Tag Archives: American Chemical Society

Cyborg bacteria to reduce carbon dioxide

This video is a bit technical but then it is about work being presented to chemists at the American Chemical Society’s (ACS) at the 254th National Meeting & Exposition Aug. 20 -24, 2017,

For a more plain language explanation, there’s an August 22, 2017 ACS news release (also on EurekAlert),

Photosynthesis provides energy for the vast majority of life on Earth. But chlorophyll, the green pigment that plants use to harvest sunlight, is relatively inefficient. To enable humans to capture more of the sun’s energy than natural photosynthesis can, scientists have taught bacteria to cover themselves in tiny, highly efficient solar panels to produce useful compounds.

“Rather than rely on inefficient chlorophyll to harvest sunlight, I’ve taught bacteria how to grow and cover their bodies with tiny semiconductor nanocrystals,” says Kelsey K. Sakimoto, Ph.D., who carried out the research in the lab of Peidong Yang, Ph.D. “These nanocrystals are much more efficient than chlorophyll and can be grown at a fraction of the cost of manufactured solar panels.”

Humans increasingly are looking to find alternatives to fossil fuels as sources of energy and feedstocks for chemical production. Many scientists have worked to create artificial photosynthetic systems to generate renewable energy and simple organic chemicals using sunlight. Progress has been made, but the systems are not efficient enough for commercial production of fuels and feedstocks.

Research in Yang’s lab at the University of California, Berkeley, where Sakimoto earned his Ph.D., focuses on harnessing inorganic semiconductors that can capture sunlight to organisms such as bacteria that can then use the energy to produce useful chemicals from carbon dioxide and water. “The thrust of research in my lab is to essentially ‘supercharge’ nonphotosynthetic bacteria by providing them energy in the form of electrons from inorganic semiconductors, like cadmium sulfide, that are efficient light absorbers,” Yang says. “We are now looking for more benign light absorbers than cadmium sulfide to provide bacteria with energy from light.”

Sakimoto worked with a naturally occurring, nonphotosynthetic bacterium, Moorella thermoacetica, which, as part of its normal respiration, produces acetic acid from carbon dioxide (CO2). Acetic acid is a versatile chemical that can be readily upgraded to a number of fuels, polymers, pharmaceuticals and commodity chemicals through complementary, genetically engineered bacteria.

When Sakimoto fed cadmium and the amino acid cysteine, which contains a sulfur atom, to the bacteria, they synthesized cadmium sulfide (CdS) nanoparticles, which function as solar panels on their surfaces. The hybrid organism, M. thermoacetica-CdS, produces acetic acid from CO2, water and light. “Once covered with these tiny solar panels, the bacteria can synthesize food, fuels and plastics, all using solar energy,” Sakimoto says. “These bacteria outperform natural photosynthesis.”

The bacteria operate at an efficiency of more than 80 percent, and the process is self-replicating and self-regenerating, making this a zero-waste technology. “Synthetic biology and the ability to expand the product scope of CO2 reduction will be crucial to poising this technology as a replacement, or one of many replacements, for the petrochemical industry,” Sakimoto says.

So, do the inorganic-biological hybrids have commercial potential? “I sure hope so!” he says. “Many current systems in artificial photosynthesis require solid electrodes, which is a huge cost. Our algal biofuels are much more attractive, as the whole CO2-to-chemical apparatus is self-contained and only requires a big vat out in the sun.” But he points out that the system still requires some tweaking to tune both the semiconductor and the bacteria. He also suggests that it is possible that the hybrid bacteria he created may have some naturally occurring analog. “A future direction, if this phenomenon exists in nature, would be to bioprospect for these organisms and put them to use,” he says.

For more insight into the work, check out Dexter Johnson’s Aug. 22, 2017 posting on his Nanoclast blog (on the IEEE [Institute of Electrical and Electronics Engineers] website),

“It’s actually a natural, overlooked feature of their biology,” explains Sakimoto in an e-mail interview with IEEE Spectrum. “This bacterium has a detoxification pathway, meaning if it encounters a toxic metal, like cadmium, it will try to precipitate it out, thereby detoxifying it. So when we introduce cadmium ions into the growth medium in which M. thermoacetica is hanging out, it will convert the amino acid cysteine into sulfide, which precipitates out cadmium as cadmium sulfide. The crystals then assemble and stick onto the bacterium through normal electrostatic interactions.”

