Tools for Surface Treatment of Silicon Planar Intracortical Microelectrodes

This protocol provides handling tools for the surface modification of intracortical microelectrode devices by gas-phase deposition and aqueous solution reaction. These handling methods maintain device integrity throughout extended reaction times. Methods for handling intracortical microelectrode devices are often not disclosed.

This technique can benefit the research efforts to improve the performance of these devices by developing surface treatments and coatings. To begin, acquire intracortical microelectrode devices or nonfunctional probes for surface treatment. To facilitate material testing, acquire one-centimeter-squared samples of the substrate material for treatment alongside the devices.

3D print or acquire pieces 1A and 1B. Attach a double-sided polyimide tape to piece 1A. Also, attach a 3.17-millimeter-thick foam strip with one-side adhesive to piece 1B.

Then, adhere the connector packaging of the device to the tape on piece 1A. Join pieces 1A and 1B by aligning the holes and securing using stainless steel screws and wing nuts. Fasten the assembly to the vacuum desiccator tray using zip ties, utilizing the holes in the bottom of piece 1A.

Place square material samples into the slits at the bottom of the frame. Place the solution in an appropriate receptacle in the vacuum desiccate opposite and in-line with the secured assembly. Put a vacuum gauge in the desiccator to record the exact pressure.

Then, position the port of the desiccated lid near the secured assembly and in-line with the solution and complete the gas-phase deposition. First, cut rectangular holes of dimensions 19-by-10.5 millimeters into the lid of the well plate to suspend the electrode array of the device in solution. 3D print or acquire the guides.

Align the rectangular holes in the guides to the holes in the lid, ensuring that the hole in the guide is unobstructed. Secure the guides to the lid using cyanoacrylate adhesive. Then, fill the desired solution in the wells where treatment will occur.

To confirm surface treatment, submerge the square substrate samples in the reaction solution in a well of the plate. To assemble the probe device, tape piece 2B to a bench top. Place a double-sided polyimide tape to cover the base of piece 2C.

Also, place a 3.17-millimeter foam tape with single-side adhesive to cover the base of piece 2D. Then, fit piece 2C into the groove of piece 2B. Adhere the connector packaging of the device onto the tape, oriented so the length of the device shank is suspended.

Secure the device by sliding piece 2D into piece 2C. Hold the edges of the assembly and carefully lift to remove from piece 2B. Align the outward-facing semi-circles on pieces 2C and 2D with the corresponding guides on piece 2A to fit the assembly into the lid of the well plate.

Secure assembly placement by press-fitting piece 2E over the guides. After suspending the devices in the well plate, transfer the assembly to a shaker and run at speeds under 100 rotations per minute. For reactions requiring multiple solutions or wash steps, carefully transfer the lid to a new well plate containing the desired solution in the appropriate well.

After this step, tape piece 2B to a bench top. To remove devices from the well plate, remove piece 2E from the lid. Then, carefully remove the assembly by holding the device.

Orient the assembly such that piece 2C faces the bench top and piece 2D faces upward. Align the shank of the device parallel to the bench top. Fit piece 2C of the assembly into piece 2B.

Apply slight pressure on the tabs of piece 2C into the bench to separate piece 2D from piece 2C. Using forceps, remove the connector packaging of the device from the tape and transfer the device to a storage container. The surface treatment of Michigan-style microelectrode arrays in silicon square samples was demonstrated using this protocol.

The gas-phase deposition method was applied for amine functionalization using APTES. Following this, carbodiimide cross-linking chemistry was used to immobilize manganese TBAP. After deposition ellipsometry measurements from the silicon samples produced a mean APTES layer thickness of 8.5 angstroms, compared to the theoretical monolayer thickness of 7 angstroms.

X-ray photo-electron spectroscopy analysis showed an increase in the percentage atomic concentrations of nitrogen and carbon after the gas-phase APTES treatment, indicating chemical deposit. Similarly, manganese was detected following the solution-phase immobilization. Further, the Bode plot for electrical impedance spectroscopy analysis of the microelectrode arrays showed no statistical difference between the impedance magnitudes before and after the coating process.

Thus, successful coating of the electrode array was performed using the coating processes. This protocol facilitates surface modification of intracortical microelectrodes by minimizing the risk of damage to the device. Others in the field may adapt the methodology to their devices and chemical procedures.