#Team develops ultra sensitive biosensor from molybdenite semiconductor Move over graphene. An atomically thin two-dimensional ultrasensitive semiconductor material for biosensing developed by researchers at UC Santa barbara promises to push the boundaries of biosensing technology in many fields from health care to environmental protection to forensic industries.
Based on molybdenum disulfide or molybdenite (Mos2) the biosensor materialsed commonly as a dry lubricanturpasses graphene's already high sensitivity offers better scalability
and lends itself to high-volume manufacturing. Results of the researchers'study have been published in ACS Nano.
This invention has established the foundation for a new generation of ultrasensitive and low-cost biosensors that can eventually allow single-molecule detectionhe holy grail of diagnostics
and bioengineering research said Samir Mitragotri co-author and professor of chemical engineering and director of the Center for Bioengineering at UCSB.
Detection and diagnostics are a key area of bioengineering research at UCSB and this study represents an excellent example of UCSB's multifaceted competencies in this exciting field.
The key according to UCSB professor of electrical and computer engineering Kaustav Banerjee who led this research is Mos2's band gap the characteristic of a material that determines its electrical conductivity.
Semiconductor materials have a small but nonzero band gap and can be switched between conductive and insulated states controllably.
The larger the band gap the better its ability to switch states and to insulate leakage current in an insulated state.
Mos2's wide band gap allows current to travel but also prevents leakage and results in more sensitive and accurate readings.
While graphene has attracted wide interest as a biosensor due to its two-dimensional nature that allows excellent electrostatic control of the transistor channel by the gate
and high surface-to-volume ratio the sensitivity of a graphene field-effect transistor (FET) biosensor is restricted fundamentally by the zero band gap of graphene that results in increased leakage current leading to reduced sensitivity explained Banerjee
who is also the director of the Nanoelectronics Research Lab at UCSB. Graphene has been used among other things to design FETSEVICES that regulate the flow of electrons through a channel via a vertical electric field directed into the channel by a terminal called a gate.
In digital electronics these transistors control the flow of electricity throughout an integrated circuit and allow for amplification and switching.
In the realm of biosensing the physical gate is removed and the current in the channel is modulated by the binding between embedded receptor molecules and the charged target biomolecules to
which they are exposed. Graphene has received wide interest in the biosensing field and has been used to line the channel
and act as a sensing element whose surface potential (or conductivity) can be modulated by the interaction (known as conjugation) between the receptor and target molecules that results in net accumulation of charges over the gate region.
However said the research team despite graphene's excellent characteristics its performance is limited by its zero band gap.
Electrons travel freely across a graphene FETENCE it cannot be switched offhich in this case results in current leakages and higher potential for inaccuracies.
Much research in the graphene community has been devoted to compensating for this deficiency either by patterning graphene to make nanoribbons
or by introducing defects in the graphene layerr using bilayer graphene stacked in a certain pattern that allows band gap opening upon application of a vertical electric fieldor better control and detection of current.
Enter Mos2 a material already making waves in the semiconductor world for the similarities it shares with graphene including its atomically thin hexagonal structure and planar nature as well as
what it can do that graphene can't: act like a semiconductor. Monolayer or few-layer Mos2 have a key advantage over graphene for designing an FET biosensor:
They have a relatively large and uniform band gap (1. 2-1. 8 ev depending on the number of layers) that significantly reduces the leakage current
and increases the abruptness of the turn-on behavior of the FETS thereby increasing the sensitivity of the biosensor said Banerjee.
Additionally according to Deblina Sarkar a Phd student in Banerjee's lab and the lead author of the article two-dimensional Mos2 is relatively simple to manufacture.
While one-dimensional materials such as carbon nanotubes and nanowires also allow excellent electrostatics and at the same time possess band gap they are not suitable for low-cost mass production due to their process complexities she said.
Moreover the channel length of Mos2 FET biosensor can be scaled down to the dimensions similar to those of small biomolecules such as DNA
or small proteins still maintaining good electrostatics which can lead to high sensitivity even for detection of single quanta of these biomolecular species she added.
In fact atomically thin Mos2 provides the best of everything: great electrostatics due to their ultra-thin body scalability (due to large band gap) as well as patternability due to their planar nature that is essential for high-volume manufacturing said Banerjee.
The Mos2 biosensors demonstrated by the UCSB team have provided already ultrasensitive and specific protein sensing with a sensitivity of 196 even at 100 femtomolar (a billionth of a millionth of a mole) concentrations.