I’ve just excerpted one bit, there’s more in Dexter’s posting.

Nanoparticle fertilizer and dreams of a new ‘Green’ revolution

There were hints even while it was happening that the ‘Green Revolution’ of the 1960s was not all it was touted to be. (For those who haven’t come across the term before, the Green Revolution was a better way to farm, a way that would feed everyone on earth. Or, that was the dream.)

Perhaps this time, they’ll be more successful. From a Jan. 15, 2017 news item on ScienceDaily, which offers a perspective on the ‘Green Revolution’ that differs from mine,

The “Green Revolution” of the ’60s and ’70s has been credited with helping to feed billions around the world, with fertilizers being one of the key drivers spurring the agricultural boom. But in developing countries, the cost of fertilizer remains relatively high and can limit food production. Now researchers report in the journal ACS Nano a simple way to make a benign, more efficient fertilizer that could contribute to a second food revolution.

A Jan. 25, 2017 American Chemical Society news release on EurekAlert, which originated the news item, expands on the theme,

Farmers often use urea, a rich source of nitrogen, as fertilizer. Its flaw, however, is that it breaks down quickly in wet soil and forms ammonia. The ammonia is washed away, creating a major environmental issue as it leads to eutrophication of water ways and ultimately enters the atmosphere as nitrogen dioxide, the main greenhouse gas associated with agriculture. This fast decomposition also limits the amount of nitrogen that can get absorbed by crop roots and requires farmers to apply more fertilizer to boost production. However, in low-income regions where populations continue to grow and the food supply is unstable, the cost of fertilizer can hinder additional applications and cripple crop yields. Nilwala Kottegoda, Veranja Karunaratne, Gehan Amaratunga and colleagues wanted to find a way to slow the breakdown of urea and make one application of fertilizer last longer.

To do this, the researchers developed a simple and scalable method for coating hydroxyapatite (HA) nanoparticles with urea molecules. HA is a mineral found in human and animal tissues and is considered to be environmentally friendly. In water, the hybridization of the HA nanoparticles and urea slowly released nitrogen, 12 times slower than urea by itself. Initial field tests on rice farms showed that the HA-urea nanohybrid lowered the need for fertilizer by one-half. The researchers say their development could help contribute to a new green revolution to help feed the world’s continuously growing population and also improve the environmental sustainability of agriculture.

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

Urea-Hydroxyapatite Nanohybrids for Slow Release of Nitrogen by Nilwala Kottegoda, Chanaka Sandaruwan, Gayan Priyadarshana, Asitha Siriwardhana, Upendra A. Rathnayake, Danushka Madushanka Berugoda Arachchige, Asurusinghe R. Kumarasinghe, Damayanthi Dahanayake, Veranja Karunaratne, and Gehan A. J. Amaratunga. ACS Nano, Article ASAP DOI: 10.1021/acsnano.6b07781 Publication Date (Web): January 25, 2017

Copyright © 2017 American Chemical Society

This paper is open access.

Curcumin: a scientific literature review concludes health benefits may be overstated

Given the number of times I’ve featured ‘curcumin research’, it seems only right to include this latest work. A Jan. 11, 2017 American Chemical Society (ACS) news release (also on EurekAlert) describes the results of a review of the scientific literature on curcumin’s (a constituent of turmeric) medicinal effectiveness,

Curcumin, a compound in turmeric, continues to be hailed as a natural treatment for a wide range of health conditions, including cancer and Alzheimer’s disease. But a new review of the scientific literature on curcumin has found it’s probably not all it’s ground up to be. The report in ACS’ Journal of Medicinal Chemistry instead cites evidence that, contrary to numerous reports, the compound has limited — if any — therapeutic benefit.

Turmeric, a spice often added to curries and mustards because of its distinct flavor and color, has been used for centuries in traditional medicine. Since the early 1990’s, scientists have zeroed in on curcumin, which makes up about 3 to 5 percent of turmeric, as the potential constituent that might give turmeric its health-boosting properties. More than 120 clinical trials to test these claims have been or are in the process of being run by clinical investigators. To get to the root of curcumin’s essential medicinal chemistry, the research groups of Michael A. Walters and Guido F. Pauli teamed up to extract key findings from thousands of scientific articles on the topic.

