‘Nanorust’ and Clean Water
Looking back on the years I have lived in the central Asian country of Kyrgyzstan, one of my lasting memories takes place in the small, crowded kitchen of our home. Upon our first arrival to the country, my parents and I were strictly warned by other Korean expatriates that it was unsafe to consume tap water that had not been processed. Consequently, my family promptly learned and adopted the purification process. The task is simple, consisting of boiling, cooling, decanting, and filtration (aided by our faithful Brita® jug). Since drinking water is an every day necessity, this ritual has run its course in our kitchen on an endless loop for fourteen years to this very day. If I was bored, I could always count on finding a ten-gallon pot of cooling water on the kitchen stove, waiting to be filtered. All this to say, water is a daily essential, and clean water even more so. Yet many regions of the world do not have this luxury; in effect, countless lives are claimed each year by the harmful pollutants present in the drinking water. However, a recently discovered property of iron oxides may hold a promising application to alleviating the problem of water contamination around the globe.
Here in the United States, every municipal water system is accountable to Environmental Protection Agency (EPA) regulations to provide safe drinking water to each home.1 Nonetheless, there are many developing countries and cities that cannot afford such a system, and thus to pour a cup of tap water is perilous for their inhabitants. In a number of Asian countries groundwater — a key resource for rural communities — is contaminated with dangerous levels of harmful microorganisms, inorganic chemicals, and organic chemicals. A giant among these various contaminants is the inorganic chemical, arsenic.2 Arsenic – a colorless, odorless, and tasteless element – causes various health defects upon ingestions, including skin damage, failure of the circulatory system, and cancer.1 On March 2005, The World Bank and Water and Sanitation Program presented a report on their comprehensive study of groundwater in Asian countries. The study revealed that parts of Bangladesh, China, India, Vietnam, Nepal, and Myanmar were just a few of the numerous hotspots for arsenic contamination. Overall, an estimated sixty-five million people were subject to health risks due to critical levels of arsenic in water.2 “Crisis” understates the potentially deadly arsenic situation at hand in Asia, as well as many other parts of the world not mentioned. Furthermore, Asia is only one of many other regions facing this problem. The influence of arsenic contamination is so lethal and widespread that the word “crisis” understates the situation at hand.
Meanwhile in the western hemisphere, a handful of scientists at Rice University’s Center for Biological and Environmental Nanotechnology (CBEN) are studying a promising remedy for arsenic contamination. The key to this solution was the discovery of strange magnetic properties among nano-scale magnetite particles. Magnetite (Fe3O4) is an iron oxide, much like rust, so the term “nanorust” was coined for magnetite nano-particles. Whereas rust (FeO) only contains iron in +2 oxidation states, Fe3O4 has iron in both +2 and +3 states. Nanorust crystals are so tiny that they are measured in the scale of nanometers (10-9 meters). At this size, magnetite was found to behave differently under the influence of a magnetic field in comparison to its counterpart with more conventional dimensions. For instance, based on observations made on bulk material it would take an extraordinarily large magnetic field to extract magnetite nanoparticles suspended in a solution. Yet Dr. Vicki Colvin, the director of CBEN, and her colleagues discovered to their surprise that removing nanorust particles from a solution required only a small electric field. Dr. Colvin told Chemical and Engineering News, “We were surprised to find that we didn’t need large elecromagnets to move our nanoparticles, and in some cases, handheld magnets could do the trick.”3 Another property of nanorust is that it has a very high surface area per mass because the particles are so small. The principle here is simple. Picture a very large copper sphere and a very small copper sphere. Most of the atoms in the large sphere are inside the sphere, not on its surface; the opposite is true for the small sphere. Therefore, comparing a one kilogram copper sphere to a kilogram of nano-sized spheres will show that the latter mass has much more surface area. In the case of nanorust particles, a kilogram has enough surface area to cover an entire football field.4
So how exactly do the properties of nano-scale magnetite help solve the arsenic problem? Arsenic has a high affinity toward iron oxides. Regardless, the use of conventional-sized iron oxides for purifying water has largely proven to be impractical, inefficient, and tedious.4 On the other hand, using nanocrystals of iron oxide for the job is an entirely different matter. Due to its exceptional surface area (which translates to more binding spots for arsenic) a given mass of magnetite particles twelve nanometers in diameter can capture one hundred times more arsenic than the equal mass of the larger iron oxide counterparts used in filters today.5 Once all the arsenic has been collected by the magnetite, these nanoparticles are easily removed from the water using a simple hand magnet. In describing this process to Science Daily, Dr. Colvin claimed, “Arsenic contamination in drinking water is a global problem and while there are ways to remove arsenic, they require extensive hardware and high-pressure pumps that run on electricity . . . . Our approach is simple and requires no electricity.”6 The only problem is the cost; nanorust particles assembled from pure laboratory chemicals can be very expensive. Key ingredients for water soluble nanorust are rust (FeO) and a fatty acid mixture (oleic acid). Heating rust yields magnetite. A double layer coating of oleic acid is then applied to each magnetite nanoparticle; by doing so, the nanoparticles will not stick to one another but instead be dispersed throughout water. Cafer Yuvez, a graduate student working under Dr. Colvin, is developing a method to create nanorust particles using inexpensive household items such as rust, olive oil (source of fatty acid), drain opener, and vinegar. Once perfected, this method will drastically reduce the production cost of nanorust from $2,624 to $21.5 per kilogram.7 Perhaps one day millions of people threatened by arsenic will be saved by nanorust cooked up on their kitchen stoves.
