Salicylic acid doped silica nanoparticles as a fluorescent nanosensor for the detection of Fe³⁺ in aqueous solution

A novel organic-inorganic hybrid nanosensor (SASP) was prepared by a one-step sol-gel method and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, N₂ adsorption-desorption, fluorescence spectroscopy, etc. The nanosensor showed almost 3-fold fluorescence emission quenching upon excitation with a 293 nm wavelength in the presence of 20 μM Fe³⁺ ions. The presence of 18 other metal ions had no observable effect on the sensitivity and selectivity of the nanosensor. A fluorescence analysis method based on the SASP for the selective detection of Fe³⁺ was established under optimal conditions. The results showed that there was a linear relationship between the log luminescence value and the concentration of Fe³⁺ over the range of 2.0 × 10^-7-9.0 × 10^-5 mol L^-1 with a detection limit (3σ) of 2.5 × 10^-8 mol L^-1. Furthermore, the proposed method was successfully applied for the determination of trace Fe³⁺ in fetal bovine serum without the interference of other molecules and ions. Good recovery (96.5-104.5%) and a relative standard deviation of less than 8.6% were obtained from serum samples spiked with four levels of Fe³⁺. Additionally, the nanosensor showed a good reversibility; the fluorescence could be switched "off" and "on" in two ways, by adjusting the pH of the solution and adding metal chelating agent EDTA.