The researchers’ review of the vast curcumin literature provides evidence that curcumin is unstable under physiological conditions and not readily absorbed by the body, properties that make it a poor therapeutic candidate. Additionally, they could find no evidence of a double-blind, placebo-controlled clinical trial on curcumin to support its status as a potential cure-all. But, the authors say, this doesn’t necessarily mean research on turmeric should halt [emphasis mine]. Turmeric extracts and preparations could have health benefits, although probably not for the number of conditions currently touted. The researchers suggest that future studies should take a more holistic approach to account for the spice’s chemically diverse constituents that may synergistically contribute to its potential benefits.

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

The Essential Medicinal Chemistry of Curcumin by Kathryn M. Nelson, Jayme L. Dahlin, Jonathan Bisson, James Graham, Guido F. Pauli, and Michael A. Walters. J. Med. Chem., Article ASAP DOI: 10.1021/acs.jmedchem.6b00975 Publication Date (Web): January 11, 2017

Copyright © 2017 American Chemical Society

This paper is open access.

Mostafa El-Sayed: 2016 Priestly medalist

A Dec. 19, 2016 American Chemical Society news release on EurekAlert announces a video interview with Mostafa El-Sayed, winner of the American Chemical Society’s highest honor,

It’s difficult to sum up Mostafa El-Sayed’s nearly 60-year career as a chemist in just a few sentences. He uses lasers and other tools to better understand the properties and behavior of molecules and the nanoscale world. He is a pioneer in the use of nanomedicine to fight cancer. He even has a spectroscopy rule named after him: the “El-Sayed rule.” For all of these reasons and more, El-Sayed received the Priestley Medal in 2016, the highest honor given by the American Chemical Society. His work is the focus of the latest episode of ACS’ Prized Science series, available here: https://youtu.be/Vm8OBZuy-Fk.

I’ve embedded the interview here,


Sniffing for art conservation

The American Chemical Society (ACS) has produced a video titled, “How that ‘old book smell’ could save priceless artifacts” according to their Sept. 6, 2016 news release on EurekAlert,

Odor-detecting devices like Breathalyzers have been used for years to determine blood-alcohol levels in drunk drivers. Now, researchers are using a similar method to sniff out the rate of decay in historic art and artifacts. By tracking the chemicals in “old book smell” and similar odors, conservators can react quickly to preserve priceless art and artifacts at the first signs of decay. In this Speaking of Chemistry, Sarah Everts explains how cultural-heritage science uses the chemistry of odors to save books, vintage jewelry and even early Legos. …

Here’s the video,

Heritage Smells, the UK project mentioned in the video, is now completed but it was hosted by the University of Strathclyde and more project information can be found here.

Nanoparticles could make blood clot faster

It was the 252nd meeting for the American Chemical Society from Aug. 21 – 25, 2016 and that meant a flurry of news about the latest research. From an Aug. 23, 2016 news item on Nanowerk,

Whether severe trauma occurs on the battlefield or the highway, saving lives often comes down to stopping the bleeding as quickly as possible. Many methods for controlling external bleeding exist, but at this point, only surgery can halt blood loss inside the body from injury to internal organs. Now, researchers have developed nanoparticles that congregate wherever injury occurs in the body to help it form blood clots, and they’ve validated these particles in test tubes and in vivo [animal testing].

The researchers will present their work today [Aug. 22, 2016] at the 252nd National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 9,000 presentations on a wide range of science topics.

An Aug. 22, 2016 American Chemical Society (ACS) news release (also on EurekAlert), which originated the news item, provided more detail,

“When you have uncontrolled internal bleeding, that’s when these particles could really make a difference,” says Erin B. Lavik, Sc.D. “Compared to injuries that aren’t treated with the nanoparticles, we can cut bleeding time in half and reduce total blood loss.”

Trauma remains a top killer of children and younger adults, and doctors have few options for treating internal bleeding. To address this great need, Lavik’s team developed a nanoparticle that acts as a bridge, binding to activated platelets and helping them join together to form clots. To do this, the nanoparticle is decorated with a molecule that sticks to a glycoprotein found only on the activated platelets.

Initial studies suggested that the nanoparticles, delivered intravenously, helped keep rodents from bleeding out due to brain and spinal injury, Lavik says. But, she acknowledges, there was still one key question: “If you are a rodent, we can save your life, but will it be safe for humans?”

