Substrate Control
Definition
A sample of the unstained surface material from an area adjacent to a body fluid stain, collected alongside the stain and processed through the same analytical workflow. The substrate control distinguishes background DNA or chemicals in the surface material from evidence contributed by the biological stain.
- Collected from
- Unstained area adjacent to the stain
- Purpose
- Distinguishes background material from stain-derived evidence
- Processed
- Through the same analytical workflow as the stain
- Used with
- DNA and body fluid identification testing
Common questions
What does a positive result on a substrate control indicate?+
It suggests the surface material itself, rather than the biological stain, is contributing DNA or a chemical reaction, which undermines confidence that a positive result from the actual stain came from the fluid being tested rather than background contamination.
Why must the substrate control be collected adjacent to the stain rather than from a distant area?+
Background contamination can vary across a surface, so a control taken far from the stain may not represent the material actually surrounding it, weakening the comparison. Adjacent collection keeps the surface composition as close as possible to the tested area.
Is a substrate control the same as a negative control?+
They serve a related but distinct purpose. A substrate control tests the specific surface material near the stain for background interference, while a general negative control checks the reagents and process itself for contamination, independent of the case sample.
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Explained in these topics
- Biological Evidence Collection ProtocolsA sample of the surface material on which a stain was deposited, collected from an unstained area adjacent to the stain. Used by the laboratory to detect backg...
- Leucomalachite Green TestA test of the same material (fabric, surface, soil) at an area that shows no visible staining. A positive substrate control indicates the material itself conta...
- Semen, Saliva and Other Body Fluids as Evidence