Direct-Laser Scribing of Electrodes Using Metal-Organic Frameworks for Electrochemical Detection

Electrochemical sensors have gained widespread recognition and utilization across diverse domains, encompassing applications such as clinical diagnosis, biochemical detection, and environmental monitoring. In the pursuit of enhancing these sensors, metal-organic frameworks (MOFs) have emerged as highly promising material candidates. MOFs are known for their porous structures, which exhibit substantial surface areas, remarkable stability, and a unique capacity for functionalization.<br/>Here, we aim to integrate MOF structures into laser-induced graphitic (LIG) electrodes to improve the performance of electrochemical sensing devices. LIG electrodes present certain advantages over classical noble metal electrodes, such as reduced cost and ease of fabrication. We investigate the disparities between LIG sensors and LIG-MOF sensors, both of which are fabricated using direct laser scribing, a fabrication technique with the remarkable capability to convert non-conductive materials into active electrode materials, all the while generating desired patterns directly onto polymer substrates. Central to this investigation is the conversion of MOFs into patterned derived carbon utilizing an ultraviolet (UV) laser system. The process entails several steps. Initially, a solution containing MOFs is drop-cast onto a polyimide (PI) foil substrate. Once the MOFs composite is deposited onto the substrate, the electrode is directly patterned with the UV laser. Importantly, the MOFs composites are confined to the electrode area, while the feedline and contact pad exclusively consist of LIG. For the passivation of the structures, Parylene C (poly(p-xylylene)), a flexible dielectric polymer, is chosen due to its good insulation properties and conformability. A thin film of Parylene C, approximately 5 micrometers thick, is deposited via chemical vapor deposition. Subsequently, the electrode area and contact pad are precisely opened using the laser.<br/>The characterization of the resultant sensors was conducted using scanning electron microscopy, Raman spectroscopy, impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry. These characterizations revealed the emergence of a highly porous carbonaceous material, with low-impedance observed in the case of the LIG-MOF sensors. This approach not only expands our understanding of MOF integration into electrochemical sensing but also underscores the potential for applications where high charge injection capabilities and low impedance at an electrode/electrolyte interface are required.