Natural chiral materials have an intrinsically weak chiroptical response, limiting their use in high–sensitivity detection and optical manipulation. Although artificial chiral nanostructures can enhance this response, most studies focus on the visible range, where poor tissue penetration hinders biomedical applications. Core–shell architectures offer a versatile platform, but current designs mainly rely on complex geometric chirality, while structures based on intrinsic material chirality remain largely unexplored. Designing simple core–shell configurations that provide strong near‑infrared (NIR) chiroptical enhancement remains a challenge.
Here, the finite element method is employed to calculate the scattering cross–section, optical torque, and optical chirality density. Four configurations are compared: a pure chiral sphere, a chiral core with a dielectric shell (chiral@dielectric), a chiral core with an Ag shell (chiral@Ag), and the full three‑layer chiral core–dielectric–Ag shell concentric sphere (chiral@dielectric@Ag). A systematic parametric study is performed to reveal the tuning rules of the chiral optical response.
The results show that the proposed three‑layer structure simultaneously achieves significant enhancement of both optical torque and optical chirality density in the NIR band. Compared with chiral@Ag, the dielectric layer shifts the enhanced response to the NIR region and improves biocompatibility. The parametric study reveals key tuning rules: an excessively thick Ag shell suppresses the internal chiral response; increasing the core permittivity red–shifts the electric multipole resonances; the dielectric spacer has an optimal thickness that maximizes the chiroptical enhancement; and increasing the spacer refractive index red‑shifts all resonances and differentially affects the intensities of the electric dipole, magnetic multipole, and electric quadrupole responses.
In conclusion, the proposed chiral@dielectric@Ag concentric sphere structure extends the enhanced chiroptical response to the NIR region while enhancing both optical torque and chirality density. The design is structurally simple, biocompatible, and provides new strategies for optical sorting and precise manipulation of chiral particles.