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Graphene microbubbles make perfect lenses

Posted By Terrance Barkan, Monday, October 12, 2020
Tiny bubbles can solve large problems. Microbubbles -- around 1-50 micrometers in diameter -- have widespread applications. They're used for drug delivery, membrane cleaning, biofilm control, and water treatment. They've been applied as actuators in lab-on-a-chip devices for microfluidic mixing, ink-jet printing, and logic circuitry, and in photonics lithography and optical resonators. And they've contributed remarkably to biomedical imaging and applications like DNA trapping and manipulation.

Given the broad range of applications for microbubbles, many methods for generating them have been developed, including air stream compression to dissolve air into liquid, ultrasound to induce bubbles in water, and laser pulses to expose substrates immersed in liquids. However, these bubbles tend to be randomly dispersed in liquid and rather unstable.

According to Baohua Jia, professor and founding director of the Centre for Translational Atomaterials at Swinburne University of Technology, "For applications requiring precise bubble position and size, as well as high stability -- for example, in photonic applications like imaging and trapping -- creation of bubbles at accurate positions with controllable volume, curvature, and stability is essential." Jia explains that, for integration into biological or photonic platforms, it is highly desirable to have well controlled and stable microbubbles fabricated using a technique compatible with current processing technologies.

Balloons in graphene

Jia and fellow researchers from Swinburne University of Technology recently teamed up with researchers from National University of Singapore, Rutgers University, University of Melbourne, and Monash University, to develop a method to generate precisely controlled graphene microbubbles on a glass surface using laser pulses. Their report is published in the peer-reviewed, open-access journal, Advanced Photonics.

The group used graphene oxide materials, which consist of graphene film decorated with oxygen functional groups. Gases cannot penetrate through graphene oxide materials, so the researchers used laser to locally irradiate the graphene oxide film to generate gases to be encapsulated inside the film to form microbubbles -- like balloons. Han Lin, Senior Research Fellow at Swinburne University and first author on the paper, explains, "In this way, the positions of the microbubbles can be well controlled by the laser, and the microbubbles can be created and eliminated at will. In the meantime, the amount of gases can be controlled by the irradiating area and irradiating power. Therefore, high precision can be achieved."

Such a high-quality bubble can be used for advanced optoelectronic and micromechanical devices with high precision requirements.

The researchers found that the high uniformity of the graphene oxide films creates microbubbles with a perfect spherical curvature that can be used as concave reflective lenses. As a showcase, they used the concave reflective lenses to focus light. The team reports that the lens presents a high-quality focal spot in a very good shape and can be used as light source for microscopic imaging.

Lin explains that the reflective lenses are also able to focus light at different wavelengths at the same focal point without chromatic aberration. The team demonstrates the focusing of a ultrabroadband white light, covering visible to near-infrared range, with the same high performance, which is particularly useful in compact microscopy and spectroscopy.

Jia remarks that the research provides "a pathway for generating highly controlled microbubbles at will and integration of graphene microbubbles as dynamic and high precision nanophotonic components for miniaturized lab-on-a-chip devices, along with broad potential applications in high resolution spectroscopy and medical imaging."

Tags:  Baohua Jia  Graphene  graphene oxide  Han Lin  medical devices  Monash University  National University of Singapore  optoelectronics  Photonics  Rutgers University  Swinburne University of Technology  University of Melbourne 

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New Device Can Measure Toxic Lead Within Minutes

Posted By Graphene Council, Wednesday, August 26, 2020
Rutgers researchers have created a miniature device for measuring trace levels of toxic lead in sediments at the bottom of harbors, rivers and other waterways within minutes – far faster than currently available laboratory-based tests, which take days.

The affordable lab-on-a-chip device could also allow municipalities, water companies, universities, K-12 schools, daycares and homeowners to easily and swiftly test their water supplies. The research is published in the IEEE Sensors Journal.

