Evaluation of SpermTracker paper and spray for the visualization of seminal stains

In a single day’s work in the serology unit of a forensic laboratory, an analyst may encounter a wide array of evidentiary items ranging in size, shape, color, texture, porosity etc. When an item is received, the analyst must first decipher what biological fluid is suspected to be present, and then how to analyze the item for that fluid. Blood, saliva, and semen are all common body fluids that may be detected in everyday casework. The identification of semen plays a key role in the investigation of a sexual assault case. When an item is received for analysis, semen stains may be undetectable to the naked eye, so a proper visualization method is crucial. Throughout this study, two presumptive tests for semen, STK® SpermTracker-Lab and STK® SpermTracker-Spray were compared to each other and the existing Acid Phosphatase Spot Test (AP-Spot) to assess their efficacy for visualizing seminal stains. Six different commonly encountered substrates varying in color, texture, and porosity were tested. Four semen dilutions were added in triplicate to each of the six substrates, to aid in the evaluation of each test’s sensitivity. A total of 324 presumptive tests for seminal stains were completed and examined both with the naked eye and with the aid of an alternate light source. STK® SpermTracker-Lab proved to be the most sensitive, closely followed by the AP-Spot test. STK® SpermTracker-Spray was least effective at detecting semen stains, however, many of the negative results obtained with STK®-Spray were on porous substrates that the manufacturer does not recommend for this product. While the data shows that STK®-Lab is more sensitive than AP-Spot test, the STK products are more costly and require the use of a UV light