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 R՛² 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 R՛² 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.