“In addition to detecting lead contamination in environmental samples or water in pipes in homes or elementary schools, with a tool like this, someday you could go to a sushi bar and check whether the fish you ordered has lead or mercury in it,” said senior author Mehdi Javanmard, an associate professor in the Department of Electrical and Computer Engineering in the School of Engineering at Rutgers University–New Brunswick.

“Detecting toxic metals like lead, mercury and copper normally requires collecting samples and sending them to a lab for costly analysis, with results returned in days,” Javanmard said. “Our goal was to bypass this process and build a sensitive, inexpensive device that can easily be carried around and analyze samples on-site within minutes to rapidly identify hot spots of contamination.”

The research focused on analyzing lead in sediment samples.  Many river sediments in New Jersey and nationwide are contaminated by industrial and other waste dumped decades ago. Proper management of contaminated dredged materials from navigational channels is important to limit potential impacts on wildlife, agriculture, plants and food supplies. Quick identification of contaminated areas could enable timely and cost-effective programs to manage dredged materials.

The new device extracts lead from a sediment sample and purifies it, with a thin film of graphene oxide as a lead detector. Graphene is an atom thick layer of graphite, the writing material in pencils.

More research is needed to further validate the device’s performance and increase its durability so it can become a viable commercial product, possibly in two to four years.

This project was done in collaboration with the Department of Electrical and Computer Engineering and Rutgers’ Center for Advanced Infrastructure and Transportation (CAIT). It was funded by CAIT, the USDOT-University Transportation Research Center–Region II.

Tags:  Graphene  graphene oxide  Mehdi Javanmard  Rutgers University  Sensors  water purification 

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Quantum Materials Quest Could Benefit From Graphene That Buckles

Posted By Graphene Council, Friday, August 14, 2020
Graphene, an extremely thin two-dimensional layer of the graphite used in pencils, buckles when cooled while attached to a flat surface, resulting in beautiful pucker patterns that could benefit the search for novel quantum materials and superconductors, according to Rutgers-led research in the journal Nature.

Quantum materials host strongly interacting electrons with special properties, such as entangled trajectories, that could provide building blocks for super-fast quantum computers. They also can become superconductors that could slash energy consumption by making power transmission and electronic devices more efficient.

“The buckling we discovered in graphene mimics the effect of colossally large magnetic fields that are unattainable with today’s magnet technologies, leading to dramatic changes in the material’s electronic properties,” said lead author Eva Y. Andrei, Board of Governors professor in the Department of Physics and Astronomy in the School of Arts and Sciences at Rutgers University–New Brunswick. “Buckling of stiff thin films like graphene laminated on flexible materials is gaining ground as a platform for stretchable electronics with many important applications, including eye-like digital cameras, energy harvesting, skin sensors, health monitoring devices like tiny robots and intelligent surgical gloves. Our discovery opens the way to the development of devices for controlling nano-robots that may one day play a role in biological diagnostics and tissue repair.” 

The scientists studied buckled graphene crystals whose properties change radically when they’re cooled, creating essentially new materials with electrons that slow down, become aware of each other and interact strongly, enabling the emergence of fascinating phenomena such as superconductivity and magnetism, according to Andrei.

Using high-tech imaging and computer simulations, the scientists showed that graphene placed on a flat surface made of niobium diselenide, buckles when cooled to 4 degrees above absolute zero. To the electrons in graphene, the mountain and valley landscape created by the buckling appears as gigantic magnetic fields. These pseudo-magnetic fields are an electronic illusion, but they act as real magnetic fields, according to Andrei.

“Our research demonstrates that buckling in 2D materials can dramatically alter their electronic properties,” she said.

The next steps include developing ways to engineer buckled 2D materials with novel electronic and mechanical properties that could be beneficial in nano-robotics and quantum computing, according to Andrei.

Tags:  2D materials  Eva Y. Andrei  Graphene  quantum materials  Rutgers University 

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