Ultrasensitive fluorescence detection of Fe³⁺ ions using fluorescein isothiocyanate functionalized Ag/SiO₂/SiO₂ core–shell nanocomposites

Fluorescein isothiocyanate (FITC) functionalized Ag/SiO₂/SiO₂ core–shell (CS) nanoparticles (NPs) and nanorods (NRs) are synthesized by chemical method to perform the fluorescence detection of Fe³⁺ in aqueous medium. The Fe³⁺ ion sensing is performed on the basis of metal-enhanced fluorescence and subsequent fluorescence quenching of fluorophore (fluorescein isothiocyanate) in aqueous medium. The intensity of fluorescence of FITC is found to get enhanced with increasing the silica shell thickness. The fluorescence intensity of FITC of spherical Ag/SiO₂/SiO₂ (FITC) CS NPs (AgSiF50) is amplified up to 2.25-folds whereas, in case of Ag/SiO₂/SiO₂ (FITC) CS NRs (AgSiFNR), the fluorescence intensity of FITC is amplified up to 3.63-folds compared to that of pure FITC. Owing to the amplified fluorescence of FITC, AgSiF50 and AgSiFNR samples are evaluated for detection of Fe³⁺ in an aqueous medium and the proposed nanoprobes exhibit good sensitivity towards Fe³⁺ detection because of strong binding affinity of Fe³⁺ with isothiocyanate group of FITC. The limit of detections for AgSiF50 and AgSiFNR are found to be 19.4 nM and 0.8 nM, respectively. The BET surface areas of AgSiF50 and AgSiFNR are calculated to be 157.64 m² g⁻¹ and 193.42 m² g⁻¹, respectively. The higher sensitivity of AgSiFNR compared to AgSiF50 for Fe³⁺ ion sensing is accredited to the higher adsorption capacity and higher fluorescence of FITC. This Ag/SiO₂/SiO₂ (FITC) CS NRs probe is a very simple and efficient sensor for Fe³⁺ ion detection and thus, using this sample, a very simple Arduino based electronic device is fabricated which can give real-time application of the idea.