Amine-Functionalized Lanthanide-Doped Zirconia Nanoparticles: Optical Spectroscopy, Time-Resolved Fluorescence Resonance Energy Transfer Biodetection, and Targeted Imaging

Abstract

Ultrasmall inorganic oxide nanoparticles doped with trivalent lanthanide ions (Ln(3+)), a new and huge family of luminescent bioprobes, remain nearly untouched. Currently it is a challenge to synthesize biocompatible ultrasmall oxide bioprobes. Herein, we report a new inorganic oxide bioprobe based on sub-5 nm amine-functionalized tetragonal ZrO(2)-Ln(3+) nanoparticles synthesized via a facile solvothermal method and ligand exchange. By utilizing the long-lived luminescence of Ln(3+), we demonstrate its application as a sensitive time-resolved fluorescence resonance energy transfer (FRET) bioprobe to detect avidin with a record-low detection limit of 3.0 nM. The oxide nanoparticles also exhibit specific recognition of cancer cells overexpressed with urokinase plasminogen activator receptor (uPAR, an important marker of tumor biology and metastasis) and thus may have great potentials in targeted bioimaging.

Ultrasensitive Luminescent In Vitro Detection for Tumor Markers Based on Inorganic Lanthanide Nano‐Bioprobes

“…Through ligand exchange from the as‐prepared hydrophobic NPs by using AEP as surfactants, we synthesized amine‐functionalized CaF 2 :Ln 3+ and ZrO 2 :Ln 3+ NPs for the conjugation of amino terminal fragment (ATF) of urokinase plasminogen activator (uPA) 19. The ATP‐capped NPs were able to specifically recognize uPA receptor (uPAR, an important tumor marker) and were explored as sensitive TRPL and upconverting luminescence (UCL) nanoprobes for the in vitro detection of uPAR and for uPAR‐targeted cancer cell imaging.…”

“…For instance, avidin was conjugated to the surface of ultrasmall citrate‐modified Lu 6 O 5 F 8 :Eu 3+ NPs following a standard EDC/NHS bioconjugation protocol 16. Biotin and ATF of uPA were coupled with amine‐functionalized CaF 2 :Ln 3+ and ZrO 2 :Ln 3+ NPs in N,N ‐dimethylformamide (DMF) by using HBTU/DIEA as cross‐linking reagents 19. Note that the bioactivity of the conjugating biomolecules as well as the dispersability of the NPs may decrease during the bioconjugation, therefore the species and the amounts of the cross‐linking reagents should be carefully selected.…”

Inorganic lanthanide nanoprobes for background-free luminescent bioassays

“…For example, by utilizing the positively charged Ln 3+ ions exposed on ligand-free LiLuF 4 :Yb, Er UCNPs, we have succeeded in the avidin functionalization of the UCNPs through electrostatic interaction [62]. Likewise, Lu and coworkers [101] developed an exceptionally simple strategy for the direct synthesis of DNA-func- -Benzotriazole-N,N,N',N'-tetramethyluronium-hexafluoro-phosphate (HBTU) and N,N-diisopropylethy (DIEA) as cross-linking reagents [65,102]. Despite the validity of these methods, the functional groups are omnipresent in biological systems and cannot be labeled specifically in complex biological systems.…”

“…By employing biotinylated NaYF 4 :Ce,Tb NPs as an energy donor and fluorescein isothiocyanate (FITC)-labeled avidin as an energy acceptor, we constructed the first TR-FRET pair for the detection of avidin with an LOD of ~4.8 nM [27]. Later on, this novel TR-FRET technique was refined and extended to other Ln 3+ -NPs such as KGdF 4 : Tb 3+ and ZrO 2 : Tb 3+ NPs for avidin assays with LODs of ~5.5 nM and ~3.0 nM, respectively [102,111].Since the efficiency of nonradiative FRET relies heavily on the distance between the donor and acceptor and competes with the radiative transitions of the donor, small particle size and long PL lifetime of the donor are highly desirable. To maximize the FRET efficiency and achieve a lower detection limit, we developed a unique strategy through sodium co-doping for the synthesis of ultrasmall (~3.8 nm) and highly emissive (QY of 51%) CaF 2 : Ce,Tb NPs with a long PL lifetime (~12.5 ms) for TR-FRET bioassay [65].…”

Recent Advances on Functionalized Upconversion Nanoparticles for Detection of Small Molecules and Ions in Biosystems

“…Although this phenomenon has been known more than 60 years,29 for a long time, the application of this phenomenon was only limited to bulk glass and crystalline materials 30, 31. Until the late 1990s, the advance of nanotechnology provided new opportunities to UCNPs and these materials have become one of the most attractive research fields within nanoscience community including many progresses in biodetection 32, 33, 34, 35, 36…”