Influence of CO₂ laser beam modelling on electronic and electrochemical properties of paper-based laser-induced graphene for disposable pH electrochemical sensors

Laser-induced graphene (LIG) allows for the fabrication of cost-effective, flexible electrodes on a multitude of recyclable and sustainable substrates, for implementation within electrochemical biosensors. This work expands on current LIG research, by experimentally modeling the effects of several CO₂ laser irradiation variables towards resulting conductive and electrochemical properties of paper-derived LIG. Instead of relying on the established paradigm of manipulating power and scan speed of the laser irradiation process for optimized outcomes, modeling of underlying laser operation principles for pulse modulation, regarding pulse repetition frequencies, pulse duration and defocus are presented as the key aspects dominating graphitization processes of materials. This approach shows that graphitization is dominated by appropriate pulse durations, dictating the time the substrate is exposed to each laser pulse, with laser fluence and irradiation defocus influencing the resulting conductive properties, with sheet resistances as low as 14 Ω sq⁻¹. Similarly, fabrication settings controlled by these parameters have a direct influence on the properties of LIG-based electrochemical three-electrode cells, with optimized fabrication settings reaching electrochemically active surface area as high as 35 mm² and heterogeneous electron transfer rates of 3.4 × 10⁻³ cm.s⁻¹. As a proof-of-concept, the production of environmentally friendly, accessible, and biocompatible pH sensors is demonstrated, using two modification approaches, employing riboflavin and polyaniline as pH-sensitive elements.