How many cells are required for successful DNA profiling?

Area of Science:

• Forensic Science
• Molecular Biology
• Genetics

Background:

• Advances in fluorescent nucleic acid dye staining enable targeted collection of cellular material from touch and saliva deposits.
• Determining the minimum cell number for informative DNA profiles is crucial for forensic investigations.

Purpose of the Study:

• To establish the cellular threshold requirements for generating DNA profiles from touch and saliva samples using different collection and processing methods.
• To correlate DNA quantification and profile data with the number of cells collected to optimize forensic workflows.

Main Methods:

• Diamond™ Nucleic Acid Dye (DD) staining and portable fluorescence microscopy were used to visualize and target cells.
• Cellular material was collected using swabs and tapelifts from touch and saliva samples.
• Samples were processed via direct PCR and PCR post-extraction to generate DNA profiles.

Main Results:

• Full DNA profiles were consistently generated with direct PCR using ≥40 buccal cells (swab or tapelift).
• Touch samples required ≥800 corneocytes (swab) or ≥4,000 (tapelift) for direct PCR.
• DNA extraction workflows increased requirements to ≥80 buccal cells and ≥4,000-8,000 corneocytes for touch samples.

Conclusions:

• The study provides data for informed sample triage and workflow decisions in forensic DNA analysis.
• Visual quantification of stained cells aids in optimizing STR amplification based on sample type and collection method.