Graphene enables nano ‘tweezers’ that can grab individual bio-molecules: Application for ‘hand-held’ Diagnostics on a Smartphone


Graphene Tweezers 182-researchersdThe University of Minnesota team produced a microchip containing a large array of graphene electronic tweezers. Fluorescence images show DNA molecules and polystyrene nanoparticles trapped on the chip. Credit: Barik et al., University of Minnesota

Researchers from the University of Minnesota College of Science and Engineering have found yet another remarkable use for the wonder material graphene—tiny electronic “tweezers” that can grab biomolecules floating in water with incredible efficiency. This capability could lead to a revolutionary handheld disease diagnostic system that could be run on a smart phone.

Graphene, a material made of a single layer of carbon atoms, was discovered more than a decade ago and has enthralled researchers with its range of amazing properties that have found uses in many new applications from microelectronics to solar cells.

The graphene  developed at the University of Minnesota are vastly more effective at trapping particles compared to other techniques used in the past due to the fact that graphene is a single atom thick, less than 1 billionth of a meter.

The research study was published today in Nature Communications, a leading journal in the field of nanomaterials and devices.

The world’s sharpest tweezers

The physical principle of tweezing or trapping nanometer-scale objects, known as dielectrophoresis, has been known for a long time and is typically practiced by using a pair of metal electrodes. From the viewpoint of grabbing molecules, however, metal electrodes are very blunt. They simply lack the “sharpness” to pick up and control nanometer-scale objects.

“Graphene is the thinnest material ever discovered, and it is this property that allows us to make these tweezers so efficient. No other material can come close,” said research team leader Sang-Hyun Oh, a Sanford P. Bordeau Professor in the University of Minnesota’s Department of Electrical and Computer Engineering. “To build efficient electronic tweezers to grab biomolecules, basically we need to create miniaturized lightning rods and concentrate huge amount of electrical flux on the sharp tip. The edges of graphene are the sharpest lightning rods.”

The team also showed that the graphene tweezers could be used for a wide range of physical and biological applications by trapping semiconductor nanocrystals, nanodiamond particles, and even DNA molecules. Normally this type of trapping would require high voltages, restricting it to a laboratory environment, but graphene tweezers can trap small DNA molecules at around 1 Volt, meaning that this could work on portable devices such as mobile phones.

Using the University of Minnesota’s state-of-the-art nanofabrication facilities at the Minnesota Nano Center, electrical and computer engineering Professor Steven Koester’s team made the graphene tweezers by creating a sandwich structure where a thin insulating material call hafnium dioxide is sandwiched between a metal electrode on one side and graphene on the other. Hafnium dioxide is a material that is commonly used in today’s advanced microchips.

Researchers develop graphene nano 'tweezers' that can grab individual biomolecules
Atomically sharp edges of electrically driven graphene can act as ‘tweezers’ that rapidly trap biomolecules from the surrounding solution. Credit: In-Ho Lee, University of Minnesota

“One of the great things about graphene is it is compatible with standard processing tools in the semiconductor industry, which will make it much easier to commercialize these devices in the future,” said Koester, who led the effort to fabricate the graphene devices.

“Since we are the first to demonstrate such low-power trapping of biomolecules using graphene tweezers, more work still needs to be done to determine the theoretical limits for a fully optimized device,” said Avijit Barik, a University of Minnesota electrical and computer engineering graduate student and lead author of the study. “For this initial demonstration, we have used sophisticated laboratory tools such as a fluorescence microscope and electronic instruments. Our ultimate goal is to miniaturize the entire apparatus into a single microchip that is operated by a mobile phone.”

Tweezers that can ‘feel’

Another exciting prospect for this technology that separates graphene tweezers from metal-based devices is that graphene can also “feel” the trapped biomolecules. In other words, the tweezers can be used as biosensors with exquisite sensitivity that can be displayed using simple electronic techniques.

