Advance optical waveguide biosensors for the detection of illicit drugs and explosives

Heroin, cocaine and 'crack' cocaine are now considered to be the most powerfully addictive drugs Western society has ever had to confront. In the inner city areas of the United States, and now in Europe, illicit drugs are generating an unprecedented wave of violence and social disruption. The impact of the dramatic increase in the importation of concealed illicit drugs into the UK over the last few years has prompted a critical appraisal of current technology for the detection of such drugs of abuse. The proliferation of illicit drugs, explosives, new technologies, and expertise increases the potential for drug smugglers and terrorists to evade our existing countermeasures at points of entry to and exit from the UK. Present methods for the detection of illicit drugs and explosives leave much to be desired. To allow analysis to occur in the 'field' there is an urgent need for the development of on-site testing. To address this challenge, we are aiming to develop novel inexpensive sensors to rapidly and effectively detect particulate drugs and explosives.

We have identified microbial enzymes that have high activity and specificity towards illicit drugs and explosives and have shown that these enzymes can be used as recognition components in sensors. The challenge is to incorporate these enzymes into sensor configurations that retain the enzyme activity while allowing the sensor to work in air as a particle or vapour detector. Originally, we proposed to use ionic liquids (IL) as solvents for the enzymes and cofactors because they have effectively zero vapour pressure, so would not evaporate even when deposited as a very thin (sub-micron) liquid film. We have shown during the course of this project that the enzymes required to detect the analytes of interest are not functional in ionic liquids containing less than ~ 40% water. This has forced a major change to the objectives and methodology of the project. To continue to use ionic liquids would have required the identification of a hydrophilic ionic liquid that would permit the enzymes to function with low water content and would be sufficiently hydrophilic to retain the water even when exposed to air. Given the vast range of possible ionic liquids, this was felt to be infeasible. Once the problem of enzyme instability in ILs was discovered, other hydromimetic liquids such as glycerol, ethanediol and propanediol were tested as enzyme solvents. These liquids would not form stable thin films as their vapour pressure was far too high.

To overcome these problems, the enzymes would be kept in an aqueous environment but would be separated from the sample by a membrane or by entrapment in a hydrogel which would then be covered by a hydrophobic ionic liquid. The IL would solubilise the analytes and allow them to diffuse to the aqueous enzyme layer while acting as a barrier to the evaporation of water.

We propose to utilize a unique collaboration between Dstl, PSDB, RTIL producers Bioniqs Ltd., and a multidisciplinary team of academics with expertise in enzymology, ionic liquid chemistry and sensor technologies to develop a commercially viable enzyme-based, prototype handheld biosensor for the detection of particulate illicit drugs and high explosives.