Silica‐Coated CaF2:Eu3+ Nanoparticles Functionalized with Oxalic Acid for Bio‐conjugation to BSA Proteins

Abstract

AbstractA new method for silica‐coated CaF2:Eu3+ core‐shell nanoparticles functionalized with oxalic acid for bio‐conjugation to bovine serum albumin (BSA) proteins has been developed. Moreover, CaF2:Eu3+/SiO2 core‐shell nanoparticles modified with oxalic acid are biocompatible and can be dispersed in water. As an organic functional molecule, oxalic acid is able to react with hydroxyl groups existed on the surface of SiO2 layer by esterification reaction to form carboxylic acid for further bio‐conjugation with BSA. The final products were characterized by means of X‐ray diffraction (XRD), transmission electron microscope (TEM), field‐emission scanning electron microscopy (FE‐SEM), ultraviolet (UV) spectrophotometer, infrared (IR) spectrophotometer and photoluminescence (PL) spectra. XRD result confirmed the phase purity of CaF2:10 mol% Eu3+ and CaF2:10 mol% Eu3+/SiO2 nanoparticles obtained from the quaternary reverse micelles of cetyltrimethylammonium bromide (CTAB), cyclohexane, n‐pentanol and water. Images of TEM and FE‐SEM showed that the average grain sizes of CaF2:10 mol% Eu3+/SiO2 and bio‐conjugation of CaF2:10 mol% Eu3+/SiO2 nanoparticles with BSA were about 17 nm. The patterns of UV and IR spectra showed that BSA was linked to CaF2:10 mol% Eu3+/SiO2 nanoparticles. In the emission spectrum of CaF2:10 mol% Eu3+/SiO2 conjugated by BSA nanoparticles, characteristic emission peaks of Eu3+ within the wavelength ranging from 500 to 700 nm were observed, which is corresponding to the transitions from the excited 5D0 levels to 7FJ levels. This confirmed that the Eu3+ dopant ion is located in a Ca2+ crystal site with Td symmetry. CaF2:10 mol% Eu3+/SiO2 conjugated by BSA nanoparticles remain stable in aqueous media within 15 d with pH ranging from 2 to 9. Therefore, these luminescent colloidal nanoparticles can be potentially employed as targeted fluorescent labels in biomedical research applications.