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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.; Sayers, Edward J.; Magnusson, Jo-Hannes P.; Pope, Iestyn; Payne, Lukas; Alexander, Cameron; Jones, Arwyn T.; Langbein, Wolfgang; Watson, Peter; Borri, Paola


Naya Giannakopoulou

Joseph B. Williams

Paul R. Moody

Edward J. Sayers

Jo-Hannes P. Magnusson

Iestyn Pope

Lukas Payne

Arwyn T. Jones

Wolfgang Langbein

Peter Watson

Paola Borri


Gold nanoparticles have been researched for many biomedical applications in diagnostics, ther-anostics, 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 extinc-tion/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.


Giannakopoulou, N., Williams, J. B., Moody, P. R., Sayers, E. J., Magnusson, J. P., Pope, I., …Borri, P. (2020). Four-wave-mixing microscopy reveals non- colocalisation between gold nanoparticles and fluorophore conjugates inside cells. Nanoscale, 12(7), 4622-4635.

Journal Article Type Article
Acceptance Date Dec 21, 2019
Online Publication Date Feb 11, 2020
Publication Date Feb 21, 2020
Deposit Date Jan 6, 2020
Publicly Available Date Feb 17, 2020
Journal Nanoscale
Print ISSN 2040-3364
Electronic ISSN 2040-3372
Publisher Royal Society of Chemistry
Peer Reviewed Peer Reviewed
Volume 12
Issue 7
Pages 4622-4635
Public URL
Publisher URL


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