Tag Archives: silver nanoparticles

Printing wearable circuits onto skin

It seems that this new technique for creating wearable electronics will be more like getting a permanent tattoo where the circuits are applied directly to your skin as opposed to being like a temporary tattoo where the circuits are printed onto a substrate and then applied to then, worn on your skin.

Caption: On-body sensors, such as electrodes and temperature sensors, were directly printed and sintered on the skin surface. Credit: Adapted from ACS Applied Materials & Interfaces 2020, DOI: 10.1021/acsami.0c11479

An Oct. 14, 2020 American Chemical Society (ACS) news release (also on EurekAlert) announced this latest development in wearable electronics,

Wearable electronics are getting smaller, more comfortable and increasingly capable of interfacing with the human body. To achieve a truly seamless integration, electronics could someday be printed directly on people’s skin. As a step toward this goal, researchers reporting in ACS Applied Materials & Interfaces have safely placed wearable circuits directly onto the surface of human skin to monitor health indicators, such as temperature, blood oxygen, heart rate and blood pressure.

The latest generation of wearable electronics for health monitoring combines soft on-body sensors with flexible printed circuit boards (FPCBs) for signal readout and wireless transmission to health care workers. However, before the sensor is attached to the body, it must be printed or lithographed onto a carrier material, which can involve sophisticated fabrication approaches. To simplify the process and improve the performance of the devices, Peng He, Weiwei Zhao, Huanyu Cheng and colleagues wanted to develop a room-temperature method to sinter metal nanoparticles onto paper or fabric for FPCBs and directly onto human skin for on-body sensors. Sintering — the process of fusing metal or other particles together — usually requires heat, which wouldn’t be suitable for attaching circuits directly to skin.

The researchers designed an electronic health monitoring system that consisted of sensor circuits printed directly on the back of a human hand, as well as a paper-based FPCB attached to the inside of a shirt sleeve. To make the FPCB part of the system, the researchers coated a piece of paper with a novel sintering aid and used an inkjet printer with silver nanoparticle ink to print circuits onto the coating. As solvent evaporated from the ink, the silver nanoparticles sintered at room temperature to form circuits. A commercially available chip was added to wirelessly transmit the data, and the resulting FPCB was attached to a volunteer’s sleeve. The team used the same process to sinter circuits on the volunteer’s hand, except printing was done with a polymer stamp. As a proof of concept, the researchers made a full electronic health monitoring system that sensed temperature, humidity, blood oxygen, heart rate, blood pressure and electrophysiological signals and analyzed its performance. The signals obtained by these sensors were comparable to or better than those measured by conventional commercial devices. 

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

Wearable Circuits Sintered at Room Temperature Directly on the Skin Surface for Health Monitoring by Ling Zhang, Hongjun Ji, Houbing Huang, Ning Yi, Xiaoming Shi, Senpei Xie, Yaoyin Li, Ziheng Ye, Pengdong Feng, Tiesong Lin, Xiangli Liu, Xuesong Leng, Mingyu Li, Jiaheng Zhang, Xing Ma, Peng He, Weiwei Zhao, and Huanyu Cheng. ACS Appl. Mater. Interfaces 2020, 12, 40, 45504–45515 Publication Date:September 11, 2020 DOI: https://doi.org/10.1021/acsami.0c11479 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Norwegian Institute for Water Research (NIVA) releases study on silver and titanium nanomaterials in wastewater

It turns out that silver and titanium nanomaterials (e.g. silver nanoparticles washed out of athletic clothing) in wastewater may have ‘negative’ and ‘positive’ effects on freshwater and marine life depending on the species.

A November 18, 2019 news item on Nanowerk provides an introduction to the research (Note: Links have been removed),

You may not always think about it when you do your laundry or flush the toilet; but whatever you eat, wear or apply on your skin ends up in wastewater and eventually reaches the environment. The use of nanoparticles in consumer products like textiles, foods and personal care products is increasing.

What is so special about nanoparticles, is their tiny size: One nanometer is one billionth of a meter. The small size gives nanoparticles unique and novel properties compared to their bigger counterparts and may for example reach locations that bigger particles cannot reach.
Further, pristine nanoparticles behave differently from nanoparticles in the environment. In the environment, nanoparticles are transformed by interacting and forming aggregates with other particles, elements or solids, and thereby obtain other physicochemical properties.

The transformation of these tiny particles in wastewater treatment processes and their effect on freshwater and marine organisms, have largely been unknown.
Increased mortality of marine crustaceans.

In a study (“Ecotoxicological Effects of Transformed Silver and Titanium Dioxide Nanoparticles in the Effluent from a Lab-Scale Wastewater Treatment System”) conducted at the Norwegian Institute for Water Research (NIVA), Anastasia Georgantzopoulou and colleagues from NIVA and SINTEF investigated how silver and titanium dioxide nanoparticles behave in wastewater treatment plants, and how marine and freshwater organisms are affected by them.

