Here, we developed a novel and facile method to control the local water adhesion force of a thin and stretchable superhydrophobic polydimethylsiloxane (PDMS) substrate with micro-pillar arrays that allows the individual manipulation of droplet motions including moving, merging and mixing. When a vacuum pressure was applied below the PDMS substrate, a local dimple structure was formed and the water adhesion force of structure was significantly changed owing to the dynamically varied pillar density. With the help of the lowered water adhesion force and the slope angle of the formed dimple structure, the motion of individual water droplets could be precisely controlled, which facilitated the creation of a droplet-based microfluidic platform capable of a programmable manipulation of droplets. We showed that the platform could be used in newer and emerging microfluidic operations such as surface-enhanced Raman spectroscopy with extremely high sensing capability (10-15 M) and in vitro small interfering RNA transfection with enhanced transfection efficiency of ∼80%.
Bibliographical noteFunding Information:
This work was supported by the grant (2012-0006689, 2014R1A2A2A09053061, CASE-2014M3A6A5060933 and 2013R1A1A2A10061422) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology. This work was partially supported by the Yonsei University Future-leading Research Initiative. We thank the Tanaka Kikinzoku Kogyo K.K. for comments on the usage of silver nanoparticles.
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