Laser-induced hierarchical carbon patterns on polyimide substrates for flexible urea sensors

Abstract

Thermochemical decomposition of organic materials under heat-treatment in the absence of oxygen, known as the pyrolysis process, is often employed to convert micro and nano patterned polymers into carbon structures, which are subsequently used as device components. Pyrolysis is performed at ≥900°C, which entails substrate materials with a high thermal stability that excludes flexible, polymeric substrates. We use optimized laser radiation to pattern graphitic carbon structures onto commercially available polyimide (Kapton) sheets in the micrometer to millimeter scale by inducing a localized, rapid pyrolysis, for the fabrication of flexible devices. Resulting laser carbon films are electrically conductive and exhibit a high-surface area with a hierarchical porosity distribution along their cross-section. The material is obtained using various combinations of laser parameters and pyrolysis environment (oxygen-containing and inert). Extensive characterization of laser carbon is performed to understand the correlation between the material properties and laser parameters, primarily fluence and power. A photothermal carbonization mechanism based on the plume formation is proposed. Further, laser carbon is used for the fabrication of enzymatic, pH-based urea sensors using two approaches: (i) direct urease enzyme immobilization onto carbon and (ii) electrodeposition of an intermediate chitosan layer prior to urease immobilization. This flexible sensor is tested for quantitative urea detection down to 10 −4 M concentrations, while a qualitative, color-indicative test is performed on a folded sensor placed inside a tube to demonstrate its compatibility with catheters. Laser carbon is suitable for a variety of other flexible electronics and sensors, can be conveniently integrated with an external circuitry, heating elements, and with other microfabrication techniques such as fluidic platforms.

Machine-learning-assisted fabrication: Bayesian optimization of laser-induced graphene patterning using in-situ Raman analysis

“…darkened region outside the delineated circular boundary, as observed in the optical micrographs in Fig. S8, Moreover, the high pressure may reduce the PI substrate from swelling when ablated at increased fluence [45].…”

“…The role of the inert gas in LIG may be related to a photothermal pathway based on the plume formation, i.e. ablated material being ejected normal to the surface plane that is shaped by pressure gradients [41,45]. In vacuum, the plume expands freely.…”

Continuous-Wave Laser-Induced Transfer of Metal Nanoparticles to Arbitrary Polymer Substrates

“…At the optimum condition, a high-quality electrode is created at the acceptor while the Ag NP layer is sharply detached from the donor substrate. When the laser power overpasses 400 mW, the acceptor PI film is pyrolyzed and carbonized [32,33] (Figure 2d) to create a highly uneven structure.…”

Flexible Bioelectronic Devices Based on Micropatterned Monolithic Carbon Fiber Mats

“…Other device components still rely on thin metal films, leading to a compromised interface durability and work‐function differences . Few studies report on laser‐induced carbonization of different polymers in order to achieve flexible structures . This serial process shows large variation in material composition depending on process and material parameters .…”

“…Few studies report on laser‐induced carbonization of different polymers in order to achieve flexible structures . This serial process shows large variation in material composition depending on process and material parameters . Consequently, such methods are currently unsuitable for reliable large‐scale manufacturing of implantable neural probes.…”