Ji-Xin Cheng, Ph.D.

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.

Purdue University researchers have created a new imaging technology that reveals subtle changes in breast tissue, representing a potential tool to determine a woman’s risk of developing breast cancer and to study ways of preventing the disease.

The researchers, using a special “3-D culture” that mimics living mammary gland tissue, also showed that a fatty acid found in some foods influences this early precancerous stage. Unlike conventional cell cultures, which are flat, the 3-D cultures have the round shape of milk-producing glands and behave like real tissue, said Sophie Lelièvre (pronounced Le-LEE-YEA-vre), an associate professor of basic medical sciences.

Researchers are studying changes that take place in epithelial cells, which make up tissues and organs where 90 percent of cancers occur. The changes in breast tissue are thought to be necessary for tumors to form, she said.

“By mimicking the early stage conducive to tumors and using a new imaging tool, our goal is to be able to measure this change and then take steps to prevent it,” Lelièvre said.

The new imaging technique, called vibrational spectral microscopy, can be used to identify and track certain molecules by measuring their vibration with a laser. Whereas other imaging tools may take days to get results, the new method works at high speed, enabling researchers to measure changes in real time in live tissue, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry.

Researchers have demonstrated a new imaging tool for tracking structures called carbon nanotubes in living cells and the bloodstream, which could aid efforts to perfect their use in biomedical research and clinical medicine. 

The structures have potential applications in drug delivery to treat diseases and imaging for cancer research. Two types of nanotubes are created in the manufacturing process, metallic and semiconducting. Until now, however, there has been no technique to see both types in living cells and the bloodstream, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.

The imaging technique, called transient absorption, uses a pulsing near-infrared laser to deposit energy into the nanotubes, which then are probed by a second near-infrared laser.

The researchers have overcome key obstacles in using the imaging technology, detecting and monitoring the nanotubes in live cells and laboratory mice, Cheng said.

Researchers have developed a new type of imaging technology to diagnose cardiovascular disease and other disorders by measuring ultrasound signals from molecules exposed to a fast-pulsing laser.

The new method could be used to take precise three-dimensional images of plaques lining arteries, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.

Other imaging methods that provide molecular information are unable to penetrate tissue deep enough to reveal the three-dimensional structure of the plaques, but being able to do so would make better diagnoses possible, he said.

“You would have to cut a cross section of an artery to really see the three-dimensional structure of the plaque,” Cheng said. “Obviously, that can’t be used for living patients.”

Researchers have demonstrated a new imaging tool for rapidly screening structures called single-wall carbon nanotubes, possibly hastening their use in creating a new class of computers and electronics that are faster and consume less power than today’s.

The semiconducting nanostructures might be used to revolutionize electronics by replacing conventional silicon components and circuits. However, one obstacle in their application is that metallic versions form unavoidably during the manufacturing process, contaminating the semiconducting nanotubes.

Now researchers have discovered that an advanced imaging technology could solve this problem, said Ji-Xin Cheng, an associate professor of biomedical engineering and chemistry at Purdue University.

“The imaging system uses a pulsing laser to deposit energy into the nanotubes, pumping the nanotubes from a ground state to an excited state,” he said. “Then, another laser called a probe senses the excited nanotubes and reveals the contrast between metallic and semiconductor tubes.”

The technique, called transient absorption, measures the “metallicity” of the tubes. The detection method might be combined with another laser to zap the unwanted metallic nanotubes as they roll off of the manufacturing line, leaving only the semiconducting tubes.

Findings are detailed in a research paper appearing online this week in the journal Physical Review Letters.

New research findings suggest that an experimental ultrasensitive medical imaging technique that uses a pulsed laser and tiny metallic “nanocages” might enable both the early detection and treatment of disease.

The system works by shining near-infrared laser pulses through the skin to detect hollow nanocages and solid nanoparticles – made of an alloy of gold and silver – that are injected into the bloodstream.

Unlike previous approaches using tiny metallic nanorods and nanospheres, the new technique does not cause heat damage to tissue being imaged. Another advantage is that it does not produce a background “auto fluorescent” glow of surrounding tissues, which interferes with the imaging and reduces contrast and brightness, said Ji-Xin Cheng (pronounced Gee-Shin), an associate professor of biomedical engineering and chemistry at Purdue University.

“This lack of background fluorescence makes the images much more clear and is very important for disease detection,” he said. “It allows us to clearly identify the nanocages and the tissues.”