References
1. Drinking water Contaminants. http://www.epa.gov/safewater/contaminants/index.html (accessed 03/20/08), part of United States Environmental Protection Agency.
2. Arsenic Contamination in Asia. http://siteresources.worldbank.org/INTSAREGTOPWATRES/Resources/ARSENIC_BRIEF.pdf (accessed 03/20/08), part of a World Bank and Water and Sanitation program Report.
3. Cleaning Water With ‘Nanorust’. http://pubs.acs.org/cen/news/84/i46/8446notw4.html (accessed 03/20/08), part of Chemical and Engineering News.
4. Merali, Zeeya. Cooking up ‘Nanorust’ Could Purify Water. http://technology.newscientist.com/article.ns?id=dn10496&print=true (accessed 03/20/08), part of New Scientist Tech.
5. Feder, Barnaby J. Rustlike Crystals Found to Cleanse Water of Arsenic Cheaply. http://www.nytimes.com/2006/11/10/science/10rust.html (accessed 03/20/08), part of The New York Times.
The Embryonic Stem Cell Controversy
Most innovative scientific ideas initially face vehement opposition, followed by a gradual process of testing and evolving into a universally accepted dogma. Religion and politics — and their delineation of ethics and morality — have historically played a large role in the scientific process, and in bioethics today, they continue to assume a large role in morally controversial topics, one of the most prominent of which is embryonic stem cell research. The current Embryonic Stem Cell (ESC) revolution was ignited by Dr. James A. Thompson at the University of Wisconsin in 1998. The call to explore stem cells’ potential to regenerate tissues and more effectively treat Parkinson’s, Alzheimer’s, among many other diseases, has sparked a great deal of political and ethical controversy. Due to the debate over the ethics of using fertilized embryos in stem cell research, this issue has also led to groundbreaking findings on the possibility of using other kinds of cells to derive the same benefits.
The isolation of the Human ESC was a great scientific achievement with an even greater therapeutic potential. An embryonic stem cell is defined as a stem cell derived from the inner cell mass at the blastocyst stage of a fertilized oocyte. The cells are considered pluripotent, because they posses the capacity to divide and produce cells derived from the three germ layers (ectoderm, endoderm, and mesoderm). However, ESCs are limited in their inability to differentiate into the trophoblasts, which give rise to the placenta. Scientists believe that one day damaged tissue will be regenerated by those “shimmering spheres of human potential” (National Geographic, July 2006) to spark a renaissance of life in damaged tissue.1 However, there are risks: if ESCs are left undifferentiated in the body, they can differentiate uncontrollably, causing a Teratoma, a benign tumor. On the other hand, ESCs may offer a cure for Parkinson’s, Alzheimer’s, Diabetes, cancer, Hemophilia, and many other diseases.
