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 EuF₃ nanoparticles (NPs). Both types of microgels are based upon copolymers of N-isopropylacrylamide (NIPAm) and methacrylic acid (MAA), poly(NIPAm/VCL/MAA) (VCL = N-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 EuF₃ 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 EuCl₃ added to the neutralized microgels. we could vary the atomic content of individual microgels from ca. 10⁶ to 10⁷ Eu atoms, either in the form of Eu³⁺ ions or EuF₃ NPs. Leaching profiles of Eu ions from the hybrid microgels were measured by traditional ICP-MS.