Exposure to treated wastewater did not have any adverse effects on the freshwater crustacean Daphnia magna. (Photo: NIVA)

A November 18, 2019 NIVA press release, which originated the news item, fills in the details,

The researchers made a laboratory-scale wastewater treatment plant, using sludge from a wastewater treatment plant in Norway. They added environmentally relevant concentrations of silver (Ag) and titanium dioxide (TiO2) nanoparticles over a 5-week period and used the treated wastewater to assess the effects of transformed nanoparticles on freshwater and marine organisms, as well as on gill cells from rainbow trout.

The experiment demonstrated contrasting effects on the two crustacean species. For the marine copepod (Tisbe battagliai), mortality increased by 20-45%, whereas exposure to ttreated wastewater did not have any adverse effects on the freshwater crustacean (Daphnia magna).

“These differences are probably due, at least partly, to the two species’ different feeding habits, in combination with the fact that the nanoparticles showed a strong association to solids present in the wastewater”, Georgantzopoulou says, and explains:

“Daphnia magna is an organism that filters water for food, whereas the marine copepod feeds on bottom surfaces – like effluent solids that have settled out from the water. The bottom feeding crustacean is therefore more likely to ingest nanoparticles, and thereby be affected by solid-associated nanoparticles”. 

Effects on algal species

Nanoparticle-containing treated wastewater also affected algal growth, but the two algae species did not have a common response: The marine algae (Skeletonema pseudocostatum) responded with a 20-40 % growth inhibition, while the algal growth of the freshwater algae (Raphidocelis subcapitata) was actually stimulated, by a 40 % increase, accompanied by increased cell aggregation. The latter is probably some kind of a defense mechanism, aiming to decrease the surface area exposed to toxic particles.

“The results from our study indicate that algal responses to the treated wastewater exposure are species-dependent. This is possibly due to differences in algal cell size, surface area, and cell wall composition”, the NIVA researcher explains.

Increased permeability of fish gill cells

The researchers also found effects of silver and titanium nanoparticles on fish gill cells using an in vitro gill cell line model. As large amounts of water are passing through the gills, and they constitute a barrier to the external environment, this organ is highly exposed to water-borne contaminants, including nanoparticles.

“Exposure to nanoparticle-containing wastewater lead to an increase in reactive oxygen species, a group of molecules that can easily react with and damage cells. This was followed by increased permeability of the gill cells, leading to a compromised barrier function”, Georgantzopoulou says.

“However, the concentrations of silver and titanium nanoparticles in the treated wastewater were too low to fully account for the effects on cell permeability alone. The wastewater effluent is a complex mixture of materials, and the permeability response is probably caused by a combination of the presence of nanoparticles and other stressors”, Georgantzopoulou adds.

Wastewater treatment-transformation of nanoparticles

“We carried out this study on wastewater treatment plant-transformed nanoparticles, and compared them to pristine nanoparticles, as the former is more relevant to what is actually happening in the environment. The increased toxicity of the transformed nanomaterials observed in the study indicates that the effects cannot be predicted by assessing the effects of nanomaterials in their pristine form and highlights the importance of understanding their behavior, environmental transformation and interaction with organisms. Future studies should take nanoparticle transformation into account and focus on a more relevant experimental exposure conditions incorporating transformed nanoparticles in more long-term impact studies to provide a better understanding of their potential impacts”, Georgantzopoulou concludes.

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

Ecotoxicological Effects of Transformed Silver and Titanium Dioxide Nanoparticles in the Effluent from a Lab-Scale Wastewater Treatment System by Anastasia Georgantzopoulou, Patricia Almeida Carvalho, Christian Vogelsang, Mengstab Tilahun, Kuria Ndungu, Andy M. Booth, Kevin V. Thomas, Ailbhe Macken. Environ. Sci. Technol. 2018, 52, 16, 9431-9441 DOI: https://doi.org/10.1021/acs.est.8b01663 Publication Date:July 26, 2018 Copyright © 2018 American Chemical Society

This paper is behind a paywall.

Nanocellulose sensors: 3D printed and biocompatible

I do like to keep up with nanocellulose doings, especially when there’s some Canadian involvement, and an October 8, 2019 news item on Nanowerk alerted me to a newish application for the product,

Physiological parameters in our blood can be determined without painful punctures. Empa researchers are currently working with a Canadian team to develop flexible, biocompatible nanocellulose sensors that can be attached to the skin. The 3D-printed analytic chips made of renewable raw materials will even be biodegradable in future.

The idea of measuring parameters that are relevant for our health via the skin has already taken hold in medical diagnostics. Diabetics, for example, can painlessly determine their blood sugar level with a sensor instead of having to prick their fingers.

