The development of three-dimensional (3D) porous graphitic structures is of great interest for electrochemical sensing applications as they can support fast charge transfer and mass transport through their extended, large surface area networks. In this work, we present the facile fabrication of conductive and porous graphitic electrodes by direct laser writing techniques. Irradiation of commercial polyimide sheets (Kapton tape) was performed using a low-cost laser engraving machine with visible excitation wavelength (405 nm) at low power (500 mW), leading to formation of 3D laser-induced graphene (LIG) structures. Systematic correlation between applied laser dwell time per pixel (“dwell time”) and morphological/structural properties of fabricated electrodes showed that conductive and highly 3D porous structures with spectral signatures of nanocrystalline graphitic carbon materials were obtained at laser dwell times between 20 and 110 ms/pix, with graphenelike carbon produced at 50 ms/pix dwell time, with comparable properties to LIG obtained with high cost CO2 lasers. Electrochemical characterization with inner and outer sphere mediators showed fast electron transfer rates, comparable to previously reported 2D/3D graphene-based materials and other graphitic carbon electrodes. This work opens the way to the facile fabrication of low-cost, disposable electrochemical sensor platforms for decentralized assays.

Interdigitated and square laser-induced graphene (LIG) electrodes were successfully fabricated by direct laser writing of common natural cork bottle stoppers. The laser graphitization process was performed with a low-cost hobbyist visible laser in a simple, fast, and one-step process under ambient conditions. The formation of LIG material was revealed by extensive characterization using Raman, attenuated total reflection-Fourier transform infrared (ATR-FTIR), and X-ray photoelectron (XPS) spectroscopies. Electron microscopy investigation showed that the formed LIG structure maintained the hierarchical alveolar structure of the pristine cork but displayed increased surface area, disorder, and electrical conductivity, promising for electrochemical applications. Open planar and sandwich supercapacitors, assembled from fabricated electrodes using poly(vinyl alcohol) PVA/H + as an electrolyte, exhibited a maximum areal capacitance of 1.56 mF/cm 2 and 3.77 mF/cm 2 at a current density 0.1 mA/cm 2 , respectively. Upon treatment with boric acid (H 3 BO 3 ), the areal capacitance of the resulting boron-doped LIG devices increased by ca. three times, reaching 4.67 mF/cm 2 and 11.24 mF/cm 2 at 0.1 mA/cm 2 current density for planar and sandwich configurations, respectively. Supercapacitor devices showed excellent stability over time with only a 14% loss after >10 000 charge/discharge cycles. The easy, fast, scalable, and energy-efficient method of fabrication illustrated in this work, combined with the use of natural and abundant materials, opens avenues for future large-scale production of "green" supercapacitor devices.

Porous graphitic carbon electrodes were fabricated by laser scribing of commercial polyimide tape. The process was performed by a simple one-step procedure using visible wavelength laser irradiation from a low-cost hobbyist laser cutter. The obtained electrodes displayed a highly porous morphology, rich in three-dimensional (3D) interconnected networks and edge planes, suitable for electrochemical sensing applications. Spectral characterization by Raman and X-ray photoelectron spectroscopy (XPS) techniques revealed a crystalline graphitic carbon structure with a high percentage of sp2 carbon bonds. Extensive electrochemical characterization performed with outer-sphere [Ru­(NH3)6]3+ and inner-sphere [Fe­(CN)6]4–, Fe2+/3+, and dopamine redox mediators showed quasi-reversible electron transfer on the graphitic carbon surface, mainly dominated by a mass diffusion process. Fast heterogeneous electron-transfer rates, higher than similar carbon-based materials and higher than other graphitic carbon electrodes produced by either visible or infrared laser irradiation, were obtained for these electrodes. Thin-layer transport mechanisms occurring in parallel to the main diffusion-limited mechanism were taken into consideration, but overall, the observed enhanced electron-transfer rate effects were ascribed to the large specific surface area of the extended 3D porous network, rich in defects and edge planes. The superior electrocatalytic properties of the fabricated electrodes allowed electrochemical differentiation between the biomarkers ascorbic acid, dopamine, and uric acid in solution. The compatibility of fabricated electrodes with lightweight portable and handheld instrumentation makes such electrodes highly promising for the realization of low-cost disposable sensing platforms for point-of-care applications.

Laser‐fabrication of graphene from cellulose‐based feedstock materials often requires extensive preprocessing. This work demonstrates laser fabrication of porous, 3D graphene from a new class of marine‐based sustainable materials–chitosan biopolymers. The biopolymer films contain only chitosan, acetic acid, glycerol, and water. Fourier transform infrared spectroscopy studies indicate that the cured chitosan films still retain a significant water content (≈30%), enabling production of flexible films. A simple 3‐step laser fabrication process is presented using low‐cost infrared (CO2, 2.1 W) and visible (405 nm, 0.5 W) hobbyist laser engravers, with measured sheet resistance values as low as 40 ohms sq.−1. Transient electrochemical detection of an inner sphere redox molecule is demonstrated using a graphene‐like carbon working electrode fabricated on a water‐soluble chitosan substrate.

Cork laser induced graphene (cork‐LIG) electrochemical sensors are fabricated by direct laser writing of natural cork sheets. Laser writing is performed with a hobbyist visible laser. The obtained cork‐LIG structures display graphene‐like Raman signatures, high conductivity, and fast electron‐transfer rates. After a 10 min electrochemical pretreatment, electrodes are used for detection of Tyrosine (Tyr) in the presence of uric acid, dopamine, ascorbic acid, urea, and glucose. linear detection of tyrosine is achieved in the 5–150 µm range with a limit of detection (LOD) of 3.03 µm. Calibration of dopamine detection is achieved with a LOD of 1.1 µm. Finally, the cork‐LIG electrochemical sensors show linear response of Tyr in artificial sweat in the relevant physiological range of 5–250 μm (sensitivity, 1.8×10−2 A m−1). The LOD is calculated as 3.75 μm. These results open the door to the exploitation of renewable materials such as cork for the development of high‐quality, green sensors for the monitoring of health and wellbeing parameters.