Tag Archives: gold nanoparticles

Joint Mexican/Finnish research team analyzes circulating currents inside gold nanoparticles

An April 30, 2021 news item on ScienceDaily announces the research,

Researchers in the Nanoscience Center of University of Jyvaskyla, in Finland and in the Guadalajara University in Mexico developed a method that allows for simulation and visualization of magnetic-field-induced electron currents inside gold nanoparticles. The method facilitates accurate analysis of magnetic field effects inside complex nanostructures in nuclear magnetic resonance measurements and establishes quantitative criteria for aromaticity of nanoparticles. The work was published 30.4.2021 as an Open Access article in Nature Communications.

An April 30, 2021 University of Jyväskylä – Jyväskylän yliopisto news release (also on EurekAlert), which originated the news item, describes the work in greater technical detail,

According to the classical electromagnetism, a charged particle moving in an external magnetic field experiences a force that makes the particle’s path circular. This basic law of physics is used, e.g., in designing cyclotrons that work as particle accelerators. When nanometer-size metal particles are placed in a magnetic field, the field induces a circulating electron current inside the particle. The circulating current in turn creates an internal magnetic field that opposes the external field. This physical effect is called magnetic shielding.

The strength of the shielding can be investigated by using nuclear magnetic resonance (NMR) spectroscopy. The internal magnetic shielding varies strongly in an atomic length scale even inside a nanometer-size particle. Understanding these atom-scale variations is possible only by employing quantum mechanical theory of the electronic properties of each atom making the nanoparticle.

Now, the research group of Professor Hannu Häkkinen in the University of Jyväskylä, in collaboration with University of Guadalajara in Mexico, developed a method to compute, visualize, and analyze the circulating electron currents inside complex 3D nanostructures. The method was applied to gold nanoparticles with a diameter of only about one nanometer. The calculations shed light onto unexplained experimental results from previous NMR measurements in the literature regarding how magnetic shielding inside the particle changes when one gold atom is replaced by one platinum atom.

A new quantitative measure to characterize aromaticity inside metal nanoparticles was also developed based on the total integrated strength of the shielding electron current.

“Aromaticity of molecules is one of the oldest concepts in chemistry, and it has been traditionally connected to ring-like organic molecules and to their delocalized valence electron density that can develop circulating currents in an external magnetic field. However, generally accepted quantitative criteria for the degree of aromaticity have been lacking. Our method yields now a new tool to study and analyze electron currents at the resolution of one atom inside any nanostructure, in principle. The peer reviewers of our work considered this as a significant advancement in the field”, says Professor Häkkinen who coordinated the research.

This image illustrates the work,

Caption: The atomic structure of a gold nanoparticle protected by phosphine molecules (left) and magnetic-field-induced electron currents in a plane intersecting the center of the particle (right). The total electron current consists of two (paratropic and diatropic) components circulating in opposite directions. Credit: University of Jyväskylä/Omar Lopez Estrada

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

Magnetically induced currents and aromaticity in ligand-stabilized Au and AuPt superatoms by Omar López-Estrada, Bernardo Zuniga-Gutierrez, Elli Selenius, Sami Malola & Hannu Häkkinen . Nature Communications volume 12, Article number: 2477 (2021) DOI: https://doi.org/10.1038/s41467-021-22715 Published: 30 April 2021

This paper is open access.

Gold nanoparticle tattoo changes medical diagnostics?

The tattoos are in fact implantable sensors. Here’s more from an April 6, 2021 news item on ScienceDaily,

The idea of implantable sensors that continuously transmit information on vital values and concentrations of substances or drugs in the body has fascinated physicians and scientists for a long time. Such sensors enable the constant monitoring of disease progression and therapeutic success. However, until now implantable sensors have not been suitable to remain in the body permanently but had to be replaced after a few days or weeks. On the one hand, there is the problem of implant rejection because the body recognizes the sensor as a foreign object. On the other hand, the sensor’s color which indicates concentration changes has been unstable so far and faded over time. Scientists at Johannes Gutenberg University Mainz (JGU) have developed a novel type of implantable sensor which can be operated in the body for several months. The sensor is based on color-stable gold nanoparticles that are modified with receptors for specific molecules. Embedded into an artificial polymeric tissue, the nanogold is implanted under the skin where it reports changes in drug concentrations by changing its color.

An April 6, 2021 Johannes Gutenberg Universitaet Mainz press release (also on EurekAlert), which originated the news item, provides more detail about the proposed tattoo/implantable sensors,

Implant reports information as an “invisible tattoo”

Professor Carsten Sönnichsen’s research group at JGU has been using gold nanoparticles as sensors to detect tiny amounts of proteins in microscopic flow cells for many years. Gold nanoparticles act as small antennas for light: They strongly absorb and scatter it and, therefore, appear colorful. They react to alterations in their surrounding by changing color. Sönnichsen’s team has exploited this concept for implanted medical sensing.