In light of the fact that ESCs have been the center of much controversy, useful insight may be gained through studying the history of religions and secular debate on the beginning of life. In scientific terms, an embryo is defined as the stage when the dividing cells in the recently-fertilized egg gain control of their cellular machinery by beginning to produce their own enzymes; this stage occurs in the cleaving cell one to two days after conception. The current Roman Catholic Church’s stand on the human status of the blastocyst is that “the ablation of the inner cell mass (ICM) of the blastocyst, which critically and irredeemably damages the human embryo, curtailing its development, is gravely immoral and consequently is gravely illicit”.2 However, this has not always been the stand of the Roman Catholic Church; until the twelfth century it believed in Saint Augustine’s doctrine of “the quickening” that stated the embryo acquires humanhood through the acquisition of sentience. From the twelfth century to 1869, the Church believed in Saint Thomas Aquinas’s doctrine of “delayed hominization,” which stated that of the vegetative, animal, and rational stages, the last stage must be reached for embryo to fully attain humanhood. In 1869, Pope Pius IX decreed the beginning of life at the moment of conception due to knowledge that fertilization involved sperm and eggs. Thus, for nearly 2,000 years The Church had accepted the doctrine of “late humanhood” in one form or another, and the new cannon has been in place for about 150 years. Just as the Roman Catholic Church has not been a picture of unwavering conviction on the status of life and its beginning, neither have other faiths such as Islam, Judaism, and protestant branches of Christianity in which religious and secular scholars are split on this issue.
Some regard ESC research as tantamount to abortion, claiming that the blastocyst is being destroyed. According to Anne Kiessling, a stem cell researcher, the irony of the situation is that when opponents of research on fertilized eggs and early embryonic development try to stop such research, they actually inhibit the scientific understanding of the process. This in turn impedes the development of new ways to prevent pregnancy, perpetuating the need for abortion itself.2 Many proponents of ESC research find that conferring humanhood to the original blastocyst is problematic because until it has reached the morula stage (14th day blastocyst), the blastocyst has the potential to split, forming twins. On this basis, they reason that it is at least counterintuitive for a person to split in two, so one cannot confer humanhood until the potential for a unique human is actually manifested in the embryo through a propensity to acquire a unique biological personality. Whether or not ESC research implies terminating life, one thing is certain: there are hundreds of thousands of frozen blastocysts in fertility clinics around the world destined to be destroyed.
Because of the ethical controversies regarding the use of fertilized embryos for the isolation of embryonic stem cells, scientists looked for a way to turn a somatic (or body) cell into a human ESC. In theory, all somatic cells in the body are the same because they contain the same number of chromosomes. The amount of gene expression guides the differentiation of cells along commitment pathways to their lineages: from embryonic to adult stem cells and then to somatic cells. In other words, genes are upregulated and downregulated in different sequences, with varying levels yielding a cell type. Therefore, it is theoretically possible to take a fibroblast (skin) cell and turn it into a pluripotent cell by inducing the expression of the necessary factors that match with the expression profile of ESC. The induction of pluripotency on fibroblasts was first performed in mice by two different research groups, creating high expectations for the possibility of reproducing the work with human fibroblasts. Then, on November 11, 2007, the research journals Cell and Science each published an article on the induction of pluripotency on human fibroblasts by two different independent research groups. This news made the headlines across the world as a monumental achievement in ESC research. Some scientists in the embryonic stem cell research community insist that this breakthrough is far from a replacement to embryonic stem cell research, and that the methods to induce pluripotency are problematic for therapeutic application in human beings.
Despite the controversies, it is indisputable that there lies a great potential in stem cell research to cure a myriad of diseases. The new research on fibroblasts is part of a strong social and scientific movement to make such treatments possible, and perhaps it marks a beginning of the end to the ethical controversy.
References
1. Rick Weiss. Stem Cells, The Power to Divide. National Geographic Magazine. July 2005.
2. Kiessling, A., Anderson, S.C. Human Embryonic Stem Cells (second edition). Jones & Bartlett: October 31, 2006.
Exploring Carbon Nanotubes
In a list of the most important materials in nanotechnology today, carbon nanotubes are ranked near the top.1 Consisting solely of carbon atoms linked in a hexagonal pattern, these cylindrical molecules are far longer than they are wide, similar to rods or ropes. The prefix nano- means one billionth, which refers to a nanotube’s diameter of a few nanometers. In part because of their unique size, shape, and structure, carbon nanotubes (CNTs) are exceedingly versatile. Proposed areas of application for CNTs range from electronics and semiconductors, to molecular-level microscopes and sensors, to hydrogen storage and batteries.2 However, CNTs’ special combination of strength, low density, and ductility has also led to speculation about their role as “superstrong materials”3 in structural applications, such as a “space elevator”4. Before these science fiction claims become engineering feats, basic questions about carbon nanotubes’ mechanical behavior must be answered. In his research over the past twelve years, Dr. Boris Yakobson, a Rice Professor in Materials Science, has tackled several fundamental questions concerning the failure of nanotubes and the behavior of dislocations. The materials science term “dislocation” refers to a line imperfection or defect in the arrangement of atoms in a CNT; dislocations are important because they affect a material’s mechanical properties.5
How do nanotubes fail?
