Single-Shot Aspect Ratio and Orientation Imaging of Nanoparticles

Abstract

Plasmonic nanoparticleswith surface plasmon resonance (SPR) andscattering response dependent on their geometry and surrounding environmentare predestinated to be used as optical probes for sensing and imaging.Optical microscopy is capable of observing nanoparticles in variousmedia, but their geometry remains hidden below the diffraction limit.Here, a wide-field optical imaging technique is demonstrated, restoringthe aspect ratio and orientation of individual nanoparticles via thepolarization anisotropy (PA) measurement of the scattered light. ThePA is mapped into a single nanoparticle image, formed by decomposingthe scattered light into longitudinal and transverse SPR modes andmanipulating their angular momentum. The wide-field images providethe aspect ratio and orientation of many deposited nanoparticles allowingtheir assessment in heterogeneous suspensions or time-resolved measurements.In calibration experiments, orientation measurement accuracy and excellentsensitivity to nanoparticles with specific aspect ratios are demonstrated.Subsequently, the method is deployed in the automatic shape-dependentcategorization of hundreds of nanoparticles in a heterogeneous mixture.The single-shot capability is demonstrated in the time-resolved imagingof the electrophoretic deposition process.Plasmonic nanoparticleswith surface plasmon resonance (SPR) andscattering response dependent on their geometry and surrounding environmentare predestinated to be used as optical probes for sensing and imaging.Optical microscopy is capable of observing nanoparticles in variousmedia, but their geometry remains hidden below the diffraction limit.Here, a wide-field optical imaging technique is demonstrated, restoringthe aspect ratio and orientation of individual nanoparticles via thepolarization anisotropy (PA) measurement of the scattered light. ThePA is mapped into a single nanoparticle image, formed by decomposingthe scattered light into longitudinal and transverse SPR modes andmanipulating their angular momentum. The wide-field images providethe aspect ratio and orientation of many deposited nanoparticles allowingtheir assessment in heterogeneous suspensions or time-resolved measurements.In calibration experiments, orientation measurement accuracy and excellentsensitivity to nanoparticles with specific aspect ratios are demonstrated.Subsequently, the method is deployed in the automatic shape-dependentcategorization of hundreds of nanoparticles in a heterogeneous mixture.The single-shot capability is demonstrated in the time-resolved imagingof the electrophoretic deposition process.