Plasmon-Mediated Two-Photon Photoluminescence-Detected Circular Dichroism in Gold Nanosphere Assemblies

We report plasmon-mediated two-photon photoluminescence (TPPL)-detected circular dichroism (CD) from colloidal metal nanoparticle assemblies. Two classes of solid gold nanosphere (SGN) dimers--heterodimers and homodimers--were examined using polarization-resolved TPPL, second harmonic generation (SHG), and one-photon photoluminescence (OPPL). Unambiguous CD was detected in both the TPPL and SHG signals, and the magnitudes of the CD responses in these measurements showed agreement for individual nanostructures. Heterodimers gave larger CD responses (average TPPL-CDR = 0.62 ± 0.33; average SHG-CDR = 0.51 ± 0.21) than homodimers (average TPPL-CDR = 0.19 ± 0.04; average SHG-CDR = 0.18 ± 0.06). OPPL-CD was not detected for either structure. Analysis of dimer emission properties suggested the CD responses were determined by properties of the one-photon-resonant mode excited by the laser. Average TPPL signals were (4.3 ± 0.6)× larger than those for SHG. Because signal amplitude is a primary determinant for spatial accuracies and precisions obtained from optical microscopy, CD contrast generated from plasmon-mediated TPPL, which we report for the first time, can extend the suite of super-resolution imaging techniques.