To prevent the tiny particles from swimming away or being degraded by immune cells, they are embedded in a porous hydrogel with a tissue-like consistency. Once implanted under the skin, small blood vessels and cells grow into the pores. The sensor is integrated in the tissue and is not rejected as a foreign body. “Our sensor is like an invisible tattoo, not much bigger than a penny and thinner than one millimeter,” said Professor Carsten Sönnichsen, head of the Nanobiotechnology Group at JGU. Since the gold nanoparticles are infrared, they are not visible to the eye. However, a special kind of measurement device can detect their color noninvasively through the skin.

In their study published in Nano Letters, the JGU researchers implanted their gold nanoparticle sensors under the skin of hairless rats. Color changes in these sensors were monitored following the administration of various doses of an antibiotic. The drug molecules are transported to the sensor via the bloodstream. By binding to specific receptors on the surface of the gold nanoparticles, they induce color change that is dependent on drug concentration. Thanks to the color-stable gold nanoparticles and the tissue-integrating hydrogel, the sensor was found to remain mechanically and optically stable over several months.

Huge potential of gold nanoparticles as long-lasting implantable medical sensors

“We are used to colored objects bleaching over time. Gold nanoparticles, however, do not bleach but keep their color permanently. As they can be easily coated with various different receptors, they are an ideal platform for implantable sensors,” explained Dr. Katharina Kaefer, first author of the study.

The novel concept is generalizable and has the potential to extend the lifetime of implantable sensors. In future, gold nanoparticle-based implantable sensors could be used to observe concentrations of different biomarkers or drugs in the body simultaneously. Such sensors could find application in drug development, medical research, or personalized medicine, such as the management of chronic diseases.

Interdisciplinary team work brought success

Sönnichsen had the idea of using gold nanoparticles as implanted sensors already in 2004 when he started his research in biophysical chemistry as a junior professor in Mainz. However, the project was not realized until ten years later in cooperation with Dr. Thies Schroeder and Dr. Katharina Kaefer, both scientists at JGU. Schroeder was experienced in biological research and laboratory animal science and had already completed several years of research work in the USA. Kaefer was looking for an exciting topic for her doctorate and was particularly interested in the complex and interdisciplinary nature of the project. Initial results led to a stipend awarded to Kaefer by the Max Planck Graduate Center (MPGC) as well as financial support from Stiftung Rheinland-Pfalz für Innovation. “Such a project requires many people with different scientific backgrounds. Step by step we were able to convince more and more people of our idea,” said Sönnichsen happily. Ultimately, it was interdisciplinary teamwork that resulted in the successful development of the first functional implanted sensor with gold nanoparticles.

The researchers have provided an image which illustrates several elements described in the press release,

Caption: Gold nanoparticles embedded in a porous hydrogel can be implanted under the skin and used as medical sensors. The sensor is like an invisible tattoo revealing concentration changes of substances in the blood by color change. Credit: ill./©: Nanobiotechnology Group, JGU Department of Chemistry

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

Implantable Sensors Based on Gold Nanoparticles for Continuous Long-Term Concentration Monitoring in the Body by Katharina Kaefer, Katja Krüger, Felix Schlapp, Hüseyin Uzun, Sirin Celiksoy, Bastian Flietel, Axel Heimann, Thies Schroeder, Oliver Kempski, and Carsten Sönnichsen. Nano Lett. 2021, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acs.nanolett.1c00887 Publication Date:March 30, 2021 © 2021 The Authors. Published by American Chemical Society

This paper is behind a paywall.

Put a ring on it: preventing clumps of gold nanoparticles

Caption: A comparison of how linear PEG (left) and cyclic PEG (right) attach to a gold nanoparticle Credit: Yubo Wang, Takuya Yamamoto

A January 20, 2021 news item on phys.org focuses on work designed to stop gold nanoparticles from clumping together (Note: A link has been removed),

Hokkaido University scientists have found a way to prevent gold nanoparticles from clumping, which could help towards their use as an anti-cancer therapy.

Attaching ring-shaped synthetic compounds to gold nanoparticles helps them retain their essential light-absorbing properties, Hokkaido University researchers report in the journal Nature Communications.

A January 20, 2021 Hokkaido University press release (also on EurekAlert but published Jan. 21, 2020), which originated the news item, elaborates on the work,

Metal nanoparticles have unique light-absorbing properties, making them interesting for a wide range of optical, electronic and biomedical applications. For example, if delivered to a tumour, they could react with applied light to kill cancerous tissue. A problem with this approach, though, is that they easily clump together in solution, losing their ability to absorb light. This clumping happens in response to a variety of factors, including temperature, salt concentration and acidity.

