Re: Max resistor voltage

[Simon Quellen Field]

It isn't clear if you were still discussing piezoelectric igniters, or if you had changed the subject.

Your concerns are valid for systems with appreciable current (say half a milliampere), but are not so much a concern with piezoelectric igniters. I often test my igniters by making the spark jump from or to my finger.

Let's say the power produced by a piezoelectric igniter is in the range of half a microwatt.

The current is thus 0.03 nanoamperes.

At currents like this, there is no appreciable heating of a carbon composite resistor, and the resistors are long enough that the spark does not arc around from lead wire to lead wire. So you can pretty much ignore voltage ratings.

If the cuvette is really 40,000 ohms, then we might have a problem, as the voltage drop across that gives you 0.8 microvolts. You might want to simply place two wires very close to one another inside the cuvette (or Petri dish -- we don't need the cuvette anymore) and hit the igniter a couple dozen times.

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On Wed, Jul 30, 2014 at 2:51 PM, Tom Knight <t...@ginkgobioworks.com> wrote:

Most carbon composition resistors have a voltage rating of 500 volts. You need a set in series to keep the voltage rating under control. The typical time constants for electroporation are in the 3-7 millisecond range. High voltage capacitors can kill you. Make sure you have bleeder resistors across them. They also have a memory, so even if you discharge them, they can spontaneously charge again.

[John Griessen]

On 07/30/2014 05:15 PM, Simon Quellen Field wrote:
> not so much a concern with piezoelectric igniters. I often test my igniters by making the spark jump from or to my finger.

Is it good statistically? No Chinese ignitors of a certain physical size will deliver more current?

John
just wondering...

[John Griessen]

On 07/30/2014 05:15 PM, Simon Quellen Field wrote:

> At currents like this, there is no appreciable heating of a carbon composite resistor, and the resistors are long enough that the
> spark does not arc around from lead wire to lead wire. So you can pretty much ignore voltage ratings.
>

Same physics reasoning I was using...

[John Griessen]

On 07/30/2014 05:15 PM, Simon Quellen Field wrote:

> If the cuvette is really 40,000 ohms, then we might have a problem, as the voltage drop across that gives you 0.8 microvolts

> <https://www.google.com/search?q=40000+ohms+*+.02+nanoamperes+in+microvolts>.


Hmm... if the power of an ignitor is in the range of half a microwatt,
there could be another problem: even if you salt the sample, there's not enough energy to zap the cells.

Maybe that's why some recipes talk of capacitors the size of a house central air motor run capacitor...
6cm x 12cm x 16cm

[Simon Quellen Field]

Mine are Japanese. :-)

You can find specs on igniters here.

However, to answer your question, the energy in the spark comes from the force of the spring-loaded hammer that hits the piezoelectric ceramic rod in the igniter. The force on the spring comes from the pressure from your finger. You can measure the force and the stroke, and compare that from one igniter to another. Or you can just judge subjectively -- they will most likely be the same within a factor of two.

All of them will have enough energy to light butane. That chemical reaction is on a par with the energy needed for electrophoresis. Neither one requires a lot.

That said, we now must look at the rest of the system -- the cuvette and the solution in it.

The size of the cuvette is huge compared to the actual size required.

We might aim for an efficiency of 10 cells per nanogram of DNA, and use anywhere from 5 to 100 nanograms of DNA in a run. So we need a container big enough to zap 10,000 cells.

Let's use ten times that to make the arithmetic easy. A cube 100 cells wide, tall, and high.

Let's not crowd our critters, let's give each one a cube 10 microns on a side.

Now we have a millimeter cube for our cuvette.

Normal saline solution has a resistivity of 0.20 ohm-meter. Resistivity is convertible to resistance by multiplying by the length and then dividing by the area. Our length is 0.001, and our area is 0.000001,

so we have a resistance of 200 ohms.

In trying to find a source for the energy in a piezoelectric spark, I found this reference.

It says they measured 67.61 milliwatts of power. Since power is current squared times resistance,

we have a current in our cuvette of 18 milliamperes. From Ohm's Law, that gives us 3.67 volts.

Does anyone have any data on the currents used in commercial electroporators? Or the wattage delivered to the cuvette? If they use 1,000 volts and a 40,000 ohm cuvette, we get 25 milliamperes of current, which is in the same ballpark as the 18 milliamperes we get from the igniter in our 1 cubic millimeter 'milli-cuvette'. But they use 25 watts, while we use only 67.61 milliwatts.

