title: Bacterial imaging with photostable upconversion fluorescent nanoparticles.
abstract: Autofluorescence, photodamage and photobleaching are often encountered when using downconverting fluorophores and fluorescent proteins for bacteria labeling. These caveats represent a serious limitation when trying to map bacteria dissemination for prolonged periods. Upconversion nanoparticles (UCNs), which are able to convert low energy near-infrared (NIR) excitation light into higher energy visible or NIR light, can address these limitations. These particles' unique optical properties translate into attractive advantages of minimal autofluorescence, reduced photodamage, deeper tissue penetration and prolonged photostability. Here, we report a UCN-based bacteria labeling strategy using Escherichia coli as prototypic bacteria. A comparative analysis highlighted the superior photostability of UCN-labeled bacteria over green fluorescent protein-expressing bacteria. Infection study of UCN-labeled bacteria in dendritic cells indicated co-localization of the UCN signal with bacterial position for up to 6 h post-infection. Furthermore, long-term monitoring of the same infected cells demonstrated the potential to utilize photostable UCN-based imaging for bacterial trafficking purposes.
authors.affiliation: Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences (CeLS), #05-01, 28 Medical Drive, Singapore 117456, Singapore.
authors.forename: Li Ching
authors.initials: LC
authors.lastname: Ong
authors.affiliation: Department of Microbiology, Immunology Program, National University of Singapore, Centre for Life Sciences (CeLS), #03-05, 28 Medical Drive, Singapore 117456, Singapore.
authors.forename: Lei Yin
authors.initials: LY
authors.lastname: Ang
authors.affiliation: Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences (CeLS), #05-01, 28 Medical Drive, Singapore 117456, Singapore; Department of Microbiology, Immunology Program, National University of Singapore, Centre for Life Sciences (CeLS), #03-05, 28 Medical Drive, Singapore 117456, Singapore. Electronic address: micas@nus.edu.sg.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Alonso
authors.affiliation: Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences (CeLS), #05-01, 28 Medical Drive, Singapore 117456, Singapore; Department of Biomedical Engineering, Faculty of Engineering, National University of Singapore, Block EA #03-12, 9 Engineering Drive 1, Singapore 117575, Singapore. Electronic address: biezy@nus.edu.sg.
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000818:Animals; D000906:Antibodies / Q000378:metabolism; D002460:Cell Line; D002951:Citrates / Q000737:chemistry; D003713:Dendritic Cells / Q000378:metabolism / Q000382:microbiology; D004926:Escherichia coli / Q000378:metabolism* / Q000648:ultrastructure; D005456:Fluorescent Dyes / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D051379:Mice; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D061848:Optical Imaging / Q000379:methods*; D012996:Solutions; D013194:Staining and Labeling
chemical_list: D000906:Antibodies; D002951:Citrates; D005456:Fluorescent Dyes; D012996:Solutions; D049452:Green Fluorescent Proteins
keywords: Bacteria labeling; Escherichia coli; Fluorescence imaging; Upconversion nanoparticles