Application of lateral flow immunoassays for fingermark analysis in forensic investigations

In forensic investigations, fingermarks serve as crucial traces at crime scenes, offering valuable information about their donor. Traditionally, their ridge pattern is examined for individualization. However, fingermark analysis is often limited by challenges such as poor mark development, distortion, or the absence of reference prints in databases, which may lead to the exclusion of potentially relevant marks. Beyond individualization, fingermarks contain a diverse array of chemical compounds that could provide additional forensic insights into the donor's identity or past activities. The feasibility of lateral flow assays (LFAs) for extracting specific donor information was evaluated using a generic protein as a proof of principle. The present work proves that LFAs can specifically detect trace amounts of human serum albumin (HSA), down to 0.001 μg in control samples, and 0.0075 μg of HSA in swabbed control samples. An LFA was developed that was able to detect HSA, in natural fingermarks, for all ten donors of the five-stacked and single marks. Furthermore, HSA was detected in single natural marks up to seven days after deposition onto a glass slide for five out of ten donors. The developed extraction protocol and LFA design successfully detected HSA in fingermarks deposited and sampled from non-porous surfaces in six out of ten cases. Our research provides insight into the endogenous HSA levels that can be detected in fingermarks upon swabbing and into the potential differences between donors. Future research could explore alternative biomarkers beyond HSA to provide information about the donor's lifestyle. Overall, LFAs are a portable, user-friendly, and time- and cost-efficient method that, in future developments, can detect specific (bio)chemical compounds in fingermarks.