As a step toward assessing whether their approach would be safe in humans, they tested the immune response toward the particles in pig’s blood. If a treatment triggers an immune response, it would indicate that the body is mounting a defense against the nanoparticle and that side effects are likely. The team added their nanoparticles to pig’s blood and watched for an uptick in complement, a key indicator of immune activation. The particles triggered complement in this experiment, so the researchers set out to engineer around the problem.

“We made a battery of particles with different charges and tested to see which ones didn’t have this immune-response effect,” Lavik explains. “The best ones had a neutral charge.” But neutral nanoparticles had their own problems. Without repulsive charge-charge interactions, the nanoparticles have a propensity to aggregate even before being injected. To fix this issue, the researchers tweaked their nanoparticle storage solution, adding a slippery polymer to keep the nanoparticles from sticking to each other.

Lavik also developed nanoparticles that are stable at higher temperatures, up to 50 degrees Celsius (122 degrees Fahrenheit). This would allow the particles to be stored in a hot ambulance or on a sweltering battlefield.

In future studies, the researchers will test whether the new particles activate complement in human blood. Lavik also plans to identify additional critical safety studies they can perform to move the research forward. For example, the team needs to be sure that the nanoparticles do not cause non-specific clotting, which could lead to a stroke. Lavik is hopeful though that they could develop a useful clinical product in the next five to 10 years.

It’s not unusual for scientists to give an estimate of 5 – 10 years before their science reaches the market.  Another popular range is 3 – 5 years.

Eggshell-based bioplastics

Adding eggshell nanoparticles to a bioplastic (shown above) increases the strength and flexibility of the material, potentially making it more attractive for use in the packaging industry. Credit: Vijaya Rangari/Tuskegee University

Adding eggshell nanoparticles to a bioplastic (shown above) increases the strength and flexibility of the material, potentially making it more attractive for use in the packaging industry. Credit: Vijaya Rangari/Tuskegee University

A March 15, 2016 news item on Nanowerk describes the research,

Eggshells are both marvels and afterthoughts. Placed on end, they are as strong as the arches supporting ancient Roman aqueducts. Yet they readily crack in the middle, and once that happens, we discard them without a second thought. But now scientists report that adding tiny shards of eggshell to bioplastic could create a first-of-its-kind biodegradable packaging material that bends but does not easily break.

The researchers present their work today [March 15, 2016] at the 251st National Meeting & Exposition of the American Chemical Society (ACS).

A March 15, 2016 ACS news release (also on EurekAlert), which originated the news item, describes the work further,

“We’re breaking eggshells down into their most minute components and then infusing them into a special blend of bioplastics that we have developed,” says Vijaya K. Rangari, Ph.D. “These nano-sized eggshell particles add strength to the material and make them far more flexible than other bioplastics on the market. We believe that these traits — along with its biodegradability in the soil — could make this eggshell bioplastic a very attractive alternative packaging material.”

Worldwide, manufacturers produce about 300 million tons of plastic annually. Almost 99 percent of it is made with crude oil and other fossil fuels. Once it is discarded, petroleum-based plastics can last for centuries without breaking down. If burned, these plastics release carbon dioxide into the atmosphere, which can contribute to global climate change.

As an alternative, some manufacturers are producing bioplastics — a form of plastic derived from cornstarch, sweet potatoes or other renewable plant-based sources — that readily decompose or biodegrade once they are in the ground. However, most of these materials lack the strength and flexibility needed to work well in the packaging industry. And that’s a problem since the vast majority of plastic is used to hold, wrap and encase products. So petroleum-based materials continue to dominate the market, particularly in grocery and other retail stores, where estimates suggest that up to a trillion plastic bags are distributed worldwide every year.

To find a solution, Rangari, graduate student Boniface Tiimob and colleagues at Tuskegee University experimented with various plastic polymers. Eventually, they latched onto a mixture of 70 percent polybutyrate adipate terephthalate (PBAT), a petroleum polymer, and 30 percent polylactic acid (PLA), a polymer derived from cornstarch. PBAT, unlike other oil-based plastic polymers, is designed to begin degrading as soon as three months after it is put into the soil.

This mixture had many of the traits that the researchers were looking for, but they wanted to further enhance the flexibility of the material. So they created nanoparticles made of eggshells. They chose eggshells, in part, because they are porous, lightweight and mainly composed of calcium carbonate, a natural compound that easily decays.

