Laser-induced carbon nanofibers are used to create porous freestanding electrode systems for redox cycling. Either by closely spacing the interdigitated electrodes carbonized directly onto the nanofibrous network, or by fabricating an additional nanofibers layer onto the electrodes, amplification via redox cycling was achieved in these new approaches, facilitating a flow-through electroanalytical device with favorable sensitivity.

Abstract

Redox cycling is a powerful amplification strategy for reversible redox species within miniaturized electrochemical sensors. Herein, we generate three-dimensional (3D) porous carbon nanofiber electrodes by CO₂ laser-writing on electrospun polyimide (PI) nanofiber mats, referred to as laser-induced carbon nanofibers (LCNFs). The technique allowed the fabrication of interdigitated electrode (IDE) arrays with finger width and gap distance of ~400 μm and ~40 μm, respectively, offering approximately 3.5 times amplification efficiency (AF) and 95 % collection efficiency (CE). Such dimensions could not be achieved with IDEs fabricated on conventional PI film because the devices were short-circuited. Stacked electrodes were also constructed as an alternative to the IDE design. Here, nanofiber mats as thin as ~20 μm were fabricated and used as vertical insulation between two LCNF band electrodes. While redox cycling efficiency was similar, the IDE design is more favorable considering the lower complexity and better signal reproducibility. Our strategy thus paves the way for creating flexible 3D porous electrodes with redox cycling ability that can be integrated into microfluidics and lab-on-a-chip systems. In particular, the devices offer inherent flow-through features in miniaturized analytical devices where separation and sensitive detection could be further realized.