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Four-wave-mixing microscopy reveals non-colocalisation between gold nanoparticles and fluorophore conjugates inside cells

Giannakopoulou, Naya, Williams, Joseph B., Moody, Paul R. ORCID:, Sayers, Edward J. ORCID:, Magnusson, Johannes P., Pope, Iestyn ORCID:, Payne, Lukas, Alexander, Cameron, Jones, Arwyn T. ORCID:, Langbein, Wolfgang ORCID:, Watson, Peter ORCID: and Borri, Paola ORCID: 2020. Four-wave-mixing microscopy reveals non-colocalisation between gold nanoparticles and fluorophore conjugates inside cells. Nanoscale 12 (7) , pp. 4622-4635. 10.1039/C9NR08512B

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Gold nanoparticles have been researched for many biomedical applications in diagnostics, theranostics, and as drug delivery systems. When conjugated to fluorophores, their interaction with biological cells can be studied in situ and real time using fluorescence microscopy. However, an important question that has remained elusive to answer is whether the fluorophore is a faithful reporter of the nanoparticle location. Here, our recently developed four-wave-mixing optical microscopy is applied to image individual gold nanoparticles and in turn investigate their co-localisation with fluorophores inside cells. Nanoparticles from 10 nm to 40 nm diameter were conjugated to fluorescently-labeled transferrin, for internalisation via clathrin-mediated endocytosis, or to non-targeting fluorescently-labelled antibodies. Human (HeLa) and murine (3T3-L1) cells were imaged at different time points after incubation with these conjugates. Our technique identified that, in most cases, fluorescence originated from unbound fluorophores rather than from fluorophores attached to nanoparticles. Fluorescence detection was also severely limited by photobleaching, quenching and autofluorescence background. Notably, correlative extinction/fluorescence microscopy of individual particles on a glass surface indicated that commercial constructs contain large amounts of unbound fluorophores. These findings highlight the potential problems of data interpretation when reliance is solely placed on the detection of fluorescence within the cell, and are of significant importance in the context of correlative light electron microscopy.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Pharmacy
Physics and Astronomy
Additional Information: This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Publisher: Royal Society of Chemistry
ISSN: 2040-3364
Funders: EPSRC
Date of First Compliant Deposit: 11 February 2020
Date of Acceptance: 21 December 2019
Last Modified: 06 Jan 2024 04:50

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