Researchers develop blue-, yellow-, and red-emitting Graphene Quantum Dots


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PL spectra of GQDs (a), PEI1800 GQDs (b), and PEI600 GQDs (c) at different excitation wavelengths. Inset: photograph of aqueous solution of these three GQDs under room light (left) and 365 nm UV irradiation lamp (right). UV-vis absorption spectra (d) of GQDs, PEI1800 GQDs, and PEI600 GQDs dispersed in water. (© ACS) 

Graphene quantum dots (GQDs) show great potential in the fields of photoelectronics, photovoltaics, biosensing, and bioimaging owing to their unique photoluminescence (PL) properties, including excellent biocompatibility, low toxicity, and high stability against photobleaching and photoblinking.

However, further development of GQDs is limited by their synthetic methodology and unclear PL mechanism. Therefore, it is urgent to find efficient and universal methods for the synthesis of GQDs with high stability, controllable surface properties, and tunable PL emission wavelength.In new work reported in ACS Applied Materials & Interfaces (“Red, Yellow, and Blue Luminescence by Graphene Quantum Dots: Syntheses, Mechanism, and Cellular Imaging”), researchers in China have synthesized PL-tunable GQDs with blue, yellow, and red emission colors by coating with polyethyleneimine (PEI) of different molecular weights.

photoluminescence spectra of graphene quantum dotsPL spectra of GQDs (a), PEI1800 GQDs (b), and PEI600 GQDs (c) at different excitation wavelengths. Inset: photograph of aqueous solution of these three GQDs under room light (left) and 365 nm UV irradiation lamp (right). UV-vis absorption spectra (d) of GQDs, PEI1800 GQDs, and PEI600 GQDs dispersed in water. (© ACS) (click on image to enlarge)

Read More About a Company Commercializing Graphene Quantum Dots

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DotzNano … The Next Big Small Thing

Dotz Nano Ltd. is the world’s premier manufacturer of Graphene Quantum Dots (GQDs), commercializing an innovative technology that produces GQDs out of Coal and Carbon sources. Dotz Nano can supply high quality GQDs for use in a variety of applications that include:

  • Medical imaging
  • Displays/Consumer Electronics
  • Sensing
  • Optical brighteners
  • Energy Storage
  • Solar Cell
  • Data Storage
  • Anti-counterfeiting

With its modern labs and manufacturing facility, Dotz Nano is capturing the market utilizing GQDs as an alternative material in hundreds of applications.

 

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The team employed TEM, AFM, XRD, FTIR, XPS, DLS, and zeta potential to characterize the structures of the as-prepared GQDs and they stufied the PL mechanism by theoretical calculations.The average sizes of uncoated yellow-emitting GQDs, blue-emitting PEI1800 GQDs, and red-emitting PEI600 GQDs were 2.37, 6.05, and 57.31 nm, respectively. The yellow-emitting and blue-emitting GQDs were monolayer structures, whereas the red-emitting GQDs were multilayer structures. The red-emitting GQDs possessed a big PEI cage with multiple GQDs inside, whereas the blue-emitting PEI-coated GQDs had a single GQD core.The scientists found that carboxyl groups were changed to amide groups on the surface of GQDs and that this amidation reaction was crucial for PL change. By analyzing the molecular orbital and charge density, it was found that amide bonds decreased the conjugation and increased the energy gap thus inducing the blue shift of the PL.For the red-emitting GQDs, the conjugation area was enlarged by the interaction of GQDs in the PEI cage; thus, the PL peak exhibited a red shift.Remarkably, as the team points out, all GQDs exhibited good stability at high ionic strength and resisted photobleaching. Cell viability after treatment with the as-prepared GQDs indicated that GQDs had quite low cytotoxicity.”The GQDs could be used for bioimaging and are expected to be widely applied in multicolor imaging and bioanalysis applications,” the authors cocnlude their report. “We hope that this work will inspire the design of even better GQDs with tunable PL properties.”

