Abstract
Compartmentalized microfluidic devices with immobilized catalysts are a valuable tool for overcoming the incompatibility challenge in (bio) catalytic cascade reactions and high-throughput screening of multiple reaction parameters. To achieve flow control in microfluidics, stimuli-responsive hydrogel microvalves were previously introduced. However, an application of this valve concept for the control of multistep reactions was not yet shown. To fill this gap, we show the integration of thermoresponsive poly(N-isopropylacrylamide) (PNiPAAm) microvalves (diameter: 500 and 600 µm) into PDMS-on-glass microfluidic devices for the control of parallelized enzyme-catalyzed cascade reactions. As a proof-of-principle, the biocatalysts glucose oxidase (GOx), horseradish peroxidase (HRP) and myoglobin (Myo) were immobilized in photopatterned hydrogel dot arrays (diameter of the dots: 350 µm, amount of enzymes: 0.13–2.3 µg) within three compartments of the device. Switching of the microvalves was achieved within 4 to 6 s and thereby the fluid pathway of the enzyme substrate solution (5 mmol/L) in the device was determined. Consequently, either the enzyme cascade reaction GOx-HRP or GOx-Myo was performed and continuously quantified by ultraviolet-visible (UV-Vis) spectroscopy. The functionality of the microvalves was shown in four hourly switching cycles and visualized by the path-dependent substrate conversion.
Highlights
Stimulated by advancements in the fabrication of miniaturized microfluidic devices and the miniaturization of biochemical analysis, microfluidic systems have evolved to a powerful method in biomedical and chemical research over the last decades [1,2]
Thereby, the hydrogels were analyzed with a microscope to measure the time required for triggered swelling and shrinking and the successful switching was derived from observations of the flMuicirdomflaochwin.esC2l0e2a0r,l1y1,a16f7unctional valve must allow the fluid to pass when it is in the open state an1d0 foufll1y6 prevent the fluid flow when it is in the closed state
Electrothermally controlled hydrogel microvalves synthesized from PNiPAAm and the crosslinker BIS were integrated into a valve seat in the device
Summary
Stimulated by advancements in the fabrication of miniaturized microfluidic devices and the miniaturization of biochemical analysis, microfluidic systems have evolved to a powerful method in biomedical and chemical research over the last decades [1,2]. As these “labs-on-chips” allow a high integration density of multiple functions such as mixing and separation of small amounts of fluids, even complex samples can be prepared, processed, and analyzed in a short time. In onFeoorfinthteegseraatpiopnrooaf chhyedsr,ohgyedl rvoaglvelessairnetomtihceromstircurocftluurieddicbdyepvhicoetso,ptwoloymstreartiezgaiteiosnaroendaesgclraisbsesdl.idIne oannde oafPthDeMseSasphpereotaicshaelsi,ghnyeddroognetlospa.reWmitihcrtohsitsrutecctuhrneidqubey, phhigohtonpuomlybmeersrizoafthioyndroongaelgvlaaslsveslsidceananbde a PDMS sheet is aligned on top With this technique, high numbers of hydrogel valves can be simultaneously integrated into one microfluidic chip [26]. In this respect, handling issues of the device are discussed as well
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