A solvent replenishment solution for managing evaporation of biochemical reactions in air-matrix digital microfluidics devices

Abstract

Digital microfluidics (DMF) is a powerful technique for sample preparation and analysis for a broad range of biological and chemical applications. In many cases, it is desirable to carry out DMF on an open surface, such that the matrix surrounding the droplets is ambient air. However, the utility of the air-matrix DMF format has been severely limited by problems with droplet evaporation, especially when the droplet-based biochemical reactions require high temperatures for long periods of time. We present a simple solution for managing evaporation in air-matrix DMF: just-in-time replenishment of the reaction volume using droplets of solvent. We demonstrate that this solution enables DMF-mediated execution of several different biochemical reactions (RNA fragmentation, first-strand cDNA synthesis, and PCR) over a range of temperatures (4-95 °C) and incubation times (up to 1 h or more) without use of oil, humidifying chambers, or off-chip heating modules. Reaction volumes and temperatures were maintained roughly constant over the course of each experiment, such that the reaction kinetics and products generated by the air-matrix DMF device were comparable to those of conventional benchscale reactions. This simple yet effective solution for evaporation management is an important advance in developing air-matrix DMF for a wide variety of new, high-impact applications, particularly in the biomedical sciences.

Digital Microfluidics for Nucleic Acid Amplification

“…As mentioned, DMF systems usually rely on a two-plate architecture, resorting to fillers to help prevent evaporation, one of the key issues in low-volume reactions. However, Jebrail et al propose a simple approach to use a two-plate air-matrix DMF platform that prevents evaporation on PCR reactions, by refilling reaction droplets with pre-heated solvents whenever necessary [ 22 ]. This DMF platform consists of a PCB bottom-plate with Cu/Ni/Au electrodes and reservoirs, covered by a solder mask dielectric layer and a Teflon ® hydrophobic layer, and includes a hole connecting the platform to a syringe, which contains refill solvent, through a tube ( Figure 3 a).…”

Simulation of feedback-driven PCR assays on a 2D electrowetting array using a domain-specific high-level biological programming language

“…For each replenishment probability, we run the algorithm using five random number seeds and report the average execution time across the five runs. To reduce simulation time, we execute 9 thermocycles, as opposed to the 33 thermocycles suggested by the authors of the replenishment study [14]. Table 2 reports the results of this experiment.…”

“…Enzymatic reactions, for example, are sensitive to variations in reactant concentration. To address this concern, Jebrail et al [14] implemented a digital microfluidic system that pre-heats droplets of solvent and uses them to replenish an otherwise perpetually diminishing reaction volume during PCR thermocycling. Replenishment occurs when a droplet has lost 15-20% of its volume.…”

“…Secondly, control is provided exclusively through electricity, which eliminates the need for external pressure sources, which significant inhibit the ability to remove other LoCs from the laboratory for usage in the field. Thirdly, the electrical interface provided by a DMFB is a natural match for computer control; thus, there has been interest in the development of programming languages, compiler technology and software control of DMFBs in recent years [5,9,11,14,18,27,28].…”

“…The assays that we simulate are PCR variants: one uses sensory feedback to terminate thermocycling early when the initial droplet contains insufficient Microelectronic Engineering 148 (2015) 110-116 product for amplification [18]; the other uses integrated sensors to detect droplet evaporation during thermocycling in an air-matrix digital microfluidic system, and performs just-in-time replenishment using droplets of solvent to ensure that the reaction volume remains within an acceptable window [14]. This study establishes the viability and validity of software-driven programming of digital microfluidic EWoD systems, and serves to motivate further research on this topic.…”