Abstract: An assembly device and method for collecting and testing fluid samples more specifically for preparing and stabilizing nucleic acid components in a closed system. The assembly comprises a sample collection container with preloaded testing reagents and a safety separator to contain the testing reagents during sample collection. A fluid sample is delivered to the container and the assembly is subjected to centrifugation whereby the centrifugal load causes the separator to deform so that the separator migrates through the test reagents mixing the sample and reagents, and comes to rest atop the solids at the bottom of the tube.