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Case Study: RNA Testing and Analysis of DNA-Free Nylon Flock Swabs

Posted on Dec 30, 2013 1:35:00 PM

Puritan Internal Control

As a part of Puritan’s ongoing efforts to provide insight into our continuous quality testing and high production manufacturing standards, we are blogging occasional “case studies” to show our process in identifying and resolving anomalies.

Last month, we reviewed our work with the Wisconsin Department of Justice Crime Laboratory Bureau (WCLB) in singling out and replacing manufacturing glue that interfered with DNA extraction. Here, we summarize an internal control that quickly revealed the presence and source of RNA in a batch of nylon-flocked swabs.

Prior to developing Puritan’s patented HydraFlock® and PurFlock Ultra® swabs, Puritan Medical produced a series of swabs using nylon-based flock that were certified free of DNA as well as the nucleic acid-degrading enzymes RNase and DNase. These swabs are utilized in a range of DNA and RNA-sensitive applications from forensics to DNA testing to medical archiving and amplification tests. Puritan Medical partners with a laboratory at the University of Maine to rigorously test and evaluate for the presence of DNA or degraded RNA. In April of 2012, a batch of DNA-free swabs underwent routine testing, but encountered a problem. The swabs tested negative for DNA contamination, and were declared free of DNase based on agarose gel analysis. However, when swab samples were “spiked” with total RNA, an Agilent Bioanalyzer chip revealed that the RNA band was gone in all of the test swab samples.

Puritan and University of Maine researchers posited that the degradation was either the result of RNAse contamination or the binding of RNA to the nylon so it no longer eluted into the solution. A second, smaller batch of nylon-flocked swabs was produced and tested side-by-side with a control sample of RNase-free cotton swabs. The nylon samples once again lacked the presence of “spiked” total RNA, indicating that the problem was systematic in the manufacturing process. However, we still had not pinpointed the cause of the missing RNA.

A series of experiments were conducted with RNA chips containing nylon flocked swabs at various stages of production, as well as under a series of heating and adhesive conditions, all of which resulted in the same disappearance of spiked RNA. Finally, the experiments were duplicated substituting polyester-based Puritan PurFlock Ultra® swabs under the same conditions. This time, the RNA was present throughout. The aforementioned tests and molecular biology analysis allowed us to conclude that the nylon flock was indeed binding RNA to it when the University of Maine researchers spiked the samples for testing. Therefore, although there was technically no RNase in the swabs, the complete binding of RNA to the nylon material displayed the same characteristics as RNase contamination.

Although the PurFlock Ultra® swabs have different characteristics than the nylon or cotton-based swabs, based on our internal analysis we are now able to conclude how RNA will react with various materials and produce customized solutions for our customers based on their needs and applications. Research, analysis and manufacturing as shown above are just a small part of our internal efforts towards guaranteeing the quality and performance of our products for our customers.


Topics: Flocked Swabs, Forensics

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