All About Chemistry: Tec. Chem

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Uranium exposed

Hadian Taufiq, Sunday, February 8, 2009

US scientists have developed a way to tell if war veterans have been in contact with depleted uranium.

Tank

Exposure to depleted uranium in military equipment may be bad for soldier's health

Depleted uranium is a by-product of uranium enrichment for nuclear power plants. It has less uranium-235 isotope than natural uranium. It is used in a variety of materials, including tank armour and ammunition. There are concerns that it might be bad for the health of soldiers who are exposed to it through, for example, wounds or inhalation.

Todor Todorov, at the US Geological Survey in Denver, and colleagues analysed blood samples from US Gulf War I veterans who had been involved in friendly fire incidents. 'Depleted uranium exposure from the Gulf War and conflicts in the former Yugoslavia has been a health concern in the past decade for military and peace keeping forces,' says Todorov. Using inductively coupled plasma mass spectrometry, he measured the ratio of uranium isotopes in the blood samples. Because the isotope ratios for depleted and natural uranium are different, Todorov was able to work out the source of the uranium.

"Depleted uranium exposure from the Gulf War and conflicts in the former Yugoslavia has been a health concern in the past decade for military and peace keeping forces"

Other methods to identify uranium exposure analyse urine samples. Todorov explains that by using blood, he can gain information on depleted uranium transport rates in the body. 'This can be used to develop biokinetic models for depleted uranium exposure,' he says, adding that the method is simple, rapid and robust.

In the future, the team plans to focus on developing bioassays for measuring the level of uranium in semen so that the effects of depleted uranium exposure on reproductive health can be evaluated.

Madelaine Chapman

http://www.rsc.org/Publishing/ChemTech/Volume/2009/02/uranium_exposed.asp

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Microthrusters are go!

Hadian Taufiq,

Scientists have developed an efficient propulsion system for microspacecraft.

As satellites become smaller, scientists need more compact propulsion systems to guide microspacecraft through space. Ming-Hsun Wu, at National Cheng Kung University, Tainan, Taiwan, and Richard Yetter, at Pennsylvania State University, University Park, US, have made small propulsion devices called microthrusters that are ignited using electric energy.

Satellite

Microthrusters ignited with electric energy could be used to maintain satellites in their orbits

Usually microthrusters are ignited by raising the temperature of the propellant using heating elements until it catches fire. But heat energy can be lost from the system, making it inefficient. This is particularly significant on the microscale because of the large surface-to-volume ratios.

Instead, Wu and Yetter put electric energy directly into the liquid propellant, causing it to decompose and ignite at room temperature.

'This is the first time that electrolysis has been used as an ignition mechanism for a microscale liquid monopropellant microthruster,' explains Wu, 'and the results turned out to be pretty exciting.'

"This is truly an excellent demonstration of novel thinking and attention to detail"
- Frederick Dryer, Princeton University, US

Frederick Dryer, an expert on combustion science from Princeton University, US, is impressed by the results. 'This is truly an excellent demonstration of novel thinking and attention to detail. It is a real step forward in fabrication processes, use of novel fuel formulation, and ignition technologies for micropropulsion applications. In my opinion, the paper represents a seminal work in the micropropulsion field,' he enthuses.

While the current microthruster can be fired only once, Wu and Yetter plan to develop a microthruster that can be fired multiple times. Wu says the microthrusters could be used on microsatellites for maintaining spacecraft in assigned orbits and controlling their orientation.

Ruth Doherty

http://www.rsc.org/Publishing/ChemTech/Volume/2009/02/microthrusters.asp

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Polymers branch into data storage

Hadian Taufiq,

Scientists have harnessed the power of holography to store large amounts of data in a postage stamp-sized disc.

Craig Hawker, at the University of California, Santa Barbara, US, and colleagues designed photopolymers that can store up to 50 times more data than a DVD.

Data storage by photopolymerisation of dendritic monomers

When the highly branched molecules polymerise, the volume change is negligible so data can be stored and retrieved accurately

Unlike a DVD, which only uses a disc's surface, holographic data storage uses the whole volume of the disc. As a result, holography promises terabytes (1000 gigabytes) of storage capacity in a recording disc the size of a postage stamp, says Hawker. A typical DVD holds only 4.7 gigabytes.

