The rapid and portable detection of trace chemical warfare agents (CWAs) remains a challenge for the international security and monitoring community. This work reports the first use of natural photonic crystals (PhCs) as vapor sensors for CWA simulants. Dimethyl methylphosphonate, a nerve agent simulant, and dichloropentane, a mustard gas simulant, were successfully detected at the parts per million level by processing visible light reflected from the PhC inherent to the wing scales of the Morpho didius butterfly. Additionally, modeling of this natural system suggested several parameters for enhancing the sensitivity of a synthetic PhC toward CWA simulants, including materials selection, structure, and spacing of the PhC, and partial functionalization of the PhC toward the analyte of interest. Collectively, this study provides strategies for designing a sensitive, selective, rapid, and affordable means for CWA detection.

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.