Tag Archives: silver

Silver nanoparticles change shape and get ‘consumed’ when destroying bacteria

New research is looking into the interaction between silver nanoparticles and E. coli bacteria as a possible solution to the growing levels of antibiotic resistance seen in pathogens. Although the antibacterial effect of silver has been known for some time now, we didn’t understand why it had this effect.

Silver bars. Image via Pixabay.

Silver has seen growing use for pathogen control in the last few years, in things such as antimicrobial coatings, for example. So far, it definitely seems to be good at the job of killing these tiny threats. Still, a better understanding of how and why it can protect from microbes could help us better apply silver to the task.

In order to glean this information, a team of researchers monitored the interactions between silver nanoparticles and a culture of E. coli bacteria. According to the results, silver nanoparticles undergo several dramatic changes in properties such as size and shape while interacting with bacteria.

Silver for monsters

Concerning the issue of antibiotic resistance, silver poses a very exciting prospect in that it physically kills bacteria, not chemically, as our drugs do. In other words, pathogens don’t have any way of defending themselves against silver.

An international team of researchers with members from Italy, the United States, and Singapore report that silver nanoparticles go through “several dramatic” changes when interacting with E. coli bacteria. This goes against the current prevailing wisdom that the metal remains unaltered during such interactions.

These changes seem to originate in electrostatic interactions between the silver and the bacteria. This causes some of the nanoparticles to dissolve and spread as ions in the environment, eventually making their way into the bacterial cells. Their shape changes as they dissolve, getting smaller and more rounded (they start out as triangular shapes).

After observing these mechanisms, the team treated their E. coli colony with a substance that increased the permeability of the bacteria’s membranes, and then tested them again. In this case, the effects on the silver were more pronounced, they explain.

“It seems from this study that silver is ‘consumed’ from the interaction,” said Guglielmo Lanzani, one of the authors on the paper and director of the Center for Nano Science and Technology of IIT-Istituto di Tecnologia.

“We think this does not affect the efficiency of the biocidal process and, due to the tiny exchange of mass, the lifetime is essentially unlimited,” said Giuseppe Paternò, a researcher at IIT and co-author of the study. “The structural modifications, however, affect the optical properties of the metal nanostructures.”

Although the findings help us better understand the interactions between bacteria and silver nanoparticles, they’re likely not the entire story, the authors note. Laboratories are highly controlled environments, and as such cannot begin to capture everything that’s going on in the wild. These factors that are left out might have an important hand to play in shaping the final interaction between bacteria and silver.

Even so, the team will continue to explore this topic, with a particular interest in studying the chemical machinery (‘chemical pathways’) inside the bacteria that cause these structural changes in silver. They also want to understand why silver is a more powerful antibacterial agent than other materials, and why bacterial membranes seem to be so vulnerable to it while our cells are almost unaffected.

The paper “The impact of bacteria exposure on the plasmonic response of silver nanostructured surfaces” has been published in the journal Chemical Physics Reviews.

Cannon pile.

‘Holy Grail’ of shipwrecks discovered, carries up to $17 billion in gold, silver, emeralds

The wreck of the San José, a gold-laden Spanish galleon sunk in 1708, has been identified thanks to its distinctive bronze cannons.

Cannon pile.

To confirm the wreck’s identity, REMUS descended to just 30 feet above the wreck to capture photos of its cannons.
Image credits Woods Hole Oceanographic Institution.

Around 310 years ago, at the height of the War of Spanish Succession (a conflict that Spain and France were fighting against England), one ship laden with treasure set sail from the Americas towards Europe. Beset by English foes, the ship was sunk with all hands aboard in the Caribbean Sea. Now, the ship’s wreck has been officially identified.

Mind the guns

The identification was made possible by the ship’s onboard artillery: the guns, cast in bronze, still sported their ornate and distinctive dolphin engravings. The cannons were investigated by REMUS 6000, an autonomous underwater vehicle (AUV) that got within 30 feet (9.1 meters) of the shipwreck in 2015, according to Woods Hole Oceanographic Institution (WHOI).

The WHOI had determined the shipwreck’s identity in 2015, but it didn’t have approval from affiliated agencies (Maritime Archaeology Consultants, Switzerland AG, and the Colombian government) to make the findings public until now.