Recently, researchers have investigated light-sensitive polymers - which are used to make the holograms seen in driving licences - for data storage. But these photopolymers shrink as the molecules polymerise during the recording process, making it difficult to accurately retrieve the recorded data.

Hawker overcame this problem by making a series of highly branched monomers. He showed that when the molecules polymerised, the volume change was much smaller than for previous photopolymers and so the shrinkage was negligible.

"This work illustrates the power of modern polymer synthesis to custom-design organic materials with advantageous properties"
- Stefan Hecht, Humboldt University, Berlin, Germany

'Of particular note is finding that a holographic media prepared using one of our monomers exhibits 50 times more storage capacity than a conventional DVD,' says Hawker. 'To reach the terabyte goal, you need to have very high efficiency and fidelity during the recording process.'

The polymer's refractive index, which is a measure of how much it reduces the speed of light passing through it, is key to increased storage capacity, explains Hawker. He is working on a system that combines a low refractive index scaffold with ultra-high refractive index monomers, which he expects to show improved results.

'This work illustrates the power of modern polymer synthesis to custom-design organic materials with advantageous properties,' says Stefan Hecht, an expert in organic functional materials at Humboldt University, Berlin, Germany. 'By fine tuning the macromolecular architecture, Hawker and co-workers have created new high performance data storage materials overcoming limitations of conventional polymer chemistry.'

Sarah Corcoran

http://www.rsc.org/Publishing/ChemTech/Volume/2009/03/polymer_data_storage.asp

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Instant insight: Scratching at the surface of biosensors

Hadian Taufiq,

Justin Gooding, Till Böcking and Kris Kilian of the University of New South Wales discuss how surface chemistry lets porous silicon biosensors fulfil their promise.

Porous silicon photonic crystals

Porous silicon photonic crystals can be tuned to reflect different colours of light by altering their periodicity

A biosensor is a device for detecting an analyte that combines biological molecules selective for the analyte with a detector known as a signal transducer. The biological molecules provide the sensor with its selectivity while the transducer determines the extent of the interaction between the biomolecules and the analyte. The transducer converts this information into a signal that a person can read, such as a colour change. Examples of successful biosensors include glucose meters used by diabetics and home pregnancy test kits.

"Examples of successful biosensors include glucose meters used by diabetics and home pregnancy test kits"

Apart from being selective for the target analyte, biosensors should be miniaturisable, portable, robust and sensitive. In vivo biosensors also need to be biocompatible and non-toxic, so ideally a biosensor would not need an implanted power source to operate it. Porous silicon has emerged as an attractive option for biosensors. In fact, it would be the perfect material, in particular for in vivo biosensors, if it could be stabilised against degradation.

Porous silicon is made by electrochemically drilling nanoscale pores into silicon wafers in ethanolic hydrogen fluoride solutions, a process known as etching. The pore size can be adjusted from microporous to macroporous by varying the etching conditions; most biosensing applications use mesoporous materials, which have a pore size between two and 50 nanometres. By varying the current density during etching, the silicon's porosity can be altered to produce 1D periodic structures, known as photonic crystals, that reflect or transmit light at precisely defined wavelengths.

"Absorption or desorption of molecules on to the pore walls in a photonic crystal affects the optical properties of the crystal, making porous silicon an ideal label-free transducer for biosensors"

Absorption or desorption molecules on to the pore walls in a photonic crystal alters the wavelength of light that the crystal reflects, making porous silicon an ideal transducer for biosensors. In addition, the wavelength range can be tuned to the visible or infrared range simply by altering the crystal's periodicity. Porous silicon transducers require no power to operate and, if tuned to reflect near infrared light, which can penetrate living tissues, can be monitored directly through the skin using silicon diode detectors.

Porous silicon has an even more attractive feature over other photonic crystals for biosensing. In the body, mesoporous silicon degrades to orthosilicic acid, the most common naturally occurring form of silicon. Because this product is benign, porous silicon biosensors do not have to be removed from the body. But the degradation of porous silicon also results in a change in optical properties, which of has severely compromised the application of porous silicon in biosensing.

