Gold-Electroplated Laser-Induced Graphene (LIG) for Biocompatible Implantable Identification and Sensing Transponders

Laser-Induced Graphene is a novel and straightforward technique to pattern conductive traces on polymeric materials used in next-generation prostheses. To overcome the limitation of a modest electrical conductivity without compromising the biocompatibility feature, the LIG can be electroplated with inert metals, such as gold nanoparticles. This work presents an experimental comparison of two commercial gold-based plating solutions applied to LIG traces with different morphologies. The results show that the more concentrated formulation enables the formation of a compact gold coating, reducing the sheet resistance to as low as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.2 \text{ohm} / \text{sq}$</tex>, independently of the initial conductivity of the LIG mask. The optimized process was used to design, fabricate, and test a dipole antenna based on gold-coated LIG, implanted in a musclemimicking phantom at 40 mm depth. The measured transducer power gain is in agreement with numerical simulations in the band of interest, with more than 5 dB margin with respect to the minimum required value.