An October 8, 2019 Empa (Swiss Federal Laboratories for Materials Science and Technology) press release, which originated the news item, provides more detail,

A transparent foil made of wood

Nanocellulose is an inexpensive, renewable raw material, which can be obtained in form of crystals and fibers, for example from wood. However, the original appearance of a tree no longer has anything to do with the gelatinous substance, which can consist of cellulose nanocrystals and cellulose nanofibers. Other sources of the material are bacteria, algae or residues from agricultural production. Thus, nanocellulose is not only relatively easy and sustainable to obtain. Its mechanical properties also make the “super pudding” an interesting product. For instance, new composite materials based on nanocellulose can be developed that could be used as surface coatings, transparent packaging films or even to produce everyday objects like beverage bottles.

Researchers at Empa’s Cellulose & Wood Materials lab and Woo Soo Kim from the Simon Fraser University [SFU] in Burnaby, Canada, are also focusing on another feature of nanocellulose: biocompatibility. Since the material is obtained from natural resources, it is particularly suitable for biomedical research.

With the aim of producing biocompatible sensors that can measure important metabolic values, the researchers used nanocellulose as an “ink” in 3D printing processes. To make the sensors electrically conductive, the ink was mixed with silver nanowires. The researchers determined the exact ratio of nanocellulose and silver threads so that a three-dimensional network could form.

Just like spaghetti – only a wee bit smaller

It turned out that cellulose nanofibers are better suited than cellulose nanocrystals to produce a cross-linked matrix with the tiny silver wires. “Cellulose nanofibers are flexible similar to cooked spaghetti, but with a diameter of only about 20 nanometers and a length of just a few micrometers,” explains Empa researcher Gilberto Siqueira.

The team finally succeeded in developing sensors that measure medically relevant metabolic parameters such as the concentration of calcium, potassium and ammonium ions. The electrochemical skin sensor sends its results wirelessly to a computer for further data processing. The tiny biochemistry lab on the skin is only half a millimeter thin.

While the tiny biochemistry lab on the skin – which is only half a millimeter thin – is capable of determining ion concentrations specifically and reliably, the researchers are already working on an updated version. “In the future, we want to replace the silver [nano] particles with another conductive material, for example on the basis of carbon compounds,” Siqueira explains. This would make the medical nanocellulose sensor not only biocompatible, but also completely biodegradable.

I like the images from Empa better than the ones from SFU,

Using a 3D printer, the nanocellulose “ink” is applied to a carrier plate. Silver particles provide the electrical conductivity of the material. Image: Empa
Empa researcher Gilberto Siqueira demonstrates the newly printed nanocellulose circuit. After a subsequent drying, the material can be further processed. Image: Empa

SFU produced a news release about this work back in February 2019. Again, I prefer what the Swiss have done because they’re explaining/communicating the science, as well as , communicating benefits. From a February 13, 2019 SFU news release (Note: Links have been removed),

Simon Fraser University and Swiss researchers are developing an eco-friendly, 3D printable solution for producing wireless Internet-of-Things (IoT) sensors that can be used and disposed of without contaminating the environment. Their research has been published as the cover story in the February issue of the journal Advanced Electronic Materials.

SFU professor Woo Soo Kim is leading the research team’s discovery, which uses a wood-derived cellulose material to replace the plastics and polymeric materials currently used in electronics.

Additionally, 3D printing can give flexibility to add or embed functions onto 3D shapes or textiles, creating greater functionality.

“Our eco-friendly, 3D-printed cellulose sensors can wirelessly transmit data during their life, and then can be disposed without concern of environmental contamination,” says Kim, a professor in the School of Mechatronic Systems Engineering. The SFU research is being carried out at PowerTech Labs in Surrey, which houses several state-of-the-art 3D printers used to advance the research.

“This development will help to advance green electronics. For example, the waste from printed circuit boards is a hazardous source of contamination to the environment. If we are able to change the plastics in PCB to cellulose composite materials, recycling of metal components on the board could be collected in a much easier way.”

Kim’s research program spans two international collaborative projects, including the latest focusing on the eco-friendly cellulose material-based chemical sensors with collaborators from the Swiss Federal Laboratories for Materials Science.

He is also collaborating with a team of South Korean researchers from the Daegu Gyeongbuk Institute of Science and Technology’s (DGIST)’s department of Robotics Engineering, and PROTEM Co Inc, a technology-based company, for the development of printable conductive ink materials.

In this second project, researchers have developed a new breakthrough in the embossing process technology, one that can freely imprint fine circuit patterns on flexible polymer substrate, a necessary component of electronic products.

Embossing technology is applied for the mass imprinting of precise patterns at a low unit cost. However, Kim says it can only imprint circuit patterns that are imprinted beforehand on the pattern stamp, and the entire, costly stamp must be changed to put in different patterns.

The team succeeded in developing a precise location control system that can imprint patterns directly resulting in a new process technology. The result will have widespread implications for use in semiconductor processes, wearable devices and the display industry.

