On‐Demand Fabrication and Manipulation of Single Plasmonic Trimers for Ultrasensitive Enantiomer Detection

Abstract The capability of plasmonic nanostructures in generating superchiral near‐fields holds great potential for a wide range of applications, including enantioselective sensing, medical diagnosis, and chirality‐based bioimaging. To implement high‐performance chiral nanophotonic devices, achieving in situ tuning of chiroptical activity in plasmonic nanostructures is highly desirable yet remains a formidable challenge. Here, a straightforward method is developed for deterministic assembly of plasmonic nanosphere trimers using spectroscopy‐assisted nano‐manipulation. The technique offers in situ, real‐time, and site‐specific control over the chiroptical response of trimers by adjusting their vertex angle and in‐plane orientation. The combination of numerical simulations with the Born‐Kuhn model reveals that oblique excitation effectively induces the symmetry breaking of the trimer structure, resulting in a preferential response of two distinct hybridized plasmonic modes to the handedness of light. Consequently, this yields a significant chiroptical response with the g factor up to 0.37. Remarkably, the trimer with an optimized obtuse angle exhibits a 193‐fold enhancement of optical chirality density, enabling the detection of molecular chirality with a record‐large spectral dissymmetric factor of 12 nm. The study facilitates the rational design of plasmonic nanostructures, offering promising prospects for chiral sensing at the single‐molecule level and asymmetric photocatalysis.