Volume of Droplet Generated


#1

Hi,
How can we identify/calculate the volume of the generated droplet in dropbot chip ?

The way I calculated is given below. Please correct me if I am wrong;

The dimension of transportation electrode = 2.1mm * 2.06mm
Gap between top plate and bottom plate = 100 micrometer
So the total volume generated over each electrode is 0.43 microliter

Is this calculation and dimension identified is correct ?.
If wrong, could you tell me the volume generated and the way of calculation ?
is it depends on the nature of each solutions?

Thanks in advance


#2

The gap size is ~180 um and electrodes are nominally 2.25 mm x 2.25 mm (2.252.250.18=0.911 uL). Drops are usually slightly larger than a single electrode, so close to 1uL is a good approximation. It is possible to get a more accurate droplet footprint area (rather than just assuming 2.25 mm x 2.25 mm) using a camera or capacitance measurements.


#3

Dear Ryan,
Thanks for the response,

But does it varies depends on the solutions we used for droplet generation. ? For example, for solutions having different densities.


#4

Density shouldn’t have any impact since the volume depends only on the footprint area of the droplet times the gap height.


#5

Thanks for the reply,
I have cross-checked the concept and I got the same result. By activating generation electrode and one transportation electrode, a droplet of 1 micro-liter is generated. Thanks a lot for the advise.

I need to use different bio-buffers. I have checked the contact angle of each solutions and found all are having different contact angle.

Does it (different contact angle) affect the generated Volume quantity (~1 micro-liter) for respective buffers, or NO physical or chemical parameters affect the volume of generated droplet in dropbot. It just depends upon the dimension of electrode and gap.

Thanks in advance.


#6

This article may be of interest:

Elvira et al. “Droplet Dispensing in Digital Microfluidic Devices: Assessment of Long-Term Reproducibility.” Biomicrofluidics 6, no. 2 (April 6, 2012): 022003-022003–10.

The contact angle will certainly have an affect; however, it really depends how accurate your volume estimates need to be. I expect capacitance/optical measurements should be accurate to within ~2-5%. Some potential sources of error might include drop curvature/contact angle, electrical noise, capacitive fringe fields, etc. In most applications, I expect that this level of accuracy is probably sufficient as it is similar to what you can achieve with a pipette.