This paper was made available online back in December 2018 and then published in print in February 2019. As to why there’d be such large gaps between the paper’s publication dates and the two institution’s news/press releases, it’s a mystery to me. In any event, here’s a link to and a citation for the paper,

3D Printed Disposable Wireless Ion Sensors with Biocompatible Cellulose Composites by Taeil Kim, Chao Bao, Michael Hausmann, Gilberto Siqueira, Tanja Zimmermann, Woo Soo Kim. Advanced Electronic Materials DOI: https://doi.org/10.1002/aelm.201970007 First published online December 19, 2018. First published in print: 08 February 2019 (Adv. Electron. Mater. 2/2109) Volume 5, Issue 2 February 2019 1970007

This paper is behind a paywall.

Nanoparticles in combination could be more toxic

It seems that one set of nanoparticles, e.g., silver nanoparticles, in combination with another material, e.g., cadmium ions, are more dangerous than either one separately according to an August 17, 2018 University of Southern Denmark press release by Birgitte Svennevig (also on EurekAlert but dated August 20, 2018),

Researchers warn that a combination of nanoparticles and contaminants may form a cocktail that is harmful to our cells. In their study, 72 pct. of cells died after exposure to a cocktail of nano-silver and cadmium ions.

Nanoparticles are becoming increasingly widespread in our environment. Thousands of products contain nanoparticles because of their unique properties. Silver nanoparticles are one example: They have an effective antibacterial effect and can be found in refrigerators, sports clothes, cosmetics, tooth brushes, water filters, etc.

There is a significant difference between how the cells react when exposed to nanosilver alone and when they are exposed to a cocktail of nanosilver and cadmium ions. Cadmium ions are naturally found everywhere around us on Earth.

In the study, 72 pct. of the cells died, when exposed to both nanosilver and cadmiun ions. When exposed to nanosilver only, 25 pct. died. When exposed to cadmium ions only, 12 pct. died.

The study was conducted on human liver cancer cells.

  • This study indicates, that we should not look at nanoparticles isolated when we investigate and discuss the effects, they may have on our health. We need to take cocktail effects into account, said Professor Frank Kjeldsen, Dept of Biochemistry and Molecular Biology, SDU, adding:
  • Products with nano particles are being developed and manufactured every day, but in most countries there are no regulations, so there is no way of knowing what and how many nanoparticles are being released into the environment. In my opinion, this should be stopped.

Other studies, led by Professor Kjeldsen have previously shown that human cells interact with metal nanoparticles.

One study showed that nano-silver leads to the formation free radicals in cells and changes in the form and amount of proteins. Many serious diseases are characterized by an overproduction of free radicals in cells. This applies to cancer and neurological diseases such as Alzheimer’s and Parkinson’s.

This is not great news but there are a few things to note about this research. First, it was conducted on cells and therefore not subject to some of the defensive systems found in complete biological organisms such as a mouse or a dandelion plant for example.

Also, since they were cancer cells one might suspect their reactions might differ from those of healthy cells. As for how the cells were exposed to the contaminants, I think (???) they were sitting in a solution of contaminants and most of us do not live in that kind of environment.. Finally, with regard to the concentrations, I have no idea if they are greater than one might expect to encounter in one’s lifecycle but it’s always worth questioning just how much exposure you might expect during yours or a mouse’s or a dandelion’s life.

These caveats aside, Professor Frank Kjeldsen’s work raises some very concerning issues and his work adds to a growing body of evidence.

Here’s a video featuring Dr. Kjeldsen talking about his work,

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

Co-exposure to silver nanoparticles and cadmium induce metabolic adaptation in HepG2 cells by Renata Rank Miranda, Vladimir Gorshkov, Barbara Korzeniowska, Stefan J. Kempf, Francisco Filipak Neto, & Frank Kjeldsen. Nanotoxicology DOI: https://doi.org/10.1080/17435390.2018.1489987 Published online: 11 Jul 2018

This paper is open access.

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.

Algae outbreaks (dead zones) in wetlands and waterways

It’s been over seven years since I first started writing about Duke University’s  Center for the Environmental Implications of Nanotechnology and mesocosms (miniature ecosystems) and the impact that nanoparticles may have on plants and water (see August 11, 2011 posting). Since then, their focus has shifted from silver nanoparticles and their impact on plants, fish, bacteria, etc. to a more general examination of metallic nanoparticles and water. A June 25, 2018 news item on ScienceDaily announces some of their latest work,

The last 10 years have seen a surge in the use of tiny substances called nanomaterials in agrochemicals like pesticides and fungicides. The idea is to provide more disease protection and better yields for crops, while decreasing the amount of toxins sprayed on agricultural fields.

But when combined with nutrient runoff from fertilized cropland and manure-filled pastures, these “nanopesticides” could also mean more toxic algae outbreaks for nearby streams, lakes and wetlands, a new study finds.

A June 25, 2018 Duke University news release (also on EurekAlert) by Robin A. Smith, which originated the news item, provides more detail,

Too small to see with all but the most powerful microscopes, engineered nanomaterials are substances manufactured to be less than 100 nanometers in diameter, many times smaller than a hair’s breadth.

Their nano-scale gives them different chemical and physical properties from their bulk counterparts, including more surface area for reactions and interactions.

