Tag Archives: Rice University

Double-walled carbon nanotubes have superior electrical properties?

A March 27, 2020 news item on Nanowerk suggests that double-walled carbon nanotubes (DWCNTs) may offer some advantages over single-walled carbon nanotubes (SWCNTs), NOTE: A link has been removed,

One nanotube could be great for electronics applications, but there’s new evidence that two could be tops.

Rice University engineers already knew that size matters when using single-walled carbon nanotubes for their electrical properties. But until now, nobody had studied how electrons act when confronted with the Russian doll-like structure of multiwalled tubes.

There’s a diagram representing the work,

Caption: Rice University theorists have calculated flexoelectric effects in double-walled carbon nanotubes. The electrical potential (P) of atoms on either side of a graphene sheet (top) are identical, but not when the sheet is curved into a nanotube. Double-walled nanotubes (bottom) show unique effects as band gaps in inner and outer tubes are staggered. Credit: Yakobson Research Group/Rice University

A March 27, 2020 Rice University news release (also on EurekAlert), which originated the news item, delves further (NOTE: Links have been removed),

The Rice lab of materials theorist Boris Yakobson has now calculated the impact of curvature of semiconducting double-wall carbon nanotubes on their flexoelectric voltage, a measure of electrical imbalance between the nanotube’s inner and outer walls.

This affects how suitable nested nanotube pairs may be for nanoelectronics applications, especially photovoltaics.

The theoretical research by Yakobson’s Brown School of Engineering group appears in the American Chemical Society journal Nano Letters.

In an 2002 study, Yakobson and his Rice colleagues had revealed how charge transfer, the difference between positive and negative poles that allows voltage to exist between one and the other, scales linearly to the curvature of the nanotube wall. The width of the tube dictates curvature, and the lab found that the thinner the nanotube (and thus larger the curvature), the greater the potential voltage.

When carbon atoms form flat graphene, the charge density of the atoms on either side of the plane are identical, Yakobson said. Curving the graphene sheet into a tube breaks that symmetry, changing the balance.

That creates a flexoelectric local dipole in the direction of, and proportional to, the curvature, according to the researchers, who noted that the flexoelectricity of 2D carbon “is a remarkable but also fairly subtle effect.”

But more than one wall greatly complicates the balance, altering the distribution of electrons. In double-walled nanotubes, the curvature of the inner and outer tubes differ, giving each a distinct band gap. Additionally, the models showed the flexoelectric voltage of the outer wall shifts the band gap of the inner wall, creating a staggered band alignment in the nested system.

“The novelty is that the inserted tube, the ‘baby’ (inside) matryoshka has all of its quantum energy levels shifted because of the voltage created by exterior nanotube,” Yakobson said. The interplay of different curvatures, he said, causes a straddling-to-staggered band gap transition that takes place at an estimated critical diameter of about 2.4 nanometers.

“This is a huge advantage for solar cells, essentially a prerequisite for separating positive and negative charges to create a current,” Yakobson said. “When light is absorbed, an electron always jumps from the top of an occupied valence band (leaving a ‘plus’ hole behind) to the lowest state of empty conductance band.

“But in a staggered configuration they happen to be in different tubes, or layers,” he said. “The ‘plus’ and ‘minus’ get separated between the tubes and can flow away by generating current in a circuit.”

The team’s calculations also showed that modifying the nanotubes’ surfaces with either positive or negative atoms could create “substantial voltages of either sign” up to three volts. “Although functionalization could strongly perturb the electronic properties of nanotubes, it may be a very powerful way of inducing voltage for certain applications,” the researchers wrote.

The team suggested its findings may apply to other types of nanotubes, including boron nitride and molybdenum disulfide, on their own or as hybrids with carbon nanotubes.

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

Flexoelectricity and charge separation in carbon nanotubes by Vasilii I. Artyukhov, Sunny Gupta, Alex Kutana, Boris I. Yakobson. Nano Lett. 2020, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acs.nanolett.9b05345 [Online] Publication Date:March 10, 2020 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

In the future your clothing may be a health monitor

It’s not ready for the COVID-19 pandemic but if I understand it properly, wearing this clothing will be a little like wearing a thermometer and that could be very useful. A March 4, 2020 news item on Nanowerk announces the research (Note: A link has been removed),

Researchers have reported a new material, pliable enough to be woven into fabric but imbued with sensing capabilities that can serve as an early warning system for injury or illness.

The material, described in a paper published by ACS Applied Nano Materials (“Poly(octadecyl acrylate)-Grafted Multiwalled Carbon Nanotube Composites for Wearable Temperature Sensors”), involves the use of carbon nanotubes and is capable of sensing slight changes in body temperature while maintaining a pliable disordered structure – as opposed to a rigid crystalline structure – making it a good candidate for reusable or disposable wearable human body temperature sensors. Changes in body heat change the electrical resistance, alerting someone monitoring that change to the potential need for intervention.

I think this is an artistic rendering of the research,

Caption: Researchers have reported a new material, pliable enough to be woven into fabric but imbued with sensing capabilities that could serve as an early warning system for injury or illness. Credit: University of Houston

A March 4, 2020 University of Houston (Texas, US) news release (also on EurekAlert) by Jeannie Kever, which originated the news item, describes the work in more detail,

“Your body can tell you something is wrong before it becomes obvious,” said Seamus Curran, a physics professor at the University of Houston and co-author on the paper. Possible applications range from detecting dehydration in an ultra-marathoner to the beginnings of a pressure sore in a nursing home patient.

