The impact of infrared radiation, solar radiation, and burial exposure on the efficacy of forensic immunoassay testing for blood, semen, and saliva

Abstract

Determining the biological source of a stain can be important information for both investigators and the judiciary in criminal cases. Immunochromatographic assays are commonly used in forensic science for the identification of human biological material. It has previously been demonstrated that various environmental, thermal and chemical insults can affect the efficacy of ABAcard® HemaTrace® in the detection of human blood. In this study, the efficacy of three tests – ABAcard® HemaTrace®, ABAcard® p30, and RSID™-Saliva – was determined for the detection of blood, semen, and saliva respectively, after the fluids had been exposed to adverse environmental conditions. Each biological fluid was deposited on cotton swatches and exposed to infrared (IR) light using a 100 W heat lamp emitting IR light between 620 and 750 nm and heat of 32° for 24, 36 and 48 h. Cotton swatches bearing biological fluids were also buried in outdoor soil for 3, 4 and 5 weeks. To test common forensic scenarios where biological material may be exposed to solar light, samples were placed on a car bonnet and left for 24, 36 and 48 h. ABAcard® HemaTrace® was able to detect haemoglobin in blood that had been exposed to IR and solar light up to 48 h. False negative ABAcard® HemaTrace® results were obtained from 60 % of blood samples buried for 3 and 4 weeks, and 80 % of blood samples buried for 5 weeks. ABAcard® p30 was able to detect p30 in semen that had been exposed to IR and solar light up to 48 h, except for one false negative after 48 h of IR exposure. False negative ABAcard® p30 results were obtained from all semen samples buried for 3, 4 and 5 weeks. RSID™-Saliva was able to detect α-amylase in saliva in all instances, with no false negative results observed. The findings from this study highlight the need to consider the context in which human blood, semen and saliva are found when reporting on negative immunoassay results.