Those interactions could intensify harmful algal blooms in wetlands, according to experiments led by Marie Simonin, a postdoctoral associate with biology professor Emily Bernhardt at Duke University.

Carbon nanotubes and teeny tiny particles of silver, titanium dioxide and other metals are already added to hundreds of commercial products to make everything from faster, lighter electronics, self-cleaning fabrics, and smarter food packaging that can monitor food for spoilage. They are also used on farms for slow- or controlled-release plant fertilizers and pesticides and more targeted delivery, and because they are effective at lower doses than conventional products.

These and other applications have generated tremendous interest and investment in nanomaterials. However the potential risks to human health or the environment aren’t fully understood, Simonin said.

Most of the 260,000 to 309,000 metric tons of nanomaterials produced worldwide each year are eventually disposed in landfills, according to a previous study. But of the remainder, up to 80,400 metric tons per year are released into soils, and up to 29,200 metric tons end up in natural bodies of water.

“And these emerging contaminants don’t end up in water bodies alone,” Simonin said. “They probably co-occur with nutrient runoff. There are likely multiple stressors interacting.”

Algae outbreaks already plague polluted waters worldwide, said Steven Anderson, a research analyst in the Bernhardt Lab at Duke and one of the authors of the research.

Nitrogen and phosphorous pollution makes its way into wetlands and waterways in the form of agricultural runoff and untreated wastewater. The excessive nutrients cause algae to grow out of control, creating a thick mat of green scum or slime on the surface of the water that blocks sunlight from reaching other plants.

These nutrient-fueled “blooms” eventually reduce oxygen levels to the point where fish and other organisms can’t survive, creating dead zones in the water. Some algal blooms also release toxins that can make pets and people who swallow them sick.

To find out how the combined effects of nutrient runoff and nanoparticle contamination would affect this process, called eutrophication, the researchers set up 18 separate 250-liter tanks with sandy sloped bottoms to mimic small wetlands.

Each open-air tank was filled with water, soil and a variety of wetland plants and animals such as waterweed and mosquitofish.

Over the course of the nine-month experiment, some tanks got a weekly dose of algae-promoting nitrates and phosphates like those found in fertilizers, some tanks got nanoparticles — either copper or gold — and some tanks got both.

Along the way the researchers monitored water chemistry, plant and algae growth and metabolism, and nanoparticle accumulation in plant tissues.

“The results were surprising,” Simonin said. The nanoparticles had tiny effects individually, but when added together with nutrients, even low concentrations of gold and copper nanoparticles used in fungicides and other products turned the once-clear water a murky pea soup color, its surface covered with bright green smelly mats of floating algae.

Over the course of the experiment, big algal blooms were more than three times more frequent and more persistent in tanks where nanoparticles and nutrients were added together than where nutrients were added alone. The algae overgrowths also reduced dissolved oxygen in the water.

It’s not clear yet how nanoparticle exposure shifts the delicate balance between plants and algae as they compete for nutrients and other resources. But the results suggest that nanoparticles and other “metal-based synthetic chemicals may be playing an under-appreciated role in the global trends of increasing eutrophication,” the researchers said.

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

Engineered nanoparticles interact with nutrients to intensify eutrophication in a wetland ecosystem experiment by Marie Simonin, Benjamin P. Colman, Steven M. Anderson, Ryan S. King, Matthew T. Ruis, Astrid Avellan, Christina M. Bergemann, Brittany G. Perrotta, Nicholas K. Geitner, Mengchi Ho, Belen de la Barrera, Jason M. Unrine, Gregory V. Lowry, Curtis J. Richardson, Mark R. Wiesner, Emily S. Bernhardt. Ecological Applications, 2018; DOI: 10.1002/eap.1742 First published: 25 June 2018

This paper is behind a paywall.

Panning for silver nanoparticles in your clothes washer

A March 20, 2018 news item on phys.org describes a new approach to treating wastewater (Note: Links have been removed),

Humans have known since ancient times that silver kills or stops the growth of many microorganisms. Hippocrates, the father of medicine, is said to have used silver preparations for treating ulcers and healing wounds. Until the introduction of antibiotics in the 1940s, colloidal silver (tiny particles suspended in a liquid) was a mainstay for treating burns, infected wounds and ulcers. Silver is still used today in wound dressings, in creams and as a coating on medical devices.

Since the 1990s, manufacturers have added silver nanoparticles to numerous consumer products to enhance their antibacterial and anti-odor properties. Examples include clothes, towels, undergarments, socks, toothpaste and soft toys. Nanoparticles are ultra-small particles, ranging from 1 to 100 nanometers in diameter – too small to see even with a microscope. According to a widely cited database, about one-fourth of nanomaterial-based consumer products currently marketed in the United States contain nanosilver.

Multiple studies have reported that nanosilver leaches out of textiles when they are laundered. Research also reveals that nanosilver may be toxic to humans and aquatic and marine organisms. Although it is widely used, little is understood about its fate or long-term toxic effects in the environment.

