One step reverse-transcription polymerase chain reaction (RT-PCR) assays are an attractive option for further automating gene detection assays. One-step assays can reduce hands–on-time and the risk of sample crossover and contamination. The one-step chemistries are showing increasing use in virus detection and have been reported, in some cases, to be more appropriate than their two-step counterparts [1, 2].
Previous work presented by the Stokes Institute research group outlined a micro fluidic based continuous flow instrument which performed high throughput qPCR in nanolitre sized droplets . This instrument had advantages over commercially available instruments in that it could process far more than the traditional 96 or 384 reaction setup in a single run and the reaction volume was reduced from 20–50 μl down to 30–100 nl sized droplets.
Combining one-step chemistry with the technology offered by the devices being developed would lead to a high-throughput RNA-to-signal system capable of reverse transcribing and performing PCR on thousands of nanolitre sized reactions every day. It is envisaged that this technology will also lead to gene expression from single cells contained in nanolitre sized droplets.
In this paper, a study was conducted in which an extra thermal region, manufactured from aluminium, was added to the existing continuous flow instruments. This region was maintained at a temperature suitable for reverse transcription, which was 48°C for the one-step kit tested. The thermal region was also a suitable length to maintain the sample at the required temperature for 15 minutes. Using a commercially available one step RT-PCR kit (TaqMan® RNA-to-CT™ 1-Step Kit, 4392653), the device was evaluated for its potential to perform one-step RT-PCR in continuously flowing nanolitre sized droplets.
Electrophoresis gels were initially used in assessing specific amplification before an end-point detection method was utilized. RNA was extracted from the leukemic REH cell line with the housekeeping gene, glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) as the gene of interest. To investigate the possibility of further reducing sample preparation and facilitating further automation, amplification from cell lysates without nucleic acid extraction was carried out on the device. Cell lysates were prepared using the cell lysis buffer from the TaqMan® Gene Expression Cells-to-CT™ Kit (Cat #AM1728). It was found that the device was successful in one-step RT-PCR from extracted RNA samples and samples from cell lysates without nucleic acid extraction.