The researchers said it is also cost-effective because the raw materials required are used in relatively low concentrations.

The discovery builds on work Curran and fellow researchers Kang-Shyang Liao and Alexander J. Wang began nearly a decade ago, when they developed a hydrophobic nanocoating for cloth, which they envisioned as a protective coating for clothing, carpeting and other fiber-based materials.

Wang is now a Ph.D. student at Technological University Dublin, currently working with Curran at UH, and is corresponding author for the paper. In addition to Curran and Liao, other researchers involved include Surendra Maharjan, Brian P. McElhenny, Ram Neupane, Zhuan Zhu, Shuo Chen, Oomman K. Varghese and Jiming Bao, all of UH; Kourtney D. Wright and Andrew R. Barron of Rice University, and Eoghan P. Dillon of Analysis Instruments in Santa Barbara.

The material, created using poly(octadecyl acrylate)-grafted multiwalled carbon nanotubes, is technically known as a nanocarbon-based disordered, conductive, polymeric nanocomposite, or DCPN, a class of materials increasingly used in materials science. But most DCPN materials are poor electroconductors, making them unsuitable for use in wearable technologies that require the material to detect slight changes in temperature.

The new material was produced using a technique called RAFT-polymerization, Wang said, a critical step that allows the attached polymer to be electronically and phononically coupled with the multiwalled carbon nanotube through covalent bonding. As such, subtle structural arrangements associated with the glass transition temperature of the system are electronically amplified to produce the exceptionally large electronic responses reported in the paper, without the negatives associated with solid-liquid phase transitions. The subtle structural changes associated with glass transition processes are ordinarily too small to produce large enough electronic responses.

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

Poly(octadecyl acrylate)-Grafted Multiwalled Carbon Nanotube Composites for Wearable Temperature Sensors by Alexander J. Wang, Surendra Maharjan, Kang-Shyang Liao, Brian P. McElhenny, Kourtney D. Wright, Eoghan P. Dillon, Ram Neupane, Zhuan Zhu, Shuo Chen, Andrew R. Barron, Oomman K. Varghese, Jiming Bao, Seamus A. Curran. ACS Appl. Nano Mater. 2020, XXXX, XXX, XXX-XXX DOI: https://doi.org/10.1021/acsanm.9b02396 (Online) Publication Date:January 28, 2020 Copyright © 2020 American Chemical Society

This paper is behind a paywall.

Graphene fatigue

Graphene fatigue operates under the same principle as metal fatigue. Subject graphene to stress over and over and at some point it (just like metal) will fail. Scientists at the University of Toronto (Ontatrio, Canada) and Rice University (Texas, US) have determined just how much stress graphene can withstand before breaking according to a January 28, 2020 University of Toronto news release by Tyler Irving (also on EurekAlert but published on January 29, 2020),

Graphene is a paradox. It is the thinnest material known to science, yet also one of the strongest. Now, research from University of Toronto Engineering shows that graphene is also highly resistant to fatigue — able to withstand more than a billion cycles of high stress before it breaks.

Graphene resembles a sheet of interlocking hexagonal rings, similar to the pattern you might see in bathroom flooring tiles. At each corner is a single carbon atom bonded to its three nearest neighbours. While the sheet could extend laterally over any area, it is only one atom thick.

The intrinsic strength of graphene has been measured at more than 100 gigapascals, among the highest values recorded for any material. But materials don’t always fail because the load exceeds their maximum strength. Stresses that are small but repetitive can weaken materials by causing microscopic dislocations and fractures that slowly accumulate over time, a process known as fatigue.

“To understand fatigue, imagine bending a metal spoon,” says Professor Tobin Filleter, one of the senior authors of the study, which was recently published in Nature Materials. “The first time you bend it, it just deforms. But if you keep working it back and forth, eventually it’s going to break in two.”

The research team — consisting of Filleter, fellow University of Toronto Engineering professors Chandra Veer Singh and Yu Sun, their students, and collaborators at Rice University — wanted to know how graphene would stand up to repeated stresses. Their approach included both physical experiments and computer simulations.

“In our atomistic simulations, we found that cyclic loading can lead to irreversible bond reconfigurations in the graphene lattice, causing catastrophic failure on subsequent loading,” says Singh, who along with postdoctoral fellow Sankha Mukherjee led the modelling portion of the study. “This is unusual behaviour in that while the bonds change, there are no obvious cracks or dislocations, which would usually form in metals, until the moment of failure.”

PhD candidate Teng Cui, who is co-supervised by Filleter and Sun, used the Toronto Nanofabrication Centre to build a physical device for the experiments. The design consisted of a silicon chip etched with half a million tiny holes only a few micrometres in diameter. The graphene sheet was stretched over these holes, like the head of a tiny drum.

Using an atomic force microscope, Cui then lowered a diamond-tipped probe into the hole to push on the graphene sheet, applying anywhere from 20 to 85 per cent of the force that he knew would break the material.

“We ran the cycles at a rate of 100,000 times per second,” says Cui. “Even at 70 per cent of the maximum stress, the graphene didn’t break for more than three hours, which works out to over a billion cycles. At lower stress levels, some of our trials ran for more than 17 hours.”

