"Cell-On-Demand" Digital Microfluidics for Real-Time Low-Abundance Single-Cell Isolation and Sample Analysis.

Studying low-abundance cells at the single-cell level is critical for revealing unique biological functions. Efficient single-cell isolation technology can significantly enhance low-abundance single-cell detection sensitivity. However, the lack of individual control over each target cell hinders further bio-analysis. Here, a "cell-on-demand" large-scale digital microfluidics platform is reported for real-time low-abundance single-cell manipulations. Compared to the conventional strategy that sequentially identifies the target cells among the heterogeneous population, the "cell-on-demand" method can conduct targeted-search-guided target cell isolation, enabled by on-demand droplet splitting. The results demonstrate that "cell-on-demand" is nearly eightfold more effective compared to the conventional strategy in dealing with low-abundance (1%) single-cells. To validate the system's feasibility, heterogenous tumor spheroids samples are used for isolating homogeneous single-target tumor spheroids, in integration with subsequent drug sensitivity testing and analysis. Drug sensitivity results show significant differences in half-maximal inhibitory concentration (IC50) for three chemotherapy drugs: Fluorouracil, Irinotecan, and Oxaliplatin, while in high consistency with well-plate-based assays. With the capability of processing both high and low-abundance samples, the proposed platform shows potential in handling various samples and in broader applications.