Microplasma direct writing for site-selective surface functionalization of carbon microelectrodes

Abstract

Carbon micro- and nanoelectrodes fabricated by carbon microelectromechanical systems (carbon MEMS) are increasingly used in various biosensors and supercapacitor applications. Surface modification of as-produced carbon electrodes with oxygen functional groups is sometimes necessary for biofunctionalization or to improve electrochemical properties. However, conventional surface treatment methods have a limited ability for selective targeting of parts of a surface area for surface modification without using complex photoresist masks. Here, we report microplasma direct writing as a simple, low-cost, and low-power technique for site-selective plasma patterning of carbon MEMS electrodes with oxygen functionalities. In microplasma direct writing, a high-voltage source generates a microplasma discharge between a microelectrode tip and a target surface held at atmospheric pressure. In our setup, water vapor acts as an ionic precursor for the carboxylation and hydroxylation of carbon surface atoms. Plasma direct writing increases the oxygen content of an SU-8-derived pyrolytic carbon surface from ~3 to 27% while reducing the carbon-to-oxygen ratio from 35 to 2.75. Specifically, a microplasma treatment increases the number of carbonyl, carboxylic, and hydroxyl functional groups with the largest increase observed for carboxylic functionalities. Furthermore, water microplasma direct writing improves the hydrophilicity and the electrochemical performance of carbon electrodes with a contact-angle change from ~90° to ~20°, a reduction in the anodic peak to cathodic peak separation from 0.5 V to 0.17 V, and a 5-fold increase in specific capacitance from 8.82 mF∙cm−2 to 46.64 mF∙cm−2. The plasma direct-writing technology provides an efficient and easy-to-implement method for the selective surface functionalization of carbon MEMS electrodes for electrochemical and biosensor applications.

Plasmas for additive manufacturing

“…[ 41 ] Flexible microplasma stamps have been fabricated as well, to transfer hydrophilic patterns on curved substrates such as glass (Figure 3b). [ 42 ] Unique substrates are possible as well including superhydrophobic aluminum, [ 43 ] carbon MEMS electrodes, [ 44 ] and bonded poly(dimethylsiloxane) microchannels. [ 45 ] In the case of microchannels, the functionalization was performed by generating the microplasma on the inner surface (Figure 3c).…”

A Way to Close the Loop: Physicochemical and Adsorbing Properties of Soybean Hulls Recovered After Soybean Peroxidase Extraction

“…Soybean hulls have been also considered as source of carbon (obtained by either thermal or chemical transformations) for the production of micro-mesoporous adsorbents (Girgis et al, 2011 ), biofillers (Balint et al, 2020 ), and can potentially be employed in those fields where carbons are required as active substrates for electrochemistry, electronics and biomedicine (Thiha et al, 2019 ; Sun et al, 2020 ; Wang C. et al, 2020 ). Finally, also cellulose and other polysaccharides, constituting the lignocellulosic hull biomass and obtained after proper extraction processes (Camiscia et al, 2018 ; Wang S. et al, 2020 ), can find outlet in different branches of biotechnology (food, medicine, bioremediation, paper industry, etc.)…”

Microfluidic plasmas: Novel technique for chemistry and chemical engineering

“…By integration with movable platform, it is possible to perform surface modification or maskless printing of arbitrary patterns of materials on selective areas [57]. As reported by Marc et al [58], a microfluidic plasma jet integrated with a 3-axis motion platform is constructed for the site-selective surface functionalization of carbon electrodes (Figure 3(c)). A tungsten needle of 100 μm in diameter is fixed at the center of the nozzle as the electrode.…”

“…Copyright 2016 Scientific Research Publishing Inc.; (c) An integrated system of a microfluidic plasma jet with a 3-axis platform for the surface functionalization of a carbon electrode. Reprinted with permission from [58]. Copyright 2019 Springer Nature.…”