The fluidic platform facilitated the development of a unique wavy dielectrophoretic force field from a single beam of light to remarkably perform the desired loss-free manipulation of droplets and function as a "magic" wetting-proof surface. The liquid platform could navigate, fuse, pinch and cleave fluids on demand to establish cargo carriers with droplet wheels and has potential to upgrade the maximum concentration of deliverables such as protein by 4000-fold.
scientists must design a platform to enable locally addressable fluids for navigation with a low loss rate to partition and merge in a readily controlled process. Light can outperform other stimuli due to its contactless nature, high precision, and mature ray controllability relative to geometric optics, for example, to form optical tweezers that trap and dislodge micro-objects. Several approaches have therefore explored the potential to photo-manipulate liquids by leveraging the energy conversion of photoelectric, photothermal, photochemical and photomechanical properties to precisely navigate and merge fluids. Nevertheless, these techniques cannot split and manipulate fluids in a loss-free manner. Therefore, in this work, Li et al. presented an unprecedented approach.
The team simply stacked three homogenous layers, including a photothermal film using a graphene-doped polymer, pyroelectric crystal using a lithium niobate wafer, and a superomniphobic surface using a silica nanosphere. The three layers functioned in concert for loss-free applications of even, ultra-low surface tension fluids in the presence of a single beam of light.
They composed the photothermal film with a graphene monolayer composite to sense the light stimuli and sense the responses generated by uneven thermogenesis. The pyroelectric crystal converted heat into extra electric charges to form a wavy dielectrophoretic force profile that could trap, dispense and split the fluids. They employed the technique to perform four fundamental functions including movement, merging, dispensing and splitting of various liquids under well-controlled, loss-free conditions without complicated electrodes and high-voltage circuits.
When a beam of near-infrared (NIR) light irradiated the surface, the translucent superomniphobic surface and pyroelectric wafer became a transparent window allowing the NIR to readily reach the underlying composite polymer film. This led to a partially uneven, localized temperature rise, giving form to extra surface free charges, allowing droplets on the superomniphobic surface to be driven forward to the irradiated spot via a dielectric force.
Using the method, the team observed the loss-free detection of amino acids such as glycine and low-surface tension liquids such as ethanol.
reference
Wei Li et al. Photopyroelectric microfluidics, Science Advances (2020). DOI: 10.1126/sciadv.abc1693