An ultrasensitive optical fiber SPR sensor enhanced by functionalized carbon quantum dots for Fe3+ measurement

Abstract

Precise detection of ferric ions (Fe³⁺) plays a critical role in maintaining biological homeostasis, ensuring industrial process quality control, and safeguarding ecological safety. Recently, various detection methods and sensors have been widely developed for measuring Fe³⁺, but the tradeoff between their performance and practical applications has not been achieved, such as high sensitivity, excellent specificity, simple structure and fabrication, low cost, and so on. In this study, an optical fiber SPR sensor was developed sensor for detecting Fe³⁺ based on the multimode-coreless-multimode (MNM) structured optical fiber. The refractive index (RI) sensitivity of the MNM fiber coated with a 60 nm Au film modified with gold nanoparticles (AuNPs) reached 3440.45 nm/RIU. The organic groups functionalized carbon quantum dots (CQDs) were synthesized and immobilized onto the Au substrates for specifically trapping Fe³⁺, which will cause the variation of the effective RI around the fiber, thereby resulting in the SPR wavelength shift in the transmission spectrum. By recording the red shift of the SPR wavelength, the amount of Fe³⁺ could be accurately quantified. Upon detection of Fe³⁺, the sensor was demonstrated with great linearity within a wide detection range of 10^-12 to 10^-2 M. The sensor’s sensitivity was obtained to be about 2.07 nm/lg (M) and its limit of detection (LOD) was calculated to be about 2.88 × 10^-13 M. It was also experimentally proved with excellent selectivity and stability, as well as the potential application in simulated real samples. The proposed sensing platform offered a simple configuration for Fe³⁺ detection with excellent performance and had various potential practical applications such as health monitoring, disease diagnosis, dietary planning, medication treatment monitoring, environmental monitoring, etc.