Formation of Chiral Plasmonic Silver Nanocrescents Using Colloidal Lithography and Ion-Plasma Sputtering ^†

Nanomaterials based on plasmonic metal nanoparticles have a great potential for medicine, pharmaceuticals and sensors. Their unique optical properties are due to the enhancement of local near fields under the influence of external electromagnetic waves upon the excitation of a localized surface plasmon resonance. Optical properties of such nanomaterials depend on the characteristics of the nanoparticles: shape, size, material. Therefore, the development of experimental methods for the formation of new nanoparticles with a given shape is an urgent task. The plasmon resonance effect can be especially useful for studying the optical properties of chiral molecules, since they give very weak chiroptical signals due to the difference between molecular sizes and the wavelength of incident light. One of the main methods for studying chiral molecules is circular dichroism spectroscopy (CD). It can be expected that in the field of chiral plasmonic nanoparticles, the CD signal of chiral molecules will also be enhanced.

We have achieved the formation of chiral plasmonic silver nanocrescents using a combination of colloidal lithography and ion-plasma sputtering methods. The new technique makes it possible to obtain substrate-supported arrays of chiral nanocrescents with various orientations and widths by controlling the angles of deposition and sputtering. It was shown that the resulting nanoparticles are characterized by enhanced absorption at wavelengths of 470 nm, 655 nm, 1050 nm, and 1400 nm.

To sum up, the new fabrication technique provides a rapid and inexpensive way of forming chiral nanocrescents. Along with the techniques commonly used to measure the optical properties of metal nanoparticles (extinction and fluorescence spectroscopy), we anticipate that CD will play an important role due to the number of effective ways it can be used to detect interactions between biomolecules and chiral plasmonic systems. Further research is also needed to determine the relationship of crescent asymmetry with the CD signal and how to integrate such surfaces into functional commercial devices.