New Method Uses Stimulated Raman Spectroscopy for High-Throughput Cell Sorting

Boston University researchers have developed a novel high-throughput single-cell sorting technique using stimulated Raman spectroscopy (S-RACE), departing from the conventional fluorescence-activated cell sorting method. This novel approach, which will be presented by Jing Zhang at the upcoming Frontiers in Optics + Laser Science (FiO LS) conference, could transform cell sorting for various applications such as microbiology, cancer detection, and cell therapy.

According to Zhang, S-RACE introduces a pioneering strategy to sort cells based on their internal chemical composition while maintaining high throughput. Unlike traditional fluorescence-based techniques, S-RACE offers label-free and non-destructive cell analysis. This is especially advantageous for sorting small cells, including microorganisms like bacteria. For instance, S-RACE can capture specific metabolic profiles directly from natural habitats like water bodies or the gastrointestinal tract, paving the way for tasks such as cell taxonomy identification and ecological function assessment.

Conventional flow cytometry relies heavily on fluorescence signals for cell sorting. However, fluorescence labels can disturb cell functions and aren't suitable for small molecules. Stimulated Raman spectroscopy offers an alternative by providing a label-free and non-destructive approach to capturing a cell's chemical fingerprint. Overcoming the challenge of obtaining strong Raman signals and a practical microfluidic setup, the researchers harnessed stimulated Raman spectroscopy, which generates a signal several orders of magnitude higher than spontaneous Raman scattering.

In this method, stimulated Raman images identify target cells, and a pulsed laser is directed at the cells using galvo mirrors. An acousto-optic modulator acts as a fast pulse picker to push selected cells into the collector, a process taking a mere 8 milliseconds per ejection.

The researchers validated their technique using polymer beads, achieving high purity and throughput. They extended the method to live yeast cells by introducing a protective layer and a collector to ensure successful cell landing. The successful growth of ejected yeast cells after approximately 40 hours demonstrated the viability of the approach.