A sensitive and simple assay of saliva on stamps

Summary Identification of saliva on stamps or envelope flaps remains yet a not widely studied problem. In most forensic laboratories it is seldom carried out, but this fact does not reduce the importance of the assay.Most authors consider amylase a sufficiently specific marker of the presence of saliva; really, the only other human body fluid that contains high amounts of this enzyme is the pancreatic juice (and therefore feces).Here we present a simple and sensitive assay for the determination of -amylase that uses a commercially available and well-known substrate. It is hydrolyzed by amylase with the production of soluble blue fragments, that can be measured by photometry, obtaining objective results.The presented assay identifies 1×10^–6 diluted saliva or that present on 0.5 mg of a stamp; 16-year-old samples can also be identified.Intra-assay and day-to-day CV resulted in 10.8% and 13.7%, respectively. Owing to the high sensitivity of the test, handling samples or reagents can introduce contamination with saliva traces, giving false-positive results. Addition of EDTA 0.1 mol/l to the incubation mixture, lowering the sensitivity to 1 × 10^–3 diluted saliva, overcomes this problem.