“Graphene is an extremely versatile material,” Koester said. “It makes great transistors and photodetectors, and has the potential for light emission and other novel biosensor devices. By adding the capability to rapidly grab and sense molecules on graphene, we can design an ideal low-power electronics platform for a new type of handheld biosensor.”

Oh agrees that the possibilities are endless.

“Besides , we can utilize a large variety of other two-dimensional materials to build atomically sharp tweezers combined with unusual optical or electronic properties,” said Oh. “It is really exciting to think of atomically sharp tweezers that can be used to trap, sense, and release biomolecules electronically. This could have huge potential for point-of-care diagnostics, which is our ultimate goal for this powerful device.”

In addition to Oh, Koester, and Barik, other researchers on the team include University of Minnesota Department of Electrical and Computer Engineering Assistant Professor Tony Low, graduate student Yao Zhang, and postdoctoral researcher Roberto Grassi, as well as Professor Joshua Edel and research associate Binoy Paulose Nadappuram from Imperial College London.

The University of Minnesota research was funded primarily by the National Science Foundation and the Minnesota Partnership for Biotechnology and Medical Genomics, a unique collaborative venture among the University of Minnesota, Mayo Clinic, and the State of Minnesota.

 Explore further: Scientists move graphene closer to transistor applications

More information: Avijit Barik et al, Graphene-edge dielectrophoretic tweezers for trapping of biomolecules, Nature Communications (2017). DOI: 10.1038/s41467-017-01635-9

 

Source:  U of Minnesota

U of Minnesota: Discovery of new transparent thin film material – Less Costly than Indium – Could lead to smaller, faster, more powerful electronics, improve solar cells


U of Minn ThinFilm Solar 5-discoveryofnA team of researchers, led by the University of Minnesota, have discovered a new nano-scale thin film material with the highest-ever conductivity in its class.  Credit: University of Minnesota

A team of researchers, led by the University of Minnesota, have discovered a new nano-scale thin film material with the highest-ever conductivity in its class. The new material could lead to smaller, faster, and more powerful electronics, as well as more efficient solar cells.

The discovery is being published today in Nature Communications, an open access journal that publishes high-quality research from all areas of the natural sciences.

Researchers say that what makes this new material so unique is that it has a high conductivity, which helps electronics conduct more electricity and become more powerful. But the material also has a wide bandgap, which means light can easily pass through the material making it optically transparent. In most cases, materials with wide bandgap, usually have either low conductivity or poor transparency.

“The high conductivity and wide bandgap make this an ideal material for making optically transparent conducting films which could be used in a wide variety of electronic devices, including , electronic displays, touchscreens and even in which light needs to pass through the device,” said Bharat Jalan, a University of Minnesota chemical engineering and materials science professor and the lead researcher on the study.

Currently, most of the in our electronics use a chemical element called indium. The price of indium has gone up tremendously in the past few years significantly adding to the cost of current display technology. As a result, there has been tremendous effort to find alternative materials that work as well, or even better, than indium-based transparent conductors.

In this study, researchers found a solution. They developed a new transparent conducting thin film using a novel synthesis method, in which they grew a BaSnO3 thin film (a combination of barium, tin and oxygen, called barium stannate), but replaced elemental tin source with a chemical precursor of tin. The chemical precursor of tin has unique, radical properties that enhanced the chemical reactivity and greatly improved the metal oxide formation process. Both barium and tin are significantly cheaper than indium and are abundantly available.

“We were quite surprised at how well this unconventional approach worked the very first time we used the tin chemical precursor,” said University of Minnesota engineering and materials science graduate student Abhinav Prakash, the first author of the paper. “It was a big risk, but it was quite a big breakthrough for us.”

Jalan and Prakash said this new process allowed them to create this material with unprecedented control over thickness, composition, and defect concentration and that this process should be highly suitable for a number of other material systems where the element is hard to oxidize. The new process is also reproducible and scalable.

They further added that it was the structurally superior quality with improved defect concentration that allowed them to discover high conductivity in the material. They said the next step is to continue to reduce the defects at the atomic scale.