Determining how carbon nanotubes fail, or lose their capacity to support loads, is a complicated yet important matter; it must be fully understood before nanotubes are used in structural applications. In the article “Assessing Carbon Nanotube Strength” Yakobson, along with then-postdoctoral student Traian Dumitrica and graduate student Ming Hua, used computer simulation to model CNTs and investigate their failure.
According to Yakobson, simulations are valuable because “in principle you have full access to the details of the structure.” He added that one of the advantages of simulations is that the researcher has full control over the experimental conditions and variables. With respect to carbon nanotube failure, some of the most pertinent variables include the level and duration of the applied load, as well as the nanotube’s temperature, diameter, and chiral angle – the angle ranging from 0 to 30 degrees that describes how a carbon nanotube is rolled up from a graphite sheet. In addition to affecting the nanotube’s strain (stretch) at failure, these variables also determine the process by which it breaks. Yakobson found that two different mechanisms can cause nanotube failure. At low temperatures, the mechanical failure dominates as the bonds between adjacent carbon atoms literally snap. On the other hand, high temperatures induce the bonds within the nanotube’s carbon hexagons to flip, causing the hexagons to become five- and seven-sided figures. This effect weakens the nanotube structure and initiates a sequence of processes that culminate in complete nanotube failure. Combining the results of numerical simulations and analytical techniques, Yakobson constructed a carbon nanotube strength map: a single figure that illustrates the relationship between the relevant variables, the failure mechanisms, and the failure strain (figure 2). The significance of Yakobson’s research led to its publication as the cover article for the April 18, 2006 issue of Proceedings of the National Academy of Sciences.
How do dislocations behave in carbon nanotubes?
Another area covered by Yakobson’s work was the study of dislocation behaviors. While dislocation dynamics in multiwalled carbon nanotubes might seem to be a subject only a materials scientist could love, this area of research has great bearing on CNT use in mechanical and electronic applications. Multiwalled carbon nanotubes (MWCNTs) can be visualized as many single-walled carbon nanotubes, arranged concentrically like tree-trunk rings and interacting with each other via weak intermolecular forces.6,7 Although somewhat difficult to visualize, dislocations — defects in the atomic structure of a CNT —can be viewed as objects that can move, climb, and collide with one another, leading to the term “dislocation dynamics.”
In his research on this topic, Yakobson collaborated with J.Y. Huang at Sandia National Laboratory and F. Ding, a research scientist in Yakobson’s group. Their experimental procedure involves heating a MWCNT to approximately 2000° C, which causes its dislocations to mobilize. Using a transmission electron microscope, they tracked the motion and interaction of these dislocations over time. Yakobson said that this powerful microscope gives the experimenters “nearly atomic resolution.” A resolving power of this magnitude creates spectacular images that reveal a rather odd phenomenon: one can observe a dislocation climbing a carbon nanotube wall and combining with a dislocation on an adjacent wall to form a larger dislocation loop, which then continues to climb (figure 3). If this process is repeated throughout the MWCNT, its entire structure becomes a mixture of ‘nanocracks’ and kinks. More importantly, adjacent walls are cross-linked together by covalent bonds, whereas formerly they were only weakly connected by van der Waals forces. Cross-linking is important because it “lock[s] the walls together in one entity,” Yakobson said. As a result, there is an increased possibility for transfer between walls, and current can be driven through the cross-linked junction. He also believes that cross-linking is somehow responsible for the mechanical strength in MWCNTs, because the concentric cylinders can no longer easily slide past one another.
Yakobson’s research is simultaneously old and new. It is old because subjects such as dislocation dynamics and material failure are well-understood for many materials. Yet, it is also ingenuous because knowledge in these fields cannot be extended easily to carbon nanotubes.8 Researchers in this field are treading on unexplored ground that will bring the nanotube a step closer toward its applications.
References
1.Arnall, A.H. Future Technologies, Today’s Choices: Nanotechnology, Artificial Intelligence and Robotics; A Technical, Political and Institutional Map of Emerging Technologies, Greenpeace Environmental Trust, London, 2003.
2.Collins, P.; Avouris, P. Scientific American 2000, 62-69.
3.Chae, H.; Kumar, S. Science 2008, 319, 908-909.
4.University of Delaware. Space Tourism To Rocket In This Century, Researchers Predict. http://www.sciencedaily.com/releases/2008/02/080222095432.htm (accessed 02/27/08), part of Science Daily. http://www.sciencedaily.com/ (accessed 02/27/08).
