Amplified Detection of Iron Ion Based on Plasmon Enhanced Fluorescence and Subsequently Fluorescence Quenching

A facile and rapid approach for detecting low concentration of iron ion (Fe³⁺) with improved sensitivity was developed on the basis of plasmon enhanced fluorescence and subsequently amplified fluorescence quenching. Au₁Ag₄@SiO₂ nanoparticles were synthesized and dispersed into fluorescein isothiocyanate (FITC) solution. The fluorescence of the FITC solution was improved due to plasmon enhanced fluorescence. However, efficient fluorescence quenching of the FITC/Au₁Ag₄@SiO₂ solution was subsequently achieved when Fe³⁺, with a concentration ranging from 17 nM to 3.4 μM, was added into the FITC/Au₁Ag₄@SiO₂ solution, whereas almost no fluorescence quenching was observed for pure FITC solution under the same condition. FITC/Au₁Ag₄@SiO₂ solution shows a better sensitivity for detecting low concentration of Fe³⁺ compared to pure FITC solution. The quantized limit of detection toward Fe³⁺ was improved from 4.6 μM for pure FITC solution to 20 nM for FITC/Au₁Ag₄@SiO₂ solution.