Lack of droplet movement

#1

Dear Drop-botters

I have recently take over the DropBot setup here in York, UK and despite having manufactured nice devices and having a fully functional setup, I’m still struggling to get much droplet actuation going. Being fairly new to DMF I wanted to walk you through my setup and maybe someone can point out any glaring mistakes I might be making:

  1. The DropBot system is built using the instructions on the DropBot wiki and are as far as I can tell, fully functional. I’ve attached Device load calibration and High-voltage reference loads results. I have also attached a few pictures of the setup, where as far as I can tell, everything is connected correctly.

  2. The devices are fabricated in-house by me using chromium electrodes made by wet-etching in a standard clean-room photolithographic method (using the “SCI-BOTS 90 pin-array v3” mask design). The connector and ground pads are then masked off and 8µm Parylene-C is deposited. The pads are unmasked and finally I apply 100nm Teflon (AF1600). For the top layer I’m using commercially coated ITO-glass, also coated with Teflon.

  3. As for putting everything together I’ve struggled to find clear instructions, but I think I’ve managed to piece it all together from various post in this group. I use two layers of double sided tape (Scotch) to create ~140µm spacing between the two plates and tinfoil to connect the top electrode. I’ve attached a photo (ignore the gold, it’s now chromium). I’ve attached channel impedance scan for a particular device.

  4. For testing purposes I’ve simply been using DI water with 2% (w/w) Tween20.

Loading the reservoirs usually goes quite well and the liquid stays nicely on the electrode. When I start actuating other electrodes very little happens and where I’m currently stuck.

Like I said, I’m quite new to DMF so anyone has any useful inputs at all I would be very grateful. Thanks in advance,

\Casper

channel-impedances chrome etch 2.pdf (41.8 KB)

#2

Hi Casper,

It looks like all of your hardware/software is working properly, so I suspect it might be an issue with your chip.

What is the tinfoil connecting? The ITO layer should be electrically isolated from all of the other electrodes on the chip and should only be in contact with the red reference clip which connects back to the control board’s feedback input (this is the current return path). On the new DropBot v3, the top plate is connected via conductive tape and an extra row of pogo-pins so you don’t need the alligator clip.

Does the DropBot measure any capacitance when you actuate an electrode covered with a drop? I think the capacitance is dumped in the console window log, but it’s been a while since I used that instrument/software version. If everything is connected properly, the capacitance of the reservoirs should be >50 pF when filled with liquid. If you are getting something <1pF, you have a problem with the connections.

If the voltage is being applied to the electrode but the drops aren’t moving, the most likely problem is a bad Teflon layer. If you pipette a drop of water onto the surface of the chip before attaching the top plate, does it “roll off” easily?

-Ryan

···

On Mon, Oct 15, 2018 at 7:06 AM casper.kunstmann via dropbot-dev dropb...@googlegroups.com wrote:

Dear Drop-botters

I have recently take over the DropBot setup here in York, UK and despite having manufactured nice devices and having a fully functional setup, I’m still struggling to get much droplet actuation going. Being fairly new to DMF I wanted to walk you through my setup and maybe someone can point out any glaring mistakes I might be making:

  1. The DropBot system is built using the instructions on the DropBot wiki and are as far as I can tell, fully functional. I’ve attached Device load calibration and High-voltage reference loads results. I have also attached a few pictures of the setup, where as far as I can tell, everything is connected correctly.
  1. The devices are fabricated in-house by me using chromium electrodes made by wet-etching in a standard clean-room photolithographic method (using the “SCI-BOTS 90 pin-array v3” mask design). The connector and ground pads are then masked off and 8µm Parylene-C is deposited. The pads are unmasked and finally I apply 100nm Teflon (AF1600). For the top layer I’m using commercially coated ITO-glass, also coated with Teflon.
  1. As for putting everything together I’ve struggled to find clear instructions, but I think I’ve managed to piece it all together from various post in this group. I use two layers of double sided tape (Scotch) to create ~140µm spacing between the two plates and tinfoil to connect the top electrode. I’ve attached a photo (ignore the gold, it’s now chromium). I’ve attached channel impedance scan for a particular device.
  1. For testing purposes I’ve simply been using DI water with 2% (w/w) Tween20.

Loading the reservoirs usually goes quite well and the liquid stays nicely on the electrode. When I start actuating other electrodes very little happens and where I’m currently stuck.

Like I said, I’m quite new to DMF so anyone has any useful inputs at all I would be very grateful. Thanks in advance,

\Casper

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#3

Hi Ryan

Thanks for getting back to me. The tinfoil is the result of us interpreting a picture of the device wrongly as we couldn’t find any clear information. It’s now mounted correctly but I have sadly not seen any real improvement.

With respect to the Teflon coating I follow the instructions from the original Applied Physics Letter to the point and the surfaces does seem quite hydrophobic (see attached picture). Or should the contact angle be even higher?

