Second Harmonic Generation (SHG) is a coherent nonlinear optical process usually by certain engineered materials which allows conversion of two lower energy photons into single photon with twice the incident energy of an excitation laser light. Single molecule second harmonic generation spectroscopy is largely hindered due to very weak non-linear optical cross-sections of SHG processes. Thus, enhancing SHG using plasmonic nanostructures and nanoantennas have recently gained much attention owing to potential of various nanoscale geometry to tightly confine electromagnetic field into small volumes and provide substantial enhancement of electromagnetic field in nanoscale regions of interest, which can significantly boost the nonlinear signal produced by a nonlinear medium/molecules located in plasmonic nanogaps, especially when resonantly pumped. In this presentation, we would like to share our results on highly sensitive, label-free SHG microscopy methods for simultaneous visualization and three-dimensional orientation imaging of individual Rhodamine 6G (Rh6G) molecules on plasmonic silver nanohole arrays. SHG and two-photon fluorescence microscopy experiments together with numerical simulation results suggested several orders of electromagnetic field enhancement at the surface hot spots on plasmonic nanohole substrate in reference to Rh6G molecules immobilized on the glass substrate, enabling detection of significantly amplified plasmon-enhanced SHG signatures from individual Rh6G molecules on plasmonic silver nanohole device. The ability to determine position and orientation of Rh6G molecules is validated by simulations using template matching algorithm. The details of experimental methods, simulation results and mechanism of SHG enhancement from Rh6G on plasmonic nanohole substrate will be summarized and discussed in this presentation.

Orientation imaging of single molecules on plasmonic nanohole arrays by second harmonic generation microscopy

2019 Spring National Meeting

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