Generation of Linear and Parabolic Concentration Gradients by Using a Christmas Tree-Shaped Microfluidic Network

Research on cavity-driven control methods for concentration gradient microdroplets with high precision and stability

Microfluidic chip technology, an emerging interdisciplinary field, enables precise control of fluids at micro- and nano-scales and is widely applied in biomedicine, chemical analysis, and drug screening. This study investigates the effect of the parameters of chip geometry and the flow rate of fluid on the performance of the droplet concentration gradient generator using a cave-based microfluidic chip structure through numerical simulation and experimental verification. Finite element simulation software, equipped with laminar flow, phase field, and dilute substance transfer modules, was employed to analyze the impact of geometric parameters (cavity number, cavity radius, contact length between the cavity and the central channel, and cavity interval length) on the concentration gradient curve. Additionally, the effect of the fluid flow rate on the frequency, size, and concentration of the generated microdroplets was explored. Results indicate that the number, radius, and contact length of cavities significantly affect the concentration gradient curve, while the interval length has a minimal impact. Precise control of droplet concentration, generation frequency, and size can be achieved by adjusting the flow rates of the dispersed phase and the continuous phase. This study provides a theoretical basis for the design and optimization of concentration gradient microfluidic chips and promotes the application of concentration gradient microdroplet technology in high-throughput drug screening, biological detection and chemical analysis.

Automated serial dilutions for high-dynamic-range assays enabled by fill-level-coupled valving in centrifugal microfluidics

We introduce a new concept for centrifugal microfluidics that enables fully automated serial dilution generation without any additional means besides temperature control. The key feature is time-independent, serial valving of mixing chambers by fill-level-coupled temperature change rate (FLC-TCR) actuated valving. The automated dilution is realized under continuous rotation which enables reliable control of wetting liquids without the need for any additional fabrication steps such as hydrophobic coating. All fluidic features are implemented in a monolithic fashion and disks are manufactured by foil thermoforming for scalable manufacturing. The new valving concept is demonstrated to reliably prevent valving if the diluted sample is not added to the mixing chamber (n = 30) and ensure valving if the dilution stage is completed (n = 15). The accuracy and precision of automated serial dilutions are verified by on-disk generation of qPCR standard curve dilutions and compared with manually generated reference dilutions. In a first step, the 5-log-stage standard curves are evaluated in a commercial qPCR thermocycler revealing a linearity of R2 ≥ 99.92% for the proposed LabDisk method vs. R2 ≥ 99.67% in manual reference dilutions. In a second step, the disk automated serial dilutions are combined with on-disk qPCR thermocycling and readout, both inside a LabDisk player. A 4-log-stage linearity of R2 ≥ 99.81% and a sensitivity of one leukemia associated ETV6-RUNX1 mutant DNA copy in a background of 100 000 wild-type DNA copies are achieved.