The capture and detection of organophosphate (OP) chemical warfare agents generally involves a sorbent-based pre-concentrator. However, typical sorbents offer only broad-spectrum uptake capabilities, allowing them to become saturated with background contaminants prior to target exposure, substantially reducing their efficacy. Additionally, the target analyte may only be present at low concentrations and for short periods of time, further complicating capture. In order for a sorbent to be left unattended in the field until it encounters the analyte of interest, it must demonstrate: (i) a high affinity for the target molecule, (ii) selectivity for the target over background interferents, (iii) post-exposure retention of the analyte, and (iv) a remotely measureable indication of uptake. This work describes the design of a chemically selective one-dimensional photonic crystal for OP detection using electrochemically etched mesoporous silicon. In these devices, adsorption of the target within the silicon mesopores alters the composite refractive index and measurably shifts the reflectance stop-band. Porous silicon interferometers have been previously used in the detection of various analytes, such as HF, NH4, and DNA fragments. In the present work, the functionalization of the silicon surface with an oxime functional group (typically used as OP poisoning antidotes), imparts chemical selectivity toward OPs relative to a mixture of common interferents. The materials are shown to selectively uptake OPs in air at 1 ppm concentrations under humid conditions, with retention of the analyte under subsequent N2 flow, while the specific capture event is signaled by a shift in the reflectance pattern of the device. The successful incorporation of the oxime surface functionality is confirmed spectroscopically, and the identity of the captured warfare agents is verified by thermal desorption and GC-MS.

Functionalized porous silicon for the capture and detection of organophosphates from air

2019 Fall National Meeting

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