The Effect of Powders and Transfer Sheets for Detecting of Latent Fingerprints on STR Typing

  We examined whether powders and transfer sheets for detecting latent fingerprints affect DNA extraction and subsequent short tandem repeat (STR) typing adversely. To examine the powders, saliva and blood samples were smeared and dried on glass slides, and then adhered with aluminum powder, black powder, magnetic powder (NBS), magnetic powder (Sirche), SP black and indigo. To examine transfer sheets, saliva and blood samples were smeared and dried on gelatin sheets, JP sheet and Lifter. DNA was extracted from the powder-adhered samples or the samples on the sheets, quantified by a real-time PCR assay, and the STR typing was performed using the Identifiler kit.<br>   The aluminum powder and the SP black affected the storage of the DNA solution, and required a centrifugation step to remove the powders, or required TE⁻⁴ buffer for DNA elution instead of water. The magnetic powder (NBS) made the DNA extraction impossible, when an excessive amount of the powder was adhered. However, the DNA extraction was possible, when most of the powder was removed with a magnetic brush. The black powder, the magnetic powder (Sirche) and the indigo gave enough DNA concentration and full STR profiles. All the transfer sheets did not give adverse effects.<br>   As simulated casework samples, 20 fingerprints deposited on a glass slide in two different ways were enhanced with the aluminum powder and transferred to the gelatin sheets. DNA was extracted from the gelatin sheets, and the residual portion on the glass slide. The DNA concentration ≥0.01 ng/μl was obtained from 2 samples for the residual portion of 20 fingerprints deposited 2 hours after washing hands, and 7 samples for that of 20 samples deposited after touching forehead, cheeks and neck. The STR typing was performed from the samples ≥0.01 ng/μl. Full STR profiles were obtained from 6 samples (≥0.024 ng/μl) and partial STR profiles from 3 samples (0.10-0.12 ng/μl) when the residual portion used.<br>