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

Abstract

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.