Integrating microscale electrochemical energy storage devices with microelectronics can convert intermittent renewable energy sources into a usable form through portable systems.
Inkjet printing process is a promising strategy for the customizable design of smart and flexible electronics. However, it’s still a challenge to synthesize corresponding ink for inkjet printing.
Recently, Prof. WU Zhongshuai’s group and Prof. LIU Shengzhong’s group from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences developed an aqueous MXene/PH1000 (MP) hybrid ink for inkjet printing of micro-supercapacitors (MSCs).
“We developed the ink for customizable fabrication of planar MSCs (MP-MSCs) with excellent shape diversity, record volumetric capacitance, integration, and modularization capabilities,” said Prof. WU.
The printable MP-MSCs delivered higher volumetric capacitance and energy density than those of most previously reported MSCs. This was attributed to the role of PH1000 in enhancing interlayer contact in the MXene to promot electron and ion transfer.
Moreover, MP-MSCs presented good miniaturization and modularization features, with high voltage output up to 36 V from 60 serially connected cells and impressive areal voltage of 5.4 V cm-2 connected in tandem.
This work was supported by the National Natural Science Foundation of China and Dalian National Laboratory for Clean Energy of CAS.
Featured image: Schematic illustration of the fabrication of inkjet-printed MP-MSCs and the self-powered integrated system (Image by MA Jiaxin and ZHENG Shuanghao)
Reference: Ma, J., Zheng, S., Cao, Y., Zhu, Y., Das, P., Wang, H., Liu, Y., Wang, J., Chi, L., S. (F.), , Wu, Z.‐S., Aqueous MXene/PH1000 Hybrid Inks for Inkjet‐Printing Micro‐Supercapacitors with Unprecedented Volumetric Capacitance and Modular Self‐Powered Microelectronics. Adv. Energy Mater. 2021, 2100746. https://doi.org/10.1002/aenm.202100746
Advance could one day allow on-demand, on-site printing of biosensors
Researchers have developed a unique inkjet printing method for fabricating tiny biocompatible polymer microdisk lasers for biosensing applications. The approach enables production of both the laser and sensor in a room temperature, open-air environment, potentially enabling new uses of biosensing technologies for health monitoring and disease diagnostics.
“The ability to use an inexpensive and portable commercial inkjet printer to fabricate a sensor in an ambient environment could make it possible to produce biosensors on-site as needed,” said research team leader Hiroaki Yoshioka from Kyushu University in Japan. “This could help make biosensing widespread even in economically disadvantaged countries and regions, where it could be used for simple biochemical tests, including those for pathogen detection.”
In The Optical Society (OSA) journal Optical Materials Express, the researchers describe the ability to print microdisk lasers as small as the diameter of a human hair from a specially developed polymer called FC-V-50. They also show that the microdisks can successfully be used for biosensing with the widely used biotin-avidin system.
“Our technique can be used to print on almost any substrate,” said Yoshioka. “This means that it could one day be possible to print a sensor for health monitoring directly on the surface of a person’s fingernail, for example.”
Eliminating the heat
Many of today’s biosensors use the strong interaction between the molecules biotin and avidin to detect the presence of proteins that indicate infection or disease. This typically involves tagging a molecule of interest with biotin and then detecting when avidin binds to it.
One way to measure biotin-avidin binding is to add a biotin-labeled protein to the surface of an optical microcavity that acts like a miniature laser. When avidin binds to the biotin on the microcavity, its optical properties change enough to shift light emission in a way that can be used to detect binding.
However, the modification process needed to add biotin to the surface of microcavities is tedious and time-consuming. It also requires high-temperature heat treatments that aren’t compatible with all materials, such as polymers.
“We developed an organic microdisk optical cavity laser for biosensing using FC-V-50,” said Yoshioka. “This special inkjet polymer has a carboxyl functional group that is compatible with biotin, which eliminates the need for any type of heat treatment.”
To produce microdisk lasers, the researchers developed an ink that contained FC-V-50 and a laser dye. A piezo element embedded in an inkjet nozzle about the size of a hair allows a single, tiny ink droplet to be ejected when a voltage is applied. Once dry, this printed drop will emit light when excitation light is applied. As the light travels along the inside circumference of the disk it is amplified to generate laser light.
To turn the microdisk laser into a sensor, the researchers printed a microdisk using their inkjet method and then added reagents that allowed biotin to immobilize on its surface at room temperature. They then used light to excite the microdisk laser under a microscope and measured the reference laser emission spectrum. Next, they poured the avidin solution onto the surface of the microdisk and washed away any that didn’t bind to the biotin. The laser emission was measured again to see how it deviated from the reference spectrum.
