The research on Raman-activated cell sorting at QIBEBT was highlighted by The Scientist on June 1^st, 2015.

RAMAN-ACTIVATED CELL SORTING 

RESEARCHER: Jian Xu, Professor and Director, and Bo Ma, Group Lead of Microfluidics, Single-Cell Center, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences 

PROJECT: Microbial biofuels development

PROBLEM: Biofuels R&D requires identifying cells capable of specific carbon chemistries. But as these cells have yet to be cultured and studied, researchers have few if any molecular hooks for identifying and sorting them. 

SOLUTION: The team turned to a label-free method of single-cell interrogation known as Raman-activated cell sorting (RACS) (Anal Chem, 87: 2282-89, 2015). 

Raman spectroscopy captures a sample’s molecular fingerprint. When a specimen is illuminated with a laser beam of a specific wavelength, most of the light bounces back at that same wavelength, as with a mirror. A very small fraction, though, does not, reflecting the sample’s molecular composition. This is called Raman scattering. 

“Raman gives you global information about the cell—nucleic acids, proteins, lipids, starch, pigments, everything—all at the same time,” Xu says. Such information can help researchers identify which cells in a microbial consortium fix carbon dioxide, degrade cellulose, or produce starch or oil, for instance.   

Ma and Xu developed a microfluidic circuit and instrument that captures, holds, and interrogates single cells for anywhere from milliseconds to seconds, however long is necessary to acquire and interpret the Raman signal. “For most cells, it’s less than a second,” Xu says, and up to four cells per second is possible—a substantial improvement over previous efforts, which required up to three minutes per cell. 

Cell signals are compared to a database of Raman signatures to identify positives. That, in turn, activates a suction-based sorting mechanism. 

Xu and Ma used the system to sort a heterogeneous yeast population, only some of which produced carotenoids, producing an eight-fold enrichment. Now they are working to apply their system to such problems as identifying antibiotic-resistant bacteria, sorting stem cells, and selecting better biofuel producers. 

USER ACCESS: According to Xu, two microfluidic RACS systems have been installed in China, and two more are in the works. A third is being installed at Oxford University. Users will be able to request time on any of these instruments, Xu says. “Any question is welcome. We have funding to support this kind of collaboration.” (The Scientist)