Tag Archives: Huiguang Zhu

Quantum dots cycling through the food chain

Rice University (Texas, US) researchers have published a study which follows quantum dot nanoparticles as they enter the water supply and are taken up by plant roots and leaves and eaten by caterpillars. From a Dec. 16, 2014 news item on ScienceDaily,

In one of the most comprehensive laboratory studies of its kind, Rice University scientists traced the uptake and accumulation of quantum dot nanoparticles from water to plant roots, plant leaves and leaf-eating caterpillars.

The study, one of the first to examine how nanoparticles move through human-relevant food chains, found that nanoparticle accumulation in both plants and animals varied significantly depending upon the type of surface coating applied to the particles. The research is available online in the American Chemical Society’s journal Environmental Science & Technology.

A Dec. 16, 2014 Rice University news release (also on EurekAlert), which originated the news item, provides insight into some of the issues being addressed with this research (Note: Links have been removed),

“With industrial use of nanoparticles on the rise, there are increasing questions about how they move through the environment and whether they may accumulate in high levels in plants and animals that people eat,” said study co-author Janet Braam, professor and chair of the Department of BioSciences at Rice.

Braam and colleagues studied the uptake of fluorescent quantum dots by Arabidopsis thaliana, an oft-studied plant species that is a relative of mustard, broccoli and kale. In particular, the team looked at how various surface coatings affected how quantum dots moved from roots to leaves as well as how the particles accumulated in leaves. The team also studied how quantum dots behaved when caterpillars called cabbage loopers (Trichoplusia ni) fed upon plant leaves containing quantum dots.

“The impact of nanoparticle uptake on plants themselves and on the herbivores that feed upon them is an open question,” said study first author Yeonjong Koo, a postdoctoral research associate in Braam’s lab. “Very little work has been done in this area, especially in terrestrial plants, which are the cornerstone of human food webs.”

Some toxins, like mercury and DDT, tend to accumulate in higher concentrations as they move up the food chain from plants to animals. It is unknown whether nanoparticles may also be subject to this process, known as biomagnification.

While there are hundreds of types of nanoparticles in use, Koo chose to study quantum dots, submicroscopic bits of semiconductors that glow brightly under ultraviolet light. The fluorescent particles — which contained cadmium, selenium, zinc and sulfur — could easily be measured and imaged in the tests. In addition, the team treated the surface of the quantum dots with three different polymer coatings — one positively charged, one negatively charged and one neutral.

“In industrial applications, nanoparticles are often coated with a polymer to increase solubility, improve stability, enhance properties and for other reasons,” said study co-author Pedro Alvarez, professor and chair of Rice’s Department of Civil and Environmental Engineering. “We expect surface coatings to play a significant role in whether and how nanomaterials may accumulate in food webs.”

Previous lab studies had suggested that the neutral coatings might cause the nanoparticles to aggregate and form clumps that were so large that they would not readily move from a plant’s roots to its leaves. The experiments bore this out. Of the three particle types, only those with charged coatings moved readily through the plants, and only the negatively charged particles avoided clumping altogether. The study also found that the type of coating impacted the plants’ ability to biodegrade, or break down, the quantum dots.

Koo and colleagues found caterpillars that fed on plants containing quantum dots gained less weight and grew more slowly than caterpillars that fed on untainted leaves. By examining the caterpillar’s excrement, the scientists were also able to estimate whether cadmium, selenium and intact quantum dots might be accumulating in the animals. Again, the coating played an important role.

“Our tests were not specifically designed to measure bioaccumulation in caterpillars, but the data we collected suggest that particles with positively charged coatings may accumulate in cells and pose a risk of bioaccumulation,” Koo said. “Based on our findings, more tests should be conducted to determine the extent of this risk under a broader set of ecological conditions.”

The researchers have a couple of images illustrating their work,

The buildup of fluorescent quantum dots in the leaves of Arabidopsis plants is apparent in this photograph of the plants under ultraviolet light. Credit: Y. Koo/Rice University

The buildup of fluorescent quantum dots in the leaves of Arabidopsis plants is apparent in this photograph of the plants under ultraviolet light. Credit: Y. Koo/Rice University

And, there’s a caterpillar,

Cabbage looper

Cabbage looper

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

Fluorescence Reports Intact Quantum Dot Uptake into Roots and Translocation to Leaves of Arabidopsis thaliana and Subsequent Ingestion by Insect Herbivores by Yeonjong Koo, Jing Wang, Qingbo Zhang, Huiguang Zhu, E. Wassim Chehab, Vicki L. Colvin, Pedro J. J. Alvarez, and Janet Braam. Environ. Sci. Technol., Just Accepted Manuscript DOI: 10.1021/es5050562 Publication Date (Web): December 1, 2014

Copyright © 2014 American Chemical Society

This paper is open access but you must be registered on the website.

One final thought about the research, it did take place in a laboratory environment and there doesn’t seem to have been any soil involved so the uptake can not be directly compared (as I understand matters) to the uptake characteristics where plant cultivation requires soil. This seems to have been a study involving hydroponic framing practices.

Vicki Colvin’s Rice University team create a super duper antioxidant from catalytic converters found in cars

It sounds like a very exciting development but so far all the talk is about potential in an Oct. 16, 2013 news item on Azonano,

Scientists at Rice University are enhancing the natural antioxidant properties of an element found in a car’s catalytic converter to make it useful for medical applications.

