DNA yield was determined by the highly specific Fluorescence/DNase method (ref. 2, 3). The F/D method quantitates DNA using SYBR Green I dye (Molecular Probes, Inc.) and DNase treatment.
DNA from Oragene/saliva samples stored at 24C and 37C had a molecular weight > 23,000 bp and showed no evidence of degradation at various time points (Figure 1). Samples stored at 50C showed minimal degradation at 187 days. There was no change in the yield of DNA at 24C, 37C and 50C as determined by the F/D method.
Discussion and Conclusions
The rate of a typical chemical reaction decreases by half for every 10C decrease in temperature. Thus, it is expected that the degradation rate at 24C should be 5-fold less than the degradation rate at 50C. Since Oragene saliva samples remain stable for 187 days at 50C, they are expected to remain stable for 5 times as long at 24C (935 days or 30 months).
After 187 days at 50C, most of the DNA extracted from Oragene / saliva samples had a molecular weight > 23,000 bp. Since PCR is effective with DNA templates much smaller than 23,000 bp, it should take significantly longer than 30 months at room temperature for the DNA in Oragene samples to degrade to an unusable size. In summary, Oragene/ saliva samples are expected to be stable at room temperature for many years.
1. Ng, D., Koh, D., Choo, S., Ng, V., and Fu, Q. (2004) Effect of storage conditions on the extraction of PCR-quality genomic DNA from saliva. Clinica Chimica Acta. 343