As with the simulations, the graphene didn’t accumulate cracks or other tell-tale signs of stress — it either broke or it didn’t.

“Unlike metals, there is no progressive damage during fatigue loading of graphene,” says Sun. “Its failure is global and catastrophic, confirming simulation results.”

The team also tested a related material, graphene oxide, which has small groups of atoms such as oxygen and hydrogen bonded to both the top and bottom of the sheet. Its fatigue behaviour was more like traditional materials, in that the failure was more progressive and localized. This suggests that the simple, regular structure of graphene is a major contributor to its unique properties.

“There are no other materials that have been studied under fatigue conditions that behave the way graphene does,” says Filleter. “We’re still working on some new theories to try and understand this.”

In terms of commercial applications, Filleter says that graphene-containing composites — mixtures of conventional plastic and graphene — are already being produced and used in sports equipment such as tennis rackets and skis.

In the future, such materials may begin to be used in cars or in aircraft, where the emphasis on light and strong materials is driven by the need to reduce weight, improve fuel efficiency and enhance environmental performance.

“There have been some studies to suggest that graphene-containing composites offer improved resistance to fatigue, but until now, nobody had measured the fatigue behaviour of the underlying material,” he says. “Our goal in doing this was to get at that fundamental understanding so that in the future, we’ll be able to design composites that work even better.”

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

Fatigue of graphene by Teng Cui, Sankha Mukherjee, Parambath M. Sudeep, Guillaume Colas, Farzin Najafi, Jason Tam, Pulickel M. Ajayan, Chandra Veer Singh, Yu Sun & Tobin Filleter. Nature Materials (2020) DOI: DOIhttps://doi.org/10.1038/s41563-019-0586-y Published: 20 January 2020

This paper is behind a paywall.

Safe nanomaterial handling on a tiny budget

A June 3, 2019 news item on Nanowerk describes an inexpensive way to safely handle carbon nanotubes (CNTs), Note: A link has been removed,

With a little practice, it doesn’t take much more than 10 minutes, a couple of bags and a big bucket to keep nanomaterials in their place.

The Rice University lab of chemist Andrew Barron works with bulk carbon nanotubes on a variety of projects. Years ago, members of the lab became concerned that nanotubes could escape into the air, and developed a cheap and clean method to keep them contained as they were transferred from large containers into jars for experimental use.

More recently Barron himself became concerned that too few labs around the world were employing best practices to handle nanomaterials. He decided to share what his Rice team had learned.

“There was a series of studies that said if you’re going to handle nanotubes, you really need to use safety protocols,” Barron said. “Then I saw a study that said many labs didn’t use any form of hood or containment system. In the U.S., it was really bad, and in Asia it was even worse. But there are a significant number of labs scaling up to use these materials at the kilogram scale without taking the proper precautions.”

The lab’s inexpensive method is detailed in an open-access paper in the Springer Nature journal SN Applied Sciences (“The safe handling of bulk low-density nanomaterials”).

Here’s a bag and a bucket,

Caption: A plastic bucket and a plastic bag contain a 5-gallon supply of carbon nanotubes in a lab at Rice University, the beginning of the process to safely transfer the nanotubes for experimental use. The Rice lab published its technique in SN Applied Sciences. Credit: Barron Research Group/Rice University

A June 3, 2019 Rice University news release (also on EurekAlert and received separately by email), which originated the news item, provides more detail,

In bulk form, carbon nanotubes are fluffy and disperse easily if disturbed. The Rice lab typically stores the tubes in 5-gallon plastic buckets, and simply opening the lid is enough to send them flying because of their low density.

Varun Shenoy Gangoli, a research scientist in Barron’s lab, and Pavan Raja, a scientist with Rice’s Nanotechnology-Enabled Water Treatment center, developed for their own use a method that involves protecting the worker and sequestering loose tubes when removing smaller amounts of the material for use in experiments.

Full details are available in the paper, but the precautions include making sure workers are properly attired with long pants, long sleeves, lab coats, full goggles and face masks, along with two pairs of gloves duct-taped to the lab coat sleeves. The improvised glove bag involves a 25-gallon trash bin with a plastic bag taped to the rim. The unopened storage container is placed inside, and then the bin is covered with another transparent trash bag, with small holes cut in the top for access.

After transferring the nanotubes, acetone wipes are used to clean the gloves and more acetone is sprayed inside the barrel so settling nanotubes would stick to the surfaces. These can be recovered and returned to the storage container.

Barron said it took lab members time to learn to use the protocol efficiently, “but now they can get their samples in 5 to 10 minutes.” He’s sure other labs can and will enhance the technique for their own circumstances. He noted a poster presented at the Ninth Guadalupe Workshop on the proper handling of carbon nanotubes earned recognition and discussion among the world’s premier researchers in the field, noting the importance of the work for agencies in general.

“When we decided to write about this, we were originally just going to put it on the web and hope somebody would read it occasionally,” Barron said. “We couldn’t imagine who would publish it, but we heard that an editor at Springer Nature was really keen to have published articles like this.

“I think this is something people will use,” he said. “There’s nothing outrageous but it helps everybody, from high schools and colleges that are starting to use nanoparticles for experiments to small companies. That was the goal: Let’s provide a process that doesn’t cost thousands of dollars to install and allows you to transfer nanomaterials safely and on a large scale. Finally, publish said work in an open-access journal to maximize the reach across the globe.”