Scientists have been trying to find ways to ensure nanoparticles stay dispersed in their target environments. Covering them with polyethylene glycol, otherwise known as PEG, has been relatively successful at this in the case of gold nanoparticles. PEG is biocompatible and can prevent gold surfaces from clumping together in the laboratory and in living organisms, but improvements are still needed.

Applied chemist Takuya Yamamoto and colleagues at Hokkaido University, The University of Tokyo, and Tokyo Institute of Technology found that mixing gold nanoparticles with ring-shaped PEG, rather than the normally linear PEG, significantly improved dispersion. The ‘cyclic-PEG’ (c-PEG) attaches to the surfaces of the nanoparticles without forming chemical bonds with them, a process called physisorption. The coated nanoparticles remained dispersed when frozen, freeze-dried and heated.

The team tested the c-PEG-covered gold nanoparticles in mice and found that they cleared slowly from the blood and accumulated better in tumours compared to gold nanoparticles coated with linear PEG. However, accumulation was lower than desired levels, so the researchers recommend further investigations to fine-tune the nanoparticles for this purpose.

Associate Professor Takuya Yamamoto is part of the Laboratory of Chemistry of Molecular Assemblies at Hokkaido University, where he studies the properties and applications of various cyclic chemical compounds.

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

Enhanced dispersion stability of gold nanoparticles by the physisorption of cyclic poly(ethylene glycol) by Yubo Wang, Jose Enrico Q. Quinsaat, Tomoko Ono, Masatoshi Maeki, Manabu Tokeshi, Takuya Isono, Kenji Tajima, Toshifumi Satoh, Shin-ichiro Sato, Yutaka Miura & Takuya Yamamoto. Nature Communications volume 11, Article number: 6089 (2020) DOI: https://doi.org/10.1038/s41467-020-19947-8 Published: 30 November 2020

This paper is open access.

Spotting the difference between dengue and Zika infections with gold nanosensors

This July 29, 2020 news item on Nanowerk features research from Brazil,

A new class of nanosensor developed in Brazil could more accurately identify dengue and Zika infections, a task that is complicated by their genetic similarities and which can result in misdiagnosis.

The technique uses gold nanoparticles and can “observe” viruses at the atomic level, according to a study published in Scientific Reports (“Nanosensors based on LSPR are able to serologically differentiate dengue from Zika infections”).

Belonging to the Flavivirus genus in the Flaviviridae family, Zika and dengue viruses share more than 50 per cent similarity in their amino acid sequence. Both viruses are spread by mosquitos and can have long-term side effects. The Flaviviridae virus family was named after the yellow fever virus and comes from the Latin word for golden, or yellow, in colour.

“Diagnosing [dengue virus] infections is a high priority in countries affected by annual epidemics of dengue fever. The correct diagnostic is essential for patient managing and prognostic as there are no specific antiviral drugs to treat the infection,” the authors say.

More than 1.8 million people are suspected to have been infected with dengue so far this year in the Americas, with 4000 severe cases and almost 700 deaths, the Pan American Health Organization says. The annual global average is estimated to be between 100 million and 400 million dengue infections, according to the World Health Organization.

Flávio Fonseca, study co-author and researcher at the Federal University of Minas Gerais, tells SciDev.Net it is almost impossible to differentiate between dengue and Zika viruses.

“A serologic test that detects antibodies against dengue also captures Zika-generated antibodies. We call it cross-reactivity,” he says.

Meghie Rodrigues’ July 29, 2020 article for SciDev.net, which originated the news item, delves further into the work,

Co-author and virologist, Maurício Nogueira, tells SciDev.Net that avoiding cross-reactivity is crucial because “dengue is a disease that kills — and can do so quickly if the right diagnosis is not made. As for Zika, it offers risks for foetuses to develop microcephaly, and we can’t let pregnant women spend seven or eight months wondering whether they have the virus or not.”

There is also no specific antiviral treatment for Zika and the search for a vaccine is ongoing.

Virus differentiation is important to accurately measure the real impact of both diseases on public health. The most widely used blood test, the enzyme-linked immunosorbent assay (ELISA), is limited in its ability to tell the difference between the viruses, the authors say.

As dengue has four variations, known as serotypes, the team created four different nanoparticles and covered each of them with a different dengue protein. They applied ELISA serum and a blood sample. The researchers found that sample antibodies bound with the viruses’ proteins, changing the pattern of electrons on the gold nanoparticle surface.

Should you check out Rodrigues’ entire article, you might want to take some time to explore SciDev.net to find science news from countries that don’t often get the coverage they should.

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

Nanosensors based on LSPR are able to serologically differentiate dengue from Zika infections by Alice F. Versiani, Estefânia M. N. Martins, Lidia M. Andrade, Laura Cox, Glauco C. Pereira, Edel F. Barbosa-Stancioli, Mauricio L. Nogueira, Luiz O. Ladeira & Flávio G. da Fonseca. Scientific Reports volume 10, Article number: 11302 (2020) DOI: https://doi.org/10.1038/s41598-020-68357-9 Published: 09 July 2020

This paper is open access.

