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.
Highlights
Conversion of micro and nano patterned polymer structures into carbon via pyrolysis is a widespread technique for the fabrication of graphitic carbon-based devices.[1,2] This process is typically performed at ≥900 °C, such that the polymer undergoes a thermochemical decomposition and yields carbon with a characteristic dimensional shrinkage
There are two major challenges in the fabrication of ureaselaser carbon. In this contribution we report on (i) an extensive characterization of Kapton-derived laser carbon produced in air and nitrogen based urea sensor: (i) the chemisorption of urease onto a substrate typically leads to a drastic decrease in its activity,[37] and (ii) the shortening of the useful life-time of urease.[30,32]
Laser-induced carbonization entails a thermochemical decomposition of Kapton, similar to the pyrolysis performed in a furnace
Summary
Conversion of micro and nano patterned polymer structures into carbon via pyrolysis is a widespread technique for the fabrication of graphitic carbon-based devices.[1,2] This process is typically performed at ≥900 °C, such that the polymer undergoes a thermochemical decomposition and yields carbon with a characteristic dimensional shrinkage The properties of such carbons are similar to those of glassy (IUPAC name: glass-like) carbon,[1,2] which are attributed to a complex three-dimensional graphene network that constitutes the material.[3,4,5] Carbon obtained from pyrolysis below 900 °C does not feature the desired graphenic network,[6] its mechanical strength as well as electrical conductivity are compromised. Five samples (each prepared in air and nitrogen) that exhibited relatively high graphitic contents and the corresponding optical micrographs are provided in the electrical conductivity values were selected for further analysis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
