I see what you are doing now, "saline experiment". I thought, you were working on a "signaling". I just become interested for seeing puzzles. This is not an opinion, but an answer, if you are looking for a solution; the other way around, if you are looking for yes/no.
I have a 105V/3A output current source, and I am trying to get a current mirror circuit to pass 10-100 uA DC across 5 lanes that have very high impedance (around 1 MOhm).
It is possible. You may get 100uA through 1M ohm, assuming the power and the medium stay stable. But, in practice, electrical side will suffer from the operating margin, if the accuracy was desired,or the conductivity/voltage-source cause noise/variation. It is simple to see it as an EE, but will take your intuition.
-. The voltage developed on the DUT/subject = 100uA x 1M ohm = 100V.
-. Operating margin, given to the circuitry, without considering other variables:
105V - 100V = 5V
-. The freedom of control, of the 100uA on 'varying' variables:
5V/100V => 5%
What is the best/quickest way to design this and what transistors should I be getting?
Transistors will only reduce the operating margin. All you need is a few resistors, assuming many parameters are fixed stable.
-. For an example: 105V / (1M + R) = 100uA --> R = 50K ohm
I'm passing current through a saline solution and studying the electrochemical reactions. I want to test the setup with 5 lanes at once -- one passing 10 uA, the next passing 20 uA, the next passing 30 uA, then 40 uA, and finally 50 uA. But I only have one current source to do this.
That implies many.. things.., and, I will try to cover many, dealing with a Chemist :).
-. What you described is more of voltage source, not a current source. Thus, no current mirror is needed.
-. That is only true, if the medium gets separated for each current path, like separate tube for each current source.
-. A constant current as a source works, if the condition of the medium stays in operating range while giving enough margin to the control circuitry.
-. If the 3 probes go in the same 'bath', then there is no way to control the current path away from the source.
-. However, you may be able to force the source and sink point, multiple of them in a bath, by isolating (electrically) each probe sets.
My point is: If you show us more of what you are doing and how it works, then EEs can provide better/right solutions.Besides, you did not explain how and what to detect from the "reactions".