Some things are too small for conventional technology to see. Others are just hidden. From the nanoscale to the nearly-visible, Yizheng Zhu is creating fiber optic devices to image concealed areas of all sizes.
Zhu joined the ECE faculty in August as an assistant professor. He comes to Virginia Tech from Duke University, where he was a research scientist in the Department of Biomedical Engineering.
Seeing things at the nano level
Zhu's smallest-scale research is smaller than microscopy: he's trying to see things at the nano level. At this size, photons are too "large" for light to be usable in a conventional fashion. Zhu explains that the diffraction limit of light, or the smallest resolution light can depict, is approximately a quarter of a micron. "If you want to go even smaller," he says, "you haveto think of other ways to do it. I'm trying to develop new techniques that can break into the nano scale."
Existing technologies using fluorescence can have a resolution on the scale of tens of nanometers, but Zhu has a different technique in mind. He is using the intrinsic properties of the specimens, such as thickness, to detect light in a non-fluorescence way. According to Zhu, his technique and fluorescence are complementary. Fluorescence has more specificity to determine what kinds of molecules are present, while his method focuses on topography.
"At this level, I'm trying to very sensitively detect tiny changes between an object and its surroundings, so itwill stand out from the background," he says. Zhu expects the techniques he is developing to eventually image a nanoscale object in three dimensions. He can already see changes in the axial direction that are only tens of picometers.
In vivo imaging probes
On a larger scale, Zhu is designing tools that can study the progression of a disease in vivo. With Biological Sciences professor Liwu Li, Zhu is studying atherosclerosis, or the buildup of plaque in blood vessels. "If cells go through a transformation like this, their morphology will change. We plan to use my microscopy techniques to study these changes," Zhu explains. One of his goals is to build imaging probes that can be inserted into a blood vessel in vivo to monitor how plaque forms.
Zhu is establishing his laboratory in Durham Hall. Commercial equipment, such as the microscope shown here, will connect to his custom optics system.
Previously, Zhu developed another in vivo monitoring device — an endoscope that can easily enter a human esophagus or colon for early cancer detection. Zhu explains that fiber optic devices are perfect for this kind of work because of their small size and flexibility.
"By measuring the unmeasurable, we can visualize the invisible," says Zhu.
He has had much success in that effort. While at Duke, he developed biomedical devices using fiber-optic technology. He has designed quantitative optical microscopy techniques with high sensitivity, novel fiber-optic interferometers for studying depth-resolved one- and two-dimensional light scattering, and a clinical endoscopic system based on angle-resolved low coherence interferometry.
He participated in two clinical studies relating to his biomedical research. One trial tested his clinicalendoscopic system design for detection of dysplasia in Barrett's Esophagus and included helping an industrial partner with commercialization of the system. In another study, he studied light scattering signatures of resected colon tissue for the identification of intestinal dysplasia.
Zhu has written more than 40 journal and conference papers and three book chapters. He holds two granted and three pending patents, of which two have been exclusively licensed.