Hyperspectral Dark Field Optical Microscopy of Single Silver Nanospheres

• Published in: Journal of physical chemistry. C Vol. 120; no. 13; pp. 7295 - 7298
• Main Authors: El-Khoury, Patrick Z, Joly, Alan G, Hess, Wayne P
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 07.04.2016
• Subjects: Dark Field Scattering; Environmental Molecular Sciences Laboratory; Hyperspectral; Micro-Spectroscopy; Nanoparticles; Plasmonics
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.6b02401

We record spectrally (400 ≤ λ ≤ 675 nm, Δλ < 4.69 nm) and spatially (diffraction-limited, sampled at 85 nm2/pixel) resolved dark field (DF) scattering from single silver nanospheres of 100 nm in diameter. Hyperspectral DF optical microscopy is achieved by coupling a hyperspectral detector to an optical microscope, whereby spectrally resolved diffraction-limited images of hundreds of silver nanoparticles can be recorded in ∼30 s. We demonstrate how the centers and edges of individual particles can be localized in two dimensions to within a single pixel (85 nm2), using a statistical method for examining texture based on a co-occurrence matrix. Subsequently, spatial averaging of the spectral response in a 3 × 3 pixel area around the particle centers affords ample signal to noise to resolve the plasmon resonance of a single silver nanosphere. A close inspection of the scattering spectra of 31 different nanospheres reveals that each particle has its unique (i) relative scattering efficiency and (ii) plasmon resonance maximum and dephasing time. These observations are suggestive of nanometric structural variations over length scales much finer than the spatial resolution attainable using the all-optical technique described herein.