Simultaneous development and detection of drug metabolites in latent fingermarks using antibody-magnetic particle conjugates

Latent fingermarks can be particularly difficult to visualise on highly reflective surfaces such as white porcelain. Here we use a combination of anti-cotinine magnetic particle conjugates and fluorescently tagged secondary antibody fragments in order to develop latent fingermarks on porcelain. Further, the anti-cotinine magnetic particle conjugates were used to distinguish between fingermarks from smoker and non-smoker volunteers by detecting the presence of cotinine, a metabolite of nicotine, within the fingermarks of smokers. For both sets of fingermarks, the anti-cotinine magnetic particle conjugates enabled the development of the fingermarks. Importantly, the brightfield and fluorescence microscopy images of the developed fingermarks were of high resolution and suitable for identification purposes. The anti-cotinine particle conjugates specifically bound to the cotinine antigen present in the sweat within the ridges of the fingermarks of the smoker volunteers as shown by the presence of ridges, minutiae, ridge shape and pores. However, with the absence of the cotinine antigen in the non-smoker fingermarks, the anti-cotinine magnetic particle conjugates non-specifically bound to the porcelain surface to produce a ‘negative’, or inverse, image of the fingermark. The difference in specific and non-specific binding of the antibody–particle conjugates on the porcelain surface enables the high quality images to be used to identify an individual and distinguish between smokers and non-smokers.