Fabrication of chiral-molecular@ nanoparticle complex materials with great chiroptical effect in visible region

Abstract

Chirality plays a key role in biochemical reaction and the self-assembled mechanism of life. The detection of chiral molecules is one crucial issue in biology, clinic, pharmacy and food security fields, which usually refers to the detectable chiroptical effect, i.e. circular dichroism (CD) and optical rotatory dispersion (ORD) Gansel et al. (2009), Quake and Scherer (2000), Pendry (2004), Zhang et al. (2009), Kastel et al. (2007) [1–5]. However, the chiroptical effect from chiral molecules in nature (such as proteins and DNAs) is usually very small and located in ultraviolet spectral region. This limits the detection sensitivity of chiral molecules and their ability to control electromagnetic wave. In this paper, we report a scalable fabrication of a new kind of chiral molecule@nanoparticle complex materials, which are composed of an achiral nano-cup array and a pair of chiral molecules (l-/d-cysteine). The nano-cup array with localized surface plasmonic response peak of 630nm is obtained with the micro-sphere assembly technique, which is a kind of scalable, low-cost and material-independent fabrication method. After coating a layer of chiral molecules on the surface of the nano-cup array, a clear induced-CD peak in visible region is demonstrated from the l/d-cysteine@nano-cups complex materials, the intensity of which can be much greater than the existing results [9–16]. Full-wave electromagnetic simulation method has been performed to get insight into the mechanism of the induced chiroptical effect. The simulation results indicate that this giant induced CD signal should be attributed to the electromagnetic interaction between chiral molecules and plasmonic nanostructures, especially for the wave at the plasmonic resonance peak. These results indicate the potential application prospect of these newly-fabricated complex chiral materials.