Rice chemist Vicki Colvin led a team that created small, uniform spheres of cerium oxide and gave them a thin coating of fatty oleic acid to make them biocompatible. The researchers say their discovery has the potential to help treat traumatic brain injury, cardiac arrest and Alzheimer’s patients and can guard against radiation-induced side effects suffered by cancer patients.

Their nanoparticles also have potential to protect astronauts from long-term exposure to radiation in space and perhaps even slow the effects of aging, they reported.

The Oct. 15, 2013 Rice University news release on EurekAlert, which originated the news item, describes the work in greater detail,

Cerium oxide nanocrystals have the ability to absorb and release oxygen ions — a chemical reaction known as reduction oxidation, or redox, for short. It’s the same process that allows catalytic converters in cars to absorb and eliminate pollutants.

The particles made at Rice are small enough to be injected into the bloodstream when organs need protection from oxidation, particularly after traumatic injuries, when damaging reactive oxygen species (ROS) increase dramatically.

The cerium particles go to work immediately, absorbing ROS free radicals, and they continue to work over time as the particles revert to their initial state, a process that remains a mystery, she said. The oxygen species released in the process “won’t be super reactive,” she said.

Colvin said cerium oxide, a form of the rare earth metal cerium, remains relatively stable as it cycles between cerium oxide III and IV. In the first state, the nanoparticles have gaps in their surface that absorb oxygen ions like a sponge. When cerium oxide III is mixed with free radicals, it catalyzes a reaction that effectively defangs the ROS by capturing oxygen atoms and turning into cerium oxide IV. She said cerium oxide IV particles slowly release their captured oxygen and revert to cerium oxide III, and can break down free radicals again and again.

Colvin said the nanoparticles’ tiny size makes them effective scavengers of oxygen.

“The smaller the particles, the more surface area they have available to capture free radicals,” Colvin said. “A gram of these nanoparticles can have the surface area of a football field, and that provides a lot of space to absorb oxygen.”

None of the cerium oxide particles made before Rice tackled the problem were stable enough to be used in biological settings, she said. “We created uniform particles whose surfaces are really well-defined, and we found a water-free production method to maximize the surface gaps available for oxygen scavenging.”

Colvin said it’s relatively simple to add a polymer coating to the 3.8-nanometer spheres. The coating is thin enough to let oxygen pass through to the particle, but robust enough to protect it through many cycles of ROS absorption.

In testing with hydrogen peroxide, a strong oxidizing agent, the researchers found their most effective cerium oxide III nanoparticles performed nine times better than a common antioxidant, Trolox, at first exposure, and held up well through 20 redox cycles.

“The next logical step for us is to do some passive targeting,” Colvin said. “For that, we plan to attach antibodies to the surface of the nanoparticles so they will be attracted to particular cell types, and we will evaluate these modified particles in more realistic biological settings.”

Colvin is most excited by the potential to help cancer patients undergoing radiation therapy.

“Existing radioprotectants have to be given in incredibly high doses,” she said. “They have their own side effects, and there are not a lot of great options.”

She said a self-renewing antioxidant that can stay in place to protect organs would have clear benefits over toxic radioprotectants that must be eliminated from the body before they damage good tissue.

“Probably the neatest thing about this is that so much of nanomedicine has been about exploiting the magnetic and optical properties of nanomaterials, and we have great examples of that at Rice,” Colvin said. “But the special properties of nanoparticles have rarely been leveraged in medical applications.

“What I like about this work is that it opens a part of nanochemistry — namely catalysis — to the medical world. Cerium III and IV are electron shuttles that have broad applications if we can make the chemistry accessible in a biological setting.

“And of all things, this humble material comes from a catalytic converter,” she said.

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

Antioxidant Properties of Cerium Oxide Nanocrystals as a Function of Nanocrystal Diameter and Surface Coating by Seung Soo Lee, Wensi Song, Minjung Cho, Hema L. Puppala, Phuc Nguyen, Huiguang Zhu, Laura Segatori, and Vicki L. Colvin. ACS Nano,  DOI: 10.1021/nn4026806 Publication Date (Web): September 30, 2013
Copyright © 2013 American Chemical Society

This article is behind a paywall.

Finally, here’s an image which illustrates a cerium oxide nanosphere,

Oleylamine (red dots) and oleac acid (blue) layers serve to protect a cerium oxide nanosphere that catalyzes reactive oxygen species by absorbing them and turning them into less-harmful molecules. The finding could help treat injuries, guard against radiation-induced side effects of cancer therapy and protect astronauts from space radiation. (Credit: Colvin Group/Rice University)

Oleylamine (red dots) and oleac acid (blue) layers serve to protect a cerium oxide nanosphere that catalyzes reactive oxygen species by absorbing them and turning them into less-harmful molecules. The finding could help treat injuries, guard against radiation-induced side effects of cancer therapy and protect astronauts from space radiation. (Credit: Colvin Group/Rice University)

Good luck to Colvin and her team as they try to take this exciting discovery from the laboratory to real life.

I have mentioned Colvin here before including this July 18, 2012 posting which features Colvin, as well as, silver nanoparticles and Neitzsche.