New Framework for Nanoantenna Light Absorption

Harnessing light’s energy into nanoscale volumes requires novel engineering approaches to overcome the diffraction limit. However, Univer­sity of Illinois researchers have breached this barrier by developing nano­antennas that pack the energy captured from light sources, such as LEDs, into particles with nano­meter-scale diameters, making it possible to detect individual bio­molecules, catalyze chemical reactions, and generate photons with desirable properties for quantum computing. The results have a broad array of appli­cations that may include better cancer diagnostic tools.

Illustration of a new nanoantenna technology to harvest light. (Source: Micro and Nanotechnology Lab, Univ. of Illinois at Urbana-Champaign)

To create a device capable of overcoming the diffraction limit, graduate student Qinglan Huang and her adviser, Holonyak Lab Director Brian T. Cunningham, coupled photonic crystals with a plasmonic nano­antenna, an innovative approach in the field. The photonic crystals serve as light receivers and focus the energy into an electro­magnetic field that is hundreds of times greater than that received from the original light source, such as an LED or laser. The nano­antennas, when tuned to the same wavelength, absorb the energy from the electro­magnetic field and concen­trate the energy into a smaller volume that is yet another two orders of magnitude of greater intensity. The energy feedback between the photonic crystal and the nano­antenna, the resonant hybrid coupling, can be observed by its effects on the reflected and trans­mitted light spectrum.

“To get coopera­tive coupling between two things is exciting because it’s never been done,” said Huang. “It’s a general-purpose concept that we have experi­mentally demons­trated for the first time.” To achieve this, the team carefully controlled the density of the nano­antennas to maximize their energy collection effi­ciency. They also developed a method that allowed the nanoantennas to be distri­buted uniformly across the photonic crystal surface and tuned the photonic crystal’s optical resonating wavelength to match the absorption wavelength of the nano­antennas.

In addition to changing how researchers can work with light, this new coupling method has the potential to change how and when cancer is diagnosed. One appli­cation is to use a gold nano­particle, not much larger than biomo­lecules such as DNA, as the nano­antenna. In this case, the feedback provides a way to identify a biomarker unique to a certain type of cancer cell, and the group now linking the resonant hybrid coupling technique to novel bio­chemistry methods to detect cancer-specific RNA and DNA molecules with single-molecule precision.

Cunningham, and other members of the Nano­sensor Group will soon publish another paper that focuses specifi­cally on the discovery’s applications in regards to cancer diagnostics. “The novel physics in this research and the potential for broad appli­cations are what make this research stand out. The next steps of this research involve delving into the potential appli­cations of this new process”, Cunnigham said. (Source: U. Illinois)

Reference: Q. Huang & B. T. Cunnigham: Microcavity-Mediated Spectrally Tunable Amplification of Absorption in Plasmonic Nanoantennas, Nano Lett. 19, 5297 (2019); DOI: 10.1021/acs.nanolett.9b01764

Link: Micro and Nanotechnology Laboratory, Dept. of Electrical and Computer Engineering, University of Illinois at Urbana−Champaign, Urbana, USA

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