Abstract
Label-free imaging of rapidly moving, sub-diffraction sized structures has important applications in both biology and material science, as it removes the limitations associated with fluorescence tagging. However, unlabeled nanoscale particles in suspension are difficult to image due to their transparency and fast Brownian motion. Here we describe a novel interferometric imaging technique referred to as Magnified Image Spatial Spectrum (MISS) microscopy, which overcomes these challenges. The MISS microscope provides quantitative phase information and enables dynamic light scattering investigations with an overall optical path length sensitivity of 0.95 nm at 833 frames per second acquisition rate. Using spatiotemporal filtering, we find that the sensitivity can be further pushed down to 10-3-10-2 nm. We demonstrate the instrument's capability through colloidal nanoparticle sizing down to 20 nm diameter and measurements of live neuron membrane dynamics. MISS microscopy is implemented as an upgrade module to an existing microscope, which converts it into a powerful light scattering instrument. Thus, we anticipate that MISS will be adopted broadly for both material and life sciences applications.
Highlights
Unlabeled nanoscale objects, such as colloidal nanoparticles and subcellular vesicles, are extremely challenging to image with light for several reasons [1]
We show that because of the particular interferometric geometry used, magnified image spatial spectrum (MISS) microscopy is highly sensitive to phase or optical path-length difference (OPD) changes introduced by nanoscale objects and can achieve high acquisition rates
Due to its high acquisition rates, we show that time-resolved MISS imaging data can be used to (a) accurately size colloidal particles under Brownian motion, of radii down to 1/50 of the wavelength of light and (b) measure membrane dynamics from live, electrically active mammalian neurons, without the need for labels or physical contact
Summary
Unlabeled nanoscale objects, such as colloidal nanoparticles and subcellular vesicles, are extremely challenging to image with light for several reasons [1]. Transparent samples only modulate the phase of the incident field, which makes them undetectable by intensity-based imaging systems. While systems that detect the scattered field are able to register signals from nanoparticles [2], they are unable to detect all spatial frequencies in a single acquisition which requires measurement of the phase image. We introduce magnified image spatial spectrum (MISS) microscopy, which meets these challenges. We show that because of the particular interferometric geometry used, MISS microscopy is highly sensitive to phase or optical path-length difference (OPD) changes introduced by nanoscale objects and can achieve high acquisition rates. Our measurements can quantify the dynamics of particles that are much smaller than the wavelength of light
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