Highly Luminescent Rare Earth Nanoparticles for Potential Biomedical Applications

Abstract: Rare earth (RE)-doped metal oxide nanoparticles have been synthesized and characterized for potential biomedical applications. These nanoparticles are a promising new class of material that can serve as a luminescent tag or reporter for affinity or immunoassays in biomedical, environmental, food quality, and drug testing probe. They possess several attractive attributes such as a small size, a large Stokes shift, sharp emission spectra, long luminescence lifetime, and excellent photo-stability. The large Stokes shift enables one to subtract the excitation wavelength by filtering, while the long lifetime allows the time-gated detection and subtraction of the background autofluoresence. These unique properties of the RE-doped metal oxide nanoparticles make them promising candidates for low-cost applications in biochemistry and biotechnology. The use of RE-doped metal oxide nanoparticles is an alternative to using fluorescent organic dye for the labeling of biomolecules. Organic dyes give rise to the usual problems of broad spectral features, short lifetime, photobleaching, and potential toxicity to cells. In contrast, the RE-doped nanoparticles have a potential to overcome these problems by providing sharp line emission spectra, distinct lifetimes that are a thousand times longer, and particles encapsulated in neutral environments to avoid toxic reactions. The optimized nanoparticles can be useful for various applications such as nanosensors, bioprobes, drug discovery, diagnostics, genetic analysis, flow cytometry, and high-throughput screening. Furthermore, due to the high quantum yield, excellent photostability, and non-toxicity unlike the semiconductor-based quantum dots (QD), the RE nanoparticles can be used as one of the most suitable fluorescent labels. Therefore, an in-depth discussion will be made on the advantages and disadvantages of RE-based nanoparticles for their potential applications in biomedicine.