This Gold Nano-Slinky Is a Cancer-Detecting Hyperlens
The future-optics that may one day save your life.
Image: Litchinitser et al
Or maybe it looks more like a peacock? Either way, what you see above is really what's known as a hyperlens, a metamaterial-based composite allowing for imaging beyond the diffraction limit. For the first time, it will allow scientists to see (optically) at the scales of individual molecules, opening a whole new realm of super-tiny biology previously inaccessible to optical microscopes, including DNA strands and viruses.
The new hyperlens comes courtesy of electrical engineer Natalia Litchinitser and a team of researchers based at the University at Buffalo. Their work is published in the current Nature Communications.
The diffraction limit is a more or less fundamental lower limit on image resolution at very high magnifications, which has to do with the wave nature of light itself. If the size of an object to be imaged is smaller than half the wavelength of a light source, the result is that the image just kind of gets blurred out as it hits the lens of the microscope (or camera or telescope or whatever). When this blurring increases beyond the normal aberrations of the imaging system, it becomes impossible to distinguish between the target and the system itself.
The slinky lens works by capturing so-called evanescent waves, which are a lot like they sound. As light passes through some medium and encounters a boundary—light passing from air to water, for example, but any two media with different refractive indexes—some of it is reflected inward, where it becomes effectively "lost." The slinky's slinky-ness is actually a radial pattern of tiny slivers of gold, which act to convert decaying evanescent waves back into propagating waves—refocusing or recapturing them, in a sense.
The gold slivers work together to tweak what's known as "dialectric permittivity," which is a measure of how an electric field interacts or is resisted by free space. Manipulating it just so lets the lens grab these loose waves and scoot them outward across the lens, converting inaccessible "near-field" information into far-field information.
"Evanescent waves with high angular momenta are radiated by the objects [being imaged]—subwavelength slits in our case—on the inside surface the hyperlens," Litchinitser told me. "They carry near-field information about the object, information about the smallest features of the object. The hyperlens is made of a specially-designed, strongly anisotropic material. Due to the unique dispersive properties of the hyperlens, these evanescent waves excite propagating modes inside the hyperlens, which can be used to transfer the near-field information to the far-field region of the outer surface of the hyperlens."
And so these formerly decaying evanescent components can now be collected and transmitted using standard optical components. It's all pretty clever.
This may prove to be vital if not revolutionary research in a large number of fields, but biology and medicine is where the need would seem to be most immediate. "For instance," Litchinitser and co. note, "it was shown that an ability to visualize nanoscale structures might be critical for early detection of various cancers, such as ovarian cancer, which is the fifth leading cause of death due to cancer in women, or adenocarcinoma in patients with chronic gastroesophageal reflux disease."
A slinky-based microscope might one day save your life.