Schematic drawing of the sensing platform. Credit: Cheng Xu et al.
A team of scientists at the National University of Singapore has developed a new metamaterial as an enhanced VCD sensing platform. By varying the thickness and position of nanorods, the material was able to be optimized for greater detection limits and higher sensitivity.
Chiral signals are important to detect in a variety of applications including drug delivery and diagnosis. However, current testing methodologies are difficult to accurately operate in chiral mixtures due to the limited dimensionality of the signal. Expanding the wavelength to mid-infrared provides increased dimensionality, however, the signals achieved are around 3 magnitudes smaller than traditional electronic circular dichroism spectroscopy.
In a paper published in Light Science & Applications, researchers were able to develop a novel infrared chiral plasmonic metamaterial (IRCPM) that increased these weak signals and maintained improved dimensionality. The IRCPM was created utilizing perpendicular nanorods with a metal-insulator-metal configuration. By utilizing gold as the bottom to function as a reflector, the researchers were able to calculate the absorption spectrum by reading only the reflection spectrum.
"Our contribution is fourfold. Firstly, we develop an enhanced VCD sensing platform consisting of chiral metamaterials that achieves an enhancement of 6 magnitudes compared with traditional VCD spectroscopy. Secondly, we illustrate the methodology of design and optimization of MIR chiral metamaterials leveraging temporal coupled-mode theory, which indicates the importance of near-field coupling coefficient and loss ratios, leading to the design of both in-plane and out-of-plane symmetry-breaking dimensions. Thirdly, leveraging the mentioned sensing platform, we demonstrate the protein thin-film sensing process and achieve the lowest detection limit down to ~23 zeptomole level. Fourthly, we—for the first time—report the enhanced VCD sensing process for mixed protein secondary structures with high selectivity from vibrational transition," - the others stated when summarizing the research.
Thanks to the high detectivity and scalability of the metamaterial the IRCPM is a promising new chiral sensing platform that will likely lead to future advancements in biomedical applications.