Tag Archives: carbon dots (CDs)

Pressure-cooking birch leaves to produce nanoscale carbon particles for organic semiconductors

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By pressure cooking birch leaves picked on campus the scientists produced carbon particles that can be used as raw material for the production of organic semiconductors. Image: Mattias Pettersson

A November 28, 2023 news item on phys.org announces work on an organic semiconductor,

Today, petrochemical compounds and rare metals such as platinum and iridium are used to produce semiconductors for optoelectronics, such as organic LEDs for super-thin TV and mobile phone screens. Physicists at Umeå University in collaboration with researchers in Denmark and China, have discovered a more sustainable alternative. By pressure-cooking birch leaves picked on the Umeå University campus, they have produced a nanosized carbon particle with desired optical properties.

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A January 28, 2023 Umeå University press release by Anna-Lena Lindskog, which originated the news item, provides more information about the research,

“The essence of our research is to harness nearby renewable resources for producing organic semiconductor materials” says Jia Wang, research fellow at the Department of Physics, Umeå University, and one of the authors of the study that has been published in the Green Chemistry.

Organic semiconductors are one of the most important functional materials in optoelectronic applications. One example is the organic light-emitting diodes, OLEDs, which enable ultra-thin and bright TV and mobile phone screens. Sharply increasing demand for this advanced technology is driving massive production of organic semiconductor materials.

Unfortunately, these semiconductors are currently produced mainly from petrochemical compounds and rare elements, obtained through environmentally harmful mining. Moreover, these materials often contain so-called ‘critical raw materials’ that are in short supply, such as Platinum, Indium and Phosphorus.

From a sustainability point of view, it would be ideal if we can use biomass from plants, animals and waste to produce organic semiconductor materials. These starting materials are renewable and abundantly available. Research fellow Jia Wang and her colleagues at the Department of Physics, together with international partners, have succeeded in producing such a bio-based semiconductor material.

Birch leaves in pressure cooker

The synthesis process is simple: they picked birch leaves on the Umeå campus and cooked them in a pressure cooker. That produced a kind of ‘carbon dots’ about two nanometers in size, which emit a narrow-band, deep red light when dissolved in ethanol. Some of the optical properties of these birch leaf carbon dots are comparable to commercial quantum dots currently used in semiconductor materials, but unlike them, they contain no heavy metals or critical raw materials.

”It is important to note that our method is not limited to birch leaves” explains Jia Wang. “We tested different plant leaves with the same pressure cooking method, and all of them produced similar red-emitting carbon dots. This versatility suggests that the transformation process can be used in different locations.”

Using the carbon dots in a light-emitting electrochemical cell device, the researchers were able to show that the brightness generated was 100 cd/m2, which is comparable to the light intensity from a computer screen.

“It is important to note that our method is not limited to birch leaves.”

”This result shows that it is possible to transition from depleting petroleum compounds to regenerating biomass as a raw material for organic semiconductors” says Jia Wang.

She emphasises the broader potential of carbon dots beyond just light-emitting devices.

“Carbon dots are promising across various applications, from bioimaging and sensing to anti-counterfeiting. We’re open to collaborations and eager to explore more exciting uses for these emissive and sustainable carbon dots” says Jia Wang.

Here’s a link to and a citation for the paper,

Fluorescent carbon dots from birch leaves for sustainable electroluminescent devices by Shi Tang, Yongfeng Liu, Henry Opoku, Märta Gregorsson, Peijuan Zhang, Etienne Auroux, Dongfeng Dang, Anja-Verena Mudring, Thomas Wågberg, Ludvig Edman, and Jia Wang. Green Chem., 2023, 25, 9884-9895 DOI: https://doi.org/10.1039/D3GC03827K First published: 01 Nov 2023

This paper is open access.

Using carbon dots (organic nanosensors) to detect pesticides

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Before getting to the latest about carbon dots, there’s something to be clarified (and it was news to me), a carbon dot is not a quantum dot. So says this 2020 paper, “Advances in carbon dots: from the perspective of traditional quantum dots” by Yanhong Liu, Hui Huang, Weijing Cao, Baodong Mao, Yang Liu, and Zhenhui Kang. Mater. Chem. Front., 2020,4, 1586-1613 First published March 17, 2020.

