Chemically bonded microfluidic device with integrated laser-induced graphene electrodes.

Abstract

The integration of electrochemical sensing with microfluidic platforms is essential for advancing lab-on-a-chip technologies; however, many existing approaches rely on electrodes fabricated using costly and complex techniques such as thin-film deposition and photolithography. Laser-induced graphene (LIG) offers a rapid and low-cost alternative for electrode fabrication, yet it is most commonly produced on polyimide substrates, which are not readily compatible with permanent bonding to microfluidic channels and typically require adhesives or mechanical clamping. Here, we present a novel approach to integrating LIG electrodes with microchannels fabricated in polydimethyl siloxane (PDMS), a common material for microfluidics. Electrodes were formed on SU-8 photoresist-coated glass slides using a CO₂ laser and then covalently bonded to PDMS <i>via</i> 3-aminopropyl triethoxysilane (APTES). Structural and spectroscopic characterization of the LIG on SU-8 demonstrate successful conversion into conductive turbostratic graphitic carbon, while mechanical studies demonstrate strong bond integrity between the electrode substrate and PDMS over 16 hours of continuous operation. Electrochemical validation of the electrodes both off- and on-chip demonstrate performance suitable for quantitative electroanalysis. Proof-of-principle application of the integrated device to the detection of acetaminophen (paracetamol) by differential pulse voltammetry under flow conditions reveals a clinically relevant limit of detection (0.08 mM) with high intra-device precision. The resulting platform enables seamless integration with microfluidic channels and exhibits robust electrochemical performance ideal for rapid prototyping.