Apr. 29, 2013 ? Researchers have found a way to see synthetic nanostructures and molecules using a new type of super-resolution optical microscopy that does not require fluorescent dyes, representing a practical tool for biomedical and nanotechnology research.
"Super-resolution optical microscopy has opened a new window into the nanoscopic world," said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.
Conventional optical microscopes can resolve objects no smaller than about 300 nanometers, or billionths of a meter, a restriction known as the "diffraction limit," which is defined as half the width of the wavelength of light being used to view the specimen. However, researchers want to view molecules such as proteins and lipids, as well as synthetic nanostructures like nanotubes, which are a few nanometers in diameter.
Such a capability could bring advances in a diverse range of disciplines, from medicine to nanoelectronics, Cheng said.
"The diffraction limit represents the fundamental limit of optical imaging resolution," Cheng said. "Stefan Hell at the Max Planck Institute and others have developed super-resolution imaging methods that require fluorescent labels. Here, we demonstrate a new scheme for breaking the diffraction limit in optical imaging of non-fluorescent species. Because it is label-free, the signal is directly from the object so that we can learn more about the nanostructure."
Findings are detailed in a research paper that appeared online Sunday (April 28) in the journal Nature Photonics.
The imaging system, called saturated transient absorption microscopy,or STAM,uses a trio of laser beams, including a doughnut-shaped laser beam that selectively illuminates some molecules but not others. Electrons in the atoms of illuminated molecules are kicked temporarily into a higher energy level and are said to be excited, while the others remain in their "ground state." Images are generated using a laser called a probe to compare the contrast between the excited and ground-state molecules.
The researchers demonstrated the technique, taking images of graphite "nanoplatelets" about 100 nanometers wide.
"It's a proof of concept and has great potential for the study of nanomaterials, both natural and synthetic," Cheng said.
The doughnut-shaped laser excitation technique, invented by researcher Stefan Hell, makes it possible to focus on yet smaller objects. Researchers hope to improve the imaging system to see objects about 10 nanometers in diameter, or about 30 times smaller than possible using conventional optical microscopes.
"We are not there yet, but a few schemes can be applied to further increase the resolution of our system," Cheng said.
The paper was co-authored by biomedical engineering doctoral student Pu Wang; research scientist Mikhail N. Slipchenko; mechanical engineering doctoral student James Mitchell; Chen Yang, an assistant professor of physical chemistry at Purdue; Eric O. Potma, an associate professor of chemistry at the University of California, Irvine; Xianfan Xu, Purdue's James J. and Carol L. Shuttleworth Professor of Mechanical Engineering; and Cheng.
Future research may include work to use lasers with shorter wavelengths of light. Because the wavelengths are shorter, the doughnut hole is smaller, possibly allowing researchers to focus on smaller objects.
The work will be discussed during the third annual Spectroscopic Imaging: A New Window into the Unseen World workshop on May 23 and 24 at Purdue. The workshop is hosted by the university's Weldon School of Biomedical Engineering.
The research is funded by the National Institutes of Health, National Science Foundation and the Defense Advanced Research Projects Agency.
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The above story is reprinted from materials provided by Purdue University. The original article was written by Emil Venere.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- Pu Wang, Mikhail N. Slipchenko, James Mitchell, Chen Yang, Eric O. Potma, Xianfan Xu, Ji-Xin Cheng. Far-field imaging of non-fluorescent species with subdiffraction resolution. Nature Photonics, 2013; DOI: 10.1038/nphoton.2013.97
Note: If no author is given, the source is cited instead.
Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.
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In light of the AP’s?high-profile Twitter hacking and a vicious domestic bombing, Americans have not let fear derail privacy legislation. Just this week, the Senate advanced an anti-email snooping law and the controversial Cyber Intelligence Sharing and Protection Act (CISPA) is reportedly on its way to the grave. It appears that the burden of proof has shifted to proponents of government surveillance, and they’ve been conspicuously silent about how spying will keep Americans safe. Two Bills CISPA, which gives immunity to Internet companies for sharing sensitive data with law enforcement, will reportedly not be taken up for a vote in the Senate. “We’re not taking [CISPA] up,” a representative from the Senate’s Committee on Commerce, Science and Transportation told US News, “Staff and senators are divvying up the issues and the key provisions everyone agrees would need to be handled if we’re going to strengthen cybersecurity. They’ll be drafting separate bills.” After wavering support from Facebook and other high-profile Internet companies, the White House threatened to veto the bill over privacy concerns, most likely related to ambiguous definitions of what constitutes a cyber “threat” and how agencies would be kept honest. ECPA Reform – The 1970′s law that permits security agencies to access emails opened or older than 180 days, is on its way to a privacy upgrade. Designed before users kept their email indefinitely in the cloud (i.e. Gmail), a few high-level privacy breaches, including the unearthing of General David Petraeus’s romantic affair, have created overwhelming demand to overhaul the antiquated law. Today, an amendment to require a warrant before reading emails was voted on by voice, which means there wasn’t even enough opposition among the Judiciary committee members for a debate. Staff members inside the House of Representatives, where the bill will go if it passes the senate, tell me that there also isn’t much opposition to the reforms on their side of Congress, and that a bill by Rep. Zoe Lofgren (CrunchGov Grade: A) could very well be combined with the Senate’s version for a streamlined change (yes, occasionally things are efficient in Congress). Why Not? Even after the AP’s Twitter account was hacked to spread a rumor about an explosion at the White House and two American men successfully detonated bombs at the Boston Marathon, there’s no reason to believe that either CISPA or ECPA ?would have kept Americans safer. Even Barack Obama’s freak-everyone-out op-ed last