Controlled Topology in Chiral Plasmonic Loops Enables Ultrastrong Optical Asymmetry and Enantioselective SERS

Although molecular loops with precisely defined chirality can be rationally synthesized, plasmonic analogues with controlled geometry and tunable chiroptical responses have remained unexplored. Here we report a rational design of chiral plasmonic loops with controlled turn number, handedness, and interparticle spacing, enabling strong collective plasmonic coupling and exceptionally high optical asymmetry at the colloidal level, with a dissymmetry factor greater than 0.42. The resulting chiral electromagnetic hotspots, combined with tunable surface chemistry, render these structures ultrasensitive SERS substrates capable of selectively discriminating chiral analytes at low concentrations, providing a general strategy for chiral sensing relevant to pharmacokinetics, drug metabolism, and early biomarker diagnostics.