We wanted to develop a chip which was allowed us to harness the full potential of neuron-like cells for detection, while avoiding noisy signals. Our second priority in design was the ease to use and reproduce factor. We used an Ecad design of our circuitry and printed a vinyl negative mask. This was then attached to a glass slide and sputtered with Ti-Au layer. The mask prevented some areas from being exposed to the metal ions, thus creating sharp electrodes for inputs and outputs.

This method allowed us to make chip with very high precision of the electrode dimensions. The designs could be easily changed in the software and many variations of designs were tried. Vinyl is also a cheap material to print on, thus giving an infinite potential to future neural chip designers. A design can be easily made, modified, printed and sputtered, with a wide variety of layering options, individualising each chip deign for its specific purpose.

After sputtering of the chips we added a growing well, for differentiating our cells in. This reduced the necessity for our cells to be transferred between growing flasks and the chips between uses. Once differentiated the cells would stay alive for 10-14 days at normal conditions with minimal risk of contamination. The well design was carefully thought out, to include factors such as space for growth, connection and openings for gas exchange that would not allow the entry of pathogenic bacteria.

We were careful not to expose it to unfiltered air. We immediately placed the chip inside a Laminar Airflow hood. This was done as the chips can not be autoclaved for disinfection, and the use of agents like 70% ethanol negatively affected the growth and adherence of the differentiated cells.

The circuit design was adjusted to the dimensions of a falcon neck. We used HM4100 polymer additive in fast-drying resin to attach the falcon head to the sputtered chip. This creates a well in which we can culture our Neuroblastoma cells. The sputtered circuit brings in electrical signals from the aptamers and relays the neural output to a microprocessor connected on the other end.

Before initiation of cell culture in the well, a 0.1mg/ml solution of Poly D Lysine (PDL henceforth), was pipetted to coat the insides of the well (just covering the sputtered slide) and a Millex syringe filter 0.22 was used to cap the falcon head. This was done inside the LAF to prevent contamination and then placed inside an incubator for 24hrs (37*C, CO2 - 5%, Relative humidity - 95%).

The PDL was discarded before adding the cells for differentiation. In some trial runs, we also added 20ug/ml of Laminin post-discard of PDL. This was again placed in the incubator for 3hrs. No significant improvement was observed with this addition for our cell lines.

References

1. https://microelectrodedevices.com/mea-products/
2. Inkscape
3. https://telemark.com/wp-content/uploads/Manual-TT-Series-E-Beam-Source-Power-Supply.pdf
4. Growing Human Neurons Connected to a Computer