The Intelligent Fingerprinting Process
Detection of drugs and their metabolites in body fluids including blood, urine and saliva are well known, yet often have drawbacks including the need to collect invasive samples, biohazard risks, cross reactivity with other substances in the samples, and a requirement for cold or frozen sample transport and storage. In addition to these drawbacks, often the tests are susceptible to contamination leading to ‘false positives’, or can be cheated by the person undergoing the testing procedure.
In contrast to this, the Intelligent Fingerprinting method allows the use of a simple fingerprint collection and analysis process, whereby the samples are quick and easy to collect, have an inherent watertight chain of evidence continuity making them impossible to cheat, are stable at room temperature, and without any further sample preparation can be tested for both identity and metabolites of substances ingested (knowingly or unknowingly) by the sample donor. The unique ability of the Intelligent Fingerprinting process to detect the metabolites in direct association with the sweat pores from within the fingerprint itself, also means that the tests cannot give a false positive as a result of innocent contamination.
Antibody Coated Nanoparticles
The key to the success of the Intelligent Fingerprinting process is the use of antibody coated nanoparticles (as illustrated in Figure 1). The nanoparticles are formed into antibody conjugates for the metabolite that is being detected in the fingerprint by binding antibodies to the nanoparticles using proteins and linker molecules. These antibody conjugates are then used to bind to target metabolites in the fingerprint as follows –
Firstly the fingerprint is imaged using white oblique light to create a record for comparison later in the process;
Secondly the fingerprint (or portion that has been reserved for analysis) is treated by an aqueous solution of the nanoparticle antibody conjugates;
This is then incubated for a few minutes to allow the antibodies to bind with the metabolites in the fingerprint;
Finally the excess unbound antibody conjugates are removed, and although it is possible to view the results of the analysis with white light, the fingerprint is further developed by the second application of a further antibody coupled to a fluorescent dye.
The quality of the images that are revealed when the fluorescent dye binds to the fingerprint metabolite antibody conjugates can be profound, as illustrated by the example shown in Figure 2, and can readily be used to identify the owner of the mark through conventional comparison procedures. Of greater significance however, is that the images clearly show that the detected metabolites are first released from the individual sweat pores before spreading down the ridges to create the fingerprint image. It is this evidence linking the metabolite to the individual sweat pores that proves that the metabolite of the substance being detected was actually ingested and metabolised by the owner of the fingerprint, and is not the result of innocent contamination or secondary transfer. Such a link is evidentially priceless in many criminal investigations.
Figure 1 – Schematic to illustrate the structure of nanoparticles used within the Intelligent Fingerprint process.
Structure of the nanoparticles:
Figure 2 – Images of fingerprints by visualising the fluorescent markers that have been bound to the metabolites detected in the donor fingerprints by the Intelligent Fingerprinting technique (Scale Bars: A = 5mm, B = 2mm & C = 1mm). The link of the detected metabolites to the pore structure within the fingerprints can clearly be seen, providing unambiguous evidence that the donor of the fingerprint is associated with the detected metabolite.
"Intelligent Fingerprinting: Simultaneous Identification of Drug Metabolites and Individuals by Using Antibody- Functionalized Nanoparticles" Leggett, R. et al., Angew. Chem. Int. Ed. (2007), 46, 4100 –4103
"Imaging of latent fingerprints through the detection of drugs and metabolites", Hazarika, P et al. Angew. Chem. Int. Ed. (2008), 47, 10167-10170.
"Rapid detection of drug metabolites in latent fingermarks" Hazarika et al. Analyst (2009), 134, 93-96.
"Muliplexed detection of metabolites of narcotic drugs from a single latent fingerprint" Hazarika, P. et al. Analytical Chemistry, 2010, 82, 9150-9154.