An Effective Polymer Cross-Linking Strategy To Obtain Stable Dispersions of Upconverting NaYF4 Nanoparticles in Buffers and Biological Growth Media for Biolabeling Applications

摘要

Ligands on the nanoparticle surface providensteric stabilization, resulting in good dispersion stability.nHowever, because of their highly dynamic nature, they cannbe replaced irreversibly in buffers and biological medium,nleading to poor colloidal stability. To overcome this, we reportna simple and effective cross-linking methodology to transfernoleate-stabilized upconverting NaYF4 core/shell nanoparticlesn(UCNPs) from hydrophobic to aqueous phase, with long-termndispersion stability in buffers and biological medium.nAmphiphilic poly(maleic anhydride-alt-1-octadecene)n(PMAO) modified with and without poly(ethylene glycol) (PEG) was used to intercalate with the surface oleates, enablingnthe transfer of the UCNPs to water. The PMAO units on the phase transferred UCNPs were then successfully cross-linked usingnbis(hexamethylene)triamine (BHMT). The primary advantage of cross-linking of PMAO by BHMT is that it improves thenstability of the UCNPs in water, physiological saline buffers, and biological growth media and in a wide range of pH values whenncompared to un-cross-linked PMAO. The cross-linked PMAO−BHMT coated UCNPs were found to be stable in water for morenthan 2 months and in physiological saline buffers for weeks, substantiating the effectiveness of cross-linking in providing highndispersion stability. The PMAO−BHMT cross-linked UCNPs were extensively characterized using various techniques providingnsupporting evidence for the cross-linking process. These UCNPs were found to be stable in serum supplemented growthnmedium (37 °C) for more than 2 days. Utilizing this, we demonstrate the uptake of cross-linked UCNPs by LNCaP cells (humannprostate cancer cell line), showing their utility as biolabels.