High-quality water-soluble and surface-functionalized upconversion nanocrystals as luminescent probes for bioimaging.
Rare-earth upconversion nanophosphors (UCNPs) have great potential to become excellent biological luminescent labels for fluorescence bioimaging. However, it is still difficult to directly synthesize high-quality water-soluble UCNPs bearing appropriate functional groups using a one-step synthetic strategy. Herein, we report a one-step synthetic strategy for high-quality water-soluble and surface-functionalized UCNPs using a hydrothermal reaction assisted by binary cooperative ligands (HR-BCL). In this system, 6-aminohexanoic acid and oleate were introduced to control nuclear generation and crystal growth of small nanoparticles. The UCNPs synthesized here showed high crystalline and intense upconversion luminescence emission. Fourier-transform infrared and nuclear magnetic resonance spectroscopy indicated that 6-aminohexanoic acid and oleate cooperate as surface ligands to co-control the surface of UCNPs. Thus, the water-solubility of the as-prepared UCNPs can be tuned by changing the molar ratio of 6-aminohexanoic acid to oleate. The AA-modified UCNPs provided a free amine content of (6.0 ± 0.2) × 10(-5) mol/g, which renders them dispersible in aqueous solution and allows further conjugation with folic acid (FA) for targeted bioimaging. Furthermore, the amine-functionalized UCNPs show intense near-infrared upconversion luminescence and were successfully applied in the lymphatic capillary bioimaging of small animals with a high signal-to-noise ratio, suggesting that these surface-functionalized UCNPs are promising candidates for luminescent biolabels.
Department of Chemistry & Laboratory of Advanced Materials & Institute of Biomedical Science, Fudan University, 220 Handan Road, Shanghai 200433, PR China.
Tianye
T
Cao
Yang
Y
Yang
Yuan
Y
Gao
Jing
J
Zhou
Zhengquan
Z
Li
Fuyou
F
Li
D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003952:Diagnostic Imaging / Q000379:methods*; D006801:Humans; D049449:Luminescence; D051379:Mice; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000009:adverse effects / Q000737:chemistry* / Q000648:ultrastructure; D036103:Nanotechnology / Q000379:methods; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared