S. Lutz

Dye-based coatings for hydrophobic valves and their application to polymer labs-on-a-chip

We provide a method for the selective surface patterning of microfluidic chips with hydrophobic fluoropolymers which is demonstrated by the fabrication of hydrophobic valves via dispensing. It enables efficient optical quality control for the surface patterning thus permitting the low-cost production of highly reproducible hydrophobic valves. Specifically, different dyes for fluoropolymers enabling visual quality control (QC) are investigated, and two fluoropolymer-solvent-dye solutions based on fluorescent quantum dots (QD) and carbon black (CB) are presented in detail. The latter creates superhydrophobic surfaces on arbitrary substrates, e.g. chips made from cyclic olefin copolymer (COC, water contact angle = 157.9°), provides good visibility for the visual QC in polymer labs-on-a-chip and increases the burst pressures of the hydrophobic valves. Finally, an application is presented which aims at the on-chip amplification of mRNA based on defined flow control by hydrophobic valves is presented. Here, the optimization based on QC in combination with the Teflon-CB coating improves the burst pressure reproducibility from 14.5% down to 6.1% compared to Teflon-coated valves.

Microthermoforming of microfluidic substrates by soft lithography (µTSL): optimization using design of experiments

We present a detailed analysis of microthermoforming by soft lithography (μTSL) for replication of foil-based microfluidic substrates. The process was systematically optimized by design of experiments (DOE) enabling fabrication of defect-free lab-on-a-chip devices. After the assessment of typical error patterns we optimized the process toward the minimum deviation between mold and thermoformed foil substrates. The following process parameters have most significant impact on the dimensional responses (p 40% relative impact. The DOE results in an empirical process model with a maximum deviation between the prediction and experimental proof of 2% for the optimum parameter set. Finally, process optimization is validated by the fabrication and testing of a microfluidic structure for blood plasma separation from human whole blood. The optimized process enabled metering of a nominal volume of 4.0 μl of blood plasma with an accuracy deviation of 3% and a metering precision of ±7.0%. The μTSL process takes about 30 min and easily enables the replication of 300 μm wide microchannels having vertical sidewalls without any draft angles in a well-controllable way. It proves to be suitable for multiple applications in the field of microfluidic devices. S Online supplementary data available from stacks.iop.org/JMM/21/115002/mmedia (Some figures in this article are in colour only in the electronic version)

Aliquoting structure for centrifugal microfluidics based on a new pneumatic valve

We present a new microvalve that can be monolithically integrated in centrifugally driven lab-on-a-chip systems. In contrast to existing operation principles that use hydrophobic patches, geometrically defined capillary stops or siphons, here we present a pneumatic principle. It needs neither additional local coatings nor expensive micro sized geometries. The valve is controlled by the spinning frequency and can be switched to be open when the centrifugal pressure overcomes the pneumatic pressure inside an unvented reaction cavity. We designed and characterized valves ranging in centrifugal burst pressure from 6700 Pa to 2100 Pa. Based on this valving principle we present a new structure for aliquoting of liquids. We experimentally demonstrated this by splitting 105 muL volumes into 16 aliquots with a volume CV of 3 %.

Vacuum supported liquid waste handling for dna extraction on centrifugally operated Lab-on-a-Chip systems

We present a reliable liquid waste containment for centrifugally operated Lab-on-a-Chip systems that works even for highly wetting reagents. It is based on the passive generation and enclosure of vacuum in a closed storage chamber that prevents all liquids from capillary reflux into the microfluidic channel network. The new waste handling presented here enabled the implementation of an integrated deoxyribonucleic acid (DNA) extraction chemistry without contamination risks based on purely passive structures. Using a 32 μL whole blood sample we achieved an extraction of 290 ng ± 80 ng DNA in 100 μL of eluate.