Development of a Pre-concentrator for Enhanced IMS Detection of Illicit Substances

Rapid, non-contact, presumptive identification of dangerous substances is essential for protecting law enforcement personnel and first responders during field investigations. Ion Mobility Spectrometer (IMS), when coupled with vapor sampling, offers a portable and safe screening tool. However, its effectiveness is often limited by the low vapor pressure of most controlled substances, which reduces detection sensitivity. The current study aims to improve IMS performance by developing a novel pre-concentrator that selectively captures vapor-phase analytes and releases them into the IMS detector as a concentrated bolus via Joule heating.

The pre-concentrator consists of a Silicon Nanowire (SiNW) array coated with acrylate-based polymers selected for their vapor pre-concentration capabilities. These polymers were chosen from a pre-determined library by the Naval Research Laboratory for their ability to adsorb vapor-phase analytes. Five acrylates were screened against selected vapor surrogates for key target substances. These included: methyl benzoate for cocaine, acetic acid for heroin, N-phenylpropanamide (NPPA) for fentanyl, benzaldehyde for methamphetamine, piperonal for MDMA, and triacetone triperoxide (TATP) for TATP. Quartz Crystal Microbalance (QCM) was used to evaluate polymer-vapor interactions and determine adsorption affinity. Thus far, Ethylene Glycol Monoethyl Ether Acrylate (EGMEA) and Dimethylaminoethyl acrylate (DMAEA) have shown the most promise as pre-concentration coatings.

Future work will involve coating the optimal polymers onto the SiNW array, embedding it into a microchip, and integrating it into a handheld IMS device for field deployment. This vapor-phase pre-concentrator is expected to enhance trace detection of target substances, address current limitations in vapor-based detection sensitivity, and support safer, faster identification of a broad range of controlled substances in real-world forensic and security scenarios.