5.Dumitrica, T.; Hua, M.; Yakobson, B. Proc. Nat. Aca. Sci. 2006, 103, 6105-6109.
6.Cumings, J.; Zettl, A. Science 2000, 289, 602-604.
7.Baughman, R.,; Zakhidov, A.; de Heer, W. Science 2002, 297, 787-792.
8.Huang, J.Y.; Ding, F.; Yakobson, B. Physical Review Letters 2008, 100, 035503.
The Promise of Adult Neurogenesis
Contrary to popular belief, the number of neurons in the human body is not fixed at birth. Through a process called neurogenesis, stem cells continue to differentiate into neurons throughout adulthood at specific regions of the brain — namely the olfactory bulb and hippocampus. The olfactory bulb is responsible for smell, while the hippocampus plays a role in long-term memory. Neurons in the hippocampus proliferate with enough mental and physical exercise, but their purpose had long remained unknown. A recent study by a team of investigators at the Salk Institute in La Jolla, California, finally shows some promise of shedding light on this mystery. They created a method to genetically engineer mice to turn off the processes that are responsible for neurogenesis.
In an earlier study, researchers Ronald M. Evans, Ph.D., and Fred H. Gage, Ph.D., had previously discovered a crucial mechanism that kept adult neuronal stem cells in an undifferentiated, proliferative state.3,4 After learning more about its specific function, Dr. Chun-Li Zhang, postdoctoral fellow at the Salk Institute, was able to turn off this mechanism in mice. This procedure effectively suppressed neurogenesis in the hippocampus, allowing the scientists to identify how newborn neurons affect brain functions.
The altered mice were then put through a series of behavioral and cognitive tests, one of which yielded results that conflicted with those of the control population. The Morris water maze is used to study the formation of learning strategies and spatial memories. Mice placed in deep water try to find a submerged platform with the help of cues marked along the walls of the pool. As the test was repeated, a normal mouse remembered the cues in order to locate the platform with relative ease. On the contrary, the mice that were genetically engineered to lack neurogenesis showed slower improvement. These mice experienced significant difficulty in finding the submerged platform, and their performance declined as the task was made more demanding. Although these mice were slower at forming efficient strategies, their behavior was very similar to that of the control mice by the end of the experiment. “It’s not that they didn’t learn, they were just slower at learning the task and didn’t retain as much as their normal counterparts,” Zhang said in an interview with Science Daily.1
This study suggests that neurogenesis has a specific role in the long-term storage of spatial memory, the part of memory responsible for processing and recording information from the environment. “Whatever these new neurons are doing it is not controlling whether or not these animals learn. But these new cells are regulating the efficiency and the strategy that they use to solve the problem,” Gage explained to Science Daily.1
In previous studies, Gage and his team were able to show how certain activities trigger neurogenesis. For instance, increased mental and physical exercise led to an increased amount of stem cells differentiating into neurons.3 Many of these neurons did not survive, although continued stimulation increased the number that did. Zhang’s water maze study now provides an important tool for others to study the effects of decreased neurogenesis. Previous attempts using radiation and mitotic inhibitors shut down not just neurogenesis but all cell division, and thus led to contradictory results.
The significance of Zhang’s research on adult neurogenesis is well founded. There are over 5 million people in the U.S who suffer from Alzheimer’s disease and other neurodegenerative disorders. Studies such as these give hopes that there may be a way to influence memory function by stimulating neurogenesis with therapeutic drugs. When perfected, these methods will allow a debilitating disease, such as Alzheimer’s, to be cured with a drug, followed by physical and mental stimulation. Many neurodegenerative disorders have no cure, and symptoms can only be alleviated for a short period of time before damage becomes severe. These groundbreaking studies have the potential to save millions from the trauma of memory deterioration.
References
1. Science Daily. http://www.sciencedaily.com/releases/2008/01/080130150525.htm. (accessed Feb 26, 2008).
2. Shi Y, Chichung Lie D, Taupin P, Nakashima K, Ray J, Yu RT, Gage FH, Evans RM. Expression and function of orphan nuclear receptor TLX in adult neural stem cell. Nature. 1 Jan 2004.
3. Tashiro A, Makino H, Gage FH. Experience-specific functional modification of the dentate gyrus through adult neurogenesis: a critical period during an immature stage. The Journal of Neuroscience. 21 Mar 2007.
4. Zhang CL, Zou Y, He W, Gage FH, Evans RM. A role for adult TLX-positive neural stem cells in learning and behaviour. Nature. 21 Feb 2008.