“Even though this material has the highest within the same class, there is much room for improvement in addition, to the outstanding potential for discovering new physics if we decrease the defects. That’s our next goal,” Jalan said.

Explore further: See-through circuitry: New and cheap alternative for transparent electronics

More information: Abhinav Prakash et al, Wide bandgap BaSnO3 films with room temperature conductivity exceeding 104 S cm−1, Nature Communications (2017). DOI: 10.1038/ncomms15167

 

Making Better (More Efficient) Solar Cells: Nanotechnology Changes Behavior of Materials


1-ACS Solar Band Gap nl-2014-03322a_0005One of the reasons solar cells are not used more widely is cost—the materials used to make them most efficient are expensive. Engineers are exploring ways to print solar cells from inks, but the devices don’t work as well.

Elijah Thimsen, PhD, assistant professor of energy, environmental & chemical engineering in the School of Engineering & Applied Science at Washington University in St. Louis, and a team of engineers at the University of Minnesota, have developed a technique to increase the performance and of thin films that make up these materials using nanotechnology. Their work was published in the Dec. 19, 2014, issue of Nature Communications.

Transparent conductors are thin films, which are are simply ultrathin layers of materials deposited on a surface that allow light to pass through and conduct electricity, a process in which electrons flow through a system. Thimsen and his team found by changing the structure of a thin film made of nanoparticles, electrons no longer flowed through the system in a conventional way, but hopped from place to place by a process called tunneling.

The team measured the electronic properties of a thin film made of zinc oxide nanoparticles before and after coating its surface with aluminum oxide. Both the zinc oxide nanoparticles and are electronic insulators, so only a tiny amount of electricity flows through them. However, when these insulators were combined, the researchers got a surprising result.

“The new composite became highly conductive,” Thimsen said. “The composite exhibits fundamentally different behavior than the parent compounds. We found that by controlling the structure of the material, you can control the mechanism by which electrons are transported.”

Because the reason behind this is not well understood, Thimsen and the team plan to continue to work to understand the relationship between the structure of the nanoparticle film and the electron transport mechanism, he said.SA Solar 5 191b940e-6e05-402a-bfbb-3e7be5f8a46f_16x9_600x338

“If electrons are tunneling, they’re not really moving with a classical velocity and moving from one point to the next,” Thimsen said. “If are tunneling from one point to the next, one hypothesis is that they won’t interact with strong magnetic fields. One of our long-term visions is to create a material that has high electrical conductivity but does not interact with magnetic fields.”

In addition, the new composite’s behavior also improved its performance, which could ultimately help to lower the cost of materials used in and other electronic devices.

“The performance is quite good, but not at the level it needs to be to be commercially viable, but it’s close,” Thimsen said.

Explore further: New materials for more powerful solar cells

More information: “High electron mobility in thin films formed via supersonic impact deposition of nanocrystals synthesized in nonthermal plasmas.” Nature Communications, Dec. 19, 2014. DOI: 10.1038/ncomms6822

Nanoscience research could prove a breakthrough in electronics


Nanotubes images05 August 2013

Electronic ink

 

Electronic touch pads that cost just a few dollars and solar cells that cost the same as roof shingles are one step closer to reality today.
Researchers in the University of Minnesota’s College of Science and Engineering and the National Renewable Energy Laboratory in Golden, Colo., have overcome technical hurdles in the quest for inexpensive, durable electronics and solar cells made with non-toxic chemicals.

 
The research team discovered a novel technology to produce a specialized type of ink from non-toxic nanometer-sized crystals of silicon, often called “electronic ink.” This “electronic ink” could produce inexpensive electronic devices with techniques that essentially print it onto inexpensive sheets of plastic.

 

 
“This process for producing electronics is almost like screen printing a number on a softball jersey,” said Lance Wheeler, a University of Minnesota mechanical engineering Ph.D. student and lead author of the research.

