Fig. 1: Dynamic nanocavity controlled by optical plasmonic trapping.
a Schematic illustration of the optical plasmonic tweezer-coupled SERS platform. Top: Off-state that has the 532 nm excitation laser (green) for SERS measurements. Bottom: On state that has the 532 nm excitation laser (green) and the 1064 nm trapping laser (red) to form the dynamic nanocavity among a trapped AgNP and two coated AgNP at the plasmonic junction of an AgNP-coated microbead dimer. b Brightfield image of an oligonucleotide-linked AgNP-coated silica microbead dimer by a conventional optical microscope. The scale bar is 1 μm. The micrograph is representative of at least three independent experiments. c The time-averaged SERS spectra over 5 s recorded at an AgNP-coated bead dimer in 500 nM NBA solution by the 532 nm excitation laser with the switching of the 1064 nm trapping laser between on (red) and off (black) states for 12 times. The term (arb. units) is abbreviated for arbitrary units. d Calculated trapping potential along the z-axis. The red dashed line represents the virtual trapping potential within the plasmonic junction of an AgNP-coated microbead dimer, where the trapped AgNP is confined against the coated AgNP. Insert: The confinement of the trapped AgNP due to a balance between the action force of optical plasmonic trapping (FOPT) and the reaction force at the contact surface (FR). e FDTD simulation of the E-field (|E/E0 | ) distribution at the dynamic nanocavity among the trapped AgNP and the coated AgNP in the plasmonic junction.
