Laser-induced graphene-based, flexible, and all-inorganic carbon thin-film transistor for non-invasive monitoring of cortisol.

Flexible thin-film transistors (TFTs) have emerged as promising platforms for next-generation bioelectronic devices, particularly in health monitoring and early disease diagnosis, due to their high sensitivity, mechanical flexibility, and ease of integration. However, conventional TFTs typically rely on expensive gold electrodes fabricated through complex lithographic processes, increasing production costs and introducing contamination that compromises device reproducibility and performance. To address these limitations, we report the design and fabrication of a cleanroom-free, all-inorganic carbon-based TFT using laser-induced graphene (LIG) as source, drain, and gate electrodes, coupled with a network of as-grown carbon nanotubes (CNTs) serving as the channel. The porous morphology of the LIG significantly enhances charge injection and transport, leading to excellent electrical output characteristics. The structural and compositional properties of the CNT-TFT were confirmed by SEM and Raman spectroscopy. Furthermore, the device exhibited robust electrical performance and mechanical stability under repeated bending, demonstrating its potential for wearable applications. The LIG-based CNT-TFT was further functionalized with cortisol-specific aptamers on the gate electrode, enabling real-time, highly sensitive detection of cortisol in sweat with a limit of detection (LOD) of 1.0 pM and a dynamic range spanning from 1.0 pM to 1.0 µM. This work highlights the feasibility of a simple, cost-effective, and lithography-free fabrication strategy for flexible biosensors.