Tag Archives: silver ions

Observing individual silver nanoparticles in real time

A new technique for better understanding how silver nanoparticles might affect the environment was announced in a July 30, 2018 news item on ScienceDaily,

Chemists at Ruhr-Universität Bochum have developed a new method of observing the chemical reactions of individual silver nanoparticles, which only measure a thousandth of the thickness of a human hair, in real time. The particles are used in medicine, food and sports items because they have an antibacterial and anti-inflammatory effect. However, how they react and degrade in ecological and biological systems is so far barely understood. The team in the Research Group for Electrochemistry and Nanoscale Materials showed that the nanoparticles transform into poorly soluble silver chloride particles under certain conditions. The group led by Prof Dr Kristina Tschulik reports on the results in the Journal of the American Chemical Society from July 11, 2018.

A July 30,2018 Ruhr-University Bochum (RUB) press release (also on EurekAlert) by Julia Weiler, which originated the news item, provides more information,

Even under well-defined laboratory conditions, current research has yielded different, sometimes contradictory, results on the reaction of silver nanoparticles. “In every batch of nanoparticles, the individual properties of the particles, such as size and shape, vary,” says Kristina Tschulik, a member of the Cluster of Excellence Ruhr Explores Solvation. “With previous procedures, a myriad of particles was generally investigated at the same time, meaning that the effects of these variations could not be recorded. Or the measurements took place in a high vacuum, not under natural conditions in an aqueous solution.”

The team led by Kristina Tschulik thus developed a method that enables individual silver particles to be investigated in a natural environment. “Our aim is to be able to record the reactivity of individual particles,” explains the researcher. This requires a combination of electrochemical and spectroscopic methods. With optical and hyperspectral dark-field microscopy, the group was able to observe individual nanoparticles as visible and coloured pixels. Using the change in the colour of the pixels, or more precisely their spectral information, the researchers were able to follow what was happening in an electrochemical experiment in real time.

Degradation of the particles slowed down

In the experiment, the team replicated the oxidation of silver in the presence of chloride ions, which often takes place in ecological and biological systems. “Until now, it was generally assumed that the silver particles dissolve in the form of silver ions,” describes Kristina Tschulik. However, poorly soluble silver chloride was formed in the experiment – even if only a few chloride ions were present in the solution.

“This extends the lifespan of the nanoparticles to an extreme extent and their breakdown is slowed down in an unexpectedly drastic manner,” summarises Tschulik. “This is equally important for bodies of water and for living beings because this mechanism could cause the heavy metal silver to accumulate locally, which can be toxic for many organisms.”

Further development planned

The Bochum-based group now wants to further improve its technology for analysing individual nanoparticles in order to better understand the ageing mechanisms of such particles. The researchers thus want to obtain more information about the biocompatibility of the silver particles and the lifespan and ageing of catalytically active nanoparticles in the future.

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

Simultaneous Opto- and Spectro-Electrochemistry: Reactions of Individual Nanoparticles Uncovered by Dark-Field Microscopy by Kevin Wonner, Mathies V. Evers, and Kristina Tschulik. J. Am. Chem. Soc., Article ASAP DOI: 10.1021/jacs.8b02367 Publication Date (Web): July 11, 2018

Copyright © 2018 American Chemical Society

This paper is behind a paywall.

Greening silver nanoparticles with lignin

A July 13, 2015 news item on phys.org highlights a new approach to making silver nanoparticles safer in the environment,

North Carolina State University researchers have developed an effective and environmentally benign method to combat bacteria by engineering nanoscale particles that add the antimicrobial potency of silver to a core of lignin, a ubiquitous substance found in all plant cells. The findings introduce ideas for better, greener and safer nanotechnology and could lead to enhanced efficiency of antimicrobial products used in agriculture and personal care.

A July 13, 2015 North Carolina State University (NCSU) news release (also on EurekAlert), which originated the news item, adds a bit more information,

As the nanoparticles wipe out the targeted bacteria, they become depleted of silver. The remaining particles degrade easily after disposal because of their biocompatible lignin core, limiting the risk to the environment.

