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

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.