Synthesis and Mass Cytometric Analysis of Lanthanide-Encoded Polyelectrolyte Microgels

This article describes the synthesis and characterization of two series of functional polyelectrolyte copolymer microgels intended for bioassays based upon mass cytometry, a technique that detects metals by inductively coupled plasma mass spectrometry (ICP-MS). The microgels were loaded with Eu(III) ions, which were then converted in situ to EuF<sub>3</sub> nanoparticles (NPs). Both types of microgels are based upon copolymers of <i>N</i>-isopropylacrylamide (NIPAm) and methacrylic acid (MAA), poly(NIPAm/VCL/MAA) (VCL = <i>N</i>-vinylcaprolactam, V series), and poly(NIPAm/MAA/PEGMA) (PEGMA = poly(ethylene glycol)methacrylate, PG series). Very specific conditions (full neutralization of the MAA groups) were required to confine the EuF<sub>3</sub> NPs to the core of the microgels. We used mass cytometry to measure the number and the particle-to-particle variation of Eu ions per microgel. By controlling the amount of EuCl<sub>3</sub> added to the neutralized microgels. we could vary the atomic content of individual microgels from ca. 10<sup>6</sup> to 10<sup>7</sup> Eu atoms, either in the form of Eu<sup>3+</sup> ions or EuF<sub>3</sub> NPs. Leaching profiles of Eu ions from the hybrid microgels were measured by traditional ICP-MS.