“People have been interested in using silver nanoparticles for antimicrobial purposes, but there are lingering concerns about their environmental impact due to the long-term effects of the used metal nanoparticles released in the environment,” said Velev, INVISTA Professor of Chemical and Biomolecular Engineering at NC State and the paper’s corresponding author. “We show here an inexpensive and environmentally responsible method to make effective antimicrobials with biomaterial cores.”

The researchers used the nanoparticles to attack E. coli, a bacterium that causes food poisoning; Pseudomonas aeruginosa, a common disease-causing bacterium; Ralstonia, a genus of bacteria containing numerous soil-borne pathogen species; and Staphylococcus epidermis, a bacterium that can cause harmful biofilms on plastics – like catheters – in the human body. The nanoparticles were effective against all the bacteria.

The method allows researchers the flexibility to change the nanoparticle recipe in order to target specific microbes. Alexander Richter, the paper’s first author and an NC State Ph.D. candidate who won a 2015 Lemelson-MIT prize, says that the particles could be the basis for reduced risk pesticide products with reduced cost and minimized environmental impact.

“We expect this method to have a broad impact,” Richter said. “We may include less of the antimicrobial ingredient without losing effectiveness while at the same time using an inexpensive technique that has a lower environmental burden. We are now working to scale up the process to synthesize the particles under continuous flow conditions.”

I don’t quite understand how the silver nanoparticles/ions are rendered greener. I gather the lignin is harmless but where do the silver nanoparticles/ions go after they’ve been stripped of their lignin cover and have killed the bacteria? I did try reading the paper’s abstract (not much use for someone with my science level),

Silver nanoparticles have antibacterial properties, but their use has been a cause for concern because they persist in the environment. Here, we show that lignin nanoparticles infused with silver ions and coated with a cationic polyelectrolyte layer form a biodegradable and green alternative to silver nanoparticles. The polyelectrolyte layer promotes the adhesion of the particles to bacterial cell membranes and, together with silver ions, can kill a broad spectrum of bacteria, including Escherichia coli, Pseudomonas aeruginosa and quaternary-amine-resistant Ralstonia sp. Ion depletion studies have shown that the bioactivity of these nanoparticles is time-limited because of the desorption of silver ions. High-throughput bioactivity screening did not reveal increased toxicity of the particles when compared to an equivalent mass of metallic silver nanoparticles or silver nitrate solution. Our results demonstrate that the application of green chemistry principles may allow the synthesis of nanoparticles with biodegradable cores that have higher antimicrobial activity and smaller environmental impact than metallic silver nanoparticles.

If you can explain what happens to the silver nanoparticles, please let me know.

Meanwhile, here’s a link to and a citation for the paper,

An environmentally benign antimicrobial nanoparticle based on a silver-infused lignin core by Alexander P. Richter, Joseph S. Brown, Bhuvnesh Bharti, Amy Wang, Sumit Gangwal, Keith Houck, Elaine A. Cohen Hubal, Vesselin N. Paunov, Simeon D. Stoyanov, & Orlin D. Velev. Nature Nanotechnology (2015) doi:10.1038/nnano.2015.141 Published online 13 July 2015

This paper is behind a paywall.

Silver ions in the environment

Earlier this week (Feb. 24, 2014), I published a post featuring Dr. Andrew Maynard, Director of the University of Michigan’s Risk Science Center in an introductory video describing seven surprising facts about silver nanoparticles. For those who want to delve more deeply, there’s a Feb. 25, 2014 news item on Nanowerk describing some Swiss research into silver nanoparticles and ions in aquatic environments,

It has long been known that, in the form of free ions, silver particles can be highly toxic to aquatic organisms. Yet to this day, there is a lack of detailed knowledge about the doses required to trigger a response and how the organisms deal with this kind of stress. To learn more about the cellular processes that occur in the cells, scientists from the Aquatic Research Institute, Eawag [Swiss Federal Institute of Aquatic Science and Technology], subjected algae to a range of silver concentrations.