 

 
But it’s not quite that easy. Wheeler, Kortshagen and the rest of the research team developed a method to solve fundamental problems of silicon electronic inks.
First, there is the ubiquitous need of organic “soap-like” molecules, called ligands, that are needed to produce inks with a good shelf life, but these molecules cause detrimental residues in the films after printing. This leads to films with electrical properties too poor for electronic devices. Second, nanoparticles are often deliberately implanted with impurities, a process called “doping,” to enhance their electrical properties.

 
Researchers used a new method to use an ionized gas, called nonthermal plasma, to not only produce silicon nanocrystals, but also to cover their surfaces with a layer of chlorine atoms. This surface layer of chlorine induces an interaction with many widely used solvents that allows production of stable silicon inks with excellent shelf life without the need for organic ligand molecules.

 

 
In addition, the researchers discovered that these solvents lead to doping of films printed from their silicon inks, which gave them an electrical conductivity 1,000 times larger than un-doped silicon nanoparticle films. The researchers have a provisional patent on their findings.

 

 

This story is reprinted from material from University of Minnesota, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

New Center for Sustainable Nanotechnology to study environmental footprint of nanoparticles


Posted: Nov 29th, 2012

(Nanowerk News) Northwestern University has joined  forces with four Midwestern universities and a national laboratory to establish  the Center for Sustainable Nanotechnology, which this fall received  funding from the National Science Foundation.
Chemists, environmental engineers and freshwater scientists will  work on developing a deeper understanding of nanotechnology’s environmental  footprint and potential toxicity — areas little understood, despite a rapid  increase of nanomaterials used in consumer products, from cellphones and laptops  to sunscreen and beer bottles.
“We need to know how the tiny particles interact with their  environment, and this requires advanced imaging and spectroscopic tools that can  see where no eye has seen before,” said Franz M. Geiger, a professor of chemistry in the Weinberg  College of Arts and Sciences who is leading the Northwestern team.
“And the nanoparticles must be studied without taking them out  of their biogeochemical environment or modifying them for analysis,” he said. “This is an extremely daunting challenge but one we relish.”
Geiger’s team includes Stephanie Walter, Julianne Troiano and  Laura Olenick, all doctoral students in his lab. They will utilize their unique  nonlinear optics laboratory to develop new imaging techniques and provide  testing grounds for nanoparticles created by other center members.
Robert Hamers, a professor of chemistry at the University of  Wisconsin-Madison, is director of the Center for Sustainable Nanotechnology.  Other center members are the University of Minnesota, the University of  Wisconsin-Milwaukee, the University of Illinois and Pacific Northwest National  Laboratory.
“Our center — involving the expertise of researchers at six  different institutions — takes ample advantage of synergy, which, by  definition, produces effects that cannot be produced by summing up the  individual parts,” Geiger said.
Center researchers will focus on understanding how the surfaces of new as well as aged or weathered nanoparticles interact at the molecular level with cell membranes and what kind of biochemical pathways are triggered when these interactions occur. The findings ultimately could help inform the development of federal regulations.
In addition to the molecular studies, the researchers will study  two freshwater organisms, a water flea and a bacterium, feeding them  nanoparticles and tracking the particles using methods to be developed in the  center. The biochemical pathways will be studied to determine if the  nanoparticles have any toxic effects on the organisms.
Some of the nanomaterials produce a signal by lighting up when  light of a certain color is shined on them, allowing the particles to be imaged  inside living organisms. Geiger and his team will apply nonlinear optical  approaches to study a subset of these materials: those that can be accessed  using the suite of ultrafast laser systems available in his laboratory.
The Center for Sustainable Nanotechnology received a three-year,  $1.75 million Phase 1 Center for Chemical Innovation grant from the National  Science Foundation (NSF) this fall. Following the initial phase, the researchers  will have the opportunity to apply to the NSF for a much larger grant to  continue their work.
Geiger’s research with the new center connects to Northwestern’s  strategic plan goals of discovering creative solutions to problems that will  improve lives, communities and the world as well as focusing on nanoscience, one  of Northwestern’s 10 areas of greatest strength.
Source: Northwestern  University

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