Abstract
Upconverting luminescent lanthanide-doped nanoparticles (UCNP) belong to promising new materials that absorb infrared light able to penetrate in the deep tissue level, while emitting photons in the visible or ultraviolet region, which makes them favorable for bioimaging and cell labeling. Here, we have prepared upconverting NaYF4:Yb,Er@NaYF4:Nd core–shell nanoparticles, which were coated with copolymers of N,N-dimethylacrylamide (DMA) and 2-(acryloylamino)-2-methylpropane-1-sulfonic acid (AMPS) or tert-butyl [2-(acryloylamino)ethyl]carbamate (AEC-Boc) with negative or positive charges, respectively. The copolymers were synthesized by a reversible addition-fragmentation chain transfer (RAFT) polymerization, reaching Mn ~ 11 kDa and containing ~ 5 mol% of reactive groups. All copolymers contained bisphosphonate end-groups to be firmly anchored on the surface of NaYF4:Yb,Er@NaYF4:Nd core–shell nanoparticles. To compare properties of polymer coatings, poly(ethylene glycol)-coated and neat UCNP were used as a control. UCNP with various charges were then studied as labels of carcinoma cells, including human hepatocellular carcinoma HepG2, human cervical cancer HeLa, and rat insulinoma INS-1E cells. All the particles proved to be biocompatible (nontoxic); depending on their ξ-potential, the ability to penetrate the cells differed. This ability together with the upconversion luminescence are basic prerequisites for application of particles in photodynamic therapy (PDT) of various tumors, where emission of nanoparticles in visible light range at ~ 650 nm excites photosensitizer.
Highlights
Upconverting luminescent lanthanide-doped nanoparticles (UCNP) belong to promising new materials that absorb infrared light able to penetrate in the deep tissue level, while emitting photons in the visible or ultraviolet region, which makes them favorable for bioimaging and cell labeling
We investigated di-end-functionalized poly(N,N-dimethylacrylamide) copolymers containing both bisphosphonate anchoring groups binding to the surface of UCNP and amino or sulfonate groups supporting engulfment of the particles in human hepatocellular carcinoma HepG2, human cervical cancer HeLa, and rat insulinoma INS-1E cells
The polymers were labeled with DY-615 and used as a coating of CS-UCNP to make fluorescent imaging of carcinoma cells possible, allowing at the same time to control the stability of both nanoparticles and coatings in the cell medium
Summary
Upconverting luminescent lanthanide-doped nanoparticles (UCNP) belong to promising new materials that absorb infrared light able to penetrate in the deep tissue level, while emitting photons in the visible or ultraviolet region, which makes them favorable for bioimaging and cell labeling. The presence of phosphonate groups in the resulting copolymers was confirmed by 31P NMR spectroscopy: δ 18.1 ppm for Ale-P(DMA-AEC-Boc)-DY-615 or 18.1 and 17.8 ppm for Ale-P(DMA-AMPS)-DY-615 (SI, Fig. S3). In order to obtain positively charged particles, Boc-protected amino groups of Ale-P(DMA-AEC-Boc)-DY-615 polymer were removed (Fig. 3b) as confirmed by 1H NMR (Fig. S1c) and FTIR spectroscopy due to disappearance of peaks at 1710 and 1220 cm−1 assigned to Boc groups (Fig. 2b).
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