Plasmonic Near‐Field‐Based Spatially Activated Light Microscopy for Super‐Resolved Synaptic Analysis

ABSTRACT We present plasmonic‐based spatially activated light microscopy (P‐SALM), a super‐resolution imaging approach that dynamically exploits plasmonic near‐fields formed at nanoaperture arrays. By spatially shifting localized fields, P‐SALM achieves sub‐diffraction imaging with conventional fluorophores, without requiring photoswitchable dyes or high depletion intensities. In proof‐of‐concept experiments, four‐channel P‐SALM enabled visualization of pre‐synaptic VGAT and post‐synaptic MAP2 distributions in fixed hippocampal neurons by producing peak full‐width‐at‐half‐maximum of 42 nm (VGAT) and 55 nm (MAP2) as effective localization precision. While the current implementation yields an effective resolution of ∼130 nm and remains limited by fluorophore density and aperture geometry, the results demonstrate the feasibility of plasmonic near‐field modulation as an alternative pathway to super‐resolution. Compared with PALM, STORM, and STED, P‐SALM simplifies sample preparation and operates under relatively low excitation powers; relative to conventional SIM, it achieves resolution enhancement through sub‐diffraction limited near‐field rather than far‐field interference. These features highlight its potential for future live‐cell applications requiring wide‐field, video‐rate imaging of dynamic biological processes.