We are developing ways to convert this potential ecological crisis into an opportunity by recovering pure silver nanoparticles, which have many industrial applications, from laundry wastewater. In a recently published study, we describe a technique for silver recovery and discuss the key technical challenges. Our approach tackles this problem at the source – in this case, individual washing machines. We believe that this strategy has great promise for getting newly identified contaminants out of wastewater.

A March 20, 2018 essay by Sukalyan Sengupta, Professor of Wastewater Treatment, and Tabish Nawaz. Doctoral Student, both at University of Massachusetts at Dartmouth on The Conversation website, which originated the news item, expands on the theme (Note: Links have been removed),

Use of nanosilver in consumer products has steadily risen in the past decade. The market share of silver-based textiles rose from 9 percent in 2004 to 25 percent in 2011.

Several investigators have measured the silver content of textiles and found values ranging from 0.009 to 21,600 milligrams of silver per kilogram of textile. Studies show that the amount of silver leached in the wash solution depends on many factors, including interactions between detergent and other chemicals and how silver is attached to the textiles.

In humans, exposure to silver can harm liver cells, skin and lungs. Prolonged exposure or exposure to a large dose can cause a condition called Argyria, in which the victim’s skin turns permanently bluish-gray.

Once silver goes down the drain and ends up at wastewater treatment plants, it can potentially harm bacterial treatment processes, making them less efficient, and foul treatment equipment. More than 90 percent of silver nanoparticles released in wastewater end up in nutrient-rich biosolids left over at the end of sewage treatment, which often are used on land as agricultural fertilizers.

Silver is toxic in aquatic environments, a concern that’s becoming more serious with the increased use of silver nanoparticles and awareness that oceans, rivers, and lakes are dangerously stressed.

Sengupta and Nawaz go on to describe their proposed solution (Note: Links have been removed),

Our research shows that the most efficient way to remove silver from wastewater is by treating it in the washing machine. At this point silver concentrations are relatively high, and silver is initially released from treated clothing in a chemical form that is feasible to recover.

A bit of chemistry is helpful here. Our recovery method employs a widely used chemistry process called ion exchange. Ions are atoms or molecules that have an electrical charge. In ion exchange, a solid and a liquid are brought together and exchange ions with each other.

For example, household soaps do not lather well in “hard” water, which contains high levels of ions such as magnesium and calcium. Many home water filters use ion exchange to “soften” the water, replacing those materials with other ions that do not affect its properties in the same way.

For this process to work, the ions that switch places must both be either positively or negatively charged. Nanosilver is initially released from textiles as silver ion, which is a cation – an ion with a positive charge (hence the plus sign in its chemical symbol, Ag+).

Even at the source, removing silver from washwater is challenging. Silver concentrations in the wash solution are relatively low compared to other cations, such as calcium, that could interfere with the removal process. Detergent chemistry complicates the picture further because some detergent components can potentially interact with silver.

To recover silver without picking up other chemicals, the recovery process must use materials that have a chemical affinity for silver. In a previous study, we described a potential solution: Using ion-exchange materials embedded with sulfur-based chemicals, which bind preferentially with silver.

In our new study, we passed washwater through an ion-exchange resin column and analyzed how each major detergent ingredient interacted with silver in the water and affected the resin’s ability to remove silver from the water. By manipulating process conditions such as pH, temperature and concentration of nonsilver cations, we were able to identify conditions that maximized silver recovery.

We found that pH and the levels of calcium ions (Ca2+) were critical factors. Higher levels of hydrogen or calcium ions bind up detergent ingredients and prevent them from interacting with silver ions, so the ion-exchange resin can remove the silver from the solution. We also found that some detergent ingredients – particularly bleaching and water-softening agents – made the ion-exchange resin work less efficiently. Depending on these conditions, we recovered between 20 percent and 99 percent of the silver in the washwater.

The researchers go on to propose a new approach to treating wastewater (Note: A link has been removed),

Today wastewater is collected from multiple sources, such as homes and businesses, and piped over long distances to centralized wastewater treatment plants. But increasing evidence shows that these facilities are ill-equipped to keep newly identified contaminants out of the environment, since they use one common treatment scheme for many different waste streams.

We believe the future is in decentralized systems that can treat different types of wastewater with specific technologies designed specifically for the materials they contain. If wastewater from laundromats contains different contaminants than wastewater from restaurants, why treat them the same way?

Interesting, non? In any event, here’s a link to and a citation for what I believe is the researchers’ latest paper on this subject,

Silver Recovery from Laundry Washwater: The Role of Detergent Chemistry by Tabish Nawaz and Sukalyan Sengupta. ACS Sustainable Chem. Eng., 2018, 6 (1), pp 600–608 DOI: 10.1021/acssuschemeng.7b02933 Publication Date (Web): November 21, 2017

Copyright © 2017 American Chemical Society

This paper is behind a paywall. For anyone who can’t get access, Karla Lant provides a bit more technical detail about the work in her February 2, 2018 article for fondriest.com.