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

The safe handling of bulk low-density nanomaterials by Varun Shenoy Gangoli, Pavan M. V. Raja, Gibran Liezer Esquenazi, Andrew R. Barron. SN Applied Sciences June 2019, 1:644 DOI: https://doi.org/10.1007/s42452-019-0647-5 First Online 25 May 2019

This paper is open access.

Vitamin C helps gold nanowires grow

This research gives new meaning to ‘Take your vitamin C’ as can be seen in a February 19, 2019 news item on Nanowerk,

A boost of vitamin C helped Rice University scientists turn small gold nanorods into fine gold nanowires.

Common, mild ascorbic acid is the not-so-secret sauce that helped the Rice lab of chemist Eugene Zubarev grow pure batches of nanowires from stumpy nanorods without the drawbacks of previous techniques.

“There’s no novelty per se in using vitamin C to make gold nanostructures because there are many previous examples,” Zubarev said. “But the slow and controlled reduction achieved by vitamin C is surprisingly suitable for this type of chemistry in producing extra-long nanowires.”

A February 19, 2019 Rice University news release (also on EurekAlert), which originated the news item, provides more technical detail about the research

The Rice lab’s nanorods are about 25 nanometers thick at the start of the process – and remain that way while their length grows to become long nanowires. Above 1,000 nanometers in length, the objects are considered nanowires, and that matters. The wires’ aspect ratio – length over width – dictates how they absorb and emit light and how they conduct electrons. Combined with gold’s inherent metallic properties, that could enhance their value for sensing, diagnostic, imaging and therapeutic applications.

Zubarev and lead author Bishnu Khanal, a Rice chemistry alumnus, succeeded in making their particles go far beyond the transition from nanorod to nanowire, theoretically to unlimited length.

The researchers also showed the process is fully controllable and reversible. That makes it possible to produce nanowires of any desired length, and thus the desired configuration for electronic or light-manipulating applications, especially those that involve plasmons, the light-triggered oscillation of electrons on a metal’s surface.

The nanowires’ plasmonic response can be tuned to emit light from visible to infrared and theoretically far beyond, depending on their aspect ratios.

The process is slow, so it takes hours to grow a micron-long nanowire. “In this paper, we only reported structures up to 4 to 5 microns in length,” Zubarev said. “But we’re working to make much longer nanowires.”

The growth process only appeared to work with pentahedrally twinned gold nanorods, which contain five linked crystals. These five-sided rods — “Think of a pencil, but with five sides instead of six,” Zubarev said — are stable along the flat surfaces, but not at the tips.

“The tips also have five faces, but they have a different arrangement of atoms,” he said. “The energy of those atoms is slightly lower, and when new atoms are deposited there, they don’t migrate anywhere else.”

That keeps the growing wires from gaining girth. Every added atom increases the wire’s length, and thus the aspect ratio.

The nanorods’ reactive tips get help from a surfactant, CTAB, that covers the flat surfaces of nanorods. “The surfactant forms a very dense, tight bilayer on the sides, but it cannot cover the tips effectively,” Zubarev said.

That leaves the tips open to an oxidation or reduction reaction. The ascorbic acid provides electrons that combine with gold ions and settle at the tips in the form of gold atoms. And unlike carbon nanotubes in a solution that easily aggregate, the nanowires keep their distance from one another.

“The most valuable feature is that it is truly one-dimensional elongation of nanorods to nanowires,” Zubarev said. “It does not change the diameter, so in principal we can take small rods with an aspect ratio of maybe two or three and elongate them to 100 times the length.”
He said the process should apply to other metal nanorods, including silver.

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

Chemical Transformation of Nanorods to Nanowires: Reversible Growth and Dissolution of Anisotropic Gold Nanostructures by Bishnu P. Khanal and Eugene R. Zubarev. ACS Nano, 2019, 13 (2), pp 2370–2378 DOI: 10.1021/acsnano.8b09203 Publication Date (Web): February 12, 2019

Copyright © 2019 American Chemical Society

This paper is behind a paywall. Below you’ll find an image fo what I believe to be the vitamin C-enhanced gold nanowires.

Caption: Gold nanowires grown in the Rice University lab of chemist Eugene Zubarev promise to provide tunable plasmonic properties for optical and electronic applications. The wires can be controllably grown from nanorods, or reduced. Credit: Zubarev Research Group/Rice University

Let them (Rice University scientists) show you how to restore oil-soaked soil

I did not want to cash in (so to speak) on someone else’s fun headline so I played with it. Hre is the original head, which was likely written by either David Ruth or Mike Williams at Rice University (Texas, US), “Lettuce show you how to restore oil-soaked soil.”

A February 1, 2019 news item on ScienceDaily on the science behind lettuce and oil-soaked soil,

Rice University engineers have figured out how soil contaminated by heavy oil can not only be cleaned but made fertile again.

How do they know it works? They grew lettuce.

Rice engineers Kyriacos Zygourakis and Pedro Alvarez and their colleagues have fine-tuned their method to remove petroleum contaminants from soil through the age-old process of pyrolysis. The technique gently heats soil while keeping oxygen out, which avoids the damage usually done to fertile soil when burning hydrocarbons cause temperature spikes.