Water-based gold rush

It seems water can play an important role when using nanocatalysts made of gold nanoparticles combined with metal oxides. From a July 27, 2020 news item on ScienceDaily,

Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals. They show high catalytic activity, particularly in aqueous solution. A team of researchers from Ruhr-Universität Bochum (RUB) has been able to explain why: Water molecules play an active role in facilitating the oxygen dissociation needed for the oxidation reaction. The team of Professor Dominik Marx, Chair of Theoretical Chemistry, reports in the high-impact journal ACS Catalysis on 14 July 2020.

A July 27, 2020 Ruhr-University Bochum (RUB) press release (also on EurekAlert), which originated the news item, offers more detail,

Rushing for gold

Most industrial oxidation processes involve the use of agents, such as chlorine or organic peroxides, that produce toxic or useless by-products. Instead, using molecular oxygen, O2, and splitting it to obtain the oxygen atoms needed to produce specific products would be a greener and more attractive solution. A promising medium for this approach is the gold/metal oxide (Au/TiO2) system, where the metal oxide titania (TiO2) supports nanoparticles of gold. These nanocatalysts can catalyse the selective oxidation of molecular hydrogen, carbon monoxide and especially alcohols, among others. A crucial step behind all reactions is the dissociation of O2, which comprises a usually high energy barrier. And a crucial unknown in the process is the role of water, since the reactions take place in aqueous solutions.

In a 2018 study, the RUB group of Dominik Marx, Chair of Theoretical Chemistry and Research Area coordinator in the Cluster of Excellence Ruhr Explores Solvation (Resolv), already hinted that water molecules actively participate in the oxidative reaction: They enable a stepwise charge-transfer process that leads to oxygen dissociation in the aqueous phase. Now, the same team reveals that solvation facilitates the activation of molecular oxygen (O2) at the gold/metal oxide (Au/TiO2) nanocatalyst: In fact, water molecules help to decrease the energy barrier for the O2 dissociation. The researchers quantified that the solvent curbs the energy costs by 25 per cent compared to the gas phase. “For the first time, it has been possible to gain insights into the quantitative impact of water on the critical O2 activation reaction for this nanocatalyst – and we also understood why,” says Dominik Marx.

Mind the water molecules

The RUB researchers applied computer simulations, the so-called ab initio molecular dynamics simulations, which explicitly included not only the catalyst but also as many as 80 surrounding water molecules. This was key to gain deep insights into the liquid-phase scenario, which contains water, in direct comparison to the gas phase conditions, where water is absent. “Previous computational work employed significant simplifications or approximations that didn’t account for the true complexity of such a difficult solvent, water,” adds Dr. Niklas Siemer who recently earned his PhD at RUB based on this research.

Scientists simulated the experimental conditions with high temperature and pressure to obtain the free energy profile of O2 in both liquid and gas phase. Finally, they could trace back the mechanistic reason for the solvation effect: Water molecules induce an increase of local electron charge towards oxygen that is anchored at the nanocatalyst perimeter; this in turn leads to the less energetic costs for the dissociation. In the end, say the researchers, it’s all about the unique properties of water: “We found that the polarizability of water and its ability to donate hydrogen bonds are behind oxygen activation,” says Dr. Munoz-Santiburcio. According to the authors, the new computational strategy will help to understand and improve direct oxidation catalysis in water and alcohols.

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

Solvation-Enhanced Oxygen Activation at Gold/Titania Nanocatalysts by Niklas Siemer, Daniel Muñoz-Santiburcio, and Dominik Marx. ACS Catal. 2020, 10, 15, 8530–8534 DOI: https://doi.org/10.1021/acscatal.0c01326 Publication Date: July 14, 2020 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Gold nanoparticles make a new promise: a non-invasive COVID-19 breathalyser

I believe that swab they stick up your nose to test for COVDI-19 is 10 inches long so it seems to me that discomfort or unpleasant are not the words that best describe the testing experience .

Hopefully, no one will have to find inadequate vocabulary for this new COVID-19 testing assuming that future trials are successful and they are able to put the technology into production. From an August 19, 2020 news item on Nanowerk,

Few people who have undergone nasopharyngeal swabs for coronavirus testing would describe it as a pleasant experience. The procedure involves sticking a long swab up the nose to collect a sample from the back of the nose and throat, which is then analyzed for SARS-CoV-2 RNA [ribonucleic acid] by the reverse-transcription polymerase chain reaction (RT-PCR).

Now, researchers reporting in [American Chemical Society] ACS Nano (“Multiplexed Nanomaterial-Based Sensor Array for Detection of COVID-19 in Exhaled Breath”) have developed a prototype device that non-invasively detected COVID-19 in the exhaled breath of infected patients.