As for the capacitance it does show up in the console yes (see attached screenshot for air). For MQ water I get around 1-5E-12 F/mm2. I’ve also attached a typical channel impedance scan, are these values too low? Would that imply issues with the quality of the device connectors?

Finally, I quite often get the “Failed to reach voltage” error message, even at 100V, could this also imply device issues?

Thanks again,

\Casper

channel-impedances chrome etch 4 - proper alilgn.pdf (43.7 KB)

···

On Saturday, 3 November 2018 00:49:21 UTC, Ryan Fobel wrote:

Hi Casper,

It looks like all of your hardware/software is working properly, so I suspect it might be an issue with your chip.

What is the tinfoil connecting? The ITO layer should be electrically isolated from all of the other electrodes on the chip and should only be in contact with the red reference clip which connects back to the control board’s feedback input (this is the current return path). On the new DropBot v3, the top plate is connected via conductive tape and an extra row of pogo-pins so you don’t need the alligator clip.

Does the DropBot measure any capacitance when you actuate an electrode covered with a drop? I think the capacitance is dumped in the console window log, but it’s been a while since I used that instrument/software version. If everything is connected properly, the capacitance of the reservoirs should be >50 pF when filled with liquid. If you are getting something <1pF, you have a problem with the connections.

If the voltage is being applied to the electrode but the drops aren’t moving, the most likely problem is a bad Teflon layer. If you pipette a drop of water onto the surface of the chip before attaching the top plate, does it “roll off” easily?

-Ryan

On Mon, Oct 15, 2018 at 7:06 AM casper.kunstmann via dropbot-dev drop...@googlegroups.com wrote:

Dear Drop-botters

I have recently take over the DropBot setup here in York, UK and despite having manufactured nice devices and having a fully functional setup, I’m still struggling to get much droplet actuation going. Being fairly new to DMF I wanted to walk you through my setup and maybe someone can point out any glaring mistakes I might be making:

  1. The DropBot system is built using the instructions on the DropBot wiki and are as far as I can tell, fully functional. I’ve attached Device load calibration and High-voltage reference loads results. I have also attached a few pictures of the setup, where as far as I can tell, everything is connected correctly.
  1. The devices are fabricated in-house by me using chromium electrodes made by wet-etching in a standard clean-room photolithographic method (using the “SCI-BOTS 90 pin-array v3” mask design). The connector and ground pads are then masked off and 8µm Parylene-C is deposited. The pads are unmasked and finally I apply 100nm Teflon (AF1600). For the top layer I’m using commercially coated ITO-glass, also coated with Teflon.
  1. As for putting everything together I’ve struggled to find clear instructions, but I think I’ve managed to piece it all together from various post in this group. I use two layers of double sided tape (Scotch) to create ~140µm spacing between the two plates and tinfoil to connect the top electrode. I’ve attached a photo (ignore the gold, it’s now chromium). I’ve attached channel impedance scan for a particular device.
  1. For testing purposes I’ve simply been using DI water with 2% (w/w) Tween20.

Loading the reservoirs usually goes quite well and the liquid stays nicely on the electrode. When I start actuating other electrodes very little happens and where I’m currently stuck.

Like I said, I’m quite new to DMF so anyone has any useful inputs at all I would be very grateful. Thanks in advance,

\Casper

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#4

Hi Casper,

When I look at the capacitance reading in that first image, it shows 8.3 pF/mm^2, which is actually higher that what we typically record (i.e., 4-5 pF/mm^2). This means that you should be able to move liquids at a lower actuation voltage.

I don’t have any experience working with Tween, so I don’t know if that could be a problem. I would suggest testing with Pluronics or Tetronics that are known to work (e.g. F68, L64, or Tetronic 90R4) at 0.1% w/w or try propylene glycol.

-Ryan

···

On Mon, Nov 5, 2018 at 10:36 AM casper.kunstmann via dropbot-dev dropb...@googlegroups.com wrote:

Hi Ryan

Thanks for getting back to me. The tinfoil is the result of us interpreting a picture of the device wrongly as we couldn’t find any clear information. It’s now mounted correctly but I have sadly not seen any real improvement.

With respect to the Teflon coating I follow the instructions from the original Applied Physics Letter to the point and the surfaces does seem quite hydrophobic (see attached picture). Or should the contact angle be even higher?

As for the capacitance it does show up in the console yes (see attached screenshot for air). For MQ water I get around 1-5E-12 F/mm2. I’ve also attached a typical channel impedance scan, are these values too low? Would that imply issues with the quality of the device connectors?

Finally, I quite often get the “Failed to reach voltage” error message, even at 100V, could this also imply device issues?

Thanks again,

\Casper

On Saturday, 3 November 2018 00:49:21 UTC, Ryan Fobel wrote:

Hi Casper,

It looks like all of your hardware/software is working properly, so I suspect it might be an issue with your chip.

