Orientation Sensing with Color Using Plasmonic Gold Nanorods and Assemblies

Colorimetric analysis of broadband illumination scattered from isolated gold nanorods and reduced symmetry Dolmen structures provide a visible measure of the local nanoscale orientation of the nanostructures relative to the laboratory frame of reference. Polarized dark-field scattering microscopy correlated with scanning electron microscopy of low and high aspect ratio gold nanorods demonstrated accuracies of 2.3 degrees, which is a 5-fold improvement over photothermal and defocused imaging methods. By assigning the three color channels of the imaging detector (red, green, and blue) to the plasmon resonance wavelengths of the nanostructure, the quantitative display of orientation improved by 200%. The reduced symmetry of a gold nanorod Dolmen structure further improved the sensitivity of colorimetric orientation by a factor of 2 due to the comparative intensities of the resonances. Thus the simplicity, high accuracy, and sensitivity of visual colorimetric sensing of local nanoscale orientation holds promise for high throughput, inexpensive structure and dynamics studies in biology and material science.