An elegant solution to this hurdle involves using surface chemistry to stabilise the materials. For example, by forming a monolayer of alkyl chains linked to the surface by strong silicon-carbon bonds, scientists have dramatically increased the stability of porous silicon. The same surface chemistry has also allowed researchers to explore a host of strategies for immobilising biological molecules onto the pore surfaces. These advances take us a significant step forward in applying this powerful material to biosensing and revitalise the quest for implantable smart materials.

http://www.rsc.org/Publishing/ChemTech/Volume/2009/02/biosensors.asp

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Interview: Mixing it up

Hadian Taufiq,

Steven Soper talks to Freya Mearns about interdisciplinary science and a little bit of luck

	Steven Soper is the William L and Patricia Senn, Jr Professor in the department of chemistry at Louisiana State University. He is also a professor of mechanical engineering and an adjunct professor of biological sciences. His research interests include biomicro- and bionanoelectrochemical systems, single molecule detection, and new bioassay developments. He is on the editorial board of Analyst.

What inspired you to become a scientist?
None of my family went to college or expressed an inclination to participate in any science-related area. So, being a scientist was off base for my entire family and something they did not understand when I first mentioned my professional interests. When I was in high school, I started taking some biology and physics classes and a little bit of chemistry. It was my teachers that set me on the road toward being a scientist and I am grateful for their mentoring and guidance. Many of my undergraduate college professors were also very helpful and encouraging, in particular James Wood and Ted Kuwana.

"I have just been very lucky to have such an understanding and supportive wife!"

When I went to college, my first degree was in psychology - I planned to be a psychiatrist. Then I decided to go back and get a degree in chemistry because I really enjoyed it. Afterwards I went to work in a research laboratory at a local company in Kansas City, Missouri; I was intrigued by some of the problems we were working on, so I decided to go back and get my PhD so that I could more fully understand the underlying chemical phenomena. I was married with a baby and I announced to my wife, 'Guess what: I'm going to go back to graduate school and I'm going to make $800 a month.' Then, I was given the opportunity to do a post doctoral fellowship at Los Alamos National Laboratory, New Mexico, under the direction of Richard Keller, who was doing single molecule detection. Los Alamos is a small isolated city in the mountains of New Mexico, but a great place to do some high-end science. This was a tremendous experience for me, because it gave me the opportunity to do single molecule work, which I am continuing today. After two years at Los Alamos, I decided to interview at a few universities with a view to becoming a college professor. After doing several interviews, I decided on Louisiana State University (LSU). There was never a concise plan - I just made all these decisions as I was moving along. I have just been very lucky to have such an understanding and supportive wife!

Why did you specialise in microfabricating devices for analysing biological molecules?
When I went to LSU in 1992 my intention was to do single molecule detection and ultrasensitive biological fluorescence measurements, especially related to genome analysis (I had done similar work at Los Alamos National Laboratory). But when I arrived, a new facility was opened: the Center for Advanced Microstructures and Devices. It's a synchrotron source where they do X-ray spectroscopy and X-ray lithography, but they also built a clean room to do micro- and nanofabrication. In 1993, when the first microchip electrophoresis paper by Andreas Manz and Jed Harrison appeared in Science, we merged the ideas in that paper with the resources at LSU to forge new ideas in developing microfluidic systems made from polymers. It was a little bit of luck that the resources became available just when the original paper came out.

What projects are you working on at the moment?
We've really spanned out into some intriguing areas. Our original concept was to do genome analysis and we're still doing that, but mostly for DNA sequencing applications. Now we have reached into areas that are still using genomes, but as biomarkers, for some really interesting applications. For example, we have projects in DNA forensics, looking at infectious diseases, and building point-of-care systems for developing and underdeveloped countries. We also have collaborations with people at various medical schools to do diagnostics for cancer-related diseases. We have a new project looking at building systems for doing drug discovery as well that was recently funded by the National Institutes of Health. The interesting aspect of this project is that now we are focused on merging our single molecule detection work with microfluidics and nanofluidics for compelling applications in biology and medicine.

