NanoZ_GoldPlating - KravitzLab/KreedLabWiki GitHub Wiki

Written by Eric Casey, 2022

1. Hold the nanoZ with an appropriate support (a scope’s frame with a 3D printed holder will work well, see Fig 13A), connect it to a computer and start the NanoZ software.
2. Connect the Omnetics-molex adapter to the NanoZ probe. Make sure to connect it in the appropriate orientation (see Fig 13B-C), otherwise the ground (as well as a number of channels) will be disconnected and the circuit will not be closed (see Error messages and troubleshooting using NanoZ).
3. Connect the array to the Omnetics-Molex adapter (Fig 13A-D).
4. Test impedances. To do this, immerse the tips of all tetrodes and the ground wire/s in saline (solution of NaCl 0.09% in water), select the “Test impedances” mode at the NanoZ software and set the parameters to 1004Hz of test frequency, 40 cycles and a pause of 200 msec, and click “Test probe” (Fig 14A-B, top). A report window should appear with the impedances of each channel, which can be saved as a text file (Fig 14A-B, bottom). A good sanity check is to test impedances without immersing the tetrode tips in saline, which will report high impedances (~20 MOhm or more, Fig 14A, bottom), and then test them again with the tips in saline, to confirm a reduction in the impedance (Fig 14B, bottom), which indicates that exist an electrical connection between the tetrodes wires and the connector.
5. Perform electroplating of the tetrodes. To do this, put the gold solution in a 15mL tube lid (or any vessel of similar size), and immerse the tips of all tetrodes and the ground wire/s in the gold solution (Fig 13D). Then, select the electroplating mode at the NanoZ software, set parameters to “Match impedances mode” mode, plating current of 0.2 µA and target of 200 kOhm at 1004 Hz; also set the number of runs, interval duration and pause to a reasonable trade off of result quality and duration (4 runs, 5 seconds interval and 1 second pause may be a good starting point). Finally, click “Autoplate” to start the electroplating (Fig 14C, top). A report window should appear, displaying the initial impedance and the impedance after electroplating, for each channel (Fig 14C, bottom). This report can be saved as a text file. Note that these reports will show open circuits in blue, good impedances in green and short circuits in red; however, this classification is based on thresholds set at the “Condition” field (Fig 14A-C, bottom), and channels marked in red in general will not have short circuits, but just impedances below the condition of the NanoZ. To further verify absence of short circuits, perform step 11: Final test for short-circuits and misconnections.
6. Recover gold solution. Gold solution can be reused several times and still achieve a good reduction of impedance.

Fig 1. Setup for electroplating using NanoZ. NanoZ must be holded with an appropriate frame, and the Omnetics-Molex adapter is plugged to the probe, and the array is connected to the adapter. Gold solution is also shown. A-C) Side, back and front view, respectively. D) Side view of the tetrodes tips immersed in gold solution.

Error messages and troubleshooting using NanoZ The two most common error that can be obtained during this procedures are: a. Signal clipped: this means that there is a short circuit in that channel, and the impedance will not be shown in the row of that channel but the row will be highlighted in yellow instead (Fig 14C, bottom, rows 5 and 6). If this happens in all the channels, or many of them, discarding the array will be the best option. If it happens in one or few channels, those channels can be discarded during the data analysis, once the recordings are done. b. Plating voltage out of compliance: this appears during electroplating and means that, given the current impedance, the voltage necessary to achieve the platting current is too high for the NanoZ to achieve it (Fig 14D). This happens when the circuit is open, and there are three possible scenarios: ● If it happens in a single channel, that channel may not have an electrical connection between the tetrode and the PCB, or between the PCB and the connector (the last is less likely if step 3, Testing PCB for short-circuits and misconnections, was performed correctly). In this case, that channel should be discarded during the analysis (and not used for average referencing during the recording). ● If it happens in all channels: ○ The simplest scenario is that the Omnetics-Molex adapter was plugged incorrectly, which causes the ground to not be connected. To fix it, change the orientation of the adapter and try again. Also, make sure that the ground wire is immersed in the gold solution and its tip is stripped. ○ If the prior does not fix it, the ground wire may not be well connected to the PCB. Replace the ground wire and make sure that the end that goes into the gold solution is stripped.

Fig 2. NanoZ software settings and reports. Setting (top) and report windows (bottom) for impedance testing without immersing the tetrodes tips in saline (A), impedance testing with the tetrodes tips immersed in saline (B), electroplating with gold (C), and “Plating voltage out of compliance” error during electroplating (D).