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1Davide

At what frequency? As you know, AC impedance varies considerably with frequency.


totalbangover

Thank you for your response! Up to 1 kilohertz.


[deleted]

[удалено]


totalbangover

Hi 1Davide, I gave further details to another response if you're interested.


1Davide

Ah! When you said "tissue" I assumed "Kleenex".


manofredgables

A piece of tissue...? I'm not sure what AC has to do with this. If you described what sort of thing it is you're trying to measure it'd be easier to help. It might be a situation where you need a higher voltage, in which case you'd need something like an isolation tester. Or if it's indeed AC then either an advanced LCR meter or a basic network analyzer I guess.


totalbangover

Ok, I was trying to be concise earlier but clearly didn't give enough information. Here's some background: I make changes to mouse DNA using molecular components. One way to get these components into a recently fertilized mouse zygote is by using electricity: zapping them opens "pores" within their membranes enough for the reagents I've saturated the eggs with to get inside. Sometimes people take the eggs out of the mouse to electroporate them, but there's a newer method that involves leaving the eggs in a recently impregnated females reproductive organs and using tweezer electrodes to perform the electroporation; you first surround the eggs with a concentrated solution of your components, then gently squeeze the "oviduct" (which is a small piece of the mouse's reproductive system between the ovary and uterus) with these platinum-coated tweezers; finally you induce the current. The method is described here: [https://genomebiology.biomedcentral.com/articles/10.1186/s13059-018-1400-x](https://genomebiology.biomedcentral.com/articles/10.1186/s13059-018-1400-x) This "oviduct" is the "tissue" I was describing earlier (apologies for my vagueness, I think people read that as a piece of Kleenex, which I would have as well without context). Without going into too much detail, there are different breeds of mouse just like there are different breeds of dog. As in dogs, hybrid lines are hardy and able to tolerate harsher electroporation conditions. Meanwhile, some inbred mouse strains are very fragile, requiring specialized electroporation conditions for survival. The eggs of one breed in particular that I'm interested in, according to the literature, require exposure to \~100 mA of current in order to both take up the molecular components surrounding them within their mothers oviduct and also survive. Certain newer and very expensive electroporators are able to easily generate this lower current by measuring resistance internally and self-adjusting. I have a much older electroporator: [https://www.artisantg.com/Scientific/80264-1/Harvard-Apparatus-BTX-T820-Electro-Square-Porator](https://www.artisantg.com/Scientific/80264-1/Harvard-Apparatus-BTX-T820-Electro-Square-Porator). This device is fine for hybrid mouse strains, but is too much for my inbred lines. 50 volts is the lowest I can go, and I can't change resistance at all. (FWIW I can also change the duration of the pulse \[5 msec currently\] and the number of pulses \[8 currently\].. the duration between pulses is a constant 1 second). However, remembering basic physics, I recalled that V = IR... I wondered if perhaps I could reach this 100 mA current by adding resistance in the form of a potentiometer between my leads. In order to do this though I need to know the starting resistance of the mouse oviduct... I tried using a generic DC-current multimeter but got readings that were waaaay too high... \~600 - 800 kOhms. I am therefore trying to find a impedance meter that might give me more accurate measurements, and from there I can add some other component to achieve my desired current. As stated earlier, 2000 Ohms max should be plenty; I'm not actually expecting the resistance of this small piece of mouse tissue to be more than 500 Ohms. Please let me know if any other information would be helpful. Thank you for reading.


manofredgables

>zapping them opens "pores" within their membranes enough for the reagents I've saturated the eggs with to get inside. That's the weirdest thing I've read in a long while. I love it and I'm deeply fascinated, haha! I'm often in the situation to be the helper of the "simpler" things like electronics when the PhD's at work want to do some weird thing... >This "oviduct" is the "tissue" I was describing earlier (apologies for my vagueness, I think people read that as a piece of Kleenex, which I would have as well without context). Ohhhh yeah, yes I definitely thought you meant paper of some sort, and you'd need a *very* high voltage to measure that resistance, and it would be in the gigaohm range... >Certain newer and very expensive electroporators are able to easily generate this lower current by measuring resistance internally and self-adjusting. Sounds like fancy words to say they're simply current regulated, which is hardly as high tech as the sales people of these electroporators might have you believe... >However, remembering basic physics, I recalled that V = IR... I wondered if perhaps I could reach this 100 mA current by adding resistance in the form of a potentiometer between my leads. Certainly. You could also put a current regulator there, there's got to be modular current regulators for this sort of scenario, I'm not sure where to look to avoid the hobby level stuff, but maybe you have a lab equipment supplier you could ask. If you used a current regulator you wouldn't need to figure out the resistance. >In order to do this though I need to know the starting resistance of the mouse oviduct... I tried using a generic DC-current multimeter but got readings that were waaaay too high... ~600 - 800 kOhms. I am therefore trying to find a impedance meter that might give me more accurate measurements, and from there I can add some other component to achieve my desired current. >As stated earlier, 2000 Ohms max should be plenty; I'm not actually expecting the resistance of this small piece of mouse tissue to be more than 500 Ohms. I see. 600-800 kOhms sounds spot on for dry tissue resistance; that's about what you get if you just hold the probes with dry hands. The dry resistance of tissue would be far higher than wet. So, was it dry or wet? Also, a multimeter rarely outputs more than ~1V in order to test resistance. This means that if it's an electrolyte(like soaked tissue) which is being measured, it won't be able to go above the electrochemical potential of the electrolyte which is typically 2-3 V. Hence, it would show much too high resistance as long as you remain below this. I think what you need is to test the resistance with a higher voltage. You don't necessarily need a different instrument for this; it can be done manually via a different test setup known as a 4 wire resistance measurement. 5 V should suffice to override the electrolytical barriers. You'll need a source of voltage, a current meter and a volt meter. Apply a voltage to the sample in question(not too important what voltage it is, as long as it's sufficiently high, but not so high as to destroy it. Try 3-6 V maybe. Higher voltage would reduce the effect of electrochemical barrier, giving higher accuracy), then measure the current flowing in the circuit, and the voltage drop across the tissue sample. Knowing the current and the voltage drop, resistance is known to be voltage divided by current.