Abstract

Quantum dots (QDs) have been the core concept of nanoscience and nanotechnology since their inception, and play a dominant role in the development of the nano-field. Carbon dots (CDots), defined by a feature size of <10 nm, have become a rising star in the crossover field of carbon materials and traditional QDs (TQDs). CDots possess many unique structural, physicochemical and photochemical properties that render them a promising platform for biology, devices, catalysis and other applications. …

This story is about carbon dots but you can find out more about quantum dots in my October 6, 2023 posting concerning the 2023 Nobel prizes; scroll down to the ‘Chemistry’ subhead.

An August 30, 2023 news item on phys.org describes work from Concordia University (Montréal, Canada) on carbon dots,

Researchers at Concordia have developed a new system using tiny nanosensors called carbon dots to detect the presence of the widely used chemical glyphosate. Their research, titled “Ratiometric Sensing of Glyphosate in Water Using Dual Fluorescent Carbon Dots,” is published in Sensors.

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An August 30, 2023 Concordia University news release (also on EurekAlert) by Patrick Lejtenyi, which originated the news item, explains the importance of the work and provides more technical details, Note: Links have been removed,

Glyphosate is a pesticide found in more than 750 agricultural, forestry, urban and home products, including Monsanto’s popular weed-killer Roundup. It is also controversial: studies have linked its overuse to environmental pollution and cancer in humans. Its sale is banned or restricted in dozens of countries and jurisdictions, including Canada.

The researchers’ system relies on the carbon dots’ chemical interaction with glyphosate to detect its presence. Carbon dots are exceedingly small fluorescent particles, usually no more than 10 or 15 nanometres in size (a human hair is between 80,000 and 100,000 nanometres). But when they are added to water solutions, these nanomaterials emit blue and red fluorescence.

The researchers employed an analysis technique called a ratiometric self-referencing assay to determine glyphosate levels in a solution. The red fluorescence emitted by the carbon dots when exposed to varying concentrations of the chemical and different pH levels is compared with a control in which no glyphosate is present. In all the tests, the blue fluorescence remained unchanged, giving the researchers a common reference point across the different tests.

They observed that higher levels of glyphosate quenched the red fluorescence, which they accredited to the interaction of the pesticide with the carbon dots’ surface.

“Our system differs from others because we are measuring the area between two peaks—two fluorescent signatures—on the visible spectrum,” says Adryanne Clermont-Paquette, a PhD candidate in biology and the paper’s lead author. “This is the integrated area between the two curves. Ratiometric measurement allows us to ignore variables such as temperature, pH levels or other environmental factors. That allows us to just only look at the levels of glyphosate and carbon dots that are in the system.”

“By understanding the chemistry at the surface of these very small dots and by knowing their optical properties, we can use them to our advantage for many different applications,” says Rafik Naccache, an associate professor of chemistry and biochemistry and the paper’s supervising author.

Research assistants Diego-Andrés Mendoza and Amir Sadeghi, along with associate professor of biology Alisa Piekny, are co-authors.

Starting small

Naccache says the technique is designed to detect minute amounts of the pesticide. The technique they developed is sensitive enough to be able to detect the presence of pesticide at levels as low as 0.03 parts per million.

“The challenge is always in the other direction, to see how low we can go in terms of sensitivity and selectivity,” he says.

There remains much work to be done before this technology can be used widely. But as Clermont-Paquette notes, this paper represents an important beginning.

“Understanding the interaction between glyphosate and carbon dots is a first step. If we are to move this along further, and develop it into a real-life application, we have to start with the fundamentals.”

The researchers are supported by funding from the Natural Sciences and Engineering Research Council of Canada.

Here’s a link to and a citation for the paper,

Ratiometric Sensing of Glyphosate in Water Using Dual Fluorescent Carbon Dots
by Adryanne Clermont-Paquette, Diego-Andrés Mendoza, Amir Sadeghi, Alisa Piekny, and Rafik Naccache. Sensors 2023, 23(11), 5200; DOI: https://doi.org/10.3390/s23115200 Published: 30 May 2023

This paper is open access.

Glowing suture material could reduce infection and simplify post op monitoring

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Reassuringly, you won’t be waking up in the hospital to see your sutures glowing in the dark. On that note, here’s more about the innovation in a February 1, 2023 news item on ScienceDaily,

A new antimicrobial suture material that glows in medical imaging could provide a promising alternative for mesh implants and internal stitches.

Surgical site infections are one of the most common medical infections, occurring in 2 to 4% of patients post-surgery. For some procedures, such as vaginal mesh implants to treat prolapse, infection rates can be higher.

