Fabrication of laser inscribed graphene (LIG) 3-electrode plug-and-play chip

Step 1) Fabrication of USB-A Adapter

• Heat the soldering iron, and prepare a wet sponge and solder wick.
• See the following for an introduction to soldering techniques (link)
• Solder one 28AWG jumper wire to each of the two outer contacts in the USB-A adapter.
• Create an electrical connection (i.e., “jump”) the two inner contacts in the USB-A adapter.
• Solder one 28AWG jumper wire to the “jumped” inner contact(s) in the USB-A adapter
• Place the plastic cover on the USB-A Female adapter
• Turn off soldering iron, and clean station when finished

Step 2) Preparation of Materials for LIG chip

• LIG should be prepared using the protocol developed for a 3-electrode sensor (link)
• Using scissors, cut conductive polyester metal tape into 0.3 cm by 3.5 cm strips (one strip per LIG electrode)
• Fig. 1 shows an example of a batch of 18 LIG electrodes with 18 metal tape strips
• For each LIG chip, cut a 1cm by 5 cm strip of PVC to act as the chip base
• Ample table space should be cleared to prepare the LIG chips

Step 3) Adhesion of Bonding Pads to LIG

* Using scissors, cut small 0.3 cm by 1.0 cm strips from the prepared polyester metal tape strips. One small subsection should be cut for each 3-electrode LIG sensor.

• Using steel tweezers, hold the metal tape and carefully remove the adhesive backing
• Carefully position the metal tape over one of the bonding pads on the printed LIG chip
• After coating the LIG reference electrode, the tweezers should be used to lightly squeeze the material and ensure good contact.
• Repeat the process for all three electrodes in the LIG chip ( Fig 2 )

Step 4) Coating of LIG Reference Electrode

• The reference electrode may be coated with Ag/AgCl ink, or with a small 0.3 cm by 0.5 cm strip of polyester metal tape (as shown here)
• After coating the LIG reference electrode, the tweezers should be used to lightly squeeze the material and ensure good contact.
• If Ag/AgCl ink is used to coat the reference electrode, the material should be allowed to cure at room temperature for at least 15 min

Step 5) Passivation of LIG Electrodes

• Use poly gel acrylic nail polish to passivate the electrodes between the bonding pad and the functional electrode area ( Fig 3A ).
• The passivation may cover a small portion of the polyester metal tape if used as reference electrode coating material ( Fig 3B )

  

Step 6) Mounting LIG chip to PVC Base

• Using scissors, cut a strip of double sided tape and adhere to the back of the LIG material ( Fig 4A ).
• Mount the LIG material to the PVC base and use scissors to trim any excess tape.
• The final chip should have clearance with exposed, unmodified PVC which may be handled without touching the LIG or other coating materials ( Fig 4B )
• The three electrode system is composed of working, counter, and reference electrodes. The passivation area and bonding pad are easily discernable ( Fig 4C )

Step 7) Clean up laboratory

• Any excess polyamide, metal tape, or PVC sheet should be discarded in a labeled container on the counter.
• Turn off soldering iron, and clean station
• If storing electrodes, place in a sealed Petri dish with desiccant.