An August 19, 2020 ACS news release (also received via email and on EurekAlert), which originated the news item, provides more technical details,

In addition to being uncomfortable, the current gold standard for COVID-19 testing requires RT-PCR, a time-consuming laboratory procedure. Because of backlogs, obtaining a result can take several days. To reduce transmission and mortality rates, healthcare systems need quick, inexpensive and easy-to-use tests. Hossam Haick, Hu Liu, Yueyin Pan and colleagues wanted to develop a nanomaterial-based sensor that could detect COVID-19 in exhaled breath, similar to a breathalyzer test for alcohol intoxication. Previous studies have shown that viruses and the cells they infect emit volatile organic compounds (VOCs) that can be exhaled in the breath.

The researchers made an array of gold nanoparticles linked to molecules that are sensitive to various VOCs. When VOCs interact with the molecules on a nanoparticle, the electrical resistance changes. The researchers trained the sensor to detect COVID-19 by using machine learning to compare the pattern of electrical resistance signals obtained from the breath of 49 confirmed COVID-19 patients with those from 58 healthy controls and 33 non-COVID lung infection patients in Wuhan, China. Each study participant blew into the device for 2-3 seconds from a distance of 1¬-2 cm. Once machine learning identified a potential COVID-19 signature, the team tested the accuracy of the device on a subset of participants. In the test set, the device showed 76% accuracy in distinguishing COVID-19 cases from controls and 95% accuracy in discriminating COVID-19 cases from lung infections. The sensor could also distinguish, with 88% accuracy, between sick and recovered COVID-19 patients. Although the test needs to be validated in more patients, it could be useful for screening large populations to determine which individuals need further testing, the researchers say.

The authors acknowledge funding from the Technion-Israel Institute of Technology.

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

Multiplexed Nanomaterial-Based Sensor Array for Detection of COVID-19 in Exhaled Breath by Benjie Shan, Yoav Y Broza, Wenjuan Li, Yong Wang, Sihan Wu, Zhengzheng Liu, Jiong Wang, Shuyu Gui, Lin Wang, Zhihong Zhang, Wei Liu, Shoubing Zhou, Wei Jin, Qianyu Zhang, Dandan Hu, Lin Lin, Qiujun Zhang, Wenyu Li, Jinquan Wang, Hu Liu, Yueyin Pan, and Hossam Haick. ACS Nano 2020, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acsnano.0c05657 Publication Date:August 18, 2020 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Chameleon skin (nanomaterial made of gold nanoparticles) for robots

A June 17, 2020 news item on Nanowerk trumpets research into how robots might be able to sport chameleon-like skin one day,

A new film made of gold nanoparticles changes color in response to any type of movement. Its unprecedented qualities could allow robots to mimic chameleons and octopi — among other futuristic applications.

Unlike other materials that try to emulate nature’s color changers, this one can respond to any type of movement, like bending or twisting. Robots coated in it could enter spaces that might be dangerous or impossible for humans, and offer information just based on the way they look.

For example, a camouflaged robot could enter tough-to-access underwater crevices. If the robot changes color, biologists could learn about the pressures facing animals that live in these environments.

Although some other color-changing materials can also respond to motion, this one can be printed and programmed to display different, complex patterns that are difficult to replicate.

This video from the University of California at Riverside researchers shows the material in action (Note: It gets more interesting after the first 20 secs.),

A June 15, 2020 University of California at Riverside (UCR) news release (also on EurekAlert but published on June 17, 2020) by Jules Bernstein, which originated the news item, delves further,

Nanomaterials are simply materials that have been reduced to an extremely small scale — tens of nanometers in width and length, or, about the size of a virus. When materials like silver or gold become smaller, their colors will change depending on their size, shape, and the direction they face.

“In our case, we reduced gold to nano-sized rods. We knew that if we could make the rods point in a particular direction, we could control their color,” said chemistry professor Yadong Yin. “Facing one way, they might appear red. Move them 45 degrees, and they change to green.”

The problem facing the research team was how to take millions of gold nanorods floating in a liquid solution and get them all to point in the same direction to display a uniform color.

Their solution was to fuse smaller magnetic nanorods onto the larger gold ones. The two different-sized rods were encapsulated in a polymer shield, so that they would remain side by side. That way, the orientation of both rods could be controlled by magnets.

“Just like if you hold a magnet over a pile of needles, they all point in the same direction. That’s how we control the color,” Yin said.

Once the nanorods are dried into a thin film, their orientation is fixed in place and they no longer respond to magnets. “But, if the film is flexible, you can bend and rotate it, and will still see different colors as the orientation changes,” Yin said.

Other materials, like butterfly wings, are shiny and colorful at certain angles, and can also change color when viewed at other angles. However, those materials rely on precisely ordered microstructures, which are difficult and expensive to make for large areas. But this new film can be made to coat the surface of any sized object just as easily as applying spray paint on a house.

