Saturday, September 20, 2014

Generic epitaxial graphene biosensors for ultrasensitive detection of cancer risk biomarker

An ultrasensitive biosensor made from the wonder material graphene has been used to detect molecules that indicate an increased risk of developing cancer.

The biosensor has been shown to be more than five times more sensitive than bioassay tests currently in use, and was able to provide results in a matter of minutes, opening up the possibility of a rapid, point-of-care diagnostic tool for patients.

The biosensor has been presented today, 19 September, in IOP Publishing's journal 2D Materials.

To develop a viable bionsensor, the researchers, from the University of Swansea, had to create patterned graphene devices using a large substrate area, which was not possible using the traditional exfoliation technique where layers of graphene are stripped from graphite.

Instead, they grew graphene onto a silicon carbide substrate under extremely high temperatures and low pressure to form the basis of the biosensor. The researchers then patterned graphene devices, using semiconductor processing techniques, before attaching a number of bioreceptor molecules to the graphene devices. These receptors were able to bind to, or target, a specific molecule present in blood, saliva or urine.

nanotechnology grapevine biosensor

This is an illustration of an epitaxial graphene channel biosensor for detection of targeted 8-hydroxydeoxyguanosine (8-OHdG) biomarker. (A) Schematic of MLEG device (B) Thin film of covalently attached nitro phenyl (PhNO2) groups on the MLEG channel. (C) Attachment of the 'bioreceptor' antibody anti-8-OHdG to the amine terminated MLEG channel and subsequent detection of 8-OHdG.

Credit: 2D Materials. Usage Restrictions: Credit to 2D Materials must be given and, if reproducing online, a link to the paper must be included: iopscience.iop.org/

The molecule, 8-hydroxydeoxyguanosine (8-OHdG), is produced when DNA is damaged and, in elevated levels, has been linked to an increased risk of developing several cancers. However, 8-OHdG is typically present at very low concentrations in urine, so is very difficult to detect using conventional detection assays, known as enzyme-linked immunobsorbant assays (ELISAs).

In their study, the researchers used x-ray photoelectron spectroscopy and Raman spectroscopy to confirm that the bioreceptor molecules had attached to the graphene biosensor once fabricated, and then exposed the biosensor to a range of concentrations of 8-OHdG.

When 8-OHdG attached to the bioreceptor molecules on the sensor, there was a notable difference in the graphene channel resistance, which the researchers were able to record.

Results showed that the graphene sensor was capable of detecting 8-OHdG concentrations as low as 0.1 ng mL-1, which is almost five times more sensitive compared with ELISAs. The graphene biosensor was also considerably faster at detecting the target molecules, completing the analysis in a matter of minutes.

Moving forward, the researchers highlight the potential of the biosensor to diagnose and monitor a whole range of diseases as it is quite simple to substitute the specific receptor molecules on the graphene surface.

Co-author of the study Dr Owen Guy said: "Graphene has superb electronic transport properties and has an intrinsically high surface-to-volume ratio, which make it an ideal material for fabricating biosensors.

Now that we've created the first proof-of-concept biosensor using epitaxial graphene, we will look to investigate a range of different biomarkers associated with different diseases and conditions, as well as detecting a number of different biomarkers on the same chip."

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Contact: Michael Bishop michael.bishop@iop.org 01-179-301-032 Institute of Physics @PhysicsNews

Generic epitaxial graphene biosensors for ultrasensitive detection of cancer risk biomarker

An ultrasensitive biosensor made from the wonder material graphene has been used to detect molecules that indicate an increased risk of developing cancer.

More about this image and story at Nanotechnology Today - http://nanotechnologytoday.blogspot.com/2014/09/generic-epitaxial-graphene-biosensors.html

Tuesday, September 16, 2014

Scanning tunneling microscopy/spectroscopy of picene thin films formed on Ag(111)

The future face of molecular electronics. Thin layer of picene molecules attached to a silver surface maintain their structure and function, demonstrating potential for electronic applications.

WASHINGTON, D.C., September 16, 2014 --The emerging field of molecular electronics could take our definition of portable to the next level, enabling the construction of tiny circuits from molecular components. In these highly efficient devices, individual molecules would take on the roles currently played by comparatively-bulky wires, resistors and transistors.

A team of researchers from five Japanese and Taiwanese universities has identified a potential candidate for use in small-scale electronics: a molecule called picene. In a paper published September 16 in The Journal of Chemical Physics, from AIP Publishing, they characterize the structural and electronic properties of a thin layer of picene on a silver surface, demonstrating the molecule's potential for electronic applications.

Picene's sister molecule, pentacene, has been widely studied because of its high carrier mobility—its ability to quickly transmit electrons, a critical property for nanoscale electronics. But pentacene, made of five benzene molecules joined in a line, breaks down under normal environmental conditions.

Nanotechnology picene molecules

Caption: Zigzag picene is more intact than straight pentacene on silver. Credit: Y. Hasegawa/ISSP, U. Tokyo Usage Restrictions: This image may be used only with appropriate caption and credit.

Enter picene, in which these same five benzene rings are instead bonded together in a W shape. This simple structural change alters some of the molecule's other properties: Picene retains pentacene's high carrier mobility, but is more chemically stable and therefore better suited to practical applications.

To test picene's properties when juxtaposed with a metal, as it would be in an electronic device, the researchers deposited a single layer of picene molecules onto a piece of silver. Then, they used scanning tunneling microscopy, an imaging technique that can visualize surfaces at the atomic level, to closely examine the interface between the picene and the silver.

Though previous studies had shown a strong interaction between pentacene and metal surfaces, "we found that the zigzag-shaped picene basically just sits on the silver," said University of Tokyo researcher Yukio Hasegawa. Interactions between molecules can alter their shape and therefore their behavior, but picene's weak connection to the silver surface left its properties intact.

"The weak interaction is advantageous for molecular [electronics] applications because the modification of the properties of molecular thin film by the presence of the [silver] is negligible and therefore [the] original properties of the molecule can be preserved very close to the interface," said Hasegawa.

A successful circuit requires a strong connection between the electronic components—if a wire is frayed, electrons can't flow. According to Hasegawa, picene's weak interactions with the silver allow it to deposit directly on the surface without a stabilizing layer of molecules between, a quality he said is "essential for achieving high-quality contact with metal electrodes."

Because picene displays its high carrier mobility when exposed to oxygen, the researchers hope to investigate its properties under varying levels of oxygen exposure in order to elucidate a molecular mechanism behind the behavior.

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Contact: Jason Socrates Bardi jbardi@aip.org 240-535-4954 Amtoperican Institute of Physics @AIP_Publishing

Scanning tunneling microscopy/spectroscopy of picene thin films formed on Ag(111)

The emerging field of molecular electronics could take our definition of portable to the next level, enabling the construction of tiny circuits from molecular components. In these highly efficient devices, individual molecules would take on the roles currently played by comparatively-bulky wires, resistors and transistors.

More about this image and story at Nanotechnology Today - http://nanotechnologytoday.blogspot.com/2014/09/scanning-tunneling-microscopyspectrosco.html