Taking Advantage of Reduced Droplet-surface Interaction to Optimize Transport of Bioanalytes in Digital Microfluidics

The overall goal of this procedure is to fabricate a field de wetting device capable of transporting droplets with bio analytes without additives. This is accomplished by first coating a conductive substrate with candle soot. The substrate will serve as the bottom electrode of the device.

The second step is to protect the soot layer by applying liquid fluoro polymers. Next, fabricate the top electrodes of the device. Then connect the top and bottom electrodes to the electronics of the experiment.

The final step is to place a sample between the electrodes to test the device. Ultimately, results shows that field de wetting devices can support continued droplet transfer in response to each electric pulse for at least 700 pulses. The main advantages of this technique over existing methods like Electrowetting is that the electric field does not lead to wetting, and there's no need of extra additives for droplet transport.

The implication of this technique extend toward the development of a fully automated lab on a chip platform that work regardless of droplet chemistry, Demonstrating the procedures will be Michael Kowski and Selena do undergraduate researchers from my lab. The first step is to prepare the conductive substrate for the ground electrode. For this purpose, a copper sheet has been cut into rectangles.

The rectangles are 75 millimeters by 43 millimeters with a thickness of 0.5 millimeters. Ready, A container of copper etching to clean the substrates. This video will follow the protocol using only one substrate.

Immerse the substrate in the etching for about 30 seconds. After immersion, recover the substrate and wash it by running. Tap water over it, dry it with paper, and before proceeding, place it horizontally on a support that allows access to its downward facing surface.

For this video, a mounted open ring is used. Have a mixture of liquid fluoropolymer and a dropper for its application ready. Obtain a paraffin candle to provide the soot that will be applied.

Light it and continue by sweeping the candle under the copper substrate. Maintain the top of the flame approximately one centimeter below the bottom of the substrate. Continue sweeping the candle for 30 to 45 seconds.

Taking care not to touch the soot surface. After coating the substrate with soot, remove and extinguish the candle Immediately. Use tweezers to grasp the substrate and rotate it to expose the soot covered side.

While it is still warm, use a dropper to deposit droplets of the liquid fluoro polymer on the edges to localize the disturbance of the soot layer. Once the drops have been applied, tilt the substrate so that it is almost vertical. Then deposit more droplets and let them roll over the entire soot surface spreading.

As much as possible. Continue by taking the substrate to a hot plate held at 160 degrees Celsius. Also inside the chemical hood, place the substrate soot side facing up on a hot plate to bake for 15 minutes.

After 15 minutes, take the substrate off the hot plate and let it sit overnight at room temperature before using it as a bottom electrode. The substrate can be stored indefinitely when the ground electrode is ready for use. The next step is to prepare the top electrodes.

This video uses electrodes fabricated following a protocol from the literature. The electrode design was printed on a thin copper laminate etched and cleaned to get to this point. Each of the 10 electrodes is two millimeters wide and 0.3 millimeters in width.

The electrodes will be mounted on a glass slide that is 75 millimeters by 25 millimeters and about one millimeter thick. Apply double-sided tape to one end of the slide and avoid introducing air pockets. Then carefully attach the laminate to the slide so the electrodes are close to the edge.

Next, cut a piece of per Fluor al coy film about the width of the slide. Place the film over the electrodes to prevent accidental short circuits. Attach it with tape.

The electrodes can now be used with the electronic interface. Take both the top and bottom electrodes to the experimental setup to complete the field de wetting device. In the experimental setup, the bottom electrode is electrically grounded.

Above it, the top electrodes are connected to relays via an adjustable height connector. Control the microfluidics device with a computer program that moves a droplet between adjacent electrodes. In this experiment, the motion of droplets in the microfluidics device will be visualized.

Use a 24 96 magnification assembly combined with a CCD camera. Connect a video recorder to the camera using S video. At this point, obtain a sample for the experiment in this case, C elegance and medium pipette of four microliter droplet.

Place the droplet on the soot coated bottom electrode so it is in the center of the top electrodes. Then adjust the position of the top electrodes, so they are about 0.3 millimeters above the droplet. With the electronic interface and the high voltage on, adjust the height of the top electrode until the droplet starts moving.

Do not let the electrode touch the droplet. Once droplet motion is stable, start recording with the camera until the droplet does not move in response to five to 10 pulses. This video shows the successful transfer of C elgan in medium between the electrodes of a field dueting device.

Previous work with fluorescently tagged bovine serum albumin or BSA helps demonstrate the interaction between samples and the substrate at left. The BSA sits on a soot coated surface in contrast at right on a surface using only a fluorinated liquid. The BSA sample shows a strong surface interaction.

After watching this video, you should have a good understanding of how to fabricate, feel the wedding devices. Don't forget to follow lab safety guidelines.