Though futuristic robots are an ultimate application of this film, it can be used in many other ways. UC Riverside chemist Zhiwei Li, the first author on this paper, explained that the film can be incorporated into checks or cash as an authentication feature. Under normal lighting, the film is gray, but when you put on sunglasses and look at it through polarized lenses, elaborate patterns can be seen. In addition, the color contrast of the film may change dramatically if you twist the film.

The applications, in fact, are only limited by the imagination. “Artists could use this technology to create fascinating paintings that are wildly different depending on the angle from which they are viewed,” Li said. “It would be wonderful to see how the science in our work could be combined with the beauty of art.”

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

Coupling magnetic and plasmonic anisotropy in hybrid nanorods for mechanochromic responses by Zhiwei Li, Jianbo Jin, Fan Yang, Ningning Song & Yadong Yin. Nature Communications volume 11, Article number: 2883 (2020) DOI: https://doi.org/10.1038/s41467-020-16678-8 Published: 08 June 2020

This paper is open access.

Gold nanoparticles could help detect the presence of COVID-19 in ten minutes

If this works out, it would make testing for COVID-19 an infinitely easier task. From a May 29, 2020 news item on phys.org,

Scientists from the University of Maryland School of Medicine (UMSOM) developed an experimental diagnostic test for COVID-19 that can visually detect the presence of the virus in 10 minutes. It uses a simple assay containing plasmonic gold nanoparticles to detect a color change when the virus is present. The test does not require the use of any advanced laboratory techniques, such as those commonly used to amplify DNA, for analysis. The authors published their work last week [May 21, 2020] in the American Chemical Society’s nanotechnology journal ACS Nano.

“Based on our preliminary results, we believe this promising new test may detect RNA [ribonucleic acid] material from the virus as early as the first day of infection. Additional studies are needed, however, to confirm whether this is indeed the case,” said study leader Dipanjan Pan, PhD, Professor of Diagnostic Radiology and Nuclear Medicine and Pediatrics at the UMSOM.

Caption: A nasal swab containing a test sample is mixed with a simple lab test. It contains a liquid mixed with gold nanoparticles attached to a molecule that binds to the novel coronavirus. If the virus is present, the gold nanoparticles turns the solution a deep blue color (bottom of the tube) and a precipitation is noticed. If it is not present, the solution retains its original purple color. Credit: University of Maryland School of Medicine

A May 28, 2020 University of Maryland news release (also on EurekAlert), which originated the news item, provides more detail,

Once a nasal swab or saliva sample is obtained from a patient, the RNA is extracted from the sample via a simple process that takes about 10 minutes. The test uses a highly specific molecule attached to the gold nanoparticles to detect a particular protein. This protein is part of the genetic sequence that is unique to the novel coronavirus. When the biosensor binds to the virus’s gene sequence, the gold nanoparticles respond by turning the liquid reagent from purple to blue.

“The accuracy of any COVID-19 test is based on being able to reliably detect any virus. This means it does not give a false negative result if the virus actually is present, nor a false positive result if the virus is not present,” said Dr. Pan. “Many of the diagnostic tests currently on the market cannot detect the virus until several days after infection. For this reason, they have a significant rate of false negative results.”

Dr. Pan created a company called VitruVian Bio to develop the test for commercial application. He plans to have a pre-submission meeting with the U.S. Food and Drug Administration (FDA) within the next month to discuss requirements for getting an emergency use authorization for the test. New FDA policy allows for the marketing of COVID-19 tests without requiring them to go through the usual approval or clearance process. These tests do, however, need to meet certain validation testing requirements to ensure that they provide reliable results.

“This RNA-based test appears to be very promising in terms of detecting the virus. The innovative approach provides results without the need for a sophisticated laboratory facility,” said study co-author Matthew Frieman, PhD, Associate Professor of Microbiology and Immunology at UMSOM.

Although more clinical studies are warranted, this test could be far less expensive to produce and process than a standard COVID-19 lab test; it does not require laboratory equipment or trained personnel to run the test and analyze the results. If this new test meets FDA expectations, it could potentially be used in daycare centers, nursing homes, college campuses, and work places as a surveillance technique to monitor any resurgence of infections.

In Dr. Pan’s laboratory, research scientist Parikshit Moitra, PhD, and UMSOM research fellow Maha Alafeef conducted the studies along with research fellow Ketan Dighe from UMBC.

Dr. Pan holds a joint appointment with the College of Engineering at the University of Maryland Baltimore County and is also a faculty member of the Center for Blood Oxygen Transport and Hemostasis (CBOTH).

“This is another example of how our faculty is driving innovation to fulfill a vital need to expand the capacity of COVID-19 testing,” said Dean E. Albert Reece, MD, PhD, MBA, who is also Executive Vice President for Medical Affairs, UM Baltimore, and the John Z. and Akiko K. Bowers Distinguished Professor, University of Maryland School of Medicine. “Our nation will be relying on inexpensive, rapid tests that can be dispersed widely and used often until we have effective vaccines against this pandemic.”

