Electrode shading lithography: A new method to avoid side dissolution of adhesion layer during electrodeposition of platinum black

Electrochemical biosensors often rely on the detection of hydrogen peroxide (H₂O₂), produced upon enzymatic reaction, with platinum electrodes being a preferred choice due to their catalytic efficiency. A cost-effective alternative is the use of gold electrodes functionalised through the electrodeposition of platinum black (PtB). However, direct platinum black electrodeposition on thin film electrodes can lead to the delamination of the metallic substrate layer. We present a novel fabrication strategy — Electrode Shadowing Lithography (ESL) — that protects the edges of the electrodes without the need for additional photomasks. By exploiting the transparency of silica substrates, SU8 photoresist is selectively exposed from the back side of the transparent wafer, using the electrodes themselves as shadow masks. This protocol creates a protective SU8 layer that protects the metallic adhesion layer of the electrodes from being etched during PtB deposition, preventing the flagging of the electrodes. Physical and electrochemical characterisations confirm successful protection and functionalisation. ESL offers a novel, cost-effective, and alignment-free solution which opens the way for microfabrication of electrodes for H₂O₂-sensitive biosensors that is more robust and accessible to facilities with less equipment. • A new protocol is presented to pattern SU8 using thin film metallic electrodes as an exposure mask. • The sides of metallic electrodes can be protected with SU8 resin to prevent etching of the adhesion layer of the electrodes from the side. • Protecting the side of thin film metallic electrodes is necessary when functionalizing through platinum black electrodeposition and was shown to ensure the stability of the electrode.