Circulating tumor cells (CTCs) are rare cells with extremely low abundance in peripheral blood and have shown extensive molecular heterogeneity. However, just enumeration of CTCs could not reflect the heterogeneity of tumor biology. Therefore, there is an urgent need to develop single-CTC picking method to better understand the role of individual CTC at molecular biology level.

In a study published in IEEE Xplore, a research group led by Prof. LI Bei from Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) and collaborators Prof. WANG Wei from Peking University proposed a new idea to pick single cells from 10 mL sample based on a microfiltration-Laser-induced forward transfer (LIFT) combination platform.

First, a microfiltration-LIFT platform was developed (Figure. 1). The microfiltration was composed of a contacted bilayer of micropore-arrayed filters (PERFECT filters) with two different pore diagonal diameters. The upper layer with a large pore size could isolate the liquid layer of the trapped cell, eliminating the stiction of the liquid layer to the captured cells, and thus reduce the energy required for cell transfer during the LIFT. While the lower layer with a small pore size was used for size-based cell separation and enrichment.

Figure 1. Microfiltration-LIFT platform (Image by WANG)

COMSOL simulation analysis was performed to assess the damage to cells during the single cell picking-up process. The metal film that laser spotted on was around 2700℃, while the liquid 0.6 μm away from the metal layer was less than 27°C within 100 ns. The transfer time of the pulse laser (6 ns) was far less than 100 ns. It indicated the LIFT operation was safe to the target cell.

The whole process of microfiltration-LIFT platform for single cell picking-up is that: First, the contacted bilayer of micropore-arrayed filters was attached onto the transparent glass slide of the LIFT system after filtration. Then, the target cell was identified by fluorescent staining method. Next, the target cell was instantaneously transferred off the microfiltration device at 350 nJ in 6 ns, which showed that the target cell was picked up successfully and the cell was found on the cell receiver right under the glass slide.

This study successfully developed a novel platform facilitating the pure single cell isolation and picking from a large volume sample. The heterogeneity molecular analyses of CTC will be feasible on at different time points for the patients rather than just quantitative characterization.