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

Selective Naked-Eye Detection of SARS-CoV-2 Mediated by N Gene Targeted Antisense Oligonucleotide Capped Plasmonic Nanoparticles by Parikshit Moitra, Maha Alafeef, Ketan Dighe, Matthew B. Frieman, and Dipanjan Pan. ACS Nano 2020, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acsnano.0c03822 Publication Date:May 21, 2020 Copyright © 2020 American Chemical Society

This paper appears to be open access.

I tried to find Dr. Pan’s company, VitruVian Bio and found a business with an almost identical name, Vitruvian Biomedical, which does not include Dr. Pan on its management team list and this company’s focus is on Alzheimer’s Disease. Finally, there is no mention of the COVID-19 test anywhere on the Vitruvian Biomedical website.

An artificial tongue, gold, and maple syrup

I have always imagined the love of maple syrup to be a universal love. A friend who moved to Canada from somewhere else in the world disillusioned me on that subject. She claims to be unable to grasp why anyone would love maple syrup. Should you recognize yourself in those words you may not find this post all that interesting.

However, maple syrup lovers may find this May 5, 2020 news item on Nanowerk a bit disconcerting,

It’s said that maple syrup is Quebec’s liquid gold. Now scientists at Université de Montréal have found a way to use real gold — in the form of nanoparticles — to quickly find out how the syrup tastes.

The new method — a kind of artificial tongue — is validated in a study published in Analytical Methods (“High-throughput plasmonic tongue using an aggregation assay and nonspecific interactions: classification of taste profiles in maple syrup”), the journal of the Royal Society of Chemistry, in the United Kingdom.

The “tongue” is a colorimetric test that detects changes in colour to show how a sample of maple syrup tastes. The result is visible to the naked eye in a matter of seconds and is useful to producers.

“The artificial tongue is simpler than a human tongue: it can’t distinguish the complex flavour profiles that we can detect,” said UdeM chemistry professor Jean-François Masson, who led the study. “Our device works specifically to detect flavour differences in maple syrup as it’s being produced.”

A chemistry professor at Université de Montréal has developed a new test using gold nanoparticles to establish the flavour profile of maple syrup and help producers evaluate its quality. Courtesy: Université de Montréal

There is more information but the central question as to why anyone would want an artificial tongue for tasting maple syrup is never answered (presumably they want to speed up production and ensure more consistent classification) nor is there much in the way of technical detail in a May 5, 2019 Université de Montréal news release (also on EurekAlert),

1,818 samples tested

The artificial tongue was validated by analyzing 1,818 samples of maple syrup from different regions of Quebec. The syrups that were analyzed represented the various known aromatic profiles and colours of syrup, from golden to dark brown.

“We designed the ‘tongue’ at the request of the Québec Maple Syrup Producers to detect the presence of different flavour profiles,” explained Simon Forest, the study’s first author. “The tool takes into account the product’s olfactory and taste properties.”

Maple syrup has a molecular complexity similar to that of wine. Its taste is delicate, without bitterness, and it has a subtle aroma. During the production process, specialized human tasters are employed to judge which profile each batch fits into.

“The development of the artificial tongue is intended to support the colossal work that is being done in the field to do the first sorting of syrups quickly and classify them according to their qualities,” said Masson.

Red for the best, blue for the rest

The researchers compare the artificial tongue to a pH test for a swimming pool. You simply pour a few drops of syrup into the gold nanoparticle reagent and wait about 10 seconds.

If the result stays in the red spectrum, it has the characteristics of a premium quality syrup, the kind best loved by consumers and sold in grocery stores or exported.

If, on the other hand, the test turns blue, the syrup may have a flavour “defect”, which may be treated as an industrial syrup for use in processing.

“It doesn’t mean the syrup is not good for consumption or that it has a different sugar level,” Masson said of the “blue” type syrup, which the food industry uses as a natural sweetener in other products. “It just may not have the usual desired characteristics, and so can’t be sold directly in bottles to consumers.”

60 categories of taste

Caramelized, woody, green, smoked, salty, burnt — the taste of maple syrup has as many as 60 categories to fit into. Maple syrup is essentially a concentrated sugar solution of 66 per cent sucrose and 33 per cent water; the remaining one per cent of other compounds determines the taste.

Like wine, the taste of maple syrup changes according to a variety of factors, including the harvest period, the region, production and storage methods and, of course, the weather. Too much variation in temperature over a weekend, for instance, can greatly affect the taste profile of the product.

The artificial tongue developed at UdeM could someday be adapted for tasting wine or fruit juice, Masson said, as well as be useful in a number of other agrifood contexts.