In the past, silver mostly found its way into the environment in the vicinity of silver mines or via wastewater [emphasis mine] emanating from the photo industry. More recently, silver nanoparticles have become commonplace in many applications – as ingredients in cosmetics, food packaging, disinfectants, and functional clothing. Though a recent study conducted by the Swiss National Science Foundation revealed that the bulk of silver nanoparticles is retained in wastewater treatment plants, only little is known about the persistence and the impact of the residual nano-silver in the environment.

The Feb. 25, 2014 Eawag media release, which originated the news item, describes the research in further detail,

Smitha Pillai from the Eawag Department of Environmental Toxicology and her colleagues from EPF Lausanne and ETH Zürich studied the impact of various concentrations of waterborne silver ions on the cells of the green algae Chlamydomonas reinhardtii. Silver is chemically very similar to copper, an essential metal due to its importance in several enzymes. Because of that, silver can exploit the cells’ copper transport mechanisms and sneak into them undercover. This explains why, already after a short time, concentrations of silver in the intracellular fluid can reach up to one thousand times those in the surrounding environment.

A prompt response

Because silver damages key enzymes involved in energy metabolism, even low concentrations can cut photosynthesis and growth rates by a half in just 15 minutes. Over the same time period, the researchers also detected changes in the activity of about 1000 other genes and proteins, which they interpreted as a response to the stressor – an attempt to repair silver-induced damage. At low concentrations, the cells’ photosynthesis apparatus recovered within five hours, and recovery mechanisms were sufficient to deal with all but the highest concentrations tested.

A number of unanswered questions

At first glance, the results are reassuring because the silver concentrations that the algae are subject to in the environment are rarely as high as those applied in the lab, which allows them to recover quickly – at least externally. But the experiments also showed that even low silver concentrations have a significant effect on intracellular processes and that the algae divert their energy to repairing damage incurred. This can pose a problem when other stressors act in parallel, such as increased UV-radiation or other chemical compounds. Moreover, it remains unknown to this day whether the cells have an active mechanism to shuttle out the silver. Lacking such a mechanism, the silver could have adverse effects on higher organisms, given that algae are at the bottom of the food chain.

You can find the researchers’ paper here,

Linking toxicity and adaptive responses across the transcriptome, proteome, and phenotype of Chlamydomonas reinhardtii exposed to silver by Smitha Pillai, Renata Behra, Holger Nestler, Marc J.-F. Suter, Laura Sigg, and Kristin Schirmer. Proceedings of the National Academy of Sciences (PNAS) – early edition 18.February 2014, www.pnas.org/cgi/doi/10.1073/pnas.1319388111

The paper is available through the PNAS open access option.

I have published a number of pieces about aquatic enviornments and wastewater and nanotechnology-enabled products as useful for remediation efforts and as a source of pollution. Here’s a Feb. 28, 2013 posting where I contrasted two pieces of research on silver nanoparticles. The first was research in an aquatic environment and the other concerned wastewater.

Crypton and NANO-TEX together at last

A Jan. 6, 2014 news item on Nanowerk notes that Crypton Fabrics has purchased NANO-TEX,

CRYPTON INC. has acquired NANO-TEX®, announced Randy Rubin, Chairman of The Crypton Companies. The privately held, 20-year-old Crypton Fabrics, based in Bloomfield Hills, Michigan, recently purchased NANO-TEX from private equity and venture capital investors; WL Ross and Co. LLC as major stockholders, in addition to Norwest Venture Partners, Masters Capital Nanotechnology Fund, Firelake Capital Management and Masters Capital Management.

NANO-TEX is a textile technology company whose performance finishes have enhanced leading consumer brands such as GAP, TARGET, MAIDENFORM, BASS PRO SHOPS, NORDSTROM, LAND’S END, FISHER-PRICE and many more.

The Jan. 6, 2014 Crypton (there has to be a Superman or inert gas enthusiast in that company) press release, which can be found on this page under this title: Silicon Valley to Motown, Performance Textile Leader Crypton Purchases Nano-Tex, explains why the NANO-TEX acquisition was so attractive and what it means to NANO-TEX’s major stockholders,

NANO‐TEX employs a proprietary nanotechnology approach to enhance textiles at the molecular level that provides permanent performance attributes such as stain and water resistance, moisture wicking, odor control, static elimination and wrinkle free properties. The end result is performance fabrics that maintain the original comfort, look and feel of the fabric and perform for the life of the product.