This protein concentration is similar to one drop of milk dissolved in a hundred tons of water.
An Mos2-based ph sensor achieving sensitivity as high as 713 for a ph change by one unit
along with efficient operation over a wide ph range (3-9) is demonstrated also in the same work.
This transformative technology enables highly specific low-power high-throughput physiological sensing that can be multiplexed to detect a number of significant disease-specific factors in real time commented Scott Hammond executive director of UCSB's Translational Medicine
Research Laboratories. Biosensors based on conventional FETS have been gaining momentum as a viable technology for the medical forensic
and security industries since they are cost-effective compared to optical detection procedures. Such biosensors allow for scalability
and label-free detection of biomoleculesemoving the step and expense of labeling target molecules with florescent dye.
In essence continued Hammond the promise of true evidence-based personalized medicine is finally becoming reality. This demonstration is said quite remarkable Andras Kis professor at École Polytechnique Fédérale de Lausanne in Switzerland and a leading scientist in the field of 2d materials and devices.
At present the scientific community worldwide is actively seeking practical applications of 2d semiconductor materials such as Mos2 nanosheets.
Professor Banerjee and his team have identified a breakthrough application of these nanomaterials and provided new impetus for the development of low-power
and low-cost ultrasensitive biosensors continued Kis who is connected not to the project. Explore further: New rapid synthesis developed for bilayer graphene and high-performance transistors More information:
ACS Nano pubs. acs. org/doi/abs/10.1021/nn500914 i
#Atomically thin material opens door for integrated nanophotonic circuits A new combination of materials can efficiently guide electricity
and light along the same tiny wire a finding that could be a step towards building computer chips capable of transporting digital information at the speed of light.
Reporting today in The Optical Society's (OSA) high-impact journal Optica optical and material scientists at the University of Rochester
and Swiss Federal Institute of technology in Zurich describe a basic model circuit consisting of a silver nanowire and a single-layer flake of molybendum disulfide (Mos2).
Using a laser to excite electromagnetic waves called plasmons at the surface of the wire the researchers found that the Mos2 flake at the far end of the wire generated strong light emission.
Going in the other direction as the excited electrons relaxed they were collected by the wire and converted back into plasmons
which emitted light of the same wavelength. We have found that there is pronounced nanoscale light-matter interaction between plasmons
and atomically thin material that can be exploited for nanophotonic integrated circuits said Nick Vamivakas assistant professor of quantum optics and quantum physics at the University of Rochester and senior author of the paper.
Typically about a third of the remaining energy would be lost for every few microns (millionths of a meter) the plasmons traveled along the wire explained Kenneth Goodfellow a graduate student at Rochester's Institute of Optics
and lead author of the Optica paper. It was surprising to see that enough energy was left after the round-trip said Goodfellow.
Photonic devices can be much faster than electronic ones but they are bulkier because devices that focus light cannot be miniaturized nearly as well as electronic circuits said Goodfellow.
The new results hold promise for guiding the transmission of light and maintaining the intensity of the signal in very small dimensions.
Ever since the discovery of graphene a single layer of carbon that can be extracted from graphite with adhesive tape scientists have been rapidly exploring the world of two-dimensional materials These materials have unique properties not seen in their bulk form.
Like graphene Mos2 is made up of layers that are bonded weakly to each other so they can be separated easily.
In bulk Mos2 electrons and photons interact as they would in traditional semiconductors like silicon and gallium arsenide.
As Mos2 is reduced to thinner and thinner layers the transfer of energy between electrons and photons becomes more efficient.
The key to Mos2's desirable photonic properties is in the structure of its energy band gap.
As the material's layer count decreases it transitions from an indirect to direct band gap
which allows electrons to easily move between energy bands by releasing photons. Graphene is inefficient at light emission
because it has no band gap. Combining electronics and photonics on the same integrated circuits could drastically improve the performance and efficiency of mobile technology.
The researchers say the next step is to demonstrate their primitive circuit with light emitting diodes.
Explore further: Scientists probe the next generation of 2-D materials More information: K. Goodfellow R. Beams C. Chakraborty L. Novotny A n. Vamivakas Integrated nanophotonics based on nanowire plasmons and atomically-thin material Optica Vol. 1 Issue
3 pp. 149-152 (2014
#Researcher's nanoparticle key to new malaria vaccine A self-assembling nanoparticle designed by a UCONN professor is the key component of a potent new malaria vaccine that is showing promise in early tests.
