# Amplification of nA current to get a light from the diode

#### Deleted member 911968

Joined Dec 31, 1969
0
Hi Everyone!

My name is Dawid and I plan to create a bio-detector. I'm into biology and this is my first time with circuits-like design so my question might be very silly.

I would like to build a detector of a biological substance on a screen-printed carbon electrode. The result of this detection would be current in nA lasting up to a few seconds.

How I can register this pulse and (with some battery to provide a source of energy?) inform a user with a light of diode about its presence?

#### Ian0

Joined Aug 7, 2020
8,406
You need a transimpedance amplifier
https://en.wikipedia.org/wiki/Transimpedance_amplifier
You need 3V output to light an LED. Just how many nA is your signal?
Rf = 3V/your signal in Amps.
Use a low-noise JFET op-amp.
If your signal lasts a number of seconds, you can use a (relatively) large value of Cf to reduce noise

#### Deleted member 911968

Joined Dec 31, 1969
0
Thank you Ian0
I don't understand a single word, but I'll figure it out step by step with the internet. I just need the path that you gave me.
My signal can start from even 1 nA, but in reality, can be about 10nA.

#### Ian0

Joined Aug 7, 2020
8,406
Thank you Ian0
I don't understand a single word, but I'll figure it out step by step with the internet. I just need the path that you gave me.
My signal can start from even 1 nA, but in reality, can be about 10nA.
At what threshold do you wish it to be detected? Does the substance generate the current? Or does it simply allow a current to flow when connected to a voltage (i.e. varies its )? Is the current DC or AC? If it is DC what polarity is it?

#### Deleted member 911968

Joined Dec 31, 1969
0
Well, I'd like to use the transfer of electrons (generated by biochemical reaction) to a polarised screen-printed carbon electrode surface via a direct electron transfer mechanism. I'm not sure about the threshold, but the range of 1 uA to 10 mA should be more than enough.
I would like to visualise the transfer of electrons by the light of a diode. I managed to find that the pulse is very short and I want to get a light for about 1 minute.

I found also a such concept that is very close to my general idea and it also uses the same electrode:
https://pubs.acs.org/doi/10.1021/acs.analchem.8b00850#

#### Ian0

Joined Aug 7, 2020
8,406
I wonder if you have oversimplified the requirements? The reference you quoted has an detector with a reference electrode, a working electrode and a counter.

#### Deleted member 911968

Joined Dec 31, 1969
0
I wonder if you have oversimplified the requirements? The reference you quoted has an detector with a reference electrode, a working electrode and a counter.
Of course, you're right. As I mentioned it's my first time with any electronic concepts. Anyway, I'd like to construct or just get to know if it's possible to do such the device that I attach in the photo.
The issue is that, in my case the final result of the detection would be a diode light (not a BT signal) and the current of the detection would be in the range of ~1-1000 nA.

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#### Ian0

Joined Aug 7, 2020
8,406
We engineers probably know as little about the sensor as you do about the circuitry to amplify it, so you need to post everything you know about the sensor so that we can work out how to design an amplifier for it.
I am puzzled by the label "Counter" - what does that refer to? None of the circuitry in the vicinity of the label is a counter.
And what is switch SW1 for?

#### Irving

Joined Jan 30, 2016
3,496
I am puzzled by the label "Counter" - what does that refer to? None of the circuitry in the vicinity of the label is a counter.
In electrochemistry, the auxiliary electrode, often also called the counter electrode, is an electrode used in a three-electrode electrochemical cell for voltammetric analysis or other reactions in which an electric current is expected to flow.(wikipedia)
And what is switch SW1 for?
Its detailed in the text, though the information may not help much!
" The digital switches reconfigure the potentiostat between amperometric or potentiometric modes, and between two-electrode or three-electrode modes. The exact function of OP2 depends on the electrochemical technique performed by the UWED. In the potentiometric mode, the microprocessor closes the SW1, the potentiostat is configured to the two-electrode mode, the input impedance is set to high values (GΩ), and the output of OP2 corresponds to the potential of the working electrode. In the amperometric mode, feedback is configured (by adjusting the on/off state of SW2 and SW3) to maintain a constant potential for the working electrode, while the current through electrode changes. "

Basically switches between 2- and 3-electrode working.