Technical assessment of two swab types for human and microbial DNA extraction from latent fingerprints

Latent fingerprints are a valuable yet challenging source of both human and microbial DNA, especially when ridge patterns are of poor visual quality with little to no identification potential. The efficiency of DNA collection and extraction depends on the choice of the sampling technique and the specimen conditions. This study compared two swab types for collecting and extracting human and microbial DNA from the fingers and fingerprints of two participants: 4N6FLOQSwabs® Genetics (Copan Italia) and standard cotton swabs (Dealmed Cotton-Tipped Sterile Wood Applicators). Results revealed higher DNA recovery for one participant regardless of swab type, indicating variability likely due to individual differences in natural cell/DNA shedding. Microbial DNA recovery ranged from 100% (from fingers) to 30% (from fingerprints), implying a loss of DNA during deposition, with 4N6FLOQSwabs® generally outperforming cotton swabs. Total DNA recovery from fingerprints was approximately 57% of that from fingers, comparable between both swab types, though 4N6FLOQSwabs® yields were higher overall. STR profiling via direct PCR with MicroFLOQ® showed that 4N6FLOQSwabs® performance was also superior, successfully identifying STR loci from fingers in 74% of cases, compared to 54% with cotton swabs. This figure was similar when extracting DNA from fingerprints (~40%). This comparative study underscores the importance of selecting the appropriate swab type for optimal DNA extraction from fingers and latent fingerprints in forensic investigations.