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Positive and Negative Lattice Shielding Effects Co‐existing in Gd (III) Ion Doped Bifunctional Upconversion Nanoprobes
Author(s) -
Chen Feng,
Bu Wenbo,
Zhang Shengjian,
Liu Xiaohang,
Liu Jianan,
Xing Huaiyong,
Xiao Qingfeng,
Zhou Liangping,
Peng Weijun,
Wang Lianzhou,
Shi Jianlin
Publication year - 2011
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201101663
Subject(s) - materials science , bifunctional , photon upconversion , doping , ion , lattice (music) , electromagnetic shielding , nanotechnology , optoelectronics , composite material , catalysis , biochemistry , chemistry , physics , acoustics , quantum mechanics
Gadolinium (Gd) doped upconversion nanoparticles (UCNPs) have been well documented as T 1 ‐MR and fluorescent imaging agents. However, the performance of Gd 3+ ions located differently in the crystal lattice still remains debatable. Here, a well‐designed model was built based on a seed‐mediated growth technique to systematically probe the longitudinal relaxivity of Gd 3+ ions within the crystal lattice and at the surface of UCNPs. We found, for the first time, a nearly 100% loss of relaxivity of Gd 3+ ions buried deeply within crystal lattices (> 4 nm), which we named a “negative lattice shielding effect” (n‐LSE) as compared to the “positive lattice shielding effect” (p‐LSE) for the enhanced upconversion fluorescent intensity. As‐observed n‐LSE was further found to be shell thickness dependent. By suppressing the n‐LSE as far as possible, we optimized the UCNPs' structure design and achieved the highest r 1 value (6.18 mM −1 s −1 per Gd 3+ ion) among previously reported counterparts. The potential bimodal imaging application both in vitro and in vivo of as‐designed nano‐probes was also demonstrated. This study clears the debate over the role of bulk and surface Gd 3+ ions in MRI contrast imaging and paves the way for modulation of other Gd‐doped nanostructures for highly efficient T 1 ‐MR and upconversion fluorescent bimodal imaging.