Primary Story Contributed by Micheal Berger Nanowerk

MIT: Light-emitting particles (quantum dots) open new window for biological imaging


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‘Quantum dots’ that emit infrared light enable highly detailed images of internal body structures

For certain frequencies of short-wave infrared light, most biological tissues are nearly as transparent as glass. Now, researchers have made tiny particles that can be injected into the body, where they emit those penetrating frequencies. The advance may provide a new way of making detailed images of internal body structures such as fine networks of blood vessels.

The new findings, based on the use of light-emitting particles called quantum dots, is described in a paper in the journal Nature Biomedical Engineering, by MIT research scientist Oliver Bruns, recent graduate Thomas Bischof PhD ’15, professor of chemistry Moungi Bawendi, and 21 others.

Near-infrared imaging for research on biological tissues, with wavelengths between 700 and 900 nanometers (billionths of a meter), is widely used, but wavelengths of around 1,000 to 2,000 nanometers have the potential to provide even better results, because body tissues are more transparent to that light. “We knew that this imaging mode would be better” than existing methods, Bruns explains, “but we were lacking high-quality emitters” — that is, light-emitting materials that could produce these precise wavelengths.

QD bio Image II imagesLight-emitting particles have been a specialty of Bawendi, the Lester Wolf Professor of Chemistry, whose lab has over the years developed new ways of making quantum dots. These nanocrystals, made of semiconductor materials, emit light whose frequency can be precisely tuned by controlling the exact size and composition of the particles.

The key was to develop versions of these quantum dots whose emissions matched the desired short-wave infrared frequencies and were bright enough to then be easily detected through the surrounding skin and muscle tissues. The team succeeded in making particles that are “orders of magnitude better than previous materials, and that allow unprecedented detail in biological imaging,” Bruns says. The synthesis of these new particles was initially described in a paper by graduate student Daniel Franke and others from the Bawendi group in Nature Communications last year.

The quantum dots the team produced are so bright that their emissions can be captured with very short exposure times, he says. This makes it possible to produce not just single images but video that captures details of motion, such as the flow of blood, making it possible to distinguish between veins and arteries.

QD Bio Image IV GAAlso Read About

Graphene Quantum Dots Expand Role In Cancer Treatment And Bio-Imaging

 

 

The new light-emitting particles are also the first that are bright enough to allow imaging of internal organs in mice that are awake and moving, as opposed to previous methods that required them to be anesthetized, Bruns says. Initial applications would be for preclinical research in animals, as the compounds contain some materials that are unlikely to be approved for use in humans. The researchers are also working on developing versions that would be safer for humans.QD Bio Image III 4260773298_1497232bef

 

The method also relies on the use of a newly developed camera that is highly sensitive to this particular range of short-wave infrared light. The camera is a commercially developed product, Bruns says, but his team was the first customer for the camera’s specialized detector, made of indium-gallium-arsenide. Though this camera was developed for research purposes, these frequencies of infrared light are also used as a way of seeing through fog or smoke.

Not only can the new method determine the direction of blood flow, Bruns says, it is detailed enough to track individual blood cells within that flow. “We can track the flow in each and every capillary, at super high speed,” he says. “We can get a quantitative measure of flow, and we can do such flow measurements at very high resolution, over large areas.”

Such imaging could potentially be used, for example, to study how the blood flow pattern in a tumor changes as the tumor develops, which might lead to new ways of monitoring disease progression or responsiveness to a drug treatment. “This could give a good indication of how treatments are working that was not possible before,” he says.

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The team included members from MIT’s departments of Chemistry, Chemical Engineering, Biological Engineering, and Mechanical Engineering, as well as from Harvard Medical School, the Harvard T.H. Chan School of Public Health, Raytheon Vision Systems, and University Medical Center in Hamburg, Germany. The work was supported by the National Institutes of Health, the National Cancer Institute, the National Foundation for Cancer Research, the Warshaw Institute for Pancreatic Cancer Research, the Massachusetts General Hospital Executive Committee on Research, the Army Research Office through the Institute for Soldier Nanotechnologies at MIT, the U.S. Department of Defense, and the National Science Foundation.

