Pocket chemistry: DNA helps glucose meters measure more than sugar

Glucose meters aren't just for diabetics anymore. Thanks to University of Illinois chemists, they can be used as simple, portable, inexpensive meters for a number of target molecules in blood, serum, water or food.

Chemistry professor Yi Lu and postdoctoral researcher Yu Xiang published their findings in the journal Nature Chemistry.

"The advantages of our method are high portability, low cost, wide availability and quantitative detection of a broad range of targets in medical diagnostics and environmental monitoring," Lu said. "Anyone could use it for a wide range of detections at home and in the field for targets they may care about, such as vital metabolites for a healthy living, contaminants in their drinking water or food, or potential disease markers."

A glucose meter is one of the few widely available devices that can quantitatively detect target molecules in a solution, a necessity for diagnosis and detection, but only responds to one chemical: glucose. To use them to detect another target, the researchers coupled them with a class of molecular sensors called functional DNA sensors.

Functional DNA sensors use short segments of DNA that bind to specific targets. A number of functional DNAs and RNAs are available to recognize a wide variety of targets.

They have been used in the laboratory in conjunction with complex and more expensive equipment, but Lu and Xiang saw the potential for partnering them with pocket glucose meters.

The DNA segments, immobilized on magnetic particles, are bound to the enzyme invertase, which can catalyze conversion of sucrose (table sugar) to glucose. The user adds a sample of blood, serum or water to the functional DNA sensor to test for drugs, disease markers, contaminants or other molecules. When the target molecule binds to the DNA, invertase is released into the solution. After removing the magnetic particle by a magnet, the glucose level of the sample rises in proportion to the amount of invertase released, so the user then can employ a glucose meter to quantify the target molecule in the original sample.

"Our method significantly expands the range of targets the glucose monitor can detect," said Lu, who also is affiliated with the Beckman Institute for Advanced Science and Technology and with the Frederick Seitz Materials Research Lab at U. of I. "It is simple enough for someone to use at home, without the high costs and long waiting period of going to the clinics or sending samples to professional labs."

The researchers demonstrated using functional DNA with glucose meters to detect cocaine, the disease marker interferon, adenosine and uranium. The two-step method could be used to detect any kind of molecule that a functional DNA or RNA can bind.

Next, the researchers plan to further simplify their method, which now requires users to first apply the sample to the functional DNA sensor and then to the glucose meter.

"We are working on integrating the procedures into one step to make it even simpler," Lu said. "Our technology is new and, given time, it will be developed into an even more user-friendly format."

Provided by University of Illinois at Urbana-Champaign (news : web)

Chemists examine solar energy and air purification

The abundant sunlight is no doubt making beachgoers happy this summer, but those working on their tans aren't the only beneficiaries. The sun's rays are also a key ingredient to going green.

Solar light can be used to help purify air and water and produce valuable chemicals that contribute to energy efficiency. A Rutgers–Camden professor says all that is possible through a process called photocatalysis.

"Photocatalysis is a chemical reaction that occurs under the influence of solar light," says Alexander Samokhvalov, an assistant professor of chemistry at Rutgers–Camden. "I'm researching the fundamental chemistry of how sunlight can drive chemical reactions."

In particular, the chemist is studying how water is broken down into its hydrogen and oxygen components using sunlight and a solid photocatalyst. Producing hydrogen-powered vehicles is an example of one "green" application of splitting water.

Samokhvalov is the recipient of the Cottrell Science Award from the Research Corporation for Science Advancement. The foundation provides funding for innovative scientific research and the development of academic scientists.

In addition to the two-year, $45,000 Cottrell award, Samokhvalov received a $5,000 grant from the Rutgers University Research Council for his work with photocatalysis.

Photocatalyst technology is receiving attention as an immediate means of reducing urban air pollution. Samokhvalov says come examples of this technology at work are self-cleaning windows, which chemically break down adsorbed dirt in sunlight, and portable air purifiers, like the one that sits in Samokhvalov's office on the Rutgers–Camden campus.

