title: Three-photon-excited luminescence from unsymmetrical cyanostilbene aggregates: morphology tuning and targeted bioimaging.
abstract: We report an experimental observation of aggregation-induced enhanced luminescence upon three-photon excitation in aggregates formed from a class of unsymmetrical cyanostilbene derivatives. Changing side chains (-CH3, -C6H13, -C7H15O3, and folic acid) attached to the cyanostilbene core leads to instantaneous formation of aggregates with sizes ranging from micrometer to nanometer scale in aqueous conditions. The crystal structure of a derivative with a methyl side chain reveals the planarization in the unsymmetrical cyanostilbene core, causing luminescence from corresponding aggregates upon three-photon excitation. Furthermore, folic acid attached cyanostilbene forms well-dispersed spherical nanoaggregates that show a high three-photon cross-section of 6.0 × 10(-80) cm(6) s(2) photon(-2) and high luminescence quantum yield in water. In order to demonstrate the targeted bioimaging capability of the nanoaggregates, three cell lines (HEK293 healthy cell line, MCF7 cancerous cell line, and HeLa cancerous cell line) were employed for the investigations on the basis of their different folate receptor expression level. Two kinds of nanoaggregates with and without the folic acid targeting ligand were chosen for three-photon bioimaging studies. The cell viability of three types of cells incubated with high concentration of nanoaggregates still remained above 70% after 24 h. It was observed that the nanoaggregates without the folic acid unit could not undergo the endocytosis by both healthy and cancerous cell lines. No obvious endocytosis of folic acid attached nanoaggregates was observed from the HEK293 and MCF7 cell lines having a low expression of the folate receptor. Interestingly, a significant amount of endocytosis and internalization of folic acid attached nanoaggregates was observed from HeLa cells with a high expression of the folate receptor under three-photon excitation, indicating targeted bioimaging of folic acid attached nanoaggregates to the cancer cell line. This study presents a paradigm of using organic nanoaggregates for targeted three-photon bioimaging.
authors.forename: Amal Kumar
authors.initials: AK
authors.lastname: Mandal
authors.forename: Sivaramapanicker
authors.initials: S
authors.lastname: Sreejith
authors.forename: Tingchao
authors.initials: T
authors.lastname: He
authors.forename: Swarup Kumar
authors.initials: SK
authors.lastname: Maji
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Wang
authors.forename: Shi Li
authors.initials: SL
authors.lastname: Ong
authors.forename: James
authors.initials: J
authors.lastname: Joseph
authors.forename: Handong
authors.initials: H
authors.lastname: Sun
authors.affiliation: ¶School of Materials Science and Engineering, Nanyang Technological University, 639798 Singapore.
authors.forename: Yanli
authors.initials: Y
authors.lastname: Zhao
mesh_terms: D000181:Acrylonitrile / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D045744:Cell Line, Tumor; D004705:Endocytosis; D058972:Folic Acid Transporters / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D049449:Luminescence; D057054:Molecular Imaging / Q000379:methods*; D049329:Nanostructures / Q000737:chemistry; D017785:Photons; D013267:Stilbenes / Q000737:chemistry* / Q000378:metabolism
chemical_list: D058972:Folic Acid Transporters; D013267:Stilbenes; D000181:Acrylonitrile
keywords: aggregation-induced enhanced luminescence; cyanostilbene; folic acid; targeted bioimaging; three photon