Effective Shielding of NaYF₄:Yb³⁺,Er³⁺ Upconverting Nanoparticles in Aqueous Environments Using Layer-by-Layer Assembly

Aqueous solutions are the basis for most biomedical assays, but they quench the upconversion luminescence significantly. Surface modifications of upconverting nanoparticles are vital for shielding the obtained luminescence. Modifications also provide new possibilities for further use by introducing attaching sites for biomolecule conjugation. We demonstrate the use of a layer-by-layer surface modification method combining varying lengths of...