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

A high-throughput plasmonic tongue using an aggregation assay and nonspecific interactions: classification of taste profiles in maple syrup by Simon Forest, Trevor Théorêt, Julien Coutu, and Jean-Francois Masson. Anal. Methods, 2020, Advance Article DOI: https://doi.org/10.1039/C9AY01942A First published 05 May 2020

This paper is behind a paywall.

Are nano electronics as good as gold?

“As good as gold” was a behavioural goal when I was a child. It turns out, the same can be said of gold in electronic devices according to the headline for a March 26, 2020 news item on Nanowerk (Note: Links have been removed),

As electronics shrink to nanoscale, will they still be good as gold?

Deep inside computer chips, tiny wires made of gold and other conductive metals carry the electricity used to process data.

But as these interconnected circuits shrink to nanoscale, engineers worry that pressure, such as that caused by thermal expansion when current flows through these wires, might cause gold to behave more like a liquid than a solid, making nanoelectronics unreliable. That, in turn, could force chip designers to hunt for new materials to make these critical wires.

But according to a new paper in Physical Review Letters (“Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure”), chip designers can rest easy. “Gold still behaves like a solid at these small scales,” says Stanford mechanical engineer Wendy Gu, who led a team that figured out how to pressurize gold particles just 4 nanometers in length — the smallest particles ever measured — to assess whether current flows might cause the metal’s atomic structure to collapse.

I have seen the issue about gold as a metal or liquid before but I can’t find it here (search engines, sigh). However, I found this somewhat related story from almost five years ago. In my April 14, 2015 posting (Gold atoms: sometimes they’re a metal and sometimes they’re a molecule), there was news that the number of gold atoms present means the difference between being a metal and being a molecule .This could have implications as circuit elements (which include some gold in their fabrication) shrink down past a certain point.

A March 24, 2020 Stanford University news release (also on Eurekalert but published on March 25, 2020) by Andrew Myers, which originated the news item, provides details about research designed to investigate a similar question, i.e, can we used gold as we shrink the scale?*,

To conduct the experiment, Gu’s team first had to devise a way put tiny gold particles under extreme pressure, while simultaneously measuring how much that pressure damaged gold’s atomic structure.

To solve the first problem, they turned to the field of high-pressure physics to borrow a device known as a diamond anvil cell. As the name implies, both hammer and anvil are diamonds that are used to compress the gold. As Gu explained, a nanoparticle of gold is built like a skyscraper with atoms forming a crystalline lattice of neat rows and columns. She knew that pressure from the anvil would dislodge some atoms from the crystal and create tiny defects in the gold.

The next challenge was to detect these defects in nanoscale gold. The scientists shined X-rays through the diamond onto the gold. Defects in the crystal caused the X-rays to reflect at different angles than they would on uncompressed gold. By measuring variations in the angles at which the X-rays bounced off the particles before and after pressure was applied, the team was able to tell whether the particles retained the deformations or reverted to their original state when pressure was lifted.

In practical terms, her findings mean that chipmakers can know with certainty that they’ll be able to design stable nanodevices using gold — a material they have known and trusted for decades — for years to come.

“For the foreseeable future, gold’s luster will not fade,” Gu says.

*The 2015 research measured the gold nanoclusters by the number of atoms within the cluster with the changes occurring at some where between 102 atoms and 144 atoms. This 2020 work measures the amount of gold by nanometers as in 3.9 nm gold nanocrystals . So, how many gold atoms in a nanometer? Cathy Murphy provides the answer and the way to calculate it for yourself in a July 26, 2016 posting on the Sustainable Nano blog ( a blog by the Center for Sustainable Nanotechnology),

Two years ago, I wrote a blog post called Two Ways to Make Nanoparticles, describing the difference between top-down and bottom-up methods for making nanoparticles. In the post I commented, “we can estimate, knowing how gold atoms pack into crystals, that there are about 2000 gold atoms in one 4 nm diameter gold nanoparticle.” Recently, a Sustainable Nano reader wrote in to ask about how this calculation is done. It’s a great question!

So, a 3.9 nm gold nanocrystal contains approximately 2000 gold atoms. (If you have time, do read Murphy’s description of how to determine the number of gold atoms in a gold nanoparticle.) So, this research does not answer the question posed by the 2015 research.

It may take years before researchers can devise tests for gold nanoclusters consisting of 102 atoms as opposed to nanoparticles consisting of 2000 atoms. In the meantime, here’s a link to and a citation for the latest on how gold reacts as we shrink the size of our electronics,

Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure by Abhinav Parakh, Sangryun Lee, K. Anika Harkins, Mehrdad T. Kiani, David Doan, Martin Kunz, Andrew Doran, Lindsey A. Hanson, Seunghwa Ryu, and X. Wendy Gu. Phys. Rev. Lett. 124, 106104 DOI:https://doi.org/10.1103/PhysRevLett.124.106104 Published 13 March 2020 © 2020 American Physical Society

This paper is behind a paywall.