CWAs) via passive, robust sensing remains an active area of research for the homeland defense, force protection, and treaty monitoring communities
As has been well-documented [33], the brilliant blue color of the Morpho didius arises from the complex nanostructure inherent within the wing scales
A key result of this work, was that introduction of even small vapor mass percentages of CWA simulants into a vapor mixture resulted in significant, detectable shifts in reflectance spectra
Summary
Mass spectroscopy and nuclear magnetic resonance spectroscopy are the primary means to identify CWAs at the parts per trillion level [1,2], though these techniques present challenges for portable, long-term, passive sensors suitable for field use. Piezoelectric, colorimetric, and electrochemical methods to detect CWAs and CWA simulants have been explored, but these techniques generally require improvements in selectivity, sensitivity, portability, and/or reusability before their wide-spread use as CWA sensors becomes practical [3]. The simplest PhC is a one-dimensional Bragg reflector with many alternating layers of two different materials. Light incident on the Bragg reflector is both reflected and refracted at each material interface, leading to constructive and destructive interference of the light waves as they propagate through the PhC.
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