Plasmon-Enhanced Optical Tweezers for Single Molecules on and near a Colloidal Silver Nanoaggregate

At the junction of an Ag nanoaggregate, single molecules can emit surface-enhanced Raman scattering and fluorescence (SERS and SEF) and can be optically trapped by an enhanced electromagnetic field via plasmon resonance. Blinking SERS and SEF from a single molecule on the same nanoaggregate were observed simultaneously in a bicolor movie. By super-resolution imaging, the positions of the SERS- and SEF-active molecules were detected beyond the diffraction limit. The spatial fluctuation of the molecule on the nanoaggregate was suppressed as the excitation laser intensity increased. The reason is that the single molecule was optically trapped at the junction via plasmon resonance because the mislocalization effect and the signal intensity do not influence a change in the spatial fluctuation in the super-resolution imaging. The spatial fluctuation of the SEF-active molecule near the Ag surface was larger than that of the SERS-active molecule adsorbed on the surface. The power spectral density revealed that the plasmon-enhanced optically trapped molecule by excitation at high laser intensity moved randomly rather than harmonically

Plasmon-Enhanced Optical Tweezers for Single Molecules on and near a Colloidal Silver Nanoaggregate

At the junction of an Ag nanoaggregate, single molecules can emit surface-enhanced Raman scattering and fluorescence (SERS and SEF) and can be optically trapped by an enhanced electromagnetic field via plasmon resonance. Blinking SERS and SEF from a single molecule on the same nanoaggregate were observed simultaneously in a bicolor movie. By super-resolution imaging, the positions of the SERS- and SEF-active molecules were detected beyond the diffraction limit. The spatial fluctuation of the molecule on the nanoaggregate was suppressed as the excitation laser intensity increased. The reason is that the single molecule was optically trapped at the junction via plasmon resonance because the mislocalization effect and the signal intensity do not influence a change in the spatial fluctuation in the super-resolution imaging. The spatial fluctuation of the SEF-active molecule near the Ag surface was larger than that of the SERS-active molecule adsorbed on the surface. The power spectral density revealed that the plasmon-enhanced optically trapped molecule by excitation at high laser intensity moved randomly rather than harmonically