Interferometric scattering microscopy (iSCAT) is the imaging technique based on interference between a scattered field from a weak scatterer (Escat) and a reflected field from a substrate (Erefl). The iSCAT provides high detection sensitivity and temporal resolution for imaging and tracking of an individual nanoparticle (NP) and a single biomolecule. However, it has limit to be applied to quantitative analysis or spectroscopy because an interference signal (2Re[Escat*Erefl]) of the iSCAT cannot provide separated amplitude and phase information on Escat directly. Here, we demonstrated a method to recover both the amplitude and phase spectra of an NP-scattered field (Escat) from iSCAT images using Gouy-phase interferometry. The method was validated by showing that the recovered amplitude and phase spectra of a gold nanoparticle fully reproduce well-known spectral features of localized surface plasmon resonances (LSPR). Moreover, additional measurement suggests that our method can be possibly used to estimate the radiative damping and chemical interface damping (CID) of the nanostructure separately, using phase information.

Amplitude and phase of a single nanoparticle scattering

ACS Spring 2022

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