One source I found uses 200 to 400 volts, in a 0.2 cm cuvette (200 microliters, or 200 times the volume of our 1 microliter 'milli-cuvette'). They seem to quote a resistance of 1000 ohms. They have pulse lengths of 10 to 25 milliseconds. That's a current of 400 milliamperes, and 160 watts (4 joules of energy). Four joules is just a hair under a calorie, so it would raise the temperature of a gram of water by one degree Celsius, or the 0.2 milliliter cuvette by 5 degrees C per pulse.

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[John Griessen]

On 07/30/2014 10:02 PM, Simon Quellen Field wrote:
> Four joules is just a hair under a calorie, so it would raise the temperature of a gram of water by one degree Celsius, or the 0.2
> milliliter cuvette by 5 degrees C per pulse.

Thanks for all the what if calcs on scaling and the scale of zapping enough cells
to make a batch of something. Now, how can we make a teeny cuvette that will still pipette?

Hmm... we could surround a small pocket with a larger one, and after the zap, put a drop of water in it
and suck it all up with a pipette... That would make it easy to get the results out of a
1mm cube, but how to get a sample in? If not a pipette tip, then a syringe needle will fit in a 1mm square opening.

[John Griessen]

On 07/30/2014 05:15 PM, Simon Quellen Field wrote:
> You might want to simply place two wires very close to one another inside the cuvette (or Petri dish -- we don't need the cuvette
> anymore) and hit the igniter a couple dozen times.

This idea could yield some safer lower powers to electroporate with. The concept is to make the
field strength quantified by the volume between the electrodes and not worry with it being a cuvette.
It could be just small zones of metal separated by a distance.

Then you zap a droplet in any container.

Drawbacks include:
1. needing to reuse such electrodes and so having to clean them.
2. The amount or number of cells affected will vary as the volume you put the electrodes in varies.
3. electrodes are sticking out where they could be dangerous.

So, with the drawbacks considered, I still like the idea of making teeny cuvettes to get the needed currents lower.
They would be used inside an insulated interlocked covered box.

[Nathan McCorkle]

My last trials with a piezoelectric sparker used two pieces of adhesive-backed aluminum foil on a glass microscope slide, with some wax pencil for a  hydrophobic 'corral' between the two foil strips. Seemed like it should work as long as aluminum ions weren't toxic to the cells.

I really think the next step is to add a diode (LED), and a small cap/inductor would be the next step.

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[Simon Quellen Field]

You can get copper tape at a hardware store. It is used to keep snails out of gardens, and to stick around windows for burglar alarms.

But the idea I like best is to draw two lines on paper with a pencil and let a drop of critters soak into the paper. You can make the lines quite close together, and graphite isn't toxic. Then cut the paper and drop it into some nutrient broth.

No cleaning electrodes.

You can control the volume quite easily.

Nothing dangerous.

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[Cathal (Phone)]

I expect you'd get greater efficiency with steel as copper ions are pretty cytotoxic. I like the graphite/paper concept!

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[John Griessen]

On 07/31/2014 11:26 AM, Simon Quellen Field wrote:
> the idea I like best is to draw two lines on paper with a pencil and let a drop of critters soak into the paper. You can make the
> lines quite close together, and graphite isn't toxic. Then cut the paper and drop it into some nutrient broth.
>
> No cleaning electrodes.
> You can control the volume quite easily.
> Nothing dangerous.

Hmm... that idea even upgrades from DIY to a low cost product! How about ink jet printed conductors
with some large lands that spring contacts connect to on your electroporator-with-safety-features?
The paper could come from the clean and pure sources used for old school analytic filter paper.

It could come in sealed sterile packs. Hey Nathan -- want to do some testing of that starting with
hand drawn graphite papers? The extra volume of critters outside the lines may not matter.
For apps where a tiny volume is all you have the paper could be trimmed away just outside the conductive lines
and dip it in a microdrop of bugs to load your bugs into the "zap chamber"

Fantastic lateral thinking Simon!

[John Griessen]

On 07/31/2014 12:13 PM, Cathal (Phone) wrote:
> I like the graphite/paper concept!

+1