Advanced 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. Enzyme catalysed processes naturally occur in aqueous (water-based) environments; however, the presence of water is far from ideal in a sensor that has to be exposed to air for long periods of time, because it tends to evaporate. We are therefore proposing to explore the potential for ionic liquids (salts that are molten at room temperature) as alternative media for optical waveguide sensors. Room temperature ionic liquids (RTILs) possess a range of properties that make them desirable solvents, such as zero vapour pressure and being classified as environmentally friendly. We recently designed and created a new generation of functionalized ionic liquids that have increased hydromimetic (water-like) properties yet retain all the advantages of traditional RTILs. Using these RTILs we have shown that it is possible to obtain enzyme catalysis with complex (co-factor requiring) enzymes at very low levels of water (less than 100 ppm); which was previously impossible using the traditional BMIm PF6-related RTILs. The great potential for the use of these designer RTILs has aroused much excitement from biotechnology, pharmaceutical and chemical industries, leading to the commercialization of their production. These novel funtionalized ionic liquids, along with the appropriate enzymes and reagents will be deposited as thin film wave guides on low-cost moulded polymeric devices. 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.

Enzyme catalysed processes naturally occur in aqueous environments; however, the need for the presence of water for activity can hamper the use of enzymes as biorecognition components in sensors for the detection of drug and explosives particulates in air. We propose to overcome this limitation by developing colorimetric assays in a variety of novel room temperature ionic liquids (RTILs) based upon functionalized ammonium nuclei that are optimized for enzyme-catalyzed reactions. We have a diverse range of enzymes that possess activity towards illicit drugs and explosives. The enzymes will be investigated in ionic liquids that exhibit differing physical properties, such as hydrophilicity, polarity and proticity, in order to establish broad correlations between solvent structure and enzyme activity. Colorimetric detection systems for the drugs and explosives breakdown products in the RTILs will be developed. These functionalized RTILs, enzymes and reagents will be deposited as thin film wave guides on moulded polymeric devices. The effectively zero vapour pressure of the RTILs will provide a stable thin film. To achieve high sensitivity in a colorimetric assay requires a long optical path length. Since the RTIL films will be approximately one micron thick, the change in absorbance will be very small when viewed normal to the film thickness. We can overcome this drawback by launching a leaky waveguide mode in the RTIL film. This means that the light propagates along the film, giving much longer optical path lengths and hence higher sensitivity. Light is partially confined in the waveguide film by total internal reflection at the waveguide/air interface and by Fresnel reflection at the waveguide/substrate interface. Significant enhancements of absorbance can be obtained in this way depending on the thickness and refractive index of the waveguide film.