Fotopyroelektrisk mikrofluidik udviklet af forskere

Præcis manipulation af forskellige væsker er afgørende på mange områder og i modsætning til faste genstande, væsker er iboende delelige. Væsker er også klæbrige med passende funktioner til tabsfri manipulation for at forhindre tab og forurening. I en ny rapport, der nu er offentliggjort den Videnskabens fremskridt , Wei Li og kolleger inden for maskinteknik og forskning og innovation i Kina præsenterede fotopyroelektrisk mikrofluidik for at opfylde så forskellige krav. Den fluidiske platform lettede udviklingen af ​​et unikt bølget dielektroforetisk kraftfelt fra en enkelt lysstråle til bemærkelsesværdigt at udføre den ønskede tabsfri manipulation af dråber og fungere som en "magisk" vådningssikker overflade. Den flydende platform kunne navigere, sikring, klemme og spalte væsker efter behov for at etablere fragtskibe med dråbehjul og har potentiale til at opgradere den maksimale koncentration af leverancer såsom protein med 4000 gange.

Eksisterende metoder til at fusionere væsker

Overflademanipulation af buffere og organiske opløsningsmidler er fundamental for mange biologiske anvendelser og kemiske funktioner, der er kritiske for en række forskellige termiske, optiske og medicinske applikationer. For at opnå dette, Forskere skal designe en platform, der gør det muligt for lokalt adresserbare væsker til navigation med en lav tabsrate at opdele og smelte sammen i en let styret proces. Lys kan udkonkurrere andre stimuli på grund af dets kontaktløse natur, høj præcision, og moden strålestyrbarhed i forhold til geometrisk optik, for eksempel, at danne en optisk pincet, der fanger og fjerner mikroobjekter. Adskillige tilgange har derfor udforsket potentialet til at fotomanipulere væsker ved at udnytte energiomdannelsen af ​​fotoelektriske, fototermisk, fotokemiske og fotomekaniske egenskaber til præcist at navigere og flette væsker. Alligevel, disse teknikker kan ikke opdele og manipulere væsker på en tabsfri måde. Derfor, i dette arbejde, Li et al. præsenteret en hidtil uset tilgang.

Den nye tilgang

Holdet stablede simpelthen tre homogene lag, inklusive en fototermisk film, der anvender en grafen-doteret polymer, pyroelektrisk krystal ved hjælp af en lithiumniobatwafer, og en superomnifob overflade ved hjælp af en silica nanosfære. De tre lag fungerede sammen til tabsfri påføring af jævne, væsker med ultralav overfladespænding i nærværelse af en enkelt lysstråle.

De komponerede den fototermiske film med en grafen-monolagskomposit for at fornemme lysstimuli og fornemme reaktionerne genereret af ujævn termogenese. Den pyroelektriske krystal omdannede varme til ekstra elektriske ladninger for at danne en bølget dielektroforetisk kraftprofil, der kunne fange, dispensere og dele væskerne. De brugte teknikken til at udføre fire grundlæggende funktioner, herunder bevægelse, sammensmeltning, dispensering og spaltning af forskellige væsker under velkontrolleret, tabsfrie forhold uden komplicerede elektroder og højspændingskredsløb. Tilgangen vil have betydelig indflydelse på tværs af tværfaglige områder.

Designing photopyroelectric microfluidics

Li and team used the three layers of closely sandwiched materials (the pyroelectric crystal, superomniphobic thin film and photothermal thin film) to form the platform. The top superomniphobic layer contained nanoscale fractal networks made by sintering hollow silica spheres covered with fluorinated surfactants to achieve super-repellence. In the bottom layer, they formed a uniform composite film by homogenizing graphene nanoplatelets with polydimethylsiloxane (PDMS) and cured the polymer. 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. The scientists applied the technique to a variety of liquids including organic solvents such as silicone oil, alkanes and alcohols. The platform provided a channel-free, open-space fluidic processor without the hassle of electrodes or micropatterning required for currently existing microfluidic counterparts.

Loss-free fluid interfacing, light sensitive sensing, and droplet dynamics

The superomniphobic surface was chemically resistant to corrosive acids and bases, allowing a stable cassie state to remain on the surface for chemical fluidic processing. The scientists confirmed loss-free fluid interfacing via fluorescence imaging of the omniphobic surface and compared the results with controls to show near loss-free contact with fluids on the material of interest. Li et al. thereafter noted the light-sensing capacity of the system to show the conversion of irradiated light into a sharply bulged temperature profile in the system. They then investigated the motion of a 5 microliter (µl) droplet of water placed 13 mm away from the light spot center. When they turned the laser on, the droplet was attracted to the illumination in an oscillating mode, where it initially accelerated toward the laser, then rapidly braked and reversed direction on reaching the light spot's edge. To understand the underlying physics of droplet dynamics, the team developed a numerical simulation and varied the liquid types for the calculations to show that higher the relative permittivity and surface tension, the easier for liquid motion.

The team performed a variety of fluidic functions using a single beam of laser light, where the wavy dielectrophoretic force profile could unexpectedly trap and move droplets with a volume as low as 0.001 µL. The team also handled a 200 µL puddle without loss on the platform, suited for miniaturization of biomedical systems. Imidlertid, the technique had its limits with a maximum laser-moving velocity beyond which the droplet could not keep up with laser movement. Derudover Li et al. facilitated a strong navigating force for droplets to defy gravity and ascend uphill by placing the platform vertically, allowing the superior technique to precisely manipulate various liquids at the micro-/nanoliter scale, which is of fundamental importance across multiple fields. Ved hjælp af metoden, the team observed the loss-free detection of amino acids such as glycine and low-surface tension liquids such as ethanol. The method has great potential in analytical chemistry, medical diagnosis, og biomedicin.

På denne måde Wei Li and colleagues developed a unique wavy dielectrophoretic force field in response to light stimuli with a three-layered surface for well-controlled, loss-free liquid motion, merging, dispensing and splitting functionalities. They readily modified the force by superimposing multiple light irradiations for richer fluidic functionality and droplet patterning applications. The method will facilitate fluid maneuver on demand for applications in biochemical and fluidic processing reactions, fluidic engineering and manufacturing for precision patterning and for droplet multi-compartmentalization.

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