The San José was part of what the Spanish called their ‘treasure’ or ‘silver fleets‘: crafts that would traverse the Atlantic Ocean to shuttle immense riches from the Americas towards Europe, where they would fund Spanish war efforts. Individual fleets were made up of several ships, each highly specialized, to make sure this spoliation went along as smoothly, efficiently, and uninterruptedly as possible. The San José was the largest galleon and flagship of one such treasure fleets. Bristling with 62 guns across its multiple decks made the prospect of attacking the Spanish treasure a very unattractive proposition for both pirates and rival nations.

But hubris, as it often does, would eventually prove to be the galleon’s undoing. While it was the San José’s job to actually ferry the riches every year, the other ships in the fleet were present to guard it against would-be assailants. However, in 1708, as the escorting ships were delayed in linking up with the galleon, Admiral José Fernandez de Santillan, count of Casa Alegre and the ship’s captain, decided to set sail without them.

On June 8, 1708, it was beset upon by four English ships. After a pitched battle, a stray shot ignited the San José’s gunpowder stores — sending the ship, the treasure, and its almost 600-strong crew to the bottom of the sea.

It is, to this day, one of the most expensive maritime losses in the world. The cargo, consisting of gold, silver, and emeralds mined in Peru, is estimated to value between $4 billion and $17 billion today. During the bitter war against England, it would have been a monumental loss for Spain.

The shipwreck was discovered by an international team aboard the Colombian Navy research ship ARC Malpelo on Nov. 27, 2015, at over 2,000 feet (600 meters) deep, near Colombia’s Barú Peninsula. Because the wreck’s identity couldn’t be confirmed at the time of the discovery, the WHOI sent the REMUS 6000 to the site.

“The REMUS 6000 was the ideal tool for the job, since it’s capable of conducting long-duration missions over wide areas,” Mike Purcell, WHOI engineer and expedition leader, said in a statement.

Recordings taken by the autonomous vehicle revealed the ship was partially covered in sediment — however, it also captured the decorative carvings on the cannons on a subsequent dive. From them, Roger Dooley, the lead marine archaeologist at MAC, was able to confirm the ship’s identity, the WHOI adds.

The Colombian government plans to build a museum and conservation laboratory to preserve and display the shipwreck’s contents, including its cannons and ceramics.

Cluny Gold.

Huge treasure of medieval silver and gold unearthed at the Cluny Abbey, France

French archaeologists have unearthed a breathtaking hoard of medieval riches at the Abbey of Cluny, in Saône-et-Loire. The riches include over 2,200 silver deniers and oboles, 21 Almoravid gold dinars, a signet ring and other gold objects. It’s the largest single collection of silver deniers ever discovered, and the first time European coins were found hidden alongside Arab ones and such a prohibitively expensive object as a signet ring.

Cluny Silver.

The coins as discovered in-situ, and after excavation.

This round of excavation works at the Abbey of Cluny started in 2015 under the supervision of Anne Baud, an academic at the Université Lumière Lyon 2, and Anne Flammin, an engineer at the Centre National de la Recherche Scientifique (CNRS). Working together with colleagues and 9 students enrolled in the Master of Archaeology and Archaeological Science at the Lyon 2 University, they’ve discovered a treasure likely dating from the first half of the 12th century.

Fit for Smaug

The treasure trove consists of over 2,200 European silver coins, most of which were minted at the Abbey, which were stored in a cloth bag — traces of which still remain on some of the coins. Western currency at the time was dominated by the silver denier, and such deniers would likely have been used for everyday purchases.

Inside the bag, archaeologists also found a tightly bound and knotted tanned hide bundle containing 21 Arab gold denars, minted between 1211 and 1311 in Morocco and Spain under Ali ibn Yusuf, a member of the Berber Almoravid dynasty. Gold coins at this time were largely reserved for rare and significant transactions.

Alongside the coins, the team recovered a gold signet ring with “a red intaglio depicting the bust of a god” likely created in the first half of the 12th century, a foil of gold sheet weighing 24 grams that was stored in a case, and a small circular object made of gold.

Cluny Gold.