What is the tinfoil connecting? The ITO layer should be electrically isolated from all of the other electrodes on the chip and should only be in contact with the red reference clip which connects back to the control board’s feedback input (this is the current return path). On the new DropBot v3, the top plate is connected via conductive tape and an extra row of pogo-pins so you don’t need the alligator clip.

Does the DropBot measure any capacitance when you actuate an electrode covered with a drop? I think the capacitance is dumped in the console window log, but it’s been a while since I used that instrument/software version. If everything is connected properly, the capacitance of the reservoirs should be >50 pF when filled with liquid. If you are getting something <1pF, you have a problem with the connections.

If the voltage is being applied to the electrode but the drops aren’t moving, the most likely problem is a bad Teflon layer. If you pipette a drop of water onto the surface of the chip before attaching the top plate, does it “roll off” easily?

-Ryan

On Mon, Oct 15, 2018 at 7:06 AM casper.kunstmann via dropbot-dev drop...@googlegroups.com wrote:

Dear Drop-botters

I have recently take over the DropBot setup here in York, UK and despite having manufactured nice devices and having a fully functional setup, I’m still struggling to get much droplet actuation going. Being fairly new to DMF I wanted to walk you through my setup and maybe someone can point out any glaring mistakes I might be making:

  1. The DropBot system is built using the instructions on the DropBot wiki and are as far as I can tell, fully functional. I’ve attached Device load calibration and High-voltage reference loads results. I have also attached a few pictures of the setup, where as far as I can tell, everything is connected correctly.
  1. The devices are fabricated in-house by me using chromium electrodes made by wet-etching in a standard clean-room photolithographic method (using the “SCI-BOTS 90 pin-array v3” mask design). The connector and ground pads are then masked off and 8µm Parylene-C is deposited. The pads are unmasked and finally I apply 100nm Teflon (AF1600). For the top layer I’m using commercially coated ITO-glass, also coated with Teflon.
  1. As for putting everything together I’ve struggled to find clear instructions, but I think I’ve managed to piece it all together from various post in this group. I use two layers of double sided tape (Scotch) to create ~140µm spacing between the two plates and tinfoil to connect the top electrode. I’ve attached a photo (ignore the gold, it’s now chromium). I’ve attached channel impedance scan for a particular device.
  1. For testing purposes I’ve simply been using DI water with 2% (w/w) Tween20.

Loading the reservoirs usually goes quite well and the liquid stays nicely on the electrode. When I start actuating other electrodes very little happens and where I’m currently stuck.

Like I said, I’m quite new to DMF so anyone has any useful inputs at all I would be very grateful. Thanks in advance,

\Casper

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#5

Hi Casper, Ryan,

I have some experience of DMF experiment with Tween20. Even if only 200ppm, Tween20 caused slow drop movement. I recommend you try Tween-less experiment to clarify the cause.

Regards,

Aki @U-Tokyo

#6

Hi Aki, thanks for sharing your experience re: Tween20. I sent a few sample chips to Casper last week and they seemed to work, so my best guess is that there was something wrong with his hydrophobic coating. One time we accidentally bought 0.2% Fluoropel instead of 1% and could not get drops to move at all…

···

On Mon, Nov 19, 2018 at 12:56 AM ytoyo...@nojilab.t.u-tokyo.ac.jp wrote:

Hi Casper, Ryan,

I have some experience of DMF experiment with Tween20. Even if only 200ppm, Tween20 caused slow drop movement. I recommend you try Tween-less experiment to clarify the cause.

Regards,

Aki @U-Tokyo

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#7

Thanks for sharing Aki and thanks to Ryan for the devices. I have stopped using the Tween and ordered some Tetronics which certainly seems to work better. With regard to the hydrophobic coating we are currently using 1% w/w Teflon-AF in FC-40. To dissolve this the Teflon I normally sonicate it for many hours and then spincoat it at 1000 rpm for 30s, then postbake for 15min at 160C (as per the original DropBot paper). Could there be any issues here? Would it be worth trying FluoroPel?

···

On Monday, 19 November 2018 15:10:36 UTC, Ryan Fobel wrote:

Hi Aki, thanks for sharing your experience re: Tween20. I sent a few sample chips to Casper last week and they seemed to work, so my best guess is that there was something wrong with his hydrophobic coating. One time we accidentally bought 0.2% Fluoropel instead of 1% and could not get drops to move at all…

On Mon, Nov 19, 2018 at 12:56 AM ytoyo...@nojilab.t.u-tokyo.ac.jp wrote:

Hi Casper, Ryan,

I have some experience of DMF experiment with Tween20. Even if only 200ppm, Tween20 caused slow drop movement. I recommend you try Tween-less experiment to clarify the cause.

Regards,

Aki @U-Tokyo

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