Lettuce growing in once oil-contaminated soil revived by a process developed by Rice University engineers. The Rice team determined that pyrolyzing oil-soaked soil for 15 minutes at 420 degrees Celsius is sufficient to eliminate contaminants while preserving the soil’s fertility. The lettuce plants shown here, in treated and fertilized soil, showed robust growth over 14 days. Photo by Wen Song

A February 1, 2019 Rice University news release (also on EurekAlert), which originated the news item, explains more about the work,

While large-volume marine spills get most of the attention, 98 percent of oil spills occur on land, Alvarez points out, with more than 25,000 spills a year reported to the Environmental Protection Agency. That makes the need for cost-effective remediation clear, he said.

“We saw an opportunity to convert a liability, contaminated soil, into a commodity, fertile soil,” Alvarez said.

The key to retaining fertility is to preserve the soil’s essential clays, Zygourakis said. “Clays retain water, and if you raise the temperature too high, you basically destroy them,” he said. “If you exceed 500 degrees Celsius (900 degrees Fahrenheit), dehydration is irreversible.

The researchers put soil samples from Hearne, Texas, contaminated in the lab with heavy crude, into a kiln to see what temperature best eliminated the most oil, and how long it took.

Their results showed heating samples in the rotating drum at 420 C (788 F) for 15 minutes eliminated 99.9 percent of total petroleum hydrocarbons (TPH) and 94.5 percent of polycyclic aromatic hydrocarbons (PAH), leaving the treated soils with roughly the same pollutant levels found in natural, uncontaminated soil.

The paper appears in the American Chemical Society journal Environmental Science and Technology. It follows several papers by the same group that detailed the mechanism by which pyrolysis removes contaminants and turns some of the unwanted hydrocarbons into char, while leaving behind soil almost as fertile as the original. “While heating soil to clean it isn’t a new process,” Zygourakis said, “we’ve proved we can do it quickly in a continuous reactor to remove TPH, and we’ve learned how to optimize the pyrolysis conditions to maximize contaminant removal while minimizing soil damage and loss of fertility.

“We also learned we can do it with less energy than other methods, and we have detoxified the soil so that we can safely put it back,” he said.

Heating the soil to about 420 C represents the sweet spot for treatment, Zygourakis said. Heating it to 470 C (878 F) did a marginally better job in removing contaminants, but used more energy and, more importantly, decreased the soil’s fertility to the degree that it could not be reused.

“Between 200 and 300 C (392-572 F), the light volatile compounds evaporate,” he said. “When you get to 350 to 400 C (662-752 F), you start breaking first the heteroatom bonds, and then carbon-carbon and carbon-hydrogen bonds triggering a sequence of radical reactions that convert heavier hydrocarbons to stable, low-reactivity char.”

The true test of the pilot program came when the researchers grew Simpson black-seeded lettuce, a variety for which petroleum is highly toxic, on the original clean soil, some contaminated soil and several pyrolyzed soils. While plants in the treated soils were a bit slower to start, they found that after 21 days, plants grown in pyrolyzed soil with fertilizer or simply water showed the same germination rates and had the same weight as those grown in clean soil.

“We knew we had a process that effectively cleans up oil-contaminated soil and restores its fertility,” Zygourakis said. “But, had we truly detoxified the soil?”

To answer this final question, the Rice team turned to Bhagavatula Moorthy, a professor of neonatology at Baylor College of Medicine, who studies the effects of airborne contaminants on neonatal development. Moorthy and his lab found that extracts taken from oil-contaminated soils were toxic to human lung cells, while exposing the same cell lines to extracts from treated soils had no adverse effects. The study eased concerns that pyrolyzed soil could release airborne dust particles laced with highly toxic pollutants like PAHs.

”One important lesson we learned is that different treatment objectives for regulatory compliance, detoxification and soil-fertility restoration need not be mutually exclusive and can be simultaneously achieved,” Alvarez said.

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

Pilot-Scale Pyrolytic Remediation of Crude-Oil-Contaminated Soil in a Continuously-Fed Reactor: Treatment Intensity Trade-Offs by Wen Song, Julia E. Vidonish, Roopa Kamath, Pingfeng Yu, Chun Chu, Bhagavatula Moorthy, Baoyu Gao, Kyriacos Zygourakis, and Pedro J. J. Alvarez. Environ. Sci. Technol., 2019, 53 (4), pp 2045–2053 DOI: 10.1021/acs.est.8b05825 Publication Date (Web): January 25, 2019

Copyright © 2019 American Chemical Society

This paper is behind a paywall.

Lifesaving moths and nanomagnets

Rice University bioengineers use a magnetic field to activate nanoparticle-attached baculoviruses in a tissue. The viruses, which normally infect alfalfa looper moths, are modified to deliver gene-editing DNA code only to cells that are targeted with magnetic field-induced local transduction. Courtesy of the Laboratory of Biomolecular Engineering and Nanomedicine

Kudos to whomever put that diagram together! That’s a lot of well conveyed information.

Now for the details about how this technology might save lives. From a November 13, 2018 news item on Nanowerk,

A new technology that relies on a moth-infecting virus and nanomagnets could be used to edit defective genes that give rise to diseases like sickle cell, muscular dystrophy and cystic fibrosis.

Rice University bioengineer Gang Bao has combined magnetic nanoparticles with a viral container drawn from a particular species of moth to deliver CRISPR/Cas9 payloads that modify genes in a specific tissue or organ with spatial control.