In 2013, NANO‐TEX technologies were on $280 million in branded finished products at retail worldwide.

Wilbur Ross, Jr., Chairman of WL Ross said, “We are extremely pleased by Crypton’s acquisition. This assures that NANO‐TEX will continue on a strong growth trajectory. Its expanding market reach and prominence will further enhance the competitiveness of WL Ross’s companies in the consumer and industrial fabrics industries, too; the goal that sparked our initial investment interest in NANO‐TEX eight years ago.”

It seems there was a specific product which attracted the Crypton team’s attention,

“This is a strategic acquisition as we extend our market share with apparel throughout the world. The intellectual properties and latest development, Aquapel®, a non‐fluorinated repellency treatment, is very exciting to our research team,” said Rubin.

There’s more about this product on the NANO-TEX Aquapel® page.

On a completely other note, at least one NANO-TEX product has silver in it according to a 2007 entry on the Consumer Products Inventory (Project on Emerging Nanotechnologies),

They Say:

“Nano-Tex™’s revolutionary technology fundamentally transforms fabric at the nano-level to dramatically improve your favorite everyday clothing.”

Nanomaterials:

Silver

Potential Exposure Pathways:

Dermal

How much we know:

Category 4 (Unsupported claim)

Additional Information:

Generic Product

Crypton too has silver in at least one product (from the INCASE Fabric Protection FAQs),

Q:  How does INCASE™ resist bacterial growth?
A: Silver Ion technology is used in INCASE to inhibit the growth of a broad spectrum of medically relevant microorganisms, including bacteria. Silver is one of nature’s original antimicrobials. Used thousands of years ago by Greeks in vessels to preserve water and wine, the natural benefits of silver have now been tapped to keep fabrics odor-free.

Cyrpton’s INCASE product uses sliver ions, which according to some research at Rice University (based in Texas, US), are more toxic than silver nanoparticles, from my July 13, 2012 posting,

He [Pedro Alvarez, George R. Brown Professor and chair of Rice’s Civil and Environmental Engineering Department] said the finding should shift the debate over the size, shape and coating of silver nanoparticles. [emphasis mine] “Of course they matter,” Alvarez said, “but only indirectly, as far as these variables affect the dissolution rate of the ions. The key determinant of toxicity is the silver ions. So the focus should be on mass-transfer processes and controlled-release mechanisms.”

Crypton’s About page strongly suggests an environmentally friendly and health conscious company (Note: Links have been removed),

Innovation. Industry leadership. A deep commitment to product excellence. These core elements are at the heart of the Crypton DNA – a labor of love that began in 1993 when founders Craig and Randy Rubin set out to create a new generation of stylish fabrics that were moisture-resistant and easy-to-clean, yet soft, comfortable and breathable.

From the basement of their Michigan home, a textile revolution was born.

Now based in West Bloomfield Michigan, with a green manufacturing facility in Kings Mountain, North Carolina, Crypton is the only textile solution in the world offering complete stain, moisture, mildew, bacteria and odor-resistant protection thanks to a patented process developed by some of the leading minds in the textile industry.

Early on, by offering a fabric – not a vinyl or plastic – that was capable of resisting stains, moisture, odors and bacteria, Crypton proved to be the perfect solution for the health care market. Following this initial success, Crypton solutions rapidly expanded into some of the finest restaurants, hotels, cruise ships around the world, as well as government complexes, schools and health care facilities.

Now trusted and relied on by over 90% of contract designers, there are more than 20,000 patterns of Crypton fabric available today. Crypton is the only fabric deemed a non-porous surface and can be disinfected when used in conjunction with our U.S. EPA-approved Crypton Disinfectant & Deodorizer.

From fabric, carpet, leather, wall and mattress to pet beds, home accessories, bags and luggage – our mission is to give customers more ways to live healthy, live beautifully and Live Clean®.

