Biotinylated Lipid-Coated NaLnF(4) Nanoparticles: Demonstrating the Use of Lanthanide Nanoparticle-Based Reporters in Suspension and Imaging Mass Cytometry

Lanthanide nanoparticles (LnNPs) have the potential to be used as high-sensitivity mass tag reporters in mass cytometry immunoassays. For this application, however, the LnNPs must be made colloidally stable in aqueous buffers, demonstrate minimal non-specific binding to cells, and have functional groups to attach antibodies or other targeting agents. One possible approach to address these requirements is by using lipid coating to modify the surface of the LnNPs. In this work, 39 nm diameter NaYF4:Yb, Er NPs (LnNPs) were coated with a lipid formulation consisting of egg sphingomyelin, 1,2-dioleoyl-snglycero- 3-phosphocholine, 1,2-dioleoyl-3-trimethylammonium propane, cholesterol-(polyethylene glycol-600), and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)-2000]. The resulting biotinylated lipid-coated LnNPs were characterized by dynamic light scattering to determine the hydrodynamic size and stability in phosphate buffered saline, and the composition of the lipid coatings was quantified by liquid chromatography-tandem mass spectrometry. The specific and non-specific binding of the biotinylated lipid-coated LnNPs to a model system of functionalized polystyrene microbeads were then tested by both suspension and imaging mass cytometry. We found that targeted binding with minimal non-specific binding can be achieved with the lipid-coated LnNPs and that the lipid composition of the coating has an impact on the performance of the LnNPs as mass cytometry reporters. These results additionally establish the importance of quantifying the composition of lipid-coated nanomaterials to optimize them more effectively for their desired application.