Raman activated droplet sorting

The mining of useful enzymes and microbial cells that produce them has dated back nearly a century. However, such endeavors can be very slow and difficult due to the tiny size of microbes—1000 times smaller than a human cell. Moreover, most of the microbial cells cannot be readily cultured—for this reason, microbiologists call them "biological dark matter."

 "This is a flow-mode Raman-activated Cell Sorter that can sort microbial cells and enzymes they produced, based on Single-cell Raman Spectrum and in a high-throughput manner,"

Single-cell Raman spectra can reveal the metabolic function of a cell, such as the kind of oils produced or the rate of carbon dioxide fixed, without destroying the cell. Based on these signals, cells are sorted in RACS. If the cells are sitting still during sorting, this would be easier, but very slow. To speed up the sorting, cells can be lined up and moved rapidly through a spectrum detection point one by one. However, such flow-mode RACS can be much more difficult due to the very small size of microbial cells and the weak Raman signal.

To improve the process, researchers applied positive dielectrophoresis (pDEP), which can capture or mobilize particles. This allows trapping fast-moving single microbial cells, processing them precisely yet rapidly through a Raman detection point to recognize those cells that produce particular enzymes or metabolites, and then packaging cells into droplets. In the end, the droplets that harbor target cells are sorted. In this pDEP Raman-activated droplet sorting, or pDEP-RADS, the cells do not require culturing, labeling or invasive action in order to be sorted and identified at a high speed.

"Such culture-free, label-free and non-invasive sorting of enzyme activity in vivo can save time, consumable and labor by one to two orders of magnitude, as compared to conventional approaches,"

 

 

 

 

reference

Xixian Wang et al. Positive dielectrophoresis–based Raman-activated droplet sorting for culture-free and label-free screening of enzyme function in vivo, Science Advances (2020). DOI: 10.1126/sciadv.abb3521