To test the method, the researchers fabricated biosensors and measured their ability to detect streptavidin protein at different concentrations. They were able to detect a maximum mode shift of 0.02 nanometers for a 0.1 parts per million concentration of streptavidin. Now that they have demonstrated the ability to print functioning biosensors, they plan to further evaluate and optimize sensor performance. Portable devices for measuring the light emission would also need to be developed for the sensors to be used at the point of care.
Featured image: A new inkjet printing method can be used to fabricate tiny biocompatible polymer microdisk lasers for biosensing. The new approach allows fabrication in a room temperature, open-air environment. Credit: Hiroaki Yoshioka, Kyushu University
Reference: A. Nasir, Y. Mikami, R. Yatabe, H. Yoshioka, N. Vasa, Y. Oki, “Fully room temperature and label free biosensing based on ink-jet printed polymer microdisk laser,” Opt. Mater. Express 11, 3, 592-602 (2021). DOI: https://doi.org/10.1364/OME.415000.
The University of Nottingham has cracked the conundrum of how to use inks to 3D-print novel electronic devices with useful properties, such as an ability to convert light into electricity.
The study shows that it is possible to jet inks, containing tiny flakes of 2D materials such as graphene, to build up and mesh together the different layers of these complex, customised structures.
Using quantum mechanical modelling, the researchers also pinpointed how electrons move through the 2D material layers, to completely understand how the ground-breaking devices can be modified in future.
Paper co-author, Professor Mark Fromhold, Head of the School of Physics and Astronomy said, “By linking together fundamental concepts in quantum physics with state-of-the art-engineering, we have shown how complex devices for controlling electricity and light can be made by printing layers of material that are just a few atoms thick but centimetres across.
“According to the laws of quantum mechanics, in which the electrons act as waves rather than particles, we found electrons in 2D materials travel along complex trajectories between multiple flakes. It appears as if the electrons hop from one flake to another like a frog hopping between overlapping lily pads on the surface of a pond.”
The study, ‘Inter-Flake Quantum Transport of Electrons and Holes in Inkjet-Printed Graphene Devices’, has been published in the peer-reviewed journal Advanced Functional Materials.
Often described as a ‘super material’, graphene was first created in 2004. It exhibits many unique properties including being stronger than steel, highly flexible and the best conductor of electricity ever made.
Two-dimensional materials like graphene are usually made by sequentially exfoliating a single layer of carbon atoms – arranged in a flat sheet – which are then used to produce bespoke structures.
However, producing layers and combining them to make complex, sandwich-like materials has been difficult and usually required painstaking deposition of the layers one at a time and by hand.
Since its discovery, there has been an exponential growth in the number of patents involving graphene. However, in order to fully exploit its potential, scalable manufacturing techniques need to be developed.
The new paper shows that additive manufacturing – more commonly known as 3D printing – using inks, in which tiny flakes of graphene (a few billionths of a metre across) are suspended, provides a promising solution.
By combining advanced manufacturing techniques to make devices along with sophisticated ways of measuring their properties and quantum wave modelling the team worked out exactly how inkjet-printed graphene can successfully replace single layer graphene as a contact material for 2D metal semiconductors.
Co-author, Dr Lyudmila Turyanska from the Centre for Additive Manufacturing, said, “While 2D layers and devices have been 3D printed before, this is the first time anyone has identified how electrons move through them and demonstrated potential uses for the combined, printed layers. Our results could lead to diverse applications for inkjet-printed graphene-polymer composites and a range of other 2D materials. The findings could be employed to make a new generation of functional optoelectronic devices; for example, large and efficient solar cells; wearable, flexible electronics that are powered by sunlight or the motion of the wearer; perhaps even printed computers.”
The study was carried out by engineers at the Centre for Additive Manufacturing and physicists at the School of Physics and Astronomy with a common interest in quantum technologies, under the £5.85m EPSRC-funded Programme Grant, Enabling Next Generation Additive Manufacturing.
The researchers used a wide range of characterisation techniques – including micro-Raman spectroscopy (laser scanning), thermal gravity analysis, a novel 3D orbiSIMS instrument and electrical measurements – to provide detailed structural and functional understanding of inkjet-printed graphene polymers, and the effects of heat treating (annealing) on performance.
The next steps for the research are to better control the deposition of the flakes by using polymers to influence the way they arrange and align and trying different inks with a range of flake sizes. The researchers also hope to develop more sophisticated computer simulations of the materials and the way they work together, developing ways of mass-manufacturing they devices they prototype.