A November 12, 2018 Rice University news release (also on EurekAlert published on November 13, 2018), which originated the news item, provides detail,

Because magnetic fields are simple to manipulate and, unlike light, pass easily through tissue, Bao and his colleagues want to use them to control the expression of viral payloads in target tissues by activating the virus that is otherwise inactivated in blood.

The research appears in Nature Biomedical Engineering. In nature, CRISPR/Cas9 bolsters microbes’ immune systems by recording the DNA of invaders. That gives microbes the ability to recognize and attack returning invaders, but scientists have been racing to adapt CRISPR/Cas9 to repair mutations that cause genetic diseases and to manipulate DNA in laboratory experiments.

CRISPR/Cas9 has the potential to halt hereditary disease – if scientists can get the genome-editing machinery to the right cells inside the body. But roadblocks remain, especially in delivering the gene-editing payloads with high efficiency.

Bao said it will be necessary to edit cells in the body to treat many diseases. “But efficiently delivering genome-editing machinery into target tissue in the body with spatial control remains a major challenge,” Bao said. “Even if you inject the viral vector locally, it can leak to other tissues and organs, and that could be dangerous.”

The delivery vehicle developed by Bao’s group is based on a virus that infects Autographa californica, aka the alfalfa looper, a moth native to North America. The cylindrical baculovirus vector (BV), the payload-carrying part of the virus, is considered large at up to 60 nanometers in diameter and 200-300 nanometers in length. That’s big enough to transport more than 38,000 base pairs of DNA, which is enough to supply multiple gene-editing units to a target cell, Bao said.

He said the inspiration to combine BV and magnetic nanoparticles came from discussions with Rice postdoctoral researcher and co-lead author Haibao Zhu, who learned about the virus during a postdoctoral stint in Singapore but knew nothing about magnetic nanoparticles until he joined the Bao lab. The Rice team had previous experience using iron oxide nanoparticles and an applied magnetic field to open blood vessel walls just enough to let large-molecule drugs pass through.

“We really didn’t know if this would work for gene editing or not, but we thought, ‘worth a shot,'” Bao said.

The researchers use the magnetic nanoparticles to activate BV and deliver gene-editing payloads only where they’re needed. To do this, they take advantage of an immune-system protein called C3 that normally inactivates baculoviruses.

“If we combine BV with magnetic nanoparticles, we can overcome this deactivation by applying the magnetic field,” Bao said. “The beauty is that when we deliver it, gene editing occurs only at the tissue, or the part of the tissue, where we apply the magnetic field.”

Application of the magnetic field allows BV transduction, the payload-delivery process that introduces gene-editing cargo into the target cell. The payload is also DNA, which encodes both a reporter gene and the CRISPR/Cas9 system.

In tests, the BV was loaded with green fluorescent proteins or firefly luciferase. Cells with the protein glowed brightly under a microscope, and experiments showed the magnets were highly effective at targeted delivery of BV cargoes in both cell cultures and lab animals.

Bao noted his and other labs are working on the delivery of CRISPR/Cas9 with adeno-associated viruses (AAV), but he said BV’s capacity for therapeutic cargo is roughly eight times larger. “However, it is necessary to make BV transduction into target cells more efficient,” he said.

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

Spatial control of in vivo CRISPR–Cas9 genome editing via nanomagnets by Haibao Zhu, Linlin Zhang, Sheng Tong, Ciaran M. Lee, Harshavardhan Deshmukh, & Gang Bao. Nature Biomedical Engineering (2018) DOI: https://doi.org/10.1038/s41551-018-0318-7 Published: 12 November 2018

This paper is behind a paywall.

Where do I stand? a graphene artwork

A May 2,2019 news item on Nanowerk describes some graphene-based artwork being created at Rice University (Texas, US), Note: A link has been removed,

When you read about electrifying art, “electrifying” isn’t usually a verb. But an artist working with a Rice University lab is in fact making artwork that can deliver a jolt.

The Rice lab of chemist James Tour introduced laser-induced graphene (LIG) to the world in 2014, and now the researchers are making art with the technique, which involves converting carbon in a common polymer or other material into microscopic flakes of graphene.

The “ink” in “Where Do I Stand?” by artist Joseph Cohen is actually laser-induced graphene (LIG). The design shows Cohen’s impression of what LIG looks like at the microscopic level. The work was produced in the Rice University lab where the technique of creating LIG was invented. Photo by Jeff Fitlow
A detail from “Where Do I Stand?” by artist Joseph Cohen, who created the work at Rice University using laser-induced graphene as the medium. Photo by Jeff Fitlow

A May 2, 2019 Rice university news release (also received via email), which originated the news item, describes laser-induced graphene (LIG) and the art in more detail (Note: Links have been removed),

LIG is metallic and conducts electricity. The interconnected flakes are effectively a wire that could empower electronic artworks.

The paper in the American Chemical Society journal ACS Applied Nano Materials – simply titled “Graphene Art” – lays out how the lab and Houston artist and co-author Joseph Cohen generated LIG portraits and prints, including a graphene-inspired landscape called “Where Do I Stand?”

While the work isn’t electrified, Cohen said it lays the groundwork for future possibilities.

“That’s what I would like to do,” he said. “Not make it kitsch or play off the novelty, but to have it have some true functionality that allows greater awareness about the material and opens up the experience.”

