Rational surface design of upconversion nanoparticles with polyethylenimine (PEI) coating for biomedical applications: better safe than brighter?

Anna E. Guller, Annemarie Nadort, Alla N. Generalova, Evgeny V. Khaydukov, Andrey V. Nechaev, Inna A. Kornienko, Elena V. Petersen, Liuen Liang, Anatoly B. Shekhter, Yi Qian, Ewa M. Goldys, Andrei V. Zvyagin