For years, scientists trying to develop a malaria vaccine have been stymied by the malaria parasite's ability to transform itself
and"hide"in the liver and red blood cells of an infected person to avoid detection by the immune system.
But a novel protein nanoparticle developed by Peter Burkhard, a professor in the Department of Molecular & Cell biology, in collaboration with David Lanar
an infectious disease specialist with the Walter reed Army Institute of Research, has shown to be effective at getting the immune system to attack the most lethal species of malaria parasite, Plasmodium falciparum,
after it enters the body and before it has a chance to hide and aggressively spread.
The key to the vaccine's success lies in the nanoparticle's perfect icosahedral symmetry (think of the pattern on a soccer ball)
and ability to carry on its surface up to 60 copies of the parasite's protein. The proteins are arranged in a dense,
carefully constructed cluster that the immune system perceives as a threat, prompting it to release large amounts of antibodies that can attack
and kill the parasite. In tests with mice, the vaccine was 90-100 percent effective in eradicating the Plasmodium falciparum parasite
and maintaining long-term immunity over 15 months. That success rate is considerably higher than the reported success rate for RTS, S,
the world's most advanced malaria vaccine candidate currently undergoing phase 3 clinical trials, which is the last stage of testing before licensing."
"Both vaccines are similar, it's just that the density of the RTS, S protein displays is much lower than ours,
"says Burkhard.""The homogeneity of our vaccine is much higher, which produces a stronger immune system response.
That is why we are confident that ours will be an improvement.""Every single protein chain that forms our particle displays one of the pathogen's protein molecules that are recognized by the immune system,
"adds Burkhard, an expert in structural biology affiliated with UCONN's Institute of Materials science.""With RTS, S, only about 14 percent of the vaccine's protein is from the malaria parasite.
We are able to achieve our high density because of the design of the nanoparticle, which we control."
"The research was published in Malaria Journal in 2013. The search for a malaria vaccine is one of the most important research projects in global public health.
The disease is transported commonly through the bites of nighttime mosquitoes. Those infected suffer from severe fevers, chills,
and a flu-like illness. In severe cases, malaria causes seizures, severe anemia, respiratory distress, and kidney failure.
Each year, more than 200 million cases of malaria are reported worldwide. The World health organization estimated that 627,000 people died from malaria in 2012, many of them children living in Sub-saharan africa.
It took the researchers more than 10 years to finalize the precise assembly of the nanoparticle as the critical carrier of the vaccine
and find the right parts of the malaria protein to trigger an effective immune response. The research was complicated further by the fact that the malaria parasite that impacts mice used in lab tests is structurally different from the one infecting humans.
The scientists used a creative approach to get around the problem.""Testing the vaccine's efficacy was difficult
because the parasite that causes malaria in humans only grows in humans, "Lanar says.""But we developed a little trick.
We took a mouse malaria parasite and put in its DNA a piece of DNA from the human malaria parasite that we wanted our vaccine to attack.
That allowed us to conduct inexpensive mouse studies to test the vaccine before going to expensive human trials."
"The pair's research has been supported by a $2 million grant from the National institutes of health and $2 million from the U s. Military Infectious disease Research Program.
A request for an additional $7 million in funding from the U s army to conduct the next phase of vaccine development, including manufacturing
and human trials, is pending.""We are on schedule to manufacture the vaccine for human use early next year,
"says Lanar.""It will take about six months to finish quality control and toxicology studies on the final product
and get permission from the FDA to do human trials.""Lanar says the team hopes to begin early testing in humans in 2016 and,
if the results are promising, field trials in malaria endemic areas will follow in 2017. The required field trial testing could last five years
or more before the vaccine is available for licensure and public use, Lanar says. Martin Edlund, CEO of Malaria No more, a New york-based nonprofit focused on fighting deaths from malaria,
says,"This research presents a promising new approach to developing a malaria vaccine. Innovative work such as what's being done at the University of Connecticut puts us closer than we've ever been to ending one of the world's oldest
costliest, and deadliest diseases.""A Switzerland-based company, Alpha-O-Peptides, founded by Burkhard, holds the patent on the self-assembling nanoparticle used in the malaria vaccine.
