Photopyroelectric microfluidics and virus repellency on retention-proof interfaces

Abstract

Precision manipulation of various liquids is essential in many fields. Unlike solid objects, fluids are intrinsically divisible, enriching their fundamental operations with merging, dispensing, and splitting on top of moving. Fluids are sticky as well, calling for their lossless manipulation to prevent mass loss and contamination. Fluids containing virus/bacteria can be also highly infectious, demanding effective means to prohibit their retention on surface to reduce infection risk. However, current microfluidics platforms fail to manipulate fluids in a loss-free manner, leaving substantial residues that contaminate the handling tools and producing huge amount of hazardous waste. Additional manipulation strategies together with unconventional interfaces that prevent fluids retention as well as minimize the virus or bacteria attachment are highly demanded for contamination-free manipulation of various fluids at micro-/nanoliter scale. To manipulate liquids, we present photopyroelectric microfluidics that meet all the requirements. In response to the irradiation from even one single beam of light, our platform creates a unique wavy dielectrophoretic force field that is remarkably capable of performing desired loss­free (loss being 0.5% of existing one) manipulation of droplets of surface tension from 18.9 to 98.0 mN m−1 and volume from 1 nl to 1000 µl, functioning as a “magic” wetting-proof hand to navigate, fuse, pinch, and cleave fluids on demand, enabling cargo carriers with droplet wheels and upgrading the limit of maximum concentration of deliverable protein by 4000­fold. Together with its universality over a wide range of fluid types and volumes, the technique works as a precision wetting-proof liquid tweezer to manoeuvre fluids on demand, thus being of great potential in substantially advancing vast fields, micro assays, medical diagnosis, and droplet-enabled manufacturing and engineering, to name a few. To prevent alcohols retention, we report a super-alcohol-repellent coating by covering sintered hollow silica nanospheres with fully crosslinked perfluoroalkyl silane, which is remarkably super-repellent to diverse alcohols of surface tension from 20.9 to 64.8 mN m−1 and thus enables contamination-free light-controlled manipulation of alcohol droplets on the coating. More importantly, we uncover that the un-crosslinked perfluoroalkyl silane leads to the failure of alcohol-repellency. The annealing procedure could remove the unreacted saline and promote the condensation of silanol groups, showing the key role played by heat-mediated crosslinking of perfluoroalkyl silane in preparing superomniphobic coatings. Together with its superomniphobicity, the coating enables contamination-free processing of diverse liquids, thus being of considerable significance for biological, chemical and medical applications. To prevent virus retention, we propose to innovate personal protection using super-liquid-repellent coatings, wherein the deposition and penetration of SARS-CoV-2 droplets are prohibited. On coated surfaces, SARS-CoV-2 remnants are reduced by seven orders of magnitude, yielding a repelling efficacy far outperforming the inactivation rate of disinfectants. The SARS-CoV-2 remnant scales exponentially with the liquid/solid adhesion, uncovering the mechanism and effective means for minimizing SARS-CoV-2 attachment. The composite antiviral coating that both repels and inactivates SARS-CoV-2 is demonstrated by doping the liquid-repellent coating with silver nanoparticles. The novel virus-repellent strategy and insight into SARS-CoV-2-surface interaction are of considerable value in fighting the current COVID-19 pandemic and preventing future outbreaks.