Fig 1.
Schematic of a commonly used DMF device in cross sectional view using bottom and top plates for droplet manipulation by EWOD. Drawing not to scale.
Fig 2.
Schematic block diagram of PortaDrop.
The hardware implemented on the mainboard and external devices and adapters are bordered in dashed lines. The green area indicates the main box of PortaDrop offering EWOD operation and integrated electrochemical measurements.
Fig 3.
(A) Schematic of the developed boost converter (B) Closed control loop of the boost converter to allow automated voltage level regulation independent of the load.
Fig 4.
H-bridge circuit to generate a bipolar high-voltage rectangle signal of the amplitude Vout. The optotriacs OT2 and OT4 or OT1 and OT3 are alternately switched to conducting state by a TTL rectangle signal provided by the microcontroller ATtiny45.
Fig 5.
Pull-down and pull-up network for EWOD pad control of one path electrode.
The capacity CPad# represents the path electrode and the counter electrode. By switching on OT2, the capacity is shortened and the corresponding path electrode deactivated. The path electrode is activated by making OT1 conductive instead of OT2 to apply the bipolar high-voltage signal to the Pad. Droplets overlapping the electric field lines will then be attracted, if a sufficiently high potential is applied.
Fig 6.
Photo of the assembled PortaDrop in operation.
The camera included in the lid can be placed on top of the box and provides a video of the experiment.
Fig 7.
Boost converter output voltage.
A predefined voltage profile is consequently transferred to the voltage regulator microcontroller. The output voltage of the boost converter is depicted for 3 runs.
Fig 8.
Voltage profile of a specific channel.
The voltage amplitude is adjusted to 100 V with a frequency of 10 Hz and the channel is turned on and off with an interval of 1 s. The inset depicts a magnification of one period clearly showing the applied frequency and voltage amplitude.
Fig 9.
(A) Microscope images of 10 individually dispensed droplets resting on pad 25 (B) Image processing procedure exemplary on droplet D1. The images are first converted to grayscale (B1), a threshold filtering is applied to amplify the edges (B2) and the area outside and inside the droplet is converted to black or white, respectively (B3). (B4) depicts the overlay of the droplet boundary (red) and the original image. (C) Derived droplet volume for droplet D1-D10 including mean value and standard deviation.
Fig 10.
Maximum average droplet velocity with respect to the applied voltage.
Fig 11.
EIS measurements during passive dispensing.
(A) Course of the electrical admittance at 205 kHz with respect to the number of the droplet moved across the EIS sensor normalized to droplet 0 (PBS). The droplet numbers 1 to 5 correspond to consequently applied DI water droplets. (B) Zoom plot to visualize the small deviations after the second exchange droplet.