Surface Functionalisation and Electroless Plating of 3D-Printed Microstructures

A microelectrode with a large surface area is one of the essential components in biosensors, electronic implants, and energy harvesting systems. In particular, enzymatic biofuel cells and biosensors benefit significantly from microelectrodes with a large surface area to volume ratio because of the increased enzyme loading and hence improved the power density of the final devices. Therefore, the fabrication of microelectrodes with a large surface area will advance its application in devices. Projection-microstereolitography (PµSLA) offers the ability to fabricate three-dimensional and geometrically adjustable polymeric microstructures with well-defined complex shapes in microscale. 3D polymeric microstructures produced using PµSLA can be then coated with metal to achieve high conductivity. Microelectrodes have been created via 3D printing of polymeric structures followed by electroless plating. However, the weak adhesion of the metal to the polymer limits the practical use of the produced devices as electrodes. Here, we show the method to introduce thiol groups on the surface of PµSLA-generated polymeric microstructures to improve the adhesion between the polymer surface and gold thin film. Our results demonstrate that thiol groups on the polymer surface provide the anchoring site for gold deposition during electroless plating via gold-sulfur bonding, resulting in strong adhesion between the polymer surface and the gold layer and long-term microelectrode durability. The gold coated 3D microelectrode exhibits excellent electrical conductivity up to 1.4 × 107 S/m (35% of bulk gold). This method can offer exciting potential for constructing microelectrodes for architecture-specific applications in future energy, catalysis, and sensing.