Editors' ChoiceBioengineering

One Drop, Many Possibilities

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Science Translational Medicine  07 Aug 2013:
Vol. 5, Issue 197, pp. 197ec129
DOI: 10.1126/scitranslmed.3007130

Searching for one rare cancerous cell among millions of healthy ones is akin to digging for that pesky needle in the haystack. Once one—cell, not needle—is located, its transcriptome can be analyzed to help diagnose and treat cancer. Such single-cell analysis in the clinic, however, is currently too laborious and time-consuming to be practical. To skip the search altogether and just analyze the single cell in its mixed population, Eastburn and colleagues created a droplet-based microfluidic device that measured gene expression in single cancer cells, ignoring the other cells in the sample.

One limitation of high-throughput droplet-based microfluidic reverse transcription polymerase chain reaction (RT-PCR) analysis has been inhibition of the reaction by cell lysis reagents when performed in picoliter volumes. The authors overcame this limitation by designing a microfluidic device capable of single-cell lysis followed by water dilution and splitting of drops before injection of RT-PCR reagents. In a proof-of-concept study, the authors mixed different cancer cell lines and successfully identified single cells within the mixed population. This genetic analysis was performed at a rate of ~50,000 cells within 2 hours using only 400 μl of all RT-PCR reagents. Furthermore, potential false positives from transcripts present in cell-free droplets were ignored because fluorescent imaging showed the overlap of the RT-PCR product (gene) signal with a cell-specific signal.

Eastburn et al. have not yet tested this system in a more complex clinic sample, such as whole blood from cancer patients. Additionally, this report demonstrated only the initial step in the development of a high-throughput system for sorting and gene expression analysis. Future devices should integrate cell-specific labeling and reaction mixing while enhancing analysis to include single-cell transcriptome sequencing. Nevertheless, this system may be a powerful tool to increase our understanding of diseases in the context of heterogeneous populations as well as improve our ability to diagnose and treat these diseases.

D. J. Eastburn et al., Ultrahigh-throughput mammalian single-cell RT-PCR in microfluidic drops. Anal. Chem., published online 26 July 2013 (10.1021/ac402057q). [Abstract]

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