Knotted tanned hide bundle holding the gold objects.(2) & (4) gold dinars; (3) signet ring with intaglio; (5) contents of knotted tanned hide bundle.
Image credits Alexis Grattier / Université Lumière Lyon 2

The finding is exceptional on several counts. For starters, the sheer size and value of the of riches unearthed make this hoard stand out — this is the largest single stash of deniers ever found. It’s also a very unusual to find Arab coins in a monastic setting, both because of their huge value — which prohibited use in anything but the largest transactions — especially at Cluny, which was one of the largest abbeys of Western Europe during the Middle Ages.

The riches help color the history of Cluny Abbey, a historical site open to the public and also raise some very exciting questions. How did this treasure get here, who did it belong to and who brought it? And why was it hidden?

Vincent Borrel, a PhD student at the Archaeology and Philology of East and West (CNRS / ENS) research unit is currently studying the treasure in more detail to identify and date the various pieces with greater precision, hopefully gaining some insight into what the answers to these questions might be.

Viking treasure pot, opened more than 1,000 years after it was hidden in modern Galloway

The first images of Viking treasure, stashed in a pot more than 1,000 years ago and buried in a field in Galloway, have been made public by the conservators working to preserve them. The items, including six silver disk brooches, a gold ingot and Byzantine silk, are not currently on display.

Metal detectorist Dered McLennan found the hoard in Galloway in 2014. Since then a lot of effort has been put into removing and preserving the pot and items, dated from the 9th or 10th century BC.

The pictures give the public a chance to see the items for the first time as they are not currently on display.
Image credits Historic Environment Scotland.

And it’s a literal pot of gold. Inside, archaeologists found six silver Anglo-Saxon disc brooches and one from Ireland, silk traced back to Byzantium (modern-day Istanbul,) a gold ingot as well as gold and crystal objects carefully wrapped in pieces of cloth. Historic Environment Scotland are working together with the Treasure Trove Unit and the Queen’s and Lord Treasurer’s Remembrancer (QLTR) to fund the exhaustive conservation efforts.

“Before removing the objects we took the rather unusual measure of having the pot CT scanned, in order that we could get a rough idea of what was in there and best plan the delicate extraction process,” said Richard Welander of Historic Environment Scotland.

“That exercise offered us a tantalising glimpse but didn’t prepare me for what was to come.”

A silver brooch from Ireland was found inside the pot.
Image credits Santiago Arribas Pena.

“These stunning objects provide us with an unparalleled insight to what was going on in the minds of the Vikings in Galloway all those years ago. They tell us about the sensibilities of the time, reveal displays of regal rivalries, and some of the objects even betray an underlying sense of humour, which the Vikings aren’t always renowned for!” he added.

Stuart Campbell of the Treasure Trove Unit, said there was further research to be done on the items.

“The complexity of the material in the hoard raises more questions than it answers, and like all the best archaeology, this find doesn’t give any easy answers,” he said.

A large glass bead, found among the other riches.
Image credits Santiago Arribas Pena.


“Questions about the motivations and cultural identity of the individuals who buried it will occupy scholars and researchers for years to come.”

The artifacts are now in the care of the Treasure Trove Unit, who are assessing its value on behalf of the QLTR. After this, the hoard will be offered to Scottish museums and the finder will be eligible for the market value of the items — a cost that the museums will cover.

This beautifully crafted artefact might just be the crown jewel of the hoard.
Image via Santiago Arribas Pena.

However, it’s been estimated that this might amount up to £1m in order to do so — a hefty price-tag for any museum.

The hoard’s discovery is also set to feature on the 24th of March in BBC’s latest episode of Digging for Britain hosted by Dr Alice Roberts.

golden toilet paper

You’re flushing a goldmine down the toilet, literally

At a recent meeting of the of the American Chemical Society, researchers proposed a novel source of valuable metals: waste water. They proposed a method that could be used to extract valuable metals like gold, silver or titanium which end up in waste water plants via the city’s sewage.

golden toilet paper

Who the heck throws gold down the toilet, you might ask. Well, you’ve done it plenty of times without knowing it, most likely.