Cohen created the design in an illustration program and sent it directly to the industrial engraving laser Tour’s lab uses to create LIG on a variety of materials. The laser burned the artist’s fine lines into the substrate, in this case archive-quality paper treated with fire retardant.

The piece, which was part of Cohen’s exhibit at Rice’s BioScience Research Collaborative last year, peers into the depths of what a viewer shrunken to nanoscale might see when facing a field of LIG, with overlapping hexagons – the basic lattice of atom-thick graphene – disappearing into the distance.

“You’re looking at this image of a 3D foam matrix of laser-induced graphene and it’s actually made of LIG,” he said. “I didn’t base it on anything; I was just thinking about what it would look like. When I shared it with Jim, he said, ‘Wow, that’s what it would look like if you could really blow this up.’”

Cohen said his art is about media specificity.

“In terms of the artistic application, you’re not looking at a representation of something, as traditionally we would in the history of art,” he said. “Each piece is 100% original. That’s the key.”

He developed an interest in nanomaterials as media for his art when he began work with Rice alumnus Daniel Heller, a bioengineer at Memorial Sloan Kettering Cancer Center in New York who established an artist-in-residency position in his lab.

After two years of creating with carbon nanotube-infused paint, Cohen attended an Electrochemical Society conference and met Tour, who in turn introduced him to Rice chemists Bruce Weisman and Paul Cherukuri, who further inspired his investigation of nanotechnology.

The rest is art history.

It would be incorrect to think of the process as “printing,” Tour said. Instead of adding a substance to the treated paper, substance is burned away as the laser turns the surface into foamlike flakes of interconnected graphene.

The art itself can be much more than eye candy, given LIG’s potential for electronic applications like sensors or as triboelectric generators that turn mechanical actions into current.

“You could put LIG on your back and have it flash LEDs with every step you take,” Tour said.

The fact that graphene is a conductor — unlike paint, ink or graphite from a pencil — makes it particularly appealing to Cohen, who expects to take advantage of that capability in future works.

“It’s art with a capital A that is trying to do the most that it can with advancements in science and technology,” he said. “If we look back historically, from the Renaissance to today, the highest forms of art push the limits of human understanding.”

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

Graphene Art by Yieu Chyan, Joseph Cohen, Winston Wang, Chenhao Zhang, and James M. Tour. ACS Appl. Nano Mater., Article ASAP DOI: 10.1021/acsanm.9b00391 Publication Date (Web): April 23, 2019

Copyright © 2019 American Chemical Society

This paper appears to be open access.

Because I can’t resist the delight beaming from these faces,

maging with laser-induced graphene (LIG) was taken to a new level in a Rice University lab. From left, chemist James Tour, holding a portrait of himself in LIG; artist Joseph Cohen, holding his work “Where Do I Stand?”; and Yieu Chyan, a Rice graduate student and lead author of a new paper detailing the process used to create the art. Photo by Jeff Fitlow

Probing the physical limits of plasmons in organic molecules with fewer than 50 atoms

A Sept. 5, 2018  news item on ScienceDaily introduces the work,

Rice University [Texas, US] researchers are probing the physical limits of excited electronic states called plasmons by studying them in organic molecules with fewer than 50 atoms.

A Sept. 4, 2018 Rice University news release (also on EurekAlert published on Sept. 5, 2018), which originated the news item, explains what plasmons are and why this research is being undertaken,

Plasmons are oscillations in the plasma of free electrons that constantly swirl across the surface of conductive materials like metals. In some nanomaterials, a specific color of light can resonate with the plasma and cause the electrons inside it to lose their individual identities and move as one, in rhythmic waves. Rice’s Laboratory for Nanophotonics (LANP) has pioneered a growing list of plasmonic technologies for applications as diverse as color-changing glass, molecular sensing, cancer diagnosis and treatment, optoelectronics, solar energy collection and photocatalysis.

Reporting online in the Proceedings of the National Academy of Sciences, LANP scientists detailed the results of a two-year experimental and theoretical study of plasmons in three different polycyclic aromatic hydrocarbons (PAHs). Unlike the plasmons in relatively large metal nanoparticles, which can typically be described with classical electromagnetic theory like Maxwell’s [James Clerk Maxwell] equations, the paucity of atoms in the PAHs produces plasmons that can only be understood in terms of quantum mechanics, said study co-author and co-designer Naomi Halas, the director of LANP and the lead researcher on the project.

“These PAHs are essentially scraps of graphene that contain five or six fused benzene rings surrounded by a perimeter of hydrogen atoms,” Halas said. “There are so few atoms in each that adding or removing even a single electron dramatically changes their electronic behavior.”

Halas’ team had experimentally verified the existence of molecular plasmons in several previous studies. But an investigation that combined side by side theoretical and experimental perspectives was needed, said study co-author Luca Bursi, a postdoctoral research associate and theoretical physicist in the research group of study co-designer and co-author Peter Nordlander.

“Molecular excitations are a ubiquity in nature and very well studied, especially for neutral PAHs, which have been considered as the standard of non-plasmonic excitations in the past,” Bursi said. “Given how much is already known about PAHs, they were an ideal choice for further investigation of the properties of plasmonic excitations in systems as small as actual molecules, which represent a frontier of plasmonics.”

