Tetroplater

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An open-source circuit for microwire tetrode gold plating

Tetroplater 최신버젼 다운로드

최종 버전 다운로드 (.zip)

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# Tetroplater [![DOI](https://zenodo.org/badge/DOI/10.5281/zenodo.3334859.svg)](https://doi.org/10.5281/zenodo.3334859)

An open-source circuit for microwire tetrode gold plating, designed by Jumpei Matsumoto ([Nishijo lab, Univ of Toyama](http://www.med.u-toyama.ac.jp/sysemosci/index.html)).

## Overview
*See [Nguyen et al., 2009](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2794082/) for the basics about tetrode gold plating.*

Gold plating is necessary/effective for microwire tetrodes for recording neuronal activity. 
For the gold plating, the electrode tip is electroplated with current pulses, until the impedance reaches to the target value (see Fig 1B in [Nguyen et al., 2009](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2794082/) for an example). The Tetroplater is an open-source low-cost (<200 dollars) circuit including an impedance meter and a current generator for tetrode gold plating.

Assembled circuit (left) and an example of a setup (right).

## How it works
The Tetroplater measures the electrode impedance with a “auto-balancing bridge” circuit:

Here, the 1 kHz sin-wave oscillator signal (*Vin* = 3~4 mVp-p) is input to the electrode. The operational amplifier makes the voltage at the open circle zero. So, currents passing the electrode (*Ielectrode*) and Reference resistor *Rref* (*Iref*) become equal. Therefore, from Ohm’s row,

*Relectrode / Vin = Rref / Vout*

Where *Relectrode* is the impedance of electrode and *Vout* is voltages around *Rref*. Thus, by comparing the amplitudes of *Vin* and *Vout*, the impedance can be estimated.

The Tetroplater also has a 2.5-&micro;A constant DC current source for electroplating.

## Fabricating the circuit board
1. Print the PCB from the eagle file (*tetroplater.brd*) or the gerber file (*gerber_seeed_studio.zip*; prepared for [Seeed Studio](https://www.seeedstudio.com/fusion_pcb.html)). 
2. Get the electric parts in the list (*digikey_cart.csv*; the file can be import in [DigiKey](https://www.digikey.com/) as a shopping cart. The quantities include spares).
3. Assemble them according to the figure below.

## Setting up with peripherals
1. Connect ± 9~12 V power supply to *V+*, *V-*, and *GND* terminals.
2. Connect the probes for the bath of gold plating solution and the electrode to *BATH* and *EL* terminals, respectively. Use the shield cables between the probes and the terminals and connect the shields to *SHIELD* terminal.
3. Connect the *V_MEA_IN*, *V_MEA_OUT* and *GND* terminals to an oscilloscope.
4. The rest of *GND* terminals can be used for electric shields around the electrode to reduce hum noise. 
5. Adjust oscillator amplitude (*V_MEA_IN*) to be 30~40 mVp-p by turning the trimmer potentiometer (*R12*).

An example of a setup. 1, the Tetroplater board; 2, [a dual power supply](https://www.amazon.co.uk/dp/B06VTSDLLN); 3, an electrode holder (connected to the *GND* terminal); 4, a gold plating solution bath; 5, a metal plate (connected to the *GND* terminal); 6, a set of resistors for calibration; 7, an oscilloscope.

## Usage
1. Connect the probes to gold plating solution and an electrode wire.
2. *V_MEA_IN* and *V_MEA_OUT*, shown in the oscilloscope, are 10 times amplified *Vin* and *Vout*, respectively.
3. Push the switch on the board briefly. During the switch is on, 2.5 &micro;A current passes for plating. Repeat it until the impedance (= 1 M&Omega; * *V_MEA_IN* / *V_MEA_OUT*) reaches the target range (see the video below). The target range can also be checked directly by measuring impedance of resistors of the corresponding values.

Because only *Vout* changes through the plating, oscilloscope with only one input channel also works (there is [a cheap one](https://www.amazon.com/dp/B077D62Z1P/))

## Typical results
| |Before (M&Omega;)|After (k&Omega;)|
|:--|--:|--:|
|Tetrode 1, ch 1|4.0|310| 
|Tetrode 1, ch 2|2.9|330|
|Tetrode 1, ch 3|2.9|330| 
|Tetrode 1, ch 4|2.8|340| 
|Tetrode 2, ch 1|4.8|330| 
|Tetrode 2, ch 2|3.5|320| 
|Tetrode 2, ch 3|3.0|340| 
|Tetrode 2, ch 4|2.4|320| 
|Tetrode 3, ch 1|3.5|310|
|Tetrode 3, ch 2|3.8|320|
|Tetrode 3, ch 3|2.9|320|
|Tetrode 3, ch 4|4.0|310|
|Tetrode 4, ch 1|3.7|290|
|Tetrode 4, ch 2|5.7|320|
|Tetrode 4, ch 3|4.3|300|
|Tetrode 4, ch 4|3.1|300|

Impedances of four nichrome wire tetrodes ([Sandvik Precision Fine Tetrode Wire](https://www.amazon.com/dp/B0062MNUG6)) measured before and after gold plating with the Tetroplater (using [Neuralynx Gold Plating Solution](https://neuralynx.com/hardware/gold-plating-solution)). The impedance values were checked with [Thomas Recording Impedance Tester](http://www.thomasrecording.com/products/neuroscience-products/microelectrodes/manufacturing-equipment/electrode-impedance-tester.html).

Signals from tetrodes gold plated with the Tetroplater (in neocortex, high-pass filtered)

## misc
- The circuit could be extended for multichannel automatic plating by adding a multiplexer, a microcomputer and etc. The output range of *V_MEA_OUT* is suitable for input to [the Spectrum Shield](https://www.sparkfun.com/products/13116) for Arduino. You can also find some hints in an [Open Ephys repository](https://github.com/open-ephys/autoimpedance).

- [A nice reproduction case](./imgs/gold_plater_nolan_lab.png) by [Nolan lab](https://nolanlab.mvm.ed.ac.uk/)!!

## Acknowledgements
We thank Masahiro Kato (Kato Acoustics Consulting Office) and Jon Newman (MIT, Open Ephys) for their advices for the circuit design.

- - -

*We welcome your feedback through [the topic](https://groups.google.com/d/topic/open-ephys/WM3JAaYDXw8/discussion) in open ephys forum or the issues in this repository.*

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