Researchers at Iowa State University have been looking for ways to use graphene and its amazing properties in their sensors and other technologies. Graphene is considered by many to be a wonder material, the carbon honeycomb is just an atom thick. It's great at conducting electricity and heat; it’s strong and stable. But researchers have struggled to move beyond tiny lab samples for studying its material properties to larger pieces for real-world applications.
Recent projects that used inkjet printers to print multi-layer graphene circuits and electrodes had the engineers thinking about using it for flexible, wearable and low-cost electronics.
A more specific question the researchers wanted to know was - could graphene be made at scale large enough for glucose sensors.
However, there were problems with the existing technology. Once printed, the graphene had to be treated to improve electrical conductivity and device performance. That usually meant high temperatures or chemicals – both could degrade flexible or disposable printing surfaces such as plastic films or even paper.
The researchers came up with the idea of using lasers to treat the graphene. Jonathan Claussen, an Iowa State assistant professor of mechanical engineering and an Ames Laboratory associate, worked with Gary Cheng, an associate professor at Purdue University’s School of Industrial Engineering, to develop and test the idea. And it worked: They found treating inkjet-printed, multi-layer graphene electric circuits and electrodes with a pulsed-laser process improves electrical conductivity without damaging paper, polymers or other fragile printing surfaces.
According to the researchers the breakthrough of this project is transforming the inkjet-printed graphene into a conductive material capable of being used in new applications. Those applications could include sensors with biological applications, energy storage systems, electrical conducting components and even paper-based electronics.
To make all that possible, the engineers developed computer-controlled laser technology that selectively irradiates inkjet-printed graphene oxide. The treatment removes ink binders and reduces graphene oxide to graphene – physically stitching together millions of tiny graphene flakes. The process makes electrical conductivity more than a thousand times better.
The researchers explained that the laser works with a rapid pulse of high-energy photons that do not destroy the graphene or the substrate. Instead, they heat locally, bombard locally. They process locally. That localised, laser processing also changes the shape and structure of the printed graphene from a flat surface to one with raised, 3-D nanostructures. The engineers say the 3-D structures are like tiny petals rising from the surface. The rough and ridged structure increases the electrochemical reactivity of the graphene, making it useful for chemical and biological sensors.
All of that, according to the researchers could move graphene to commercial applications. Adding that this work paves the way for not only paper-based electronics with graphene circuits, but also the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells and (medical) devices.
The Iowa State Research Foundation Inc. has filed for a patent on the technology.
Two major grants are supporting the project and related research: a three-year grant from the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 11901762 and a three-year grant from the Roy J. Carver Charitable Trust. Iowa State's College of Engineering and department of mechanical engineering are also supporting the research.
3D nanostructured inkjet printed graphene via UV-pulsed laser irradiation enables paper-based electronics and electrochemical devices1>
Suprem R. Das | Qiong Nian | Allison A. Cargill | John A. Hondred | Shaowei Ding | Mojib Saei | Gary J. Cheng | Jonathan C. Claussen
Nanoscale, 2016,8, 15870-15879 | DOI: 10.1039/C6NR04310K | Received 28 May 2016, Accepted 11 Jul 2016 | First published online 12 Jul 2016
Emerging research on printed and flexible graphene-based electronics is beginning to show tremendous promise for a wide variety of fields including wearable sensors and thin film transistors. However, post-print annealing/reduction processes that are necessary to increase the electrical conductivity of the printed graphene degrade sensitive substrates (e.g., paper) and are whole substrate processes that are unable to selectively anneal/reduce only the printed graphene—leaving sensitive device components exposed to damaging heat or chemicals. Herein a pulsed laser process is introduced that can selectively irradiate inkjet printed reduced graphene oxide (RGO) and subsequently improve the electrical conductivity (Rsheet ∼0.7 kΩ □−1) of printed graphene above previously published reports. Furthermore, the laser process is capable of developing 3D petal-like graphene nanostructures from 2D planar printed graphene. These visible morphological changes display favorable electrochemical sensing characteristics—ferricyanide cyclic voltammetry with a redox peak separation (ΔEp) ≈ 0.7 V as well as hydrogen peroxide (H2O2) amperometry with a sensitivity of 3.32 μA mM−1 and a response time of <5 s. Thus this work paves the way for not only paper-based electronics with graphene circuits, it enables the creation of low-cost and disposable graphene-based electrochemical electrodes for myriad applications including sensors, biosensors, fuel cells, and theranostic devices.