Strong Near-Field Coupling for Enhancing Plasmonic Chirality Toward Single-Molecule Sensing

Plasmonic chirality shows great potential in analytical chemistry, biomedicine, and life science due to the strong chiroptical response generated from metallic nanostructures. However, significant chiral effects are mainly realized in three-dimensional structures because of their high structural asymmetry and large plasmon mode volume. This paper describes planar plasmonic "tau"-shaped structure arrays that can obtain significantly enhanced chiroptical responses for single-molecule detection. The "tau"-shaped structure arrays based on a chiral-achiral coupling scheme are constructed to generate a large superchiral field and enhanced circular dichroism (CD). Numerical simulations show that the chiroptical responses can be efficiently manipulated by the near-field coupling strength of plasmons determined by the parameters of the arrays and the structural chirality of the unit cells. The planar "tau"-shaped structure arrays with a large CD signal and enhanced superchiral field enable ultrasensitive detection of single-molecule bovine serum albumin (BSA) protein.