The impact of substrate characteristics on the collection and persistence of biological materials, and their implications for forensic casework

The effect of the anti‐coagulant EDTA on the deposition and adhesion of whole blood deposits on non‐porous substrates

“…After a drying time of 1 week, the dislodgments increased with data suggesting that the substrate is either too smooth for blood to maintain a strong adhesion potential or too rough to effectively create sufficient intermolecular bonds to maintain a strong adhesion potential; instead, it appears that the deposit remains on the upper surface layer of the substrate. This lack of adhesion potential was also documented by Hughes et al [20,22,23], where blood had shown to have the lowest persistence on aluminum compared to touch, semen, and/or salivary deposits. Again, difference in persistence as well as the high dislodgment tendency may be driven by the formations of radial cracks (Figure 3) in the drying blood drop, due to stresses created by the diffusion of solvent molecules during the solvent evaporation phase [34].…”

“…The EDTA-treated blood was the first sample to be collected into a 4 mL K 2 EDTA sample tube (Vacutainer®, Becton Dickinson, UK). Whole blood was collected second to limit the total waiting time before deposition, in accordance with the method applied by Hughes et al [23], where blood was collected into a 9 mL EDTA-free tube (Vacutest® Kima s.r.l., Arzergrande, Italy), which was then kept warm with a self-activating heat pad (Kobayashi, HotHands Toe Warmers, Dalton, USA) and maintaining a gentle side-to-side motion to prevent the premature clotting of the blood.…”

“…TA B L E 1 Surface roughness categories R1-R6, representing average surface roughness (Sa) measurements in μm. After deposition and the completion of individual experiments (the three different drying duration tests), the substrates were cleaned according to Hughes et al [20,22,23], by submerging and cleaning the samples in an anionic soap (Earth Choice, Australia)…”

“…Whole blood was deposited first by immediately pipetting 10 μL of blood onto the center of the substrate disc, before lightly spreading the blood with the pipette tip as per procedure used by Hughes et al [20,23]. The collection tube was recapped and agitated between sets to limit the exposure of the blood to oxygen in the air and to prevent blood serum separation.…”

“…Before the deposition of blood, the substrates were decontaminated according to Hughes et al [20][21][22][23][24], using 1% sodium hypochlorite solution for polypropylene, and absolute ethanol for aluminum, followed by a rinse with deionized water. The substrates were left to dry overnight before blood deposition the next day.…”