In both cases, the photocatalyst is titanium dioxide, or TiO2, which is commonly found in sunscreen because of its ability to absorb ultraviolet light. Samokhvalov says TiO2 utilizes ultraviolet light to remove or break down harmful air pollutants.

On exposure to sunlight, the titanium dioxide reacts with contaminants in water or air and breaks them down into harmless substances. The compound has other applications when used as a photocatalyst, like converting greenhouse gas into liquid clean fuels.

"By modifying and further developing this technology, we can continue to reduce pollution in our air and water," the Rutgers–Camden chemistry scholar says. "But what is acutely missing in many research papers on photocatalysis is how electrons in the solid photocatalyst actually behave upon absorption of light to drive chemical reactions. This is something I would like to investigate."

He continues, "It is of the fundamental interest to understand if electron transfer occurs in the direct vicinity of the atom that absorbs the energy of a photon, or if the chemical reaction occurs somewhere far from the place where the photon was actually absorbed. Modern scientific instrumentation, a bit of imagination and work in the lab may answer this question."

The Cottrell Science Award includes funding for an undergraduate summer research fellowship and will help fund the purchase of an apparatus used in the research.

Samokhvalov has several undergraduate students working with him on the project.

"I believe that it is important that the interested undergraduate researcher is engaged into explorative experimental work throughout academic year," he says.

Samokhvalov says, "The Cottrell Science Award is an endorsement of the increasing importance of undergraduate research in chemistry in the emerging fields of the clean and sustainable energy."

Provided by Rutgers University (news : web)

Massive enzyme footballs control sugar metabolism

 

Images 1-4 show the different arrangements of enzymes E2 (structural - green) and E3BP (metabolising - red) within the PDC structure. The PDC molecules can exist in any of these forms within the cell depending on the rate of metabolism required. Image 1, with the highest proportion of the E3BP enzyme, would promote the highest rate of metabolism and could play a key role in bringing blood sugar levels down to normal rates following a meal.

Neutrons have shown how massive enzyme complexes inside cells might determine whether sugar is burnt for energy or stored as fat. These findings will improve understanding of diabetes and a range of metabolic diseases.

Scientists using neutrons at the Institut Laue-Langevin (ILL) have shown how pyruvate dehydrogenase complexes (PDCs) could control the rate of sugar metabolism by actively changing their own composition. The research is published in the Biochemical Journal.

PDCs are found within all cell types from bacteria to mammals and are known to help regulate the level of sugar in the blood to meet the continuously changing metabolic demands of the body. The complexes have a unique, football-shaped central scaffold, forming a hollow ball with 12 open pentagonal faces. They are composed of 60 subunits made up of two related proteins. The first is a scaffolding enzyme that acts as the structural heart of the complex, whilst the second has binding role with a third enzyme (attached to the outside of the central football) to generate rapid metabolism.

Whilst the structure of the complex is well understood, the exact composition was undetermined. Most previous purification studies had suggested a ratio of 48 scaffold enzyme units to 12 binding units.

The team at the ILL synthesised human PDC in bacteria and identified the location of the two enzymes through low angle neutron scattering. This revealed a new, unexpected ratio of 40:20 in favour of the scaffold enzyme. However experiments on PDCs from cow heart cells confirmed the expected figure of 48:12.

With further mathematical modelling the team have shown that their synthesised PDC could vary its composition, with any ratio from 60:0 to 40:20 possible. This flexibility may explain why the PDC complex is so quick to react to changes in blood sugar levels, says Dr Phil Callow, an instrument scientist at ILL. “Our models show how the structural organisation of PDC could be fine-tuned through changes in its overall composition to promote maximal metabolic efficiency.”

These findings could provide vital information for future treatments of diseases caused by unusual blood sugar levels such as diabetes and those directly related to mutations in the PDC such as Biliary cirrhosis, a progressive form of liver inflammation.

