Electrochemical Paper-based Sensors for the Trace Detection of Explosives Compounds in a Crime Scene

As submitted by the proposer:

Improvised explosive devices (IEDs) are increasingly used by criminals, insurgent, and terrorist groups when targeting transportation, large number of human targets, and military strategic points. Those "home-made" devices use readily-available materials, deviating them from their intended usage. In recent years, chlorate salts (potassium chlorate or sodium chlorate) had been increasingly reported as the oxidizer material used in IEDs. Analytical tools to detect chlorate, especially for on-site testing, are lacking. To prevent casualties and property damage, however, timing is key in the identification of the threat, the perpetrators and their affiliation, as well as for prosecution later on.

The goal of the proposed work is to develop a presumptive test for the detection of chlorate as explosive residues at a crime scene. This portable, low-cost, user-friendly electrochemical
paper-based device relies on an immobilized sensing layer containing a complex of molybdenum (Mo). Chlorate, and potentially other explosives residues such as perchlorate, bromate, will increase the redox activity of the immobilized layer, acting on the molybdenum-based complex as a catalytic agent. The changes of current correlating to the presence of chlorate will be monitored electrochemically and give a rapid, on-site response to the analyst.

Paper-based analytical devices have already been widely-recognized for their potential in point-of-care applications for health monitoring and diagnostics. In the proposed forensics application, in addition to their light weight, ruggedness, simplicity, and low-cost aspects, they propose a unique, easy sample collecting procedure by rubbing the back of the device onto a suspicious surface. The sampling of liquid will also be possible. As the assay relies on the analyte playing the role of a catalytic agent, the residues can be recovered for further confirmatory test: after the presumptive test, the paper-based device can be used to store and transport samples to a laboratory.

Furthermore, the electrochemical detection is less-sensitive to interference than commonly used colorimetric detection, and due to the catalytic action of the residues, a low-limit of detection is expected. The versatility of the proposed electrochemical paper-based sensor regarding sample collection, detection, storage, and transport could broaden its application to other aspects of forensics evidence collection and analyses than explosives residues or post-blast debris analyses, such as for contaminated fingerprints.

Note: This project contains a research and/or development component, as defined in applicable law, and complies with Part 200 Uniform Requirements - 2 CFR 200.210(a)(14).

ca/ncf