What Is the Purpose of a Reagent Blank?

According to the National Forensics Science Technology Center, a reagent blank is an experimental control reagent containing all the material in a given sample except for the component which the experiment is designed to detect. They are often used in DNA screening and analysis. Reagent blanks that contain anomalous DNA also reveal potential contamination of the experimental sample.

Contamination is a serious concern in DNA analysis and research. The National Forensics Science Technology Center explains that common contaminant sources include lab staff, other DNA samples and DNA transferred into a given sample through careless experimental preparation.

Other sources of DNA contamination are the sterile, disposable plastic laboratory tools used by many universities and forensics laboratories. These individually packaged tools sometimes contain DNA from the factory workers who packaged the tools after initial sterilization.

Reagent blanks provide an affordable and accurate avenue for identifying exogenous DNA and other biological substances with the potential to invalidate research results. In addition to one reagent blank, DNA analysis protocols established by the United States Department of Justice, Office of the Inspector General, stipulate that all DNA analysis tests must include one positive control sample and one negative control sample. Positive control samples reveal known DNA and DNA amplifiers, demonstrating the accuracy of the test. Negative control samples include only DNA amplifiers and indicate contamination if it has occurred.