Gold plating

General and Important information: 

Gold plating is done to most of the wires on the drives and linear arrays created in the lab. The process uses the Nano-Z to run a current from the wires down to gold plating solution in which the wires are dipped causing the charged gold particles to bind to the ends of the wires. This process is done to lower the impedance for each of the wire improving the signal quality once implanted into the brain.

In the attached file is Neuralynx gold plating guide for NiChrome wires that we use with Au plating it is recommend to follow that protocol.

For tetrodes or any wires used to record from spikes it is recommend to make sure your impedance are quite low less than 200 kohm.

For wires used to soley record LFP the impedance is less important though low impedance should still be the goal. Also important is to try to get the impedance measure roughly equal for each channel this consistence will help in any future analysis.

It is extremely important to make sure test and gold plate your drive well in advance of the surgery to fix any potential issues and also to test/gold plate across multiple days to make sure the impedances are stable as they naturally rise over time. 

Our gold plating solution (from Neuralynx) is mixed with PEG. The introduction of , PEG or other chemicals allows for one to drive the impedance lower than what is usually allowed with just gold solution itself before creating shorts between the wires.  For reference see: Ferguson, J. E., Boldt, C., & Redish, A. D. (2009). Creating low-impedance tetrodes by electroplating with additives. Sensors and actuators. A, Physical, 156(2), 388–393. https://doi.org/10.1016/j.sna.2009.10.001

The solution is 75% by volume PEG with 25% by volume gold plating solution. Important is that both the PG and gold plating solution are light sensitive and shouldn't be kept out in the light more than is necessary. both the PEG and the gold plating solution are kept in the fridge in the lab. the Gold plating solution comes in a large syringe. A smaller 3ml syringe should be used to draw out the necessary amount of the gold plating solution from the parent syringe and used to  create and hold the 75/25 percent mixture. 

From here after I will use gold plating solution to refer to the 75/25 mix solution. 

This picture shows the apparatus for gold plating the Nano Z (the black box) is mounted on a stereotax so that wires can be positioned into the tube which is filled with the gold plating solution. This tube is mounted to weighing dish for stability and has a wire inserted into the bottom which is resealed with hot blue. The other end of this wire is attached to clip which is connected to another wire which ends in another clip. This second clip is then attached to one of the two metal prongs located on the adaptor of the Nano Z.

Important that just like when you actually plug in the drive to the intan boards the omnetics writing on the Nano Z Adaptor needs to face the same way as the omnetics writing on the EIB. It is recommended that you apply a little bit of poster putty to the bottom of the weigh boat to make sure that it doesn't get accidentally shifted while gold plating. Only a few mms of the wires actually need to be in the solution if any metal or other conductive part of the drive/array is making contact with the solution then the impedance measures will be completely off. 

This is a picture of what the Nano-Z software looks like it is recommend that you use report view which can be selected from View at the top. 

Important: Initial and Final Impedance tests should be done in PBS instead of the gold plating solution. 

For any additional information on the Nano-Z software you should refer to the Nano Z user manual itself.