Additional background

ARCHIVE: A new contrast agent for MRI http://news.mit.edu/2017/iron-oxide-nanoparticles-contrast-agent-mri-0214

ARCHIVE: A new eye on the middle ear http://news.mit.edu/2016/shortwave-infrared-instrument-ear-infection-0822

ARCHIVE: Chemists design a quantum-dot spectrometer http://news.mit.edu/2015/quantum-dot-spectrometer-smartphone-0701

ARCHIVE: Running the color gamut http://news.mit.edu/2014/startup-quantum-dot-tv-displays-1119

ARCHIVE: Fine-tuning emissions from quantum dots http://news.mit.edu/2013/fine-tuning-emissions-from-quantum-dots-0602

Graphene Quantum Dots: Introduction and Market News


 

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What are quantum dots?

Quantum dots, or QDs, are semiconductor nanoparticles or nanocrystals, usually in the range of 2-10 nanometers (10-50 atoms) in size. Their small size and high surface-to-volume ratio affects their optical and electronic properties and makes them different from larger particles made of the same materials. Quantum dots confine the motion of conduction band electrons, valence band holes, or excitons (bound pairs of conduction band electrons and valence band holes) in all three spatial directions. Quantum dots are also sometimes referred to as ‘artificial atoms’, a term that emphasizes that they are a single object with bound, discrete electronic states, similarly to naturally occurring atoms or molecules.

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Image: Grapehene Quantum Dots 

Many types of quantum dot are fluorescent – they emit light of specific frequencies if electricity or light is applied to them. These frequencies can be tuned by changing the dots’ size, shape and material, opening the door to diverse applications. Generally speaking, smaller dots appear blue while larger ones tend to be more red. Specific colors also vary depending on the exact composition of the QD.
Applications

Thanks to their highly tunable properties, QDs are attracting interest from various application developers and researchers. Among these potential applications are displays, transistors, solar cells, diode lasers, quantum computing, and medical imaging. Additionally, their small size enables QDs to be suspended in solution, which leads to possible uses in inkjet printing and spin-coating. These processing techniques may result in less-expensive and less time consuming methods of semiconductor fabrication. Quantum dots are considered especially suitable for optical applications, thanks to their ability to emit diverse colors, coupled with their high efficiencies, longer lifetimes and high extinction coefficient.

 

Their small size also means that electrons do not have to travel as far as with larger particles, thus electronic devices can operate faster. Examples of applications that take advantage of these electronic properties include transistors, solar cells, quantum computing, and more. QDs can greatly improve LED screens, offering them higher peak brightness, better colour accuracy, higher color saturation and more. QDs are also very interesting for use in biomedical applications, since their small size allows them to travel in the body, thus making them suitable for applications like medical imaging, biosensors, etc.
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What is graphene?

 

Graphene is a material made of carbon atoms that are bonded together in a repeating pattern of hexagons. Graphene is so thin that it is considered two dimensional. Graphene’s flat honeycomb pattern gives it many extraordinary characteristics, such as being the strongest material in the world, as well as one of the lightest, most conductive and transparent. Graphene has endless potential applications, in almost every industry (like electronics, medicine, aviation and much more).

 

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Graphene structure photo
The single layers of carbon atoms provide the basis for many other materials. Graphite, like the substance found in pencil lead, is formed by stacked graphene. Carbon nanotubes are made of rolled graphene and are used in many emerging applications from sports gear to biomedicine.

 

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Graphene quantum dots

The term graphene quantum dots (GQDs) is usually used to describe miniscule fragments, limited in size, or domains, of single-layer to tens of layers of graphene. GQDs often possess properties like low toxicity, stable photoluminescence, chemical stability and pronounced quantum confinement effect, which make them attractive for biological, opto-electronics, energy and environmental applications.