“There are metals everywhere,” Kathleen Smith of the U.S. Geological Survey (USGS) says, noting they are “in your hair care products, detergents, even nanoparticles that are put in socks to prevent bad odors.” Whatever their origin, the wastes containing these metals all end up being funneled through wastewater treatment plants, where she says many metals end up in the leftover solid waste.

According to Smith, more than 7 million tons of biosolids come out of U.S. wastewater facilities each year. Half of that is used as fertilizer, while the rest is sent to landfills or is incinerated. One man’s trash, is another’s treasure, and with this in mind Smith and colleagues are currently working on ways to value solid waste, particularly rare metals. At first glance, you might think this isn’t worth it, considering the energy (money) you need to pump in the system to extract, but the waste from 1 million Americans might contain metal worth $13 million. In some places, the concentration of gold is about the same or more than that found in natural mine deposits currently being exploited.

This image shows microscopic gold-rich and lead-rich particles in a municipal biosolids sample. Image credit: Heather Lowers, USGS Denver Microbeam Laboratory

This image shows microscopic gold-rich and lead-rich particles in a municipal biosolids sample. Image credit: Heather Lowers, USGS Denver Microbeam Laboratory

To extract metals, the researchers propose methods commonly in use by the mining industry. This involves using chemicals called leachates, which this industry uses to pull metals out of rock. Typically, these are very harmful to the environment, but at the American Chemical Society meeting, the researchers claim that these can be contained to waste water plants only, with no adverse effects to the environment or the population.

So far, Smith’s group has collected samples from small towns in the Rocky Mountains, rural communities and big cities. They found traces of platinum, silver and gold, and on a case by case basis, these could be found in a high enough concentration for extraction to become economically feasible.

Elsewhere, the city of Suwa in Japan is already working on extracting the gold from its sewers. They installed a treatment plant near a large number of precision equipment manufacturers reportedly collected nearly 2 kilograms of gold in every metric ton of ash left from burning sludge, making it more gold-rich than the ore in many mines.


Sewage Sludge Contains Millions of Dollars in Gold

There are millions of dollars in gold and other metals in the sewage sludge in major cities. A new study has found that in a city with 1 million inhabitats, there’s as much as $13 million worth of valuable metals, including gold and silver.

Image via Water Desalination Plants.

It’s been known for quite a while that sewage sludge contains significant quantities of valuable metals, but this is the first study I could find which quantifies that amount. For every 1 million people, on average, you’ll find over $2.5 million worth of gold and silver, plus other metals worth millions more.

“For a community of 1 million people, metals in biosolids were valued at up to US$13 million annually,” they conclude in a paper published in Environmental Science & Technology. “A model incorporating a parameter to capture the relative potential for economic value from biosolids revealed the identity of the 13 most lucrative elements with a combined value of US $280/ton [907 kg] of sludge.” That equates to about $8 million in a hypothetical city of 1 million people.

Furthermore, these metals are actually costing governments good money; from a point of view, they’re a pollutant. If they reach a high enough quantity, then the sludge can’t be used as a fertilizer and instead has to be deposited as landfill – turning it into a cost, from an asset (60 percent of sludge produced in America ends up feeding its farms).

The amount won’t shake the world markets, but it can be a way for cities to get some extra value. The city of Suwa in Japan is already working on extracting the gold. They installed a treatment plant near a large number of precision equipment manufacturers reportedly collected nearly 2 kilograms of gold in every metric ton of ash left from burning sludge, making it more gold-rich than the ore in many mines.

Image via Discover Magazine.

Still, before we get to excited, it has to be said that there is no practical way of recovering every bit of gold, but still, scientists argue that the extraction of gold and silver from sludge can be quite profitable. Jordan Peccia from Yale University in the US, who was not involved in the study agrees.

“We’re not going to get rid of this sewage sludge. We need to make this push where we stop thinking about it as a liability and instead we think about it as a resource. And anything we can find in sewage sludge that’s valuable, it’s good.”

But gold and silver are not the only things of value from the sludge. A small number of sewage plants are already removing phosphorous and nitrogen, which can be sold as fertilizer. Sweden, which recycles most of its waste is testing the feasibility of making bioplastics from wastewater. A model sewage incinerator that generates electricity and drinking water was just promoted by the Bill & Melinda Gates Foundation, which helped fund its construction.