The shells were washed, ground up in polypropylene glycol and then exposed to ultrasonic waves that broke the shell fragments down into nanoparticles more than 350,000 times smaller than the diameter of a human hair. Then, in a laboratory study, they infused a small fraction of these particles, each shaped like a deck of cards, into the 70/30 mixture of PBAT and PLA. The researchers found that this addition made the mixture 700 percent more flexible than other bioplastic blends. They say this pliability could make it ideal for use in retail packaging, grocery bags and food containers — including egg cartons.

In addition to bioplastics, Rangari’s team is investigating using eggshell nanoparticles to enhance wound healing, bone regeneration and drug delivery.

Protecting Disney’s art with an artificial nose

Curators and conservators are acutely aware of how fragile artworks (see my Jan. 10, 2013 posting about a show where curators watched helplessly as daguerreotypes deteriorated) can be so this new technology from Disney is likely to excite a lot of interest. From a March 14, 2016 news item on phys.org,

Original drawings and sketches from Walt Disney Animation Studio’s more than 90-year history—from Steamboat Willie through Frozen—traveled internationally for the first time this summer. This gave conservators the rare opportunity to monitor the artwork with a new state-of-the-art sensor. A team of researchers report today that they developed and used a super-sensitive artificial “nose,” customized specifically to detect pollutants before they could irreversibly damage the artwork.

Here’s a sample of the art work,

Caption: To protect works of art, including this image of Disney's Steamboat Willie, scientists developed an optoelectronic "nose" to sniff out potentially damaging compounds in pollution. Credit: Steamboat Willie, 1928 Animation cel and background © Disney Enterprises, Inc. Courtesy of Walt Disney Animation Research Library

Caption: To protect works of art, including this image of Disney’s Steamboat Willie, scientists developed an optoelectronic “nose” to sniff out potentially damaging compounds in pollution. Credit: Steamboat Willie, 1928 Animation cel and background © Disney Enterprises, Inc. Courtesy of Walt Disney Animation Research Library

A March 14, 2016 American Chemical Society (ACS) news release (also on EurekAlert), provides more detail,

The researchers report on their preservation efforts at the 251st National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 12,500 presentations on a wide range of science topics.

“Many pollutants that are problematic for human beings are also problematic for works of art,” says Kenneth Suslick, Ph.D. For example, pollutants can spur oxidative damage and acid degradation that, in prints or canvases, lead to color changes or decomposition. “The ability to monitor how much pollution a drawing or painting is exposed to is an important element of art preservation,” he says.

However, works of art are susceptible to damage at far lower pollutant levels than what’s considered acceptable for humans. “The high sensitivity of artists’ materials makes a lot of sense for two reasons,” explains Suslick, who is at the University of Illinois at Urbana-Champaign. “Human beings are capable of healing, which, of course, works of art cannot do. Moreover, human beings have finite lifetimes, whereas ideally works of art should last for future generations.”

To protect valuable works of art from these effects, conservators enclose vulnerable pieces in sealed display cases. But even then, some artists’ materials may “exhale” reactive compounds that accumulate in the cases and damage the art. To counter the accumulation of pollutants, conservators often hide sorbent materials inside display cases that scrub potentially damaging compounds from the enclosed environment. But it is difficult to know precisely when to replace the sorbents.

Suslick, a self-proclaimed “museum hound,” figured he might have an answer. He had already invented an optoelectronic nose — an array of dyes that change color when exposed to various compounds. But it is used largely for biomedical purposes, and it can’t sniff out the low concentrations of pollutants that damage works of art. To redesign the nose with the aim of protecting artwork, he approached scientists at the Getty Conservation Institute (GCI), a private non-profit institution in Los Angeles that works internationally to advance art conservation practice. He proposed that his team devise a sensor several hundred times more sensitive than existing devices used for cultural heritage research. The collaboration took off, and the scientists built a keener nose.

At the time, GCI was involved in a research project with the Walt Disney Animation Research Library to investigate the impact of storage environment on their animation cels, which are transparent sheets that artists drew or painted on before computer animation was developed. Such research ultimately could help extend the life of this important collection. The new sensors would monitor levels of acetic acid and other compounds that emanate from these sheets.