Lead co-author Kyle Chapkin, a Ph.D. student in applied physics in the Halas research group, said, “Molecular plasmonics is a new area at the interface between plasmonics and molecular chemistry, which is rapidly evolving. When plasmonics reach the molecular scale, we lose any sharp distinction of what constitutes a plasmon and what doesn’t. We need to find a new rationale to explain this regime, which was one of the main motivations for this study.”

In their native state, the PAHs that were studied — anthanthrene, benzo[ghi]perylene and perylene — are charge-neutral and cannot be excited into a plasmonic state by the visible wavelengths of light used in Chapkin’s experiments. In their anionic form, the molecules contain an additional electron, which alters their “ground state” and makes them plasmonically active in the visible spectrum. By exciting both the native and anionic forms of the molecules and comparing precisely how they behaved as they relaxed back to their ground states, Chapkin and Bursi built a solid case that the anionic forms do support molecular plasmons in the visible spectrum.

The key, Chapkin said, was identifying a number of similarities between the behavior of known plasmonic particles and the anionic PAHs. By matching both the timescales and modes for relaxation behaviors, the LANP team built up a picture of a characteristic dynamics of low-energy plasmonic excitations in the anionic PAHs.

“In molecules, all excitations are molecular excitations, but select excited states show some characteristics that allow us to draw a parallel with the well-established plasmonic excitations in metal nanostructures,” Bursi said.

“This study offers a window on the sometimes surprising behavior of collective excitations in few-atom quantum systems,” Halas said. “What we’ve learned here will aid our lab and others in developing quantum-plasmonic approaches for ultrafast color-changing glass, molecular-scale optoelectronics and nonlinear plasmon-mediated optics.”

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

Lifetime dynamics of plasmons in the few-atom limit by Kyle D. Chapkin, Luca Bursi, Grant J. Stec, Adam Lauchner, Nathaniel J. Hogan, Yao Cui, Peter Nordlander, and Naomi J. Halas. PNAS September 11, 2018 115 (37) 9134-9139; published ahead of print August 27, 2018 DOI: https://doi.org/10.1073/pnas.1805357115

This paper is behind a paywall.

Change the shape of water with nanotubes

An August 24, 2018 news item on ScienceDaily describes a ‘shapeshifting’ water technique,

First, according to Rice University engineers, get a nanotube hole. Then insert water. If the nanotube is just the right width, the water molecules will align into a square rod.

Rice materials scientist Rouzbeh Shahsavari and his team used molecular models to demonstrate their theory that weak van der Waals forces between the inner surface of the nanotube and the water molecules are strong enough to snap the oxygen and hydrogen atoms into place.

Shahsavari referred to the contents as two-dimensional “ice,” because the molecules freeze regardless of the temperature. He said the research provides valuable insight on ways to leverage atomic interactions between nanotubes and water molecules to fabricate nanochannels and energy-storing nanocapacitors.

An August 24, 2018 Rice University news release (also on EurekAlert and received via email), which originated the news item, delves further,

Shahsavari and his colleagues built molecular models of carbon and boron nitride nanotubes with adjustable widths. They discovered boron nitride is best at constraining the shape of water when the nanotubes are 10.5 angstroms wide. (One angstrom is one hundred-millionth of a centimeter.)

The researchers already knew that hydrogen atoms in tightly confined water take on interesting structural properties. Recent experiments by other labs showed strong evidence for the formation of nanotube ice and prompted the researchers to build density functional theory models to analyze the forces responsible.

Shahsavari’s team modeled water molecules, which are about 3 angstroms wide, inside carbon and boron nitride nanotubes of various chiralities (the angles of their atomic lattices) and between 8 and 12 angstroms in diameter. They discovered that nanotubes in the middle diameters had the most impact on the balance between molecular interactions and van der Waals pressure that prompted the transition from a square water tube to ice.

“If the nanotube is too small and you can only fit one water molecule, you can’t judge much,” Shahsavari said. “If it’s too large, the water keeps its amorphous shape. But at about 8 angstroms, the nanotubes’ van der Waals force [if you’re not familiar with the term, see below the link and citation for my brief explanation] starts to push water molecules into organized square shapes.”

He said the strongest interactions were found in boron nitride nanotubes due to the particular polarization of their atoms.

Shahsavari said nanotube ice could find use in molecular machines or as nanoscale capillaries, or foster ways to deliver a few molecules of water or sequestered drugs to targeted cells, like a nanoscale syringe.

Lead author Farzaneh Shayeganfar, a former visiting scholar at Rice, is an instructor at Shahid Rajaee Teacher Training University in Tehran, Iran. Co-principal investigator Javad Beheshtian is a professor at Amirkabir University, Tehran.

Supercomputer resources were provided with support from the [US] National Institutes of Health and an IBM Shared Rice University Research grant.

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

First Principles Study of Water Nanotubes Captured Inside Carbon/Boron Nitride Nanotubes by Farzaneh Shayeganfar, Javad Beheshtian, and Rouzbeh Shahsavari. Langmuir, DOI: 10.1021/acs.langmuir.8b00856 Publication Date (Web): August 23, 2018

Copyright © 2018 American Chemical Society

This paper is behind a paywall.

For the purposes of the posting, van der Waals force(s) are weak adhesive forces measured at the nanoscale. Humans don’t feel them (we’re too big) but gecko lizards can exploit those forces which is why they are able to hang from the ceiling by a single toe.  There’s a more informed description here in the van der Waals force entry on Wikipedia.