Burkhard is also exploring other potential uses for the nanoparticle, including a vaccine that will fight animal flu
and one that will help people with nicotine addiction. Professor Mazhar Khan from UCONN's Department of Pathobiology is collaborating with Burkhard on the animal flu vaccine e
#Scientists shed light on organic photovoltaic characteristics However, at this time organic photovoltaic devices are hindered by low efficiency relative to commercial solar cells in part
because quantifying their electrical properties has proven challenging. Therefore, predictive models and quantitative metrics for device performance are needed critically.
Scientists from NIST's Physical Measurement Laboratory, led by the Semiconductor and Dimensional Metrology Division's David Gundlach and Curt Richter,
along with James Basham, a guest researcher from Penn State university, have developed a method that allows the prediction of the current density-voltage curve of a photovoltaic device. 1 This new method uses a common measurement technique
(impedance spectroscopy) that is affordable, widely available to manufacturers, and relatively easy to perform. The technique is repeatable, non-destructive,
reasonably fast(#15 min to test a device), andhanks to a rigorous analysis and methodology created by Bashamrovides a comprehensive readout of the device's current-voltage properties that was previously illusive to most researchers working in the field.
Finally, this technique allows the device to be tested in real-word conditions.""This measurement breakthrough should allow us to more rapidly optimize solar cells,"Richter states."
"We're able to look at what happens electronically throughout the entire device. Importantly, how long does the charge exist once created
and how long does it take to get the photogenerated charge through the semiconductor mixture to the electrodes?
The larger the difference between the charge lifetime and device transit time greatly improves the likelihood that a photovoltaic device will be a more efficient source of electrical power."
"Currently at the laboratory level, current-voltage testing of organic photovoltaic devices is done typically by analyzing device operation at either extreme of the device's bias spectrumhat is,
a short circuit or an open circuitnd trying to infer from those results what is happening electrically within the device.
But, when the device does not perform as a"textbook"or"ideal"solar cell then the picture of
what's going on in the device between these bias extremes quickly becomes clouded. Photovoltaic devices, also known as solar cells, produce electrical power
when exposed to light, and that technology has enabled a fast-growing industry. The most familiar designs use rigid layers of silicon crystal.
But recently intense interest has focused on organic photovoltaic (OP) devices which use inexpensive organic semiconductor materials sandwiched between two metal electrodes.
OP devices can be made flexible and easily portable. Imagine a tent that, once set up, acts as a large solar system that can be used to recharge portable electronics and lights for the upcoming night of camping."
"That approach only works if the recombination (where the charge carriers are eliminated rather than continuing to flow through the device) at one bias is nominally identical to the charge generation at the other,
"Gundlach says.""In a good device, those should be about equal. In a non-ideal device, they could be vastly different.
With our technique, we can actually map the full range of the characteristics from one extreme to the other
and disentangle generation, transport, and different loss mechanisms throughout the entire bias range.""The output of this new technique is the precise reproduction of the device's current density-voltage curve through the entire voltage range between the bias extremes.
This allows researchers to pinpoint where problems exist in the device and can serve as a blueprint for
and carrier concentrations with an accurate nanoscale picture of the semiconductor film's microstructure really gives a complete picture of how the device operates and
and ultimately more closely connect materials properties with processing methods and solar cell performance.""And since the physical process governing organic photovoltaics is very similar to other organic semiconductors (organic light-emitting diodes, for example,
which are prevalent in electronic displays), future applications of this technique to other industries appears straight forward."
"A lot of the understanding being developed here can also be applied to make better organic light emitting diodes, "Richter explains.
The organic photovoltaic samples used in this study were developed in house at NIST. The 100 nm thick device has a three-layer structure top semitransparent electrode, the organic photovoltaic,
and a bottom electrodelaced on a 1 inch piece of glass. For the impedance spectroscopy measurements, the sample was installed beneath an LED broadband white light,
calibrated to one Sun illumination (natural sunlight). The measurement itself is conceptually simple:""We're applying an oscillating voltage across the device
and measuring the current that comes out, "Richter explains.""We do this underneath the simulated sunlight.
and a data curve is produced based on the time it takes for the voltage to drop back down to its dark state.
These resulting data provide additional information about the recombination effects in the device that impedance spectroscopy is unable to provide.
#Electron microscopes take first measurements of nanoscale chemistry in action (Phys. org) Scientists'underwater cameras got a boost this summer from the Electron microscopy Center at the U s. Department of energy's Argonne National Laboratory.
