Research into latent fingermark detection and visualisation has taken many paths over the years as researchers and practitioners explore numerous methods to improve existing reagents. The majority of past research has resulted in providing small, incremental improvements to existing techniques. Currently, some researchers have opted to seek more transformational improvements in detection sensitivity, selectivity and visualisation. One such area being investigated is utilising immunology to target proteins, amino acids and drug metabolites in the latent fingermark deposit. Research to date has indicated that antibodies have great potential in providing these transformational improvements due to their ability to bind to certain fingermark components with high sensitivity and selectivity.
Following on from the antibody research, aptamers have been highlighted as the next potential immunogenic technique for several reasons, including reduced health and safety issues, lower cost, greater sensitivity and selectivity, and ease of design and versatility. Aptamers are specifically selected oligonucleotides comprised of either ribonucleic acid (RNA) or single-stranded deoxyribonucleic acid (ssDNA). Due to the selection strategies employed, aptamers can be designed to target most molecules and bind to them with detection limits in the sub-micromolar to nanomolar ranges. Although aptamers have been successfully used in a variety of highly sensitive and selective detection devices, they have not been investigated for use in the detection and visualisation of latent fingermarks prior to this project.
Initially, this project focussed on aptamers targeting amino acids as a means of visualising latent fingermarks. However, it was found that strong, non-specific interactions occurred with both the aptamer and the fluorescent tag, resulting in a lack of success with this approach.
In order to address these issues, aptamers selected to the protein lysozyme were used on fingermarks placed on both PVDF and plain white copier paper. Lysozyme was selected as it was found to be a component in human sweat, while aptamers selected to lysozyme, with binding affinities in the nanomolar range were available. It was found that the aptamer-based reagents possessed high levels of sensitivity with the clear detection of lysozyme at very low concentrations (1 ng). Latent fingermarks from various donors were able to be detected on both substrates, with primary and secondary level detail being clearly visible. Results, however, were very inconsistent, with marks older than a couple of days being difficult to detect. This was found to be due to the degradation of lysozyme in the latent fingermark. Unfortunately, aptamers to other, possibly more suitable, fingermark components that would circumvent this problem were not available for this project. Despite the difficulties encountered, this project has, for the first time, demonstrated the potential of detecting and visualising latent fingermarks with an aptamer-based reagent. The study has laid the groundwork for future successful investigations that exploit the benefits of aptamers while overcoming the limitations identified in this project.