All in all, there’s big money in sewage sludge – we just have to find a way to get it.

Scientific Reference: Science| DOI: 10.1126/science.aaa6359


Scientists grow graphene on silver

The wonder material

Graphene - a one atom thick layer of carbon. photo credit: CORE-Materials

Graphene – a one atom thick layer of carbon. photo credit: CORE-Materials

Graphene, the new wonder material that promises to open a new age in technology, just got a whole lot better. Researchers have reported improved interfacing of graphene with other 2-D materials – basically ‘growing’ graphene on silver. This resulted in an exceptionally pristine sample, presenting opportunities for ultrafast electronics and advanced optics/

“Silver is a widely used material to enhance optical properties,” said Northwestern’s Mark Hersam, a co-author of the paper. “More recently, graphene has emerged as a promising platform for optical technologies. With our recent development of a method for growing graphene on silver, we can now exploit the best attributes of both graphene and silver at the same time.”

Graphene, in case you didn’t know, is simply a one atom thick layer of carbon, featuring numerous remarkable properties which can be used in electronics and not only. Despite being incredibly light, in a way it’s the world’s most powerful material; it’s already making a mark with some practical applications (graphene earbuds, graphene radio, explosive detector, etc), and in the not-so-distant future, it will probably revolutionize transistors and even computer chips. But even so, we have just barely scratched the surface of what this material is capable of doing.

Growing graphene on silver

Typically, graphene is grown on a metal surface by catalytically decomposing hydrocarbons at elevated temperatures – but this method is not really suitable for silver, because silver substrates have a relatively low melting point and are chemically inert.

Using a graphite carbon source, the Northwestern and Argonne researchers were able to grow graphene by depositing atomic carbon, rather than a carbon-based molecular precursor, onto the silver substrate. This growth meant that chemical reactivity was no longer required, and the graphene was developed at lower temperatures.

“Graphene growth and transfer to a variety of substrates has allowed graphene to transform countless scientific fields,” said Brian Kiraly, a Northwestern graduate student in materials science and engineering who worked on the research with Hersam and Nathan Guisinger, a staff scientist at Argonne.

“However, conventional techniques lead to contamination issues and are not compatible with the ultra-clean vacuum environments required for the growth of the latest 2-D materials,” he said. “By growing graphene directly on silver under vacuum, we provide an atomically pristine surface for advanced graphene-based technologies.”

They were also surprised to report another discovery – the graphene they grew was electronically decoupled from the underlying silver substrate, something which was never before reported on any other metal, making this graphene-silver coupling even more promising.

Journal Reference:

Brian Kiraly, Erin V. Iski, Andrew J. Mannix, Brandon L. Fisher, Mark C. Hersam & Nathan P. Guisinger. Solid-source growth and atomic-scale characterization of graphene on Ag(111). Nature Communications 4, Article number: 2804 doi:10.1038/ncomms3804


How ingesting silver turns the skin blue

argyriaSilver nanoparticles are often used for extensive medical treatments or antimicrobial health tonics. They’re even used in skin care products, which is rather ironic considering they’ve been linked with argyria, a condition in which the skin turns grayish-blue. Although scientists have known for quite a while that too much silver can cause this condition, the exact mechanisms that cause this transformation were unknown until recently. Interestingly, the process is similar to  developing black-and-white photographs.

“It’s the first conceptual model giving the whole picture of how one develops this condition,” said Robert Hurt, professor of engineering at Brown and part of the research team. “What’s interesting here is that the particles someone ingests aren’t the particles that ultimately cause the disorder.”

The change in skin colour hue is due to silver particles arriving deep in skin tissue, but for quite a while it wasn’t clear how they winded up there. Hurt and colleagues showed that nanosilver is broken down in the stomach, absorbed into the bloodstream as a salt and finally deposited in the skin, where exposure to light turns the salt back into elemental silver, which in turn is to blame for the bluish skin.

How they did figured this out exactly is documented in a recent paper published in the journal ACS Nano, and presented more extensively at the Brown University Newsroom. In the video below, you can watch a CNN report on Paul Karason, popularly referred to on the internet as papa smurf, who for many years ingested a solution known as colloidal silver.