“Living” bandages made from biocompatible anti-burn nanofibers

A February 16, 2018 news item on Nanowerk announces research from a Russian team about their work on “living” bandages,

In regenerative medicine, and particularly in burn therapy, the effective regeneration of damaged skin tissue and the prevention of scarring are usually the main goals. Scars form when skin is badly damaged, whether through a cut, burn, or a skin problem such as acne or fungal infection.

Scar tissue mainly consists of irreversible collagen and significantly differs from the tissue it replaces, having reduced functional properties. For example, scars on skin are more sensitive to ultraviolet radiation, are not elastic, and the sweat glands and hair follicles are not restored in the area.

The solution of this medical problem was proposed by the researchers from the NUST MISIS [National University of Science and Technology {formerly Moscow Institute of Steel and Alloys State Technological University})] Inorganic Nanomaterials Laboratory, led by PhD Anton Manakhov, a senior researcher. The team of nanotechnology scientists has managed to create multi-layer ‘bandages’ made of biodegradable fibers and multifunctional bioactive nanofilms, which [the bandages] prevent scarring and accelerate tissue regeneration.

A February 14, 2018 NUST MISIS press release, which originated the news item, provides more detail,

The addition of the antibacterial effect by the introduction of silver nanoparticles or joining antibiotics, as well as the increase of biological activity to the surface of hydrophilic groups (-COOH) and the blood plasma proteins have provided unique healing properties to the material.

A significant acceleration of the healing process, the successful regeneration of normal skin covering tissue, and the prevention of scarring on the site of burnt or damaged skin have been observed when applying these bandages made of the developed material to an injured area. The antibacterial components of multifunctional nanofibers decrease inflammation, and the blood plasma with an increased platelet level — vital and multi-purposed for every element in the healing process — stimulates the regeneration of tissues. The bandages should not be removed or changed during treatment as it may cause additional pain to the patient. After a certain period of time, the biodegradable fiber simply “dissolves” without any side effects.

“With the help of chemical bonds, we were able to create a stable layer containing blood plasma components (growth factors, fibrinogens, and other important proteins that promote cell growth) on a polycaprolactone base. The base fibers were synthesized by electroforming. Then, with the help of plasma treatment, to increase the material`s hydrophilic properties, a polymer layer containing carboxyl groups was applied to the surface. The resulting layer was enriched with antibacterial and protein components”, noted Elizabeth Permyakova, one of the project members and laboratory scientists.

The researchers have made images of their work available including this one,

Courtesy NUST MISS [downloaded from http://en.misis.ru/university/news/science/2018-02/5219/]

There is doesn’t appear to be an accompanying published paper.

Taking spectroscopy to a new dimension with silver nanoparticles

This latest move towards better detection at the nanoscale comes from India (from a January 2, 2018 news item on ScienceDaily),

As medicine and pharmacology investigate nanoscale processes, it has become increasingly important to identify and characterize different molecules. Raman spectroscopy, a technique that leverages the scattering of laser light to identify molecules, has a limited capacity to detect molecules in diluted samples because of low signal yield.

A team of researchers from the University of Hyderabad in India has improved molecular detection at low concentration levels by arranging nanoparticles on nanowires to enhance Raman spectroscopy. Surface-enhanced Raman spectroscopy (SERS) uses electromagnetic fields to improve Raman scattering and boost sensitivity in standard dyes such as R6G by more than one billionfold.

Here’s an image illustrating the work,

Caption: Detection of a low concentration analyte molecule using silicon nanowires decorated with silver nanoparticles and surface enhanced Raman scattering measurements. Credit: V.S. Vendamani

A January 2, 2017 American Institute of Physics press release on EurekAlert, which originated the news item, explains further,

The team decorated vertically aligned silicon nanowires with varying densities of silver nanoparticles, utilizing and enhancing the structure’s 3-D shape. Their results, published in the Journal of Applied Physics, from AIP [American Institute of Physics] Publishing, show that their device was able to enhance the Raman signals for cytosine protein and ammonium perchlorate by a factor of 100,000.

“The beauty is that we can improve the density of these nanowires using simple chemistry,” said Soma Venugopal Rao, one of the paper’s authors. “If you have a large density of nanowires, you can put more silver nanoparticles into the substrate and can increase the sensitivity of the substrate.”

Applying the necessary nanostructures to SERS devices remains a challenge for the field. Building these structures in three dimensions with silicon nanowires has garnered attention for their higher surface area and superior performance, but silicon nanowires are still expensive to produce.

Instead, the team was able to find a cheaper way to make silicon nanowires and used a technique called electroless etching to make a wide range of nanowires. They “decorated” these wires with silver nanoparticles with variable and controlled densities, which increased the nanowires’ surface area.

“Optimizing these vertically aligned structures took a lot of time in the beginning,” said Nageswara Rao, another of the paper’s authors. “We increased the surface area and to do this we needed to change the aspect ratio.”

