Maleimide activation of photon upconverting nanoparticles for bioconjugation

: Liebherr RB, Soukka T, Wolfbeis OS, Gorris HH

Publisher: IOP PUBLISHING LTD

: 2012

: Nanotechnology

: NANOTECHNOLOGY

: ARTN 485103

: 48

: 23

: 48

: 7

: 0957-4484

DOI: https://doi.org/10.1088/0957-4484/23/48/485103

Photon upconverting nanoparticles (UCNPs) have become an important new class of optical labels. Their unique property of emitting visible light after photo-excitation with near-infrared radiation enables biological imaging without background interference or cell damage. Biological applications require UCNPs that are dispersible in water and allow the attachment of biomolecules. Oleic acid-coated UCNPs obtained by solvothermal synthesis were functionalized with both hydrophilic PEG and thiol-reactive maleimides, either by ligand exchange or by silanization. Three different types of maleimide-functionalized UCNPs were prepared and characterized by transmission electron microscopy, dynamic light scattering and Raman spectroscopy. Ligand exchange of oleic acid by maleimide-PEG-COOH yielded UCNPs that did not aggregate, were colloidally stable and reacted readily with proteins. Such luminescent labels are required for background-free imaging and many other bioanalytical applications.