Magnetic Solid-Phase Microextraction of Hazardous Light Green Dye Followed by Fluorometric and Colorimetric Modes for Detection using NiFe2O4 Nanoparticles from an Aqueous Environment

This work suggests a new, easy, useful, and cost-effective magnetic solid phase microextraction (µ-MSPE) method that is followed by dual-mode detection of dangerous light green (LG) dye in water. We utilized magnetic nickel ferrite nanoparticles (NiFe2O4NPs) as an efficient LG adsorbent. We determined LG using dual-mode colorimetric and fluorometric detection. The colorimetric mode is based on measuring LG color at a maximum wavelength of 620 nm. In contrast, the fluorescence sensing mode depends on quenching the fluorescence emission of red-emissive cationic carbon dots (RC-CDs) at λem= 680 nm after excitation at 340 nm via both electrostatic interaction and the inner-filter effect (IFE). The as-synthesized RC-CDs had a fluorescence quantum yield (Φs) of 24.4%. Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), Energy Dispersive X-ray (EDX), Fourier Transform Infrared Spectroscopy (FT-IR), Powder X-ray Diffraction (PXRD), Dynamic Light Scattering (DLS), UV/Vis Spectroscopy, and Fluorescence Spectroscopy were used to confirm the identification of NiFe2O4 NPs and RC-CDs. All µ-MSPE and determination-affecting factors were carefully optimized. The Freundlich model best suited the adsorption isotherm, with an R2 value of 0.9995 and a maximum adsorption capacity (Qmax) of 35.1 mg/g. A pseudo-second-order (PSO) model with a constant of 4.1 mg/min and R2 of 0.9965 was used to explain the adsorption kinetics. From the results, the study revealed that absorption intensities increased linearly with LG concentration in the range of 10-300 µg/mL with a detection limit (S/N=3) of 2.9µg/mL. In contrast, fluorescence intensities exhibited a linear decrease with LG concentration in the 7-100 µg/mL range with a detection limit (S/N=3) of 2.1 µg/mL. The application of μ-MSPE proved effective in determining LG in samples, with recoveries ranging from 93.7% to 101.5% and RSD % less than 3.9%, highlighting the reliability of the proposed methods.