After optimizing their system to detect Rhodamine dye on a nanomolar level, these new substrates the team built enhanced Raman sensitivity by a factor of 10,000 to 100,000. The substrates detected concentrations of cytosine, a nucleotide found in DNA, and ammonium perchlorate, a molecule with potential for detecting explosives, in as dilute concentrations as 50 and 10 micromolar, respectively.

The results have given the team reason to believe that it might soon be possible to detect compounds in concentrations on the scale of nanomolar or even picomolar, Nageswara Rao said. The team’s work has opened several avenues for future research, from experimenting with different nanoparticles such as gold, increasing the sharpness of the nanowires or testing these devices across several types of molecules.

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

Three-dimensional hybrid silicon nanostructures for surface enhanced Raman spectroscopy based molecular detection featured by V. S. Vendamani, S. V. S. Nageswara Rao, S. Venugopal Rao, D. Kanjilal, and A. P. Pathak. Journal of Applied Physics 123, 014301 (2018); Published Online: January 2018 https://doi.org/10.1063/1.5000994

This paper is open access.

Light-based computation made better with silver

It’s pretty amazing to imagine a future where computers run on light but according to a May 16, 2017 news item on ScienceDaily the idea is not beyond the realms of possibility,

Tomorrow’s computers will run on light, and gold nanoparticle chains show much promise as light conductors. Now Ludwig-Maximilians-Universitaet (LMU) in Munich scientists have demonstrated how tiny spots of silver could markedly reduce energy consumption in light-based computation.

Today’s computers are faster and smaller than ever before. The latest generation of transistors will have structural features with dimensions of only 10 nanometers. If computers are to become even faster and at the same time more energy efficient at these minuscule scales, they will probably need to process information using light particles instead of electrons. This is referred to as “optical computing.”

The silver serves as a kind of intermediary between the gold particles while not dissipating energy. Capture: Liedl/Hohmann (NIM)

A March 15, 2017 LMU press release (also one EurekAlert), which originated the news item, describes a current use of light in telecommunications technology and this latest research breakthrough (the discrepancy in dates is likely due to when the paper was made available online versus in print),

Fiber-optic networks already use light to transport data over long distances at high speed and with minimum loss. The diameters of the thinnest cables, however, are in the micrometer range, as the light waves — with a wavelength of around one micrometer — must be able to oscillate unhindered. In order to process data on a micro- or even nanochip, an entirely new system is therefore required.

One possibility would be to conduct light signals via so-called plasmon oscillations. This involves a light particle (photon) exciting the electron cloud of a gold nanoparticle so that it starts oscillating. These waves then travel along a chain of nanoparticles at approximately 10% of the speed of light. This approach achieves two goals: nanometer-scale dimensions and enormous speed. What remains, however, is the energy consumption. In a chain composed purely of gold, this would be almost as high as in conventional transistors, due to the considerable heat development in the gold particles.

A tiny spot of silver

Tim Liedl, Professor of Physics at LMU and PI at the cluster of excellence Nanosystems Initiative Munich (NIM), together with colleagues from Ohio University, has now published an article in the journal Nature Physics, which describes how silver nanoparticles can significantly reduce the energy consumption. The physicists built a sort of miniature test track with a length of around 100 nanometers, composed of three nanoparticles: one gold nanoparticle at each end, with a silver nanoparticle right in the middle.

The silver serves as a kind of intermediary between the gold particles while not dissipating energy. To make the silver particle’s plasmon oscillate, more excitation energy is required than for gold. Therefore, the energy just flows “around” the silver particle. “Transport is mediated via the coupling of the electromagnetic fields around the so-called hot spots which are created between each of the two gold particles and the silver particle,” explains Tim Liedl. “This allows the energy to be transported with almost no loss, and on a femtosecond time scale.”

Textbook quantum model

The decisive precondition for the experiments was the fact that Tim Liedl and his colleagues are experts in the exquisitely exact placement of nanostructures. This is done by the DNA origami method, which allows different crystalline nanoparticles to be placed at precisely defined nanodistances from each other. Similar experiments had previously been conducted using conventional lithography techniques. However, these do not provide the required spatial precision, in particular where different types of metals are involved.

In parallel, the physicists simulated the experimental set-up on the computer – and had their results confirmed. In addition to classical electrodynamic simulations, Alexander Govorov, Professor of Physics at Ohio University, Athens, USA, was able to establish a simple quantum-mechanical model: “In this model, the classical and the quantum-mechanical pictures match very well, which makes it a potential example for the textbooks.”

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

Hotspot-mediated non-dissipative and ultrafast plasmon passage by Eva-Maria Roller, Lucas V. Besteiro, Claudia Pupp, Larousse Khosravi Khorashad, Alexander O. Govorov, & Tim Liedl. Nature Physics (2017) doi:10.1038/nphys4120 Published online 15 May 2017

This paper is behind a paywall.