Publication date: 10th April 2014
Traditional biological labels such as organic dies, quantum dots and fluorescent proteinsrevealed several undesirable side effects, more effort were concentrated to an increasing class of fluorophores - upconverting nanoparticles (UCNP‘s). Being biocompatible, nontoxic, having longer detection times, good chemical and physical stability and lower autofluorescence rare-earth doped UCNP‘s are promising alternatives for potential biological and medical applications. These nanoparticles offer high photostability and enable deep tissue-penetration depths (up to 10 mm) by irradiation with near-infrared (NIR) light, which makes them particularly attractive for bioimaging applications. Biomedical application of UCNP‘s have also been studied in the past few years, mainly focused on the photodynamic therapy (PDT) relying on the resonance energy transfer from UCNPs to PDT photosensitive molecules under the NIR light irradiation.
In order to obtain multifunctional both fluorescent and magnetic resonance imaging (MRI) contrast agents, Gd3+ ions are used as activators in host lattice of NaREF4. Also, for comparison of luminescence properties the doped NaYF4 nanoparticles were synthesized. One of the most common route of synthesis for NaYF4 :Yb3+, Er3+, Tm3+ (or NaGdF4 with same dopant ions) the thermal decomposition in organic solvent was used for preparation of nanoparticles. By changing conditions of a synthesis, different phase (cubic or hexagonal) and size NaREF4:Yb3+, Er3+, Tm3+ nanoparticles were obtained and analyzed with fluorescence spectrometer (PL), scanning electron and transmission microscopy, (SEM and TEM), X-ray diffraction (XRD) and infrared spectroscopy (FTIR) instruments.
To achieve hydrophilic particles, surface coating ligand (oleic acid) was modified with nonionic triblock copolymer (poly(ethylene oxide)-block-poly(propilene oxide)-block-poly(ethylene oxide)). Highly efficient luminescent UCNP’s which could be used for biological applications as bioimaging dies (NaYF4 NaGdF4 ) for cell visualization and as MRI agent (NaGdF4) were prepared. Also, the data of distribution and toxicity of nanoparticles in cells or in tumor of mice will be presented.