Preparation and characterization of cetyltrimethylammonium bromide (CTAB)-stabilized Fe₃O₄ nanoparticles for electrochemistry detection of citric acid

Sensing systems containing iron oxide nanoparticles have shown high potential for improving the catalytic activity of diverse analytes. However, the role of magnetic systems in these processes is not fully understood. In addition, colloidal stability of iron oxide nanoparticles is another obstacle for their application in sensing platforms. In this study, we report the synthesis of cetyltrimethylammonium bromide (CTAB) stabilized Fe₃O₄ magnetic nanoparticles (MNPs), characterization and their electrochemistry applications for citric acid detection, which is an important addictive in industrial products. The stability of these particles was monitored and compared by zeta potential, dynamic light scattering (DLS) measurements and nanoparticle tracking analysis (NTA). X-ray diffraction (XRD) pattern confirmed the presence of the single crystalline phase. Electron paramagnetic resonance (EPR) measurements were taken at some selected temperatures showing that the main feature of the X-band solid state EPR spectrum has a strong transition at g_eff = 2 at room temperature (RT). This absorption band is correlated to the symmetry of the cubic inverse spinel structure of magnetite which reinforced the results obtained by XRD powder pattern. Thermal evolution dependence of Landé g-factor, resonance field and line width has been evaluated. The size of the superparamagnetic nanocrystallites can be easily controlled with diameter less than 5 nm (4.2 ± 0.3 nm) according to Transmission Electron Microscopy (TEM) measurement. Electrochemical measurements have been employed to investigate how the catalytic properties of Fe₃O₄ nanoparticles stabilized with CTAB immobilized by Layer-by-Layer (LbL) technique influence on the reduction of citric acid. Chronoamperometry gives a sensitivity of 3.0 nA μM^{- 1} for the citric acid in the linear range (R²: 0.997) between 50 μM and 2.5 mM with a limit of detection (LOD, s/n = 3) of 40 μM, which agreed with the dynamic chronoamperometry results. Dynamic chronoamperometry signals also demonstrate that the sensor response is not affected for some interferents such as: Ca^{2 +}, Na⁺, Mg²⁺, K⁺, Cl, uric acid, glucose, catechol and dopamine. In summary, we demonstrate that CTAB-stabilized magnetic nanoparticles improve the catalytic reduction of citric acid and present high potential for sensor applications.