Invisible impact: 3D scanning sprays do not inhibit forensic STR analysis

The 3D reconstruction of crime scenes or evidentiary objects is becoming a widely adopted forensic technique. Scanning methods struggle with transparent or reflective surfaces. A solution to this problem is the application of 3D scanning sprays, which create a matte layer on the surface of the examined object, which later sublimes. Our study aimed to examine the effects of different 3D modeling sprays on DNA recovery and forensic autosomal STR analysis. We simulated crime scene samples by depositing blood droplets or by touching separate microscope slides. Following the spray treatment, DNA was extracted and then amplified by the Qiagen Investigator ESSplex SE QS kit. The spray treatment did not interfere with the sampling procedure or the DNA extraction. All alleles were successfully detected from the blood droplet samples. The low-copy-number (LCN) touch DNA samples exhibited much higher variability, but no significant differences were observed between the tested groups. While DNA sampling should generally be prioritized to prevent contamination or degradation, additional analysis and sample collection may be needed after 3D scanning. Under the tested conditions, the evaluated 3D scanning sprays did not affect the genetic analysis. However, care should be taken, as the airflow generated by spray propellants could potentially mobilize dust, skin particles, or hair fragments, contributing to secondary transfer of biological material.