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.