What's going to be the next big thing in your field?

"Now the challenge is to develop integrated systems to carry out fully integrated assays"

People have worked extremely hard at developing microfluidic devices for specific tasks. Now the challenge, at least on the microfabrication side, is to develop integrated systems to carry out fully integrated assays. For example, we've been building devices that do solid phase extraction (to clean up samples), then the polymerase chain reaction (PCR), then a variety of devices on the back-end of the PCR step, for example electrophoresis, microarrays or some spectroscopy readout of PCR reactions. The idea is to build autonomous systems using all of these devices. So the next big challenge will be process integration. The other big project area is nanofabrication - building structures in the nanometre regime. People are starting to get a fairly good grasp on understanding the physics of what happens when you put biomolecules into confined environments that rival their molecular dimensions. Now the challenge is to take those unique opportunities evolving with nanofabrication capabilities and merge them with microfabrication to build logical interfaces between the macro, micro and nano worlds.

What is the secret to being a successful scientist?
I don't care what type of science you do, it's your students that are important - if they don't produce, you are dead in the water. If it was up to me to do all the experiments, I might publish one or two papers a year (if I was lucky). You need a great crop of students who are motivated, creative and intelligent. If students have those attributes, they're going to be successful, your group is going to be successful and you are going to be successful! Students drive the research productivity machinery. I also have a great group of colleagues in areas outside of my expertise that have been instrumental in our research efforts: in mechanical engineering, biological sciences and materials science.

Have your students and post docs primarily trained in chemistry or is there a real mix of backgrounds?
The majority of people coming into my lab do have a chemistry background but when they leave they have fairly good knowledge in biology and engineering as well. Nowadays chemists cannot afford to know only chemistry, especially analytical chemists. When they start working in my group, my students (and even postdocs) will take a class in biology to learn about clinical chemistry and DNA structure, and a class in engineering to learn about lithography (both micro- and nanofabrication techniques) and fluid dynamics. They also learn how to do computational simulations to help guide experimentation. We do a lot of simulations to help guide design before we go into the lab and start building something. That's really helped our productivity immensely.

Are the lines between the traditional sciences blurring now? Is it becoming easier to communicate?
No. Communication across disciplines that haven't been heavily engaged in cross-fertilisation is very difficult to come by. I have been working with people in mechanical engineering for over 10 years and it is only within the last two or three years that we have broken down some of the communication barriers. My students learn their jargon, their students learn chemistry jargon and we now know how to communicate. But these things take time. I still think this is a big problem. Everybody says, 'We're doing interdisciplinary science,' (which everyone should be doing) but I would argue that the only time you can really claim this is when you have joint publications and when your students are conversing with people outside chemistry on a regular basis. That's a great sign of interdisciplinary science.

If you weren't a scientist, what would you be?
This is going to sound mushy, but I couldn't really envision doing anything else. I just love what I do!

Solar power kills bacteria in water

Hadian Taufiq,

Scientists have improved solar water decontamination techniques in an attempt to reduce the spread of water borne diseases in developing countries.

Solar water disinfection is a simple way to kill bacteria in water. It is used by households in developing countries where safe drinking water is scarce. People fill plastic bottles with water and leave them in sunlight, where the UV radiation and increased water temperature kill the bacteria within six hours. But the method requires strong sunlight and can only treat limited volumes of water.

Water-filled plastic bottles for solar disinfection

Sunlight is used to disinfect water in plastic bottles but can only treat limited volumes

Kevin McGuigan from The Royal College of Surgeons in Ireland, Dublin, and colleagues investigated solar disinfection of Escherichia coli-contaminated water in large volume flow reactors. A pump circulated the water between a holding tank and a glass tube surrounded by solar collectors that focus the sun's energy onto the tube. They found that E. coli inactivation depends on the total dose of sunlight rather than the light's intensity. They also showed that the reactors can be ineffective because the bacteria receive an intermittent dose of radiation as they flow between the dark holding tank and the see-through tube. If the bacteria are not completely inactivated by the sunlight, the dark periods give them time to recover from the radiation damage, making them more resistant when reilluminated.