While there is no incontrovertible proof that silver nanoparticles and/or silver ions are a serious threat to the environment, it would be nice to see companies acknowledge some of the concerns.

The relationship of silver ions & nanoparticles, Nietzsche, and Rice University

My hat’s off to Mike Williams for introducing Nietzsche into a news item about silver nanoparticles and toxicity. Here’s the line from his July 11, 2012 Rice University news release (Note: I have removed some links),

Their work comes with a Nietzsche-esque warning: Use enough. If you don’t kill them, you make them stronger.

Scientists have long known that silver ions, which flow from nanoparticles when oxidized, are deadly to bacteria. Silver nanoparticles are used just about everywhere, including in cosmetics, socks, food containers, detergents, sprays and a wide range of other products to stop the spread of germs.

But scientists have also suspected silver nanoparticles themselves may be toxic to bacteria, particularly the smallest of them at about 3 nanometers. Not so, according to the Rice team that reported its results this month in the American Chemical Society journal Nano Letters.

This next bit describing the research is an example of what I find so compelling (curiosity and persistence) about science,

To figure that out, the researchers had to strip the particles of their powers. “Our original expectation was that the smaller a particle is, the greater the toxicity,” said Zongming Xiu, a Rice postdoctoral researcher and lead author of the paper. Xiu set out to test nanoparticles, both commercially available and custom-synthesized from 3 to 11 nanometers, to see whether there was a correlation between size and toxicity.

“We could not get consistent results,” he said. “It was very frustrating and really weird.”

Here’s what they did next, what they found, and the implications of their findings,

Xiu decided to test nanoparticle toxicity in an anaerobic environment – that is, sealed inside a chamber with no exposure to oxygen — to control the silver ions’ release. He found that the filtered particles were a lot less toxic to microbes than silver ions.

Working with the lab of Rice chemist Vicki Colvin, the team then synthesized silver nanoparticles inside the anaerobic chamber to eliminate any chance of oxidation. “We found the particles, even up to a concentration of 195 parts per million, were still not toxic to bacteria,” Xiu said. “But for the ionic silver, a concentration of about 15 parts per billion would kill all the bacteria present. That told us the particle is 7,665 times less toxic than the silver ions, indicating a negligible toxicity.”

“The point of that experiment,” Alvarez [Pedro Alvarez, George R. Brown Professor and chair of Rice’s Civil and Environmental Engineering Department] said, “was to show that a lot of people were obtaining data that was confounded by a release of ions, which was occurring during exposure they perhaps weren’t aware of.”

Alvarez suggested the team’s anaerobic method may be used to test many other kinds of metallic nanoparticles for toxicity and could help fine-tune the antibacterial qualities of silver particles. In their tests, the Rice researchers also found evidence of homesis; [e.g..,] E. coli became stimulated by silver ions when they encountered doses too small to kill them.

“Ultimately, we want to control the rate of (ion) release to obtain the desired concentrations that just do the job,” Alvarez said. “You don’t want to overshoot and overload the environment with toxic ions while depleting silver, which is a noble metal, a valuable resource – and a somewhat expensive disinfectant. But you don’t want to undershoot, either.”

He said the finding should shift the debate over the size, shape and coating of silver nanoparticles. [emphasis mine] “Of course they matter,” Alvarez said, “but only indirectly, as far as these variables affect the dissolution rate of the ions. The key determinant of toxicity is the silver ions. So the focus should be on mass-transfer processes and controlled-release mechanisms.”

Interestingly, this is a joint US-UK effort (US Environmental Protection Agency and the U.K. Natural Environment Research Council). H/T to Will Soutter’s July 12, 2012 news item on Azonano for the information about this latest silver nanoparticle research from Rice University. The July 11, 2012 news item on Nanowerk also features information about the silver nanoparticles, ions, and Rice University.

I have mentioned Vicki Colvin’s work previously including this Jan. 28, 2011 posting about a UK/US joint environmental research effort. I have also mentioned Pedro Alvarez a few times including this Aug. 2, 2010 posting about nanomaterials and the construction industry.