title: Quantifying the cellular uptake of semiconductor quantum dot nanoparticles by analytical electron microscopy.
abstract: Semiconductor quantum dot nanoparticles are in demand as optical biomarkers yet the cellular uptake process is not fully understood; quantification of numbers and the fate of internalized particles are still to be achieved. We have focussed on the characterization of cellular uptake of quantum dots using a combination of analytical electron microscopies because of the spatial resolution available to examine uptake at the nanoparticle level, using both imaging to locate particles and spectroscopy to confirm identity. In this study, commercially available quantum dots, CdSe/ZnS core/shell particles coated in peptides to target cellular uptake by endocytosis, have been investigated in terms of the agglomeration state in typical cell culture media, the traverse of particle agglomerates across U-2 OS cell membranes during endocytosis, the merging of endosomal vesicles during incubation of cells and in the correlation of imaging flow cytometry and transmission electron microscopy to measure the final nanoparticle dose internalized by the U-2 OS cells. We show that a combination of analytical transmission electron microscopy and serial block face scanning electron microscopy can provide a comprehensive description of the internalization of an initial exposure dose of nanoparticles by an endocytically active cell population and how the internalized, membrane bound nanoparticle load is processed by the cells. We present a stochastic model of an endosome merging process and show that this provides a data-driven modelling framework for the prediction of cellular uptake of engineered nanoparticles in general.
authors.affiliation: Institute for Materials Research, School of Chemical and Process Engineering, University of Leeds, Leeds, UK.
authors.forename: Nicole
authors.initials: N
authors.lastname: Hondow
authors.affiliation: Centre for Nanohealth, College of Engineering, Swansea University, Singleton Park, Swansea, UK.
authors.forename: M Rowan
authors.initials: MR
authors.lastname: Brown
authors.affiliation: Wellcome Centre for Cell Matrix Research, University of Manchester, Manchester, UK.
authors.forename: Tobias
authors.initials: T
authors.lastname: Starborg
authors.affiliation: Gatan UK, 25 Nuffield Way, Abingdon, UK.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Monteith
authors.affiliation: Institute for Materials Research, School of Chemical and Process Engineering, University of Leeds, Leeds, UK.
authors.forename: Rik
authors.initials: R
authors.lastname: Brydson
authors.affiliation: Centre for Nanohealth, College of Engineering, Swansea University, Singleton Park, Swansea, UK.
authors.forename: Huw D
authors.initials: HD
authors.lastname: Summers
authors.affiliation: Centre for Nanohealth, College of Engineering, Swansea University, Singleton Park, Swansea, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Rees
authors.affiliation: Institute for Materials Research, School of Chemical and Process Engineering, University of Leeds, Leeds, UK.
authors.forename: Andy
authors.initials: A
authors.lastname: Brown
mesh_terms: D002460:Cell Line; D004705:Endocytosis; D011992:Endosomes / Q000648:ultrastructure; D005434:Flow Cytometry; D008855:Microscopy, Electron, Scanning / Q000379:methods; D046529:Microscopy, Electron, Transmission / Q000379:methods; D053758:Nanoparticles / Q000032:analysis* / Q000737:chemistry / Q000648:ultrastructure; D045663:Quantum Dots / Q000032:analysis* / Q000648:ultrastructure; D012666:Semiconductors
keywords: Cellular uptake; SBF SEM; TEM; energy-filtered TEM; nanoparticle dose; quantum dots