High Dynamic Range Digital Assay Enabled by Dual-Volume Centrifugal Step Emulsification

We implement dual-volume centrifugal step emulsification on a single chip to extend the dynamic range of digital assays. Compared to published single-volume approaches, the range between the lower detection limit (LDL) and the upper limit of quantification (ULQ) increases by two orders of magnitude. In comparison to existing multivolume approaches, the dual-volume centrifugal step emulsification requires neither complex manufacturing nor specialized equipment. Sample metering into two subvolumes, droplet generation, and alignment of the droplets in two separate monolayers are performed automatically by microfluidic design. Digital quantification is demonstrated by exemplary droplet digital loop-mediated isothermal amplification (ddLAMP). Within 5 min, the reaction mix is split into subvolumes of 10.5 and 2.5 mu L, and 2,5k and 176k droplets are generated with diameters of 31.6 +/- 1.4 and 213.9 +/- 7.5 mu m, respectively. After 30 min of incubation, quantification over 5 log steps is demonstrated with a linearity of R-2 >= 0.992.

Automated summary

By implementing dual-volume centrifugal step emulsification on a single chip, the dynamic range of digital assays can be extended significantly, showing an increase of two orders of magnitude between the lower detection limit (LDL) and the upper limit of quantification (ULQ). This approach eliminates the need for complex manufacturing processes and specialized equipment, with sample metering, droplet generation, and quantification being automated through microfluidic design.