TY - JOUR A1 - Arppe, Riika A1 - Hyppänen, I. A1 - Perälä, N. A1 - Peltomaa, R. A1 - Kaiser, Martin A1 - Würth, Christian A1 - Christ, S. A1 - Resch-Genger, Ute A1 - Schäferling, Michael A1 - Soukka, T. T1 - Quenching of the upconversion luminescence of NaYF4:Yb3+,Er3+ and NaYF4:Yb3+,Tm3+ nanophosphors by water: the role of the sensitizer Yb3+ in non-radiative relaxation JF - Nanoscale N2 - We have studied the mechanisms of water-based quenching of the upconversion photoluminescence of upconverting nanophosphors (UCNPs) via luminescence decay measurements for a better understanding of the non-radiative deactivation pathways responsible for the relatively low upconversion luminescence efficiency in aqueous solutions. This included both upconversion luminescence measurements and the direct excitation of emissive energy states of Er3+ and Yb3+ dopants in NaYF4:Yb3+,Er3+ UCNPs by measuring the decays at 550 and 655 nm upon 380 nm excitation and at 980 nm upon 930 nm excitation, respectively. The luminescence intensities and decays were measured from both bare and silanized NaYF4:Yb3+,Er3+ and NaYF4:Yb3+,Tm3+ UCNPs in H2O and D2O. The measurements revealed up to 99.9% quenching of the upconversion photoluminescence intensity of both Er3+ and Tm3+ doped bare nanophosphors by water. Instead of the multiphonon relaxation of excited energy levels of the activators, the main mechanism of quenching was found to be the multiphonon deactivation of the Yb3+ sensitizer ion caused by OH-vibrations on the surface of the nanophosphor. Due to the nonlinear nature of upconversion, the quenching of Yb3+ has a higher order effect on the upconversion emission intensity with the efficient Yb–Yb energy migration in the ~35 nm nanocrystals making the whole nanophosphor volume susceptible to surface quenching effects. The study underlines the need of efficient surface passivation for the use of UCNPs as labels in bioanalytical applications performed in aqueous solutions. PY - 2015 DO - https://doi.org/10.1039/c5nr02100f SN - 2040-3364 SN - 2040-3372 VL - 7 IS - 27 SP - 11746 EP - 11757 PB - RSC Publ. CY - Cambridge AN - OPUS4-33815 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Näreoja, T A1 - Deguchi, T A1 - Christ, S. A1 - Peltomaa, R A1 - Prabhakar, N A1 - Fazeli, E A1 - Perälä, N A1 - Rosenholm, J A1 - Arppe, Riika A1 - Soukka, T A1 - Schäferling, Michael T1 - Ratiometric Sensing and Imaging of Intracellular pH Using Polyethylenimine-Coated Photon Upconversion Nanoprobes JF - Analytical Chemistry N2 - Measurement of changes of pH at various intracellular compartments has potential to solve questions concerning the processing of endocytosed material, regulation of the acidification process, and also acidification of vesicles destined for exocytosis. To monitor these events, the nanosized optical pH probes need to provide ratiometric signals in the optically transparent biological window, target to all relevant intracellular compartments, and to facilitate imaging at subcellular resolution without interference from the biological matrix. To meet these criteria we sensitize the surface conjugated pH sensitive indicator via an upconversion process utilizing an energy transfer from the nanoparticle to the indicator. Live cells were imaged with a scanning confocal microscope equipped with a low-energy 980 nm laser excitation, which facilitated high resolution and penetration depth into the specimen, and low phototoxicity needed for long-term imaging. Our upconversion nanoparticle resonance energy transfer based sensor with polyethylenimine-coating provides high colloidal stability, enhanced cellular uptake, and distribution across cellular compartments. This distribution was modulated with membrane integrity perturbing treatment that resulted into total loss of lysosomal compartments and a dramatic pH shift of endosomal compartments. These nanoprobes are well suited for detection of pH changes in in vitro models with high biological background fluorescence and in in vivo applications, e.g., for the bioimaging of small animal models. KW - PH sensing KW - Upconversion KW - Nanoparticles KW - Fluorescecne imaging PY - 2017 UR - http://pubs.acs.org/doi/abs/10.1021/acs.analchem.6b03223 DO - https://doi.org/10.1021/acs.analchem.6b03223 SN - 0003-2700 SN - 1520-6882 VL - 89 IS - 3 SP - 1501 EP - 1508 PB - American Chemical Society CY - Washington AN - OPUS4-39083 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -