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Sizing individual dielectric nanoparticles with quantitative differential interference contrast microscopy

Hamilton, Samuel, Regan, David ORCID:, Payne, Lukas, Langbein, Wolfgang ORCID: and Borri, Paola ORCID: 2022. Sizing individual dielectric nanoparticles with quantitative differential interference contrast microscopy. Analyst 147 (8) , pp. 1567-1580. 10.1039/D1AN02009A

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We report a method to measure the size of single dielectric nanoparticles with high accuracy and precision using quantitative differential interference contrast (DIC) microscopy. Dielectric nanoparticles are detected optically by the conversion of the optical phase change into an intensity change using DIC. Phase images of individual nanoparticles were retrieved from DIC by Wiener filtering, and a quantitative methodology to extract nanoparticle sizes was developed. Using polystyrene beads of 100 nm radius as size standard, we show that the method determines this radius within a few nm accuracy. The smallest detectable polystyrene bead is limited by background and shot-noise, which depend on acquisition and analysis parameters, including the objective numerical aperture, the DIC phase offset, and the refractive index contrast between particles and their surrounding. Measurements on small beads of 15 nm nominal radius are shown, and a sensitivity limit potentially reaching down to 1.8 nm radius was inferred. As application example, individual nanodiamonds with nominal sizes below 50 nm were measured, and were found to have a nearly exponential size distribution with 28 nm mean value. Considering the importance of dielectric nanoparticles in many fields, from naturally occurring virions to polluting nanoplastics, the proposed method could offer a powerful quantitative tool for nanoparticle analysis, combining accuracy, sensitivity and high-throughput with widely available and easy-to-use DIC microscopy.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Additional Information: This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Publisher: Royal Society of Chemistry
ISSN: 0003-2654
Funders: EPSRC
Date of First Compliant Deposit: 22 March 2022
Date of Acceptance: 14 February 2022
Last Modified: 30 Nov 2022 07:20

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