Controlling droplet size variability of a digital lab-on-a-chip for improved bio-assay performance

Although several applications of electrowetting on dielectric digital lab-on-a-chips are reported in literature, there is still a lack of knowledge about the influence of operational and design parameters on the performance of an analytical assay. This paper investigates how droplet size variability, introduced by droplet dispensing and splitting, influences the assay performance with respect to repeatability and accuracy and presents a novel method to reduce this variability. Both a theoretical and experimental approach were followed. Monte Carlo simulations were applied to study the cumulative effect of the variability caused by different droplet manipulations on the final assay performance. It is shown that a highly controllable droplet generation and manipulation is achieved with respect to droplet size variability through an accurate control of actuation voltage, activation time, relaxation time, and electrode size. As a case study, it is illustrated that through optimization of these parameters a complete on-chip calibration curve is obtained for a d-glucose assay with an average CV-value of 2%. These new insights aim to bring the digital lab-on-a-chip technology closer to researchers in the field of diagnostics offering them a valuable and accessible alternative to standard analysis platforms.