 

tour-gqds-iii-1206_coal-5-webPhoto: Dr. James M. Tour: Rice University: 

The synthesis of graphene quantum structures, such as graphene quantum dots, has become a popular topic in recent years. While graphene usually does not have a bandgap – which is a problem for many applications – graphene quantum dots do contain a bandgap due to quantum confinement and edge effects, and that bandgap modifies graphene’s carrier behaviors and can lead to versatile applications in optoelectronics. GQDs were also found to have four quantum states at a given energy level, unlike semiconductor quantum dots, which have only two. These additional quantum states, according to researchers, could make GQDs beneficial for quantum computing.
Additional properties of GQDs such as high transparency and high surface area have been proposed for energy and display applications. Because of the large surface area, electrodes using GQDs are applied for capacitors and batteries. Various techniques have been developed to produce GQDs. Top-down methods include solution chemical, microwave, and ultrasonic methods. Bottom-up methods include hydrothermal and electrochemical methods.

 

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Graphene Quantum Dots in the News

Dotz Nano secures first order of graphene quantum dots:

In January 2017, Dotz Nano, a nanotechnology company focused on the development, manufacture and commercialization of graphene quantum dots (GQDs), signed a marketing agreement with Strem Chemicals, a manufacturer and distributor of specialty chemicals headquartered in the U.S.

Strem Chemicals will aim to facilitate sales of Dotz’s GQDs to academic, industrial and government research and development laboratories, as well as commercial businesses using GQDs for research purposes.

 
Fuji Pigment announces graphene and carbon QD manufacturing process:

In April 2016, Fuji Pigment announced the development of a large-scale manufacturing process for carbon and graphene quantum dots (QDs). Fuji Pigment stated that its toxic-metal-free QDs exhibit a high light-emitting quantum efficiency and stability comparable to the toxic metal-based quantum dots.

 
Samsung developed graphene quantum dots based flash memory devices:

In June 2014, researchers from Samsung Electronics (and Korea’s Kyung Hee University) developed flash devices based on graphene quantum dots (GQDs). The performance of such a device is promising, with an electron density that is comparable to semiconductor and metal nanocrystal based memories. Those flash memory can also be made flexible and transparent.

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Read More: Graphene ‘artificial atom’ opens door to quantum computing

Cage-opening fullerene provide fluorescent graphene quantum dots


QDOT Cage Opening id39436New work by an international research team has demonstrated the simultaneous oxidation and cage-opening of fullerene C60 to provide graphene quantum dots.
Reporting their findings in ACS Nano (“Synthesis of Strongly Fluorescent Graphene Quantum Dots by Cage-Opening Buckminsterfullerene”), the team synthesized graphene quantum dots (QDs) by treating fullerene C60 with a mixture of concentrated sulfuric acid, sodium nitrate, and potassium permanganate.
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Treatment of fullerene C60 with a mixture of strong acid and chemical oxidant induced the oxidation, cage-opening, and fragmentation processes of fullerene C60. (© ACS)
Detailed characterization including LDI-TOF MS, TEM, AFM, STM, XPS, DLS, FT-IR, and Raman spectroscopy analyses revealed the formation of aggregated small fragments consisting of carbon, oxygen, and hydrogen elements, which favored the production of graphene QDs.
More importantly, the graphene QDs exhibited strong luminescence properties when excited at 340 nm.
The highly oxygenated graphene QDs showcased their broad prospects for modifications through successful functionalization reactions. The luminescence properties varied according to the types of chemical treatments, whereby hydroxylamine-functionalized graphene QDs showed a blue-shift of the emission maximum, while hydrazine-reduced graphene QDs showed a red-shift of the emission maximum.
All in all, the simplicity of this method in producing graphene QDs shows potential for further development for integration into practical devices or applications including optoelectronics and biological labeling.
Source: American Chemical Society

Read more: Cage-opening fullerene provide fluorescent graphene quantum dots