'For me, the major significance of the research is that these methods can be effective, but recalculating flow through solar disinfection reactors must be carefully designed in order to avoid the possibility of resistant sub-populations of pathogens remaining viable due to incomplete sunlight exposure,' says McGuigan.

"This work is an important contribution which points out potential advantages and limitations of solar disinfection"
- Cesar Pulgarin, Swiss Federal Institute of Technology, Lausanne, Switzerland

'This work is an important contribution which points out potential advantages and limitations of solar disinfection, depending on the type of solar photo reactor and operation mode,' comments Cesar Pulgarin, an expert in biological decontamination processes at the Swiss Federal Institute of Technology in Lausanne, Switzerland. 'It is also the first attempt that assesses the minimal UV dose required for complete bacterial inactivation by solar disinfection.'

The World Health Organization estimates that more than one billion people lack access to safe drinking water, resulting in millions of deaths each year from water-related diseases such as diarrhoea. McGuigan says he plans to introduce the flow reactor technology into developing countries, where he hopes it could provide emergency relief to communities affected by famine, flood and war.

Philippa Ross

http://www.rsc.org/Publishing/ChemTech/Volume/2009/03/solar_power_kills_bacteria.asp

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Issue 2 of Chemical Technology now published

Hadian Taufiq,

Issue 2 2009 of Chemical Technology is now available online. The complete issue can also be downloaded in pdf format.

Instant insight: Scratching at the surface

Justin Gooding and colleagues discuss how surface chemistry lets porous silicon biosensors fulfil their promise.

Interview: Mixing it up

Steven Soper talks to Freya Mearns about interdisciplinary science and a little bit of luck.

This issue's Application highlights include fluorescent drug delivery vehicles that can be used to monitor drug release.

Chemical Technology is free to view online and news items link directly to the original research articles, which are free to access for a limited period of time.

Issue 2

February

Downloadable Files

Chemical Technology issue 2 2009
PDF icon PDF (1355k)

PDF files require Link icon Adobe Acrobat Reader

http://www.rsc.org/Publishing/ChemTech/News/latest_issue_online.asp

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HIV diagnosis improved

Hadian Taufiq,

A cheaper and easier way to monitor HIV in patients could revolutionise global health care, according to scientists in the US.

The World Health Organization estimates that more than 33 million people worldwide have HIV. HIV destroys white blood cells called CD4+ T lymphocytes that are crucial for fighting disease. It also reduces the body's ability to replace these cells. Scientists use a technique called flow cytometry to monitor changes in patients' CD4+ levels - when they drop below 200 cells per microlitre, the patient is diagnosed with AIDS and prescribed anti-retroviral drugs. But flow cytometry requires expensive equipment and highly trained scientists to use it.

CD4+ T-cell counting microchip

The microfluidic device separates the monocytes from blood and counts the lymphocytes with high selectivity and sensitivity

Mehmet Toner and colleagues at Massachusetts General Hospital, Boston, have modified a microfluidic device they were previously working on to overcome its major pitfall - sample contamination with another type of white blood cell called monocytes. They developed an upstream monocyte depletion module, which separates monocytes from blood samples before the lymphocytes are counted. Using the module, Toner measured the lymphocyte count with higher selectivity and sensitivity than before. Toner says the device has 'the potential to be one of the holy grails of global health'.

"The device assertively contributes to point of care testing from whole blood and may additionally facilitate other on-chip integrated whole blood-based assays"
- Philip Day, University of Manchester, UK

'The device assertively contributes to point of care testing from whole blood and may additionally facilitate other on-chip integrated whole blood-based assays,' says Philip Day, a expert in tool miniaturisation for quantitative molecular biology from the University of Manchester, UK.

Toner says his device is simpler and cheaper than flow cytometry, meaning it could be used in the resource-scarce settings of developing countries. The method, combined with the recent fall in HIV drug prices, should lead to significant progress in the fight against HIV, he adds.

Jennifer Newton

http://www.rsc.org/Publishing/ChemTech/Volume/2009/03/HIV_diagnosis.asp

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