Before the exhibit, “Drawn from Life: The Art of Disney Animation Studios,” hit the road on tour, Suslick recommended placing the sensors in discrete places to monitor the pollution levels both inside and outside of the sealed and framed artworks. If the sensors indicated pollution levels inside the sealed frames were rising, conservators traveling with the Disney exhibit would know to replace the sorbents. An initial analysis of sensor data showed that the sorbents were effective. Suslick says he expects to continue expanding the sensors’ applications in the field of cultural heritage.

Collaborators in the project include Maria LaGasse, a graduate student in Suslick’s lab; Kristen McCormick, art exhibitions and conservation manager at the Walt Disney Animation Research Library; Herant Khanjian, assistant scientist; and Michael Schilling, senior scientist at the Getty Conservation Institute.

I was able to find one museum exhibiting “Drawn from Life: The Art of Disney Animation Studios”; it was the Museum of China which hosted the show from June 30 – August 18, 2015. There are pictures of the exhibit at the Museum of China posted by Leon Ingram here on Behance.

Spermbot alternative for infertility issues

A German team that’s been working with sperm to develop a biological motor has announced it may have an alternative treatment for infertility, according to a Jan. 13, 2016 news item on Nanowerk,

Sperm that don’t swim well [also known as low motility] rank high among the main causes of infertility. To give these cells a boost, women trying to conceive can turn to artificial insemination or other assisted reproduction techniques, but success can be elusive. In an attempt to improve these odds, scientists have developed motorized “spermbots” that can deliver poor swimmers — that are otherwise healthy — to an egg. …

A Jan. 13, 2016 American Chemical Society (ACS) news release (*also on EurekAlert*), which originated the news item, expands on the theme,

Artificial insemination is a relatively inexpensive and simple technique that involves introducing sperm to a woman’s uterus with a medical instrument. Overall, the success rate is on average under 30 percent, according to the Human Fertilisation & Embryology Authority of the United Kingdom. In vitro fertilization can be more effective, but it’s a complicated and expensive process. It requires removing eggs from a woman’s ovaries with a needle, fertilizing them outside the body and then transferring the embryos to her uterus or a surrogate’s a few days later. Each step comes with a risk for failure. Mariana Medina-Sánchez, Lukas Schwarz, Oliver G. Schmidt and colleagues from the Institute for Integrative Nanosciences at IFW Dresden in Germany wanted to see if they could come up with a better option than the existing methods.

Building on previous work on micromotors, the researchers constructed tiny metal helices just large enough to fit around the tail of a sperm. Their movements can be controlled by a rotating magnetic field. Lab testing showed that the motors can be directed to slip around a sperm cell, drive it to an egg for potential fertilization and then release it. The researchers say that although much more work needs to be done before their technique can reach clinical testing, the success of their initial demonstration is a promising start.

For those who prefer to watch their news, there’s this,

This team got a flurry of interest in 2014 when they first announced their research on using sperm as a biological motor. Tracy Staedter in a Jan. 15, 2014 article for Discovery.com describes their then results,

To create these tiny robots, the scientists first had to catch a few. First, they designed microtubes, which are essentially thin sheets of titanium and iron — which have a magnetic property — rolled into conical tubes, with one end wider than the other. Next, they put the microtubes into a solution in a Petri dish and added bovine sperm cells, which are similar size to human sperm. When a live sperm entered the wider end of the tube, it became trapped down near the narrow end. The scientists also closed the wider end, so the sperm wouldn’t swim out. And because sperm are so determined, the trapped cell pushed against the tube, moving it forward.

Next, the scientists used a magnetic field to guide the tube in the direction they wanted it to go, relying on the sperm for the propulsion.

The quick swimming spermbots could use controlled from outside a person body to deliver payloads of drugs and even sperm itself to parts of the body where its needed, whether that’s a cancer tumor or an egg.

This work isn’t nanotechnology per se but it has been published in ACS Nano Letters. Here’s a link to and a citation for the paper,

Cellular Cargo Delivery: Toward Assisted Fertilization by Sperm-Carrying Micromotors by Mariana Medina-Sánchez, Lukas Schwarz, Anne K. Meyer, Franziska Hebenstreit, and Oliver G. Schmidt. Nano Lett., 2016, 16 (1), pp 555–561 DOI: 10.1021/acs.nanolett.5b04221 Publication Date (Web): December 21, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

*'(also on EurekAlert)’ text and link added Jan. 14, 2016.