Reliable and Low Temperature Actuation of Water and Oil Slugs in Janus Photothermal Slippery Tube.

While actuating liquid with external stimuli on open surfaces has been extensively studied, the actuation in tubes or channels is much more challenging due to the lower accessibility and higher complexity in material/device design, despite its crucial importance for microfluidic applications. Of various potential actuation methods, optical ones are particularly interesting because they can be remotely controlled with high spatial/temporal resolution. Yet, previous optical methods relied on the physical deformation of tubes, raising the concern of material fatigue and compromising reliability. Here we develop a low temperature photothermal method to actuate various liquids including water and oil in a tube. The tube has Janus configuration, with the upper part allowing light transmission and lower part imparted with high photothermal property. Combining with experiments and calculation, we show that the photothermal effect induces a wettability gradient to drive the liquid transport. Compared with the methods based on physical deformation, our method is more robust and can repeatedly function for at least 20 times. Thanks to the slippery surface, the actuation can be initiated at a moderate temperature of ∼40 °C, mitigating the risk of biomolecule degradation. We therefore expect our work to pave the way toward practical biomedical microfluidic applications.