Luminol reagent control materials in bloodstain pattern analysis: A silicon sol-gel polymer alternative

Abstract

Peroxidase-based reagents that react with whole blood typically undergo internal quality control tests for reactivity prior to their use at a crime scene. This study presents a synthetic polymer alternative to using whole mammalian blood as a luminol reagent control testing material. The luminol-reactive polymer was developed by integrating horseradish peroxidase into a silicon-based sol-gel matrix. Liquid formulations of the polymer were made to simulate forensically relevant luminol reactivity with dried, whole ovine blood at dilutions up to 1:1 × 106. Photoemission from chemiluminescence reactions were characterized as a function of time using a SpectraMax® M3 microplate reader luminometer over a duration of three minutes. The maximum chemiluminescence intensity, time at maxima, reaction half-life, and overall behaviour of the sol-gels and two commercially available materials are reported. The behaviour of each material was statistically compared to the whole blood standards using a two-dimensional Kolmogorov-Smirnov test, which suggests that the sol-gels have a more realistic and statistically similar reactivity to neat (p = 0.835) and diluted (1:1 × 106) blood (p = 0.998) than the commercially available materials (p < 0.05). The operational deliverable of this sol-gel technology is a reagent control test system, where the polymer is deposited onto cotton swabs that can be sprayed with luminol to test the working order of the solution. The sol-gel’s stability in the liquid form as well as when deposited on a cotton swab was monitored under three environmental conditions based on temperature and light for six weeks. This work establishes the sol-gel material as a practical luminol reagent control test for operational bloodstain pattern analysis.