Abstract
Abstract Chirality, a property of broken mirror symmetry, prevails in nature. Chiral molecules show different biochemical behaviors to their mirror molecules. For left or right circularly polarized lights, the fundamental chiral states of electromagnetic fields interact differently with chiral matter, and this effect has been used as a powerful tool for the detection of chiral molecules. This optical sensing, also termed chiral sensing, is not only easy to implement but also non-invasive to the analytes. However, the measurements made by the optical sensing of chiral molecules are challenging, as chiroptical signals are extremely weak. Recent years have seen active research efforts into metamaterial and plasmonic platforms for manipulating local fields to enhance chiroptical signals. This metamaterial approach offers new possibilities of chiral sensing with high sensitivity. Here, we review the recent advances in chiral sensing using metamaterial and plasmonic platforms. In addition, we explain the underlying principles behind the enhancement of chiroptical signals and highlight practically efficient chiral sensing platforms. We also provide perspectives that shed light on design considerations for chiral sensing metamaterials and discuss the possibility of other types of chiral sensing based on resonant metamaterials.
Highlights
Metamaterials, artificial materials whose properties cannot be found in natural materials, have been the subject of explosive interest over the past decade because of their ability to manipulate light in both the near- and far-field zones
We provide perspectives that shed light on design considerations for chiral sensing metamaterials and discuss the possibility of other types of chiral sensing based on resonant metamaterials
Metamaterials allow electromagnetic fields to be strongly confined within a small region, the so-called hot spot, and they are applied to varied fields ranging from molecular sensing [1] to the subwavelength imaging [2]
Summary
Metamaterials, artificial materials whose properties cannot be found in natural materials, have been the subject of explosive interest over the past decade because of their ability to manipulate light in both the near- and far-field zones. The ability of metamaterials to control light energy and phase has been applied to the chiral sensing of optically active chiral systems. Chiroptical spectroscopy, which measures ORD and CD, has been widely and successfully used in chemistry and biology to obtain important information such as protein secondary structures, electronic transitions of molecules, and conformation of small molecules [7, 8] Achieving these polarizationdependent chiroptical responses in optically active chiral systems can be aided by the precise local control of light energy and phase allowed by metamaterials. This explanation covers how local fields manipulated by metamaterials can enhance the CD signals of chiral molecules, how chiral molecules and the resonance modes of metamaterials interact with each other, and how chirally fluorescent signals can be modified by optical resonators.
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