Fabrication of NaYF₄:Yb,Er Nanoprobes for Cell Imaging Directly by Using the Method of Hydrion Rivalry Aided by Ultrasonic

A novel method of fabricating water-soluble bio-probes with ultra-small size such as NaYF₄:Yb,Er (18 nm), NaGdF₄:Yb,Er (8 nm), CaF₂:Yb,Er (10 nm), PbS (7 nm), and ZnS (12 nm) has been developed to provide for the solubility switch of nanoparticles from oil-soluble to water-soluble in terms of hydrion rivalry aided by ultrasonic. Using NaYF₄:Yb,Er (18 nm) as an example, we evaluate the properties of as-prepared water-soluble nanoparticles (NPs) by using thermogravimetric analyses (TGA), Fourier transform infrared spectroscopy (FTIR), zeta potential (ζ) testing, and 1H nuclear magnetic resonance (¹HNMR). The measured ζ value shows that the newly prepared hydrophilic NaYF₄:Yb,Er NPs are the positively charged particles. Acting as reactive electrophilic moiety, the freshly prepared hydrophilic NaYF₄:Yb,Er NPs have carried out the coupling with amino acids and fluorescence labeling and imaging of HeLa cells directly. Experiments indicate that the method of hydrion rivalry aided by ultrasonic provides a simple and novel opportunity to transform hydrophobic NPs into hydrophilic NPs with good reactivity, which can be imaging some specific biological targets directly.