Along with colleagues at the University of Manchester researchers captured the world's first real-time images and simultaneous chemical analysis of nanostructures while underwater or in solution.
and materials scientists to explore never-before-measured stages of nanoscale chemical processes in materials said Argonne materials scientist Nestor Zaluzec one of the paper's authors.
Understanding how materials grow at the nanoscale level helps scientists tailor them for everything from batteries to solar cells.
Electron microscopes are prized a tool in a scientist's toolbox because they can see far smaller structures than regular light or X-ray microscopes.
and nanoscale for decades but it's usually done with the sample in a vacuum Zaluzec said.
and images of materials while they're in more natural environments. Over the last decade developments allowed scientists to take images of materials in solution
but getting chemical analysis at the same time remained inaccessible. Imagine how helpful it would be for trainers to be able to watch a baseball player pitch with simultaneous X-ray
Zaluzec and his collaborators reworked the staging of the transmission electron microscope so that the specialized detectors could take a clearer look at the sample.
With this innovation the team was finally able to obtain images as well as simultaneous chemical maps of where different elements are located in the sample.
This lets scientists watch as nanostructures grow and change with time during chemical reactions. The team is now working with the manufacturer Protochips Inc. to make this capability available to the scientific community.
Argonne scientist Dean Miller is already looking ahead to incorporate this capability into the next challenge:
which for example the next generation of batteries will operate. Engineering new materials to address today's societal problems is a complex and demanding agenda Zaluzec said.
The study Real-time imaging and local elemental analysis of nanostructures in liquids was published in the journal Chemical Communications with researchers from the University of Manchester and BP.
Researchers develop method to measure positions of atomic sites with new precision More information: Real-time imaging and local elemental analysis of nanostructures in liquids.
Edward A. Lewis et al. Chem. Commun. 201450 10019-10022. DOI: 10.1039/C4cc02743 3
#Handheld scanner could make brain tumor removal more complete reducing recurrence Cancerous brain tumors are notorious for growing back
despite surgical attempts to remove them and for leading to a dire prognosis for patients.
But scientists are developing a new way to try to root out malignant cells during surgery so fewer
or none get left behind to form new tumors. The method reported in the journal ACS Nano could someday vastly improve the outlook for patients.
Moritz F. Kircher and colleagues at Memorial Sloan Kettering Cancer Center point out that malignant brain tumors particularly the kind known as glioblastoma multiforme (GBM) are among the toughest to beat.
Although relatively rare GBM is highly aggressive and its cells multiply rapidly. Surgical removal is one of the main weapons doctors have to treat brain tumors.
The problem is that currently there's no way to know if they have taken out all of the cancerous cells.
And removing extra material just in case isn't a good option in the brain which controls so many critical processes.
The techniques surgeons have at their disposal today are not accurate enough to identify all the cells that need to be excised.
The researchers used a handheld device resembling a laser pointer that can detect Raman nanoprobes with very high accuracy.
These nanoprobes are injected the day prior to the operation and go specifically to tumor cells and not to normal brain cells.
Using a handheld Raman scanner in a mouse model that mimics human GBM the researchers successfully identified
and removed all malignant cells in the rodents'brains. Also because the technique involves steps that have made already it to human testing for other purposes the researchers conclude that it has the potential to move readily into clinical trials.
Surgeons might be able to use the device in the future to treat other types of brain cancer they say.
Neuroscientists use lightwaves to improve brain tumor surgery More information: Guiding Brain tumor Resection Using Surface-Enhanced Raman Scattering Nanoparticles and a Hand-held Raman Scanner ACS Nano Article ASAPDOI:
10.1021/nn503948abstractthe current difficulty in visualizing the true extent of malignant brain tumors during surgical resection represents one of the major reasons for the poor prognosis of brain tumor patients.
Here we evaluated the ability of a hand-held Raman scanner guided by surface-enhanced Raman scattering (SERS) nanoparticles to identify the microscopic tumor extent in a genetically engineered RCAS/tv-a glioblastoma mouse model.
In a simulated intraoperative scenario we tested both a static Raman imaging device and a mobile hand-held Raman scanner.
We show that SERS image-guided resection is more accurate than resection using white light visualization alone.
and correlation with histology showed that SERS nanoparticles accurately outlined the extent of the tumors.
but also detected additional microscopic foci of cancer in the resection bed that were seen not on static SERS images
because it uses inert gold#silica SERS nanoparticles and a hand-held Raman scanner that can guide brain tumor resection in the operating room o
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