Vapor Selectivity of a Natural Photonic Crystal to Binary and Tertiary Mixtures Containing Chemical Warfare Agent Simulants

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.

Additive Combination of Spectra Reflected from Porous Silicon and Carbon/Porous Silicon Rugate Filters to Improve Vapor Selectivity

“…The differential reflectance spectra (Δ R ) could be obtained by subtracting the baseline spectra from the analyte spectra. 37 , 38 …”

“…Again, differential reflectance spectra (Δ R ) reports the percentage difference of the reflectance with the analyte relative to the nitrogen baseline without the analyte. 38 Significant spacing between points of the same analyte indicates good sensitivity, while separation of analyte curves indicates good selectivity. 40 Thus, Figure 6 shows a tested sensitivity down to ∼30 ppm for DCP on both the oxidized and carbonized pSi substrates.…”

“…Indeed, the selectivity and sensitivity rival those of some natural photonic crystals when exposed to the same vapors and concentrations. 37 , 38 …”

“…Rather than a reflectance standard, differential reflectance spectra were collected and analyzed. 4 , 11 , 38 PCA was performed on the averaged differential spectra relative to nitrogen after mean-centering the data.…”

Biochemical Methanol Gas Sensor (MeOH Bio-Sniffer) for Non-Invasive Assessment of Intestinal Flora from Breath Methanol

“…On the other hand, sensors are expected to be used closer to the site than lab-based analytical devices. Therefore, it is required that sensors be simple to operate and compact in size along with sufficient sensitivity, selectivity, and capability of continuous measurement for some occasions [ 24 , 25 , 26 , 27 , 28 , 29 ]. However, generally, there is a trade-off between being compact in size and having high sensitivity, and it is very challenging to meet both requirements.…”