Study lead author and Vice Chancellor’s Senior Research Fellow [RMIT University, Australia], Dr Shadi Houshyar, said their suture was being developed in partnership with clinicians specifically for this type of procedure.

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Caption: The filament visible in chicken samples, as seen under CT scan. Credit: RMIT University

A February 1, 2023 RMIT University press release (also on EurekAlert but published January 31, 2023), which originated the news item, provides more context and technical detail about the research,

“Our smart surgical sutures can play an important role in preventing infection and monitoring patient recovery and the proof-of-concept material we’ve developed has several important properties that make it an exciting candidate for this,” said Houshyar, from the School of Engineering at RMIT University, Australia.

Lab tests on the surgical filament, published in OpenNano, showed it was easily visible in CT scans when threaded through samples of chicken meat, even after three weeks. It also showed strong antimicrobial properties, killing 99% of highly drug-resistant bacteria after six hours at body temperature.

Houshyar said the team was not aware of any commercially available suture products that combined these properties.

How they did it

The multidisciplinary team led by RMIT – included nano-engineering, biomedical and textile experts working in partnership with a practicing surgeon – used the university’s cutting-edge textile manufacturing facility to develop their proof-of-concept material.

The suture’s properties come from the combination of iodine and tiny nanoparticles, called carbon dots, throughout the material.

Carbon dots are inherently fluorescent, due to their particular wavelength, but they can also be tuned to various levels of luminosity that easily stand out from surrounding tissue in medical imaging.

Attaching iodine to these carbon dots, meanwhile, provides them with their strong antimicrobial properties and greater X-ray visibility.

Houshyar said carbon nano dots were safe, cheap and easy to produce in the lab from natural ingredients.

“They can be tailored to create biodegradable stitches or a permanent suture, or even to be adhesive on one side only, where required,” she said.

“This project opens up a lot of practical solutions for surgeons, which has been our aim from the start and the reason we have involved clinicians in the study.”

Clinical possibilities

Consultant colorectal surgeon and Professor of Surgery at the University of Melbourne, Justin Yeung, was involved in the study. He said it addressed a real challengefaced by surgeons in trying to identify the precise anatomical location of internal meshes on CT scans.

“This mesh will enable us to help with improved identification of the causes of symptoms, reduce the incidence of mesh infections and will help with precise preoperative planning, if there is a need to surgically remove this mesh,” he said.

“It has the potential to improve surgery outcomes and improve quality of life for a huge proportion of women, if used as vaginal mesh for example, by reducing the need for infected mesh removal.”

“It may also significantly reduce surgery duration and increase surgical accuracy in general through the ability to visualise mesh location accurately on preoperative imaging.” 

Next steps

Study co-author from RMIT’s School of Health and Biomedical Sciences, Professor Elisa Hill-Yardin, said the next steps were pre-clinical trials.

“While this research is at an early stage, we believe we are onto something very promising that could help a lot of people and are really keen to speak with industry partners who are interested in working with us to take it further,” she said.

“We see potential especially in vaginal mesh implants and similar procedures.”

The research team used Australia’s leading university-based textile manufacturing facilities at RMIT’s Centre for Materials Innovation and Future Fashion to produce the proof-of-concept material. They will soon be producing larger suture samples to use in pre-clinical trials, which they have just received seed funding for from RMIT.

Here’s a link to and a citation for the paper,

Smart suture with iodine contrasting nanoparticles for computed tomography by Shadi Houshyar, Hong Yin, Leon Pope, Rumbidzai Zizhou, Chaitali Dekiwadia, Elisa L. Hill-Yardin, Justin MC Yeung, Sabu John, Kate Fox, Nhiem Tran, Ivan Cole, Aaron Elbourne, Vi Khanh Truong, and Adam Truskewycz. OpenNano Volume 9, January 2023, 100120 DOI: https://doi.org/10.1016/j.onano.2022.100120

This paper is open access.

Light emitting diodes (LEDs) from food and beverage waste

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It’s exciting to think that with emerging technologies we’ll be able to make use of waste products rather than sending them off to fill up garbage dumps. An Oct. 13, 2015 news item on Nanowerk highlights some research where food and beverage waste products could be used to produce light emitting diodes (LEDs),

Most Christmas lights, DVD players, televisions and flashlights have one thing in common: they’re made with light emitting diodes (LEDs). LEDs are widely used for a variety of applications and have been a popular, more efficient alternative to fluorescent and incandescent bulbs for the past few decades. Two University of Utah researchers have now found a way to create LEDs from food and beverage waste. In addition to utilizing food and beverage waste that would otherwise decompose and be of no use, this development can also reduce potentially harmful waste from LEDs generally made from toxic elements.