Professor Gordon Lindsay, University of Glasgow: “Using neutron scattering at ILL, we have shown the potential of these football structures to vary their composition to allow the most efficient utilisation of sugars by the body and enables precise control of sugar breakdown. The next step is to see if this occurs naturally across different tissues of the body and in different living organisms.”

Andrew Harrison, ILL’s Director for Science: “ILL has a proud history carrying out fundamental research that underpins medical breakthroughs and potential new treatments. The PDC complexes studied by Dr Callow and his colleagues are too large for most other techniques. By using neutrons and the wide range of instruments available at ILL, they have given the medical world a new perspective on diseases that affect millions of people across the world.”

Provided by Institut Laue-Langevin

Nanotechnology: injections or sampling? New 'molecular syringes' under testing

 Which is better, a quick vertical jab on the buttock or the delicately soft entry of a blood sample? Waiting to find out "for what," some are already wondering "how" to use those tiny "molecular syringes" which are carbon nanotubes. With a diameter of less than one millionth of a millimetre (nanometre) and a maximum length of just a few millimetres, the first use that springs to mind when we think of this ethereal tubes -- the smallest ever made by man -- is as potential needles for injecting drugs or genes into sick cells. And if a syringe it is, we had better start thinking about how to use them.

A group of researchers at the Ciamician department of the University of Bologna (Unibo, Italy) has no doubt about it. The easiest and most natural way of penetrating a cell membrane with a carbon nanotube, in its simplest form, is at an angle which is almost flat against the membrane surface. Just as a nurse does to "find" a vein.

Siegfried Höfinger (Unibo) explains: "A flat entry offers the most favourable energy balance." The entry of the nano-needle is in fact twice as easy than at an angle of, say, 45°, and three times easier than vertical penetration. "We can even hypothesise that the nanotube takes on this position of its own free will when placed near the membrane," adds Tommaso Gallo, another of the young authors working on the study, which is in press in the scientific journal Biomaterials.

The scientists' doubts lie in the extreme difficulty in handling such small objects. "Probably no one is able to experimentally verify these phenomena yet," says Höfinger. The chemists from Bologna, part of Francesco Zerbetto's research group, have drawn their conclusions not from physical experiments but from theoretical simulations. Mathematical models which consider all the forces at stake and the physical and chemical properties of the elements involved, predicting their behaviour.

The encouraging aspect of the Unibo research, which also saw the participation of the Michigan Technological University and the Universidade do Porto, is that two independent simulations based on completely different theoretical approaches led to an identical response. Flat entry into the membrane is certainly preferable. The first simulation was based on the system's energy balance and the concept of "environmental free energy." The second simulation, on the other hand, is typically used to describe the behaviour of large molecules in solutions (solvents and polymers). It may be less accurate than the first, but it has the advantage of illustrating the dynamic and temporal evolution of the described phenomenon well.

To simplify the problem, the researchers considered the use of very short tubes, maximum 7 nanometres long, which could be fully included in the cell wall, which is around 5 nanometres thick. It was also seen that, once inside the membrane, the longer tubes tend to lie longitudinally, parallel to the surface. Carrying out the test with bundles of smaller tubes bound together, it was also demonstrated that compact bundles of tubes bound tightly to each other cause less cell damage.

The future that Höfinger sees for the nanotubes is not however that of molecular syringes, but of probes. Their physical properties, including their great electrical and thermal conductivity, make them particularly suited for exchanging information between the inside and outside of the cell. They may therefore also be used to test for certain substances and test certain processes beyond cell membranes. Probes or syringes, the scientist in any case feel comfortable in their role as molecular nurses, and are eager to keep on testing using all the new tools of the trade.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Universita di Bologna, via EurekAlert!, a service of AAAS.

Journal Reference:

Siegfried Höfinger, Manuel Melle-Franco, Tommaso Gallo, Andrea Cantelli, Matteo Calvaresi, José A.N.F. Gomes, Francesco Zerbetto. A computational analysis of the insertion of carbon nanotubes into cellular membranes. Biomaterials, 2011; DOI: 10.1016/j.biomaterials.2011.06.011