Dual-parameter chiral detection at the single-particle level enabled by surface cosine waves

Accurately probing optical chirality at the single-particle level is essential for chiral molecular sensing, quantum optics, and enantioselective nanophotonic technologies. However, conventional chiroptical techniques rely on ensemble-averaged measurements, obscuring particle-to-particle heterogeneity. Although single-particle circular dichroism spectroscopy has achieved nanoscale resolution, it remains limited to intensity-only detection, omitting essential phase information. Here, we present a dual-parameter chiral sensing platform based on surface cosine waves (SCWs) that simultaneously captures amplitude and phase asymmetries at the single-particle level. SCWs create a polarization-balanced interferometric field comprising equal-amplitude left and right circular components with a built-in π phase offset. When interacting with a chiral scatterer, this symmetry is broken, encoding the structural handedness into two distinct metrics: circular scattering dichroism (CSD) and circular scattering retardance (CSR). Together, these metrics provide a comprehensive electromagnetic characterization of single-particle chirality. This method provides a robust, generalizable framework for high-sensitivity, single-particle chiral sensing, paving the way toward next-generation chiroptical metrology and device development.