Abstract
This work reports the synthesis, structural characterization, and optical properties of ZrO2:Yb(3+)-Er(3+) (2–1 mol%) nanocrystals. The nanoparticles were coated with 3-aminopropyl triethoxysilane (APTES) and further modified with biomolecules, such as Biotin-Anti-rabbit (mouse IgG) and rabbit antibody-AntiKi-67, through a conjugation method. The conjugation was successfully confirmed by Fourier transform infrared, zeta potential, and dynamic light scattering. The internalization of the conjugated nanoparticles in human cervical cancer (HeLa) cells was followed by two-photon confocal microscopy. The ZrO2:Yb(3+)-Er(3+) nanocrystals exhibited strong red emission under 970-nm excitation. Moreover, the luminescence change due to the addition of APTES molecules and biomolecules on the nanocrystals was also studied. These results demonstrate that ZrO2:Yb(3+)-Er(3+) nanocrystals can be successfully functionalized with biomolecules to develop platforms for biolabeling and bioimaging.
Highlights
Biotin-Anti-rabbit protein is conjugated to the nanoparticles containing aminopropyl triethoxysilane (APTES) by forming an amide bond between the free amino groups located at the surface of ZrO2∶Yb3þ-Er3þ∕APTES and the carboxylic acid groups exposed in the IgG protein
The successful conjugation was confirmed by Fourier transform infrared (FTIR), zeta potential, and Dynamic light scattering (DLS)
The nanoparticles internalized in human cervical cancer (HeLa) cells demonstrated a strong red luminescence and were observed using a two-photon confocal microscope
Summary
Lanthanide-doped nanomaterials are promising platforms for bioapplications due to their ability to convert low-energy nearinfrared (NIR) radiation into higher-energy visible luminescence through a process called upconversion (UPC).[1,2] There are several potential benefits for the use of nanocrystals with UPC emission in biological applications, such as no damage of tissues; anti-Stokes emission; long lifetimes; photostability; increased contrast in biological specimens due to the absence of autofluorescence upon excitation with IR light; and simultaneous detection of multiple targeted analytes.[3,4,5,6] Other advantages of the UPC emission are the reduction of photobleaching and scattering in tissues, which avoid the use of complicated and high-cost femtosecond lasers and photomultiplier tubes.[7,8,9,10]. To detect and diagnose cancer, there are several biomarkers;[20,21,22,23] for example, the Ki-67 protein is expressed in all phases of the cell division cycle, but its expression level is strongly downregulated in the resting G0 phase This characteristic makes the Ki-67 protein an excellent biomarker for cell proliferation.[24,25,26] This biomolecule can be used as a prognostic marker in many types of cancers.[27,28,29,30,31] it has been demonstrated that cervical human cancer (HeLa) cells can be labeled using doped or undoped nanomaterials, such as NaYF4∶Yb3þ-Er3þ, NaYF4∶Yb3þ-Er3þ@CaF2 core@shell, NaGdF4∶Yb3þ-Er3þ∕Silica∕Au, CaF2 and carbon nanoparticles. We envision that this is a promising method for labeling different types of cancer cells for biosensing and bioimaging purposes
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