Lanthanide Phosphate Nanorods as Inorganic Fluorescent Labels in Cell Biology Research

Abstract

One of the fundamental goals in biology is to understand the complex spatiotemporal interplay of biomolecules from the cellular to the integrative level. To study these interactions, researchers commonly use fluorescent labeling for both in vivo cellular imaging and in vitro assay detection (1)(2). In this context, one of the fastest developing and most exciting interfaces of nanotechnology is the use of inorganic quantum dots or fluorescent nanoparticles in cell biology. The unique optical properties of inorganic particles make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations. In addition, the ability to make such nanoparticles and then target these particles to specific biomolecules has led to promising applications in cellular labeling, deep-tissue imaging, and assay labeling, and also as efficient fluorescence resonance energy transfer donors. Conventionally used fluorescent labels, such as organic dyes in cell biology, are prone to problems such as broad spectral features, short lifetime, photobleaching, and potential toxicity to the cells. Inorganic fluorescents, especially europium (Eu) and terbium (Tb) in the lanthanide group, have several unique optical and electronic properties, such as size- and composition-tunable emission from visible to infrared wavelengths, large absorption coefficients across a wide spectral range, symmetric emission spectrum, a large Stokes shift, simultaneous excitation of multiple fluorescent colors, very high levels of brightness, and photostability (3)(4)(5). Furthermore, analysis by cell proliferation and apoptosis assay (dUTP nick-end labeling) showed that lanthanide phosphate (LnPO4 · H2O, where Ln = Eu) and Tb nanorods synthesized by microwave (MW) were nontoxic to endothelial cells(5). In this study, we synthesized LnPO4 · H2O nanorods by an exclusive MW technique and used a transmission electron microscope (TEM) to investigate the internalization of LnPO4 · H2O …