New NIST Metamaterial Could Improve Light-Based Biosensing

By Chuck Seegert, Ph.D.

Researchers at the National Institute of Standards and Technology (NIST) have developed a new metamaterial that interacts with light in novel ways — an achievement that may improve the field of biosensing by increasing sensitivity and contrast in many light-based tests.

Metamaterials get their name because they are artificially created materials that exhibit physical properties not found in nature. Most often the effects these metamaterials have are governed by their geometries rather than their composition, which is certainly the case in NIST’s newest application. Using a multilayered approach with grate features smaller than wavelengths of light, the NIST design allows for one way transmission of light through the material in the visible spectrum, a property that hasn’t previously been achieved.  This produces a so called hyperbolic material.

Schematic of NIST's one-way metamaterial. Forward travelling green light (left) or red light passes through the multilayered block and comes out at an angle due to diffraction off of grates on the surface of the material. Light travelling in the opposite direction (right) is almost completely filtered by the metamaterial and can't pass through. (Credit: Xu/NIST)

While similar effects have been demonstrated in the microwave and infrared spectrums, the visible spectrum has remained elusive due to challenges in nanofabrication techniques.

The NIST team was able to fabricate its material using existing methods. Its extremely thin metamaterial is composed of up to 20 alternating layers of silicon dioxide glass and silver. These layers are then sandwiched between gratings with slits that have nanoscale spacings. These nanoscale spacings are what control the transmission of light and allow it to pass in one direction, while blocking it in the other. What makes this new technology possible are the nanoscale layers of silicon dioxide and silver. Without these intervening layers, the gratings on either side of the sandwich could not be aligned with the precision necessary to gain these increases in performance.  

Metamaterials are currently the subject of intense investigation, especially in applications that localize and enhance electromagnetic fields. Their unique properties enable light-based detection of objects that are even smaller than a wavelength of light. Metamaterials have also been developed recently with the interesting potential to absorb ultra-violet light (UV), as well as aid in rapid medical imaging.