An Oct. 13, 2015 University of Utah news release, which originated the news item, describes some of the issues with our current LEDs and how the researchers went about synthesizing the waste for reuse,

LEDs can be produced by using quantum dots, or tiny crystals that have luminescent properties, to produce light. Quantum dots (QDs) can be made with numerous materials, some of which are rare and expensive to synthesize, and even potentially harmful to dispose of. Some research over the past 10 years has focused on using carbon dots (CDs), or simply QDs made of carbon, to create LEDs instead.

Compared to other types of quantum dots, CDs have lower toxicity and better biocompatibility, meaning they can be used in a broader variety of applications.

U Metallurgical Engineering Research Assistant Professor Prashant Sarswat and Professor Michael Free, over the past year and a half, have successfully turned food waste such as discarded pieces of tortilla into CDs, and subsequently, LEDs.

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From bread to bulb

To synthesize waste into CDs, Sarswat and Free employed a solvothermal synthesis, or one in which the waste was placed into a solvent under pressure and high temperature until CDs were formed. In this experiment, the researchers used soft drinks and pieces of bread and tortilla.

The food and beverage waste were each placed in a solvent and heated both directly and indirectly for anywhere from 30 to 90 minutes.

After successfully finding traces of CDs from the synthesis, Sarswat and Free proceeded to illuminate the CDs to monitor their formation and color.

The pair also employed four other tests, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, Raman and AFM [atomic force microscopy] imaging to determine the CDs’ various optical and material properties.

“Synthesizing and characterizing CDs derived from waste is a very challenging task. We essentially have to determine the size of dots which are only 20 nanometers or smaller in diameter, so we have to run multiple tests to be sure CDs are present and to determine what optical properties they possess,” said Sarswat.

For comparison, a human hair is around 75,000 nanometers in diameter.

The various tests Sarswat and Free ran first measured the size of the CDs, which correlates with the intensity of the dots’ color and brightness. The tests then determined which carbon source produced the best CDs. For example, sucrose and D-fructose dissolved in soft drinks were found to be the most effective sources for production of CDs.

An environmentally sustainable alternative

Currently, one of the most common sources of QDs is cadmium selenide, a compound comprised of a two toxic elements. The ability to create QDs in the form of CDs from food and beverage waste would eliminate the need for concern over toxic waste, as the food and beverages themselves are not toxic.

“QDs derived from food and beverage waste are not based on common toxic elements such as cadmium and selenium, which makes their processing and disposal more environmentally friendly than it is for most other QDs.  In addition, the use of food and beverage waste as the starting material for QDs allows for reduced waste and cost to produce a useful material,” said Free.

In addition to being toxic when broken down, cadmium selenide is also expensive—one website listed a price of $529 for 25 ml of the compound.

“With food and beverage waste that are already there, our starting material is much less expensive. In fact, it’s essentially free,” said Sarswat.

According to a report from the US Department of Agriculture, roughly 31% of food produced in 2014 was not available for human consumption. To be able to use this waste for creating LEDs which are widely used in a number of technologies would be an environmentally sustainable approach.

Looking forward, Sarswat and Free hope to continue studying the LEDs produced from food and beverage waste for stability and long term performance.

“The ultimate goal is to do this on a mass scale and to use these LEDs in everyday devices. To successfully make use of waste that already exists, that’s the end goal,” said Sarswat.

Finally, the CDs were suspended in epoxy resins, heated and hardened to solidify the CDs for practical use in LEDs.

The researchers have made an image of the luminescent carbon dots available,

PHOTO CREDIT: Prashant Sarswat The luminescence of carbon dots can be seen when irradiated with UV light.

PHOTO CREDIT: Prashant Sarswat The luminescence of carbon dots can be seen when irradiated with UV light.

Here’s a link to and a citation for the paper,

Light emitting diodes based on carbon dots derived from food, beverage, and combustion wastes by Prashant K. Sarswat and Michael L. Free. Phys. Chem. Chem. Phys., 2015,17, 27642-27652 DOI: 10.1039/C5CP04782J First published online 01 Oct 2015

This paper appears to be behind a paywall. One final note, despite the paper’s title there doesn’t seem to be any mention of combustion waste in the news release which is a bit puzzling.