Raman flow cytometry using time-delay integration

Raman flow cytometry offers chemically sensitive, label-free measurement of cells and particles; however, the technique suffers from low cell throughput due to the weak Raman signal. Here, we demonstrate the use of time-delay integration (TDI) to achieve Raman flow cytometry combined with dual-sided line illumination. The use of line illumination from both sides of the cell flow capillary kept the cell stream in the detection area by balancing optical force from the illumination lines. The TDI allowed the accumulation of Raman signals from flowing cells without sacrificing the spectrum readout rate. With the developed system, we achieved Raman flow cytometry at throughputs of 32 and 78 events per second for cell and particle detection, respectively. We applied the technique for analyzing biological cells and successfully detected lipid uptake in HepG2 cells and degranulation in bone-marrow-derived murine mast cells. Our TDI Raman flow cytometry approach improves the throughput of Raman-spectroscopy-based cell analysis and extends its applicability to a wider range of biomedical research.