One of the major obstacles for early cancer diagnose, which can significantly increase the survival rate, is the lack of solutions for circulating tumor cells (CTCs) detection. ¹ The density of CTCs is as low as 200/mL or one tumor cell per 10⁹ haematologic cells in the blood, making it almost impossible to detect using conventional methods. Leveraging the advantages like sophisticated structure design, comparable size to cells, integrated capabilities, microfluidic technologies have emerged as a powerful tool for CTCs detection²  based on antibodies, aptamers and differences in cellular biophysics, among which aptamers are drawing more and more attention for their stability, excellent selectivity and outstanding potential for modification.³  Although the convergence of microfluidics and aptamers have led to considerable advances to detect CTCs, few methods promised the ability to detect multiple kinds of CTCs at the same time. ⁴ To confront this challenge, here we exploited a simple and robust microchip to perform multiple tumor cells capture, enrichment, detection as well as post-capture analysis. The microchip is composed of parallel straight channels linked by narrow connection channels at the ends, which will function as stop flow junctions as liquid flows through the main channels due to surface tension, enabling convenient respective manipulations in different channels. ⁵ Thus different aptamers could be immobilized in separate channels easily and capture corresponding tumor cells as the samples pass through. Then the tumor cells could be recycled for further research or directly analyzed by mass spectrometer after online extraction by on-chip solid phase extraction (SPE) columns. The proposed system is considered helpful to promote CTCs research as well as multicomponent analysis for other targets like proteins or small molecules.

This work was supported by National Natural Science Foundation of China (Nos. 91213305, 20935002).