title: Synthesis of Highly Fluorescent Copper Clusters Using Living Polymer Chains as Combined Reducing Agents and Ligands.
abstract: We present the synthesis of colloidally stable ultrasmall (diameter of 1.5 ± 0.6 nm) and fluorescent copper clusters (Cu-clusters) exhibiting outstanding quantum efficiencies (up to 67% in THF and approximately 30% in water). For this purpose, an amphiphilic block copolymer poly(ethylene glycol)-block-poly(propylene sulfide) (MPEG-b-PPS) was synthesized by living anionic ring-opening polymerization. When CuBr is mixed with the living polymer chains in THF, the formation of Cu-clusters is detected by the appearance of the fluorescence. The cluster growth is quenched by the addition of water, followed by THF removal. The structural features of the MPEG-b-PPS copolymer control the cluster formation and the stabilization: the poly(propylene sulfide) segment acts as coordinating and reducing agent for the copper ions in THF, and imparts a hydrophobic character. This hydrophobic block protects the Cu-clusters from water exposure, thus allowing to obtain a stable emission in water. The PEG segment instead provides the hydrophilicity, rendering the Cu-clusters water-soluble. To obtain fluorescent and stable Cu-clusters exhibiting outstanding quantum efficiencies, the removal of the excess of free polymer and copper salt was crucial. The Cu-clusters are also colloidally and optically stable in physiological media and showed bright fluorescence even when taken up by HeLa cells, being noncytotoxic when administered at a Cu dose between 10 nM and 1.6 μM. Given the very small size of the Cu-clusters, localization and fluorescent staining of cell nucleus is achieved, as demonstrated by confocal cell imaging performed at different Cu-cluster doses and at different incubation temperatures.
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Markus J
authors.initials: MJ
authors.lastname: Barthel
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.|Dipartimento di Chimica, Università di Genova , Via Dodecaneso 33, 16146 Genova, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Angeloni
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Alessia
authors.initials: A
authors.lastname: Petrelli
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Tommaso
authors.initials: T
authors.lastname: Avellini
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Alice
authors.initials: A
authors.lastname: Scarpellini
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.|IMEM-CNR , Parco Area delle Scienze 37/A, 43124 Parma, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Bertoni
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Armirotti
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Iwan
authors.initials: I
authors.lastname: Moreels
authors.affiliation: Istituto Italiano di Tecnologia , Via Morego 30, 16163 Genova, Italy.
authors.forename: Teresa
authors.initials: T
authors.lastname: Pellegrino
keywords: PEG; anionic polymerization; cell uptake; copper clusters; nanoparticles; photoluminescence; propylene sulfide