A novel biosensor, Lac-Cu/Fe₃O₄/MWCNTs-COOH/GCE, was prepared for the rapid and sensitive determination of polyphenols in foods by immobilizing magnetic nanosized ferric oxide (Fe₃O₄), carboxylated multi-wall carbon nanotubes (MWCNTs-COOH) and laccase-Cu (Lac-Cu) onto the surface of a glassy carbon electrode (GCE). The morphological structure of the modified material was characterized by scanning electron microscopy (SEM). This nanoenzyme sensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The CV results showed that the oxidation peak current (I_p) of gallic acid at GCE, Lac-Cu/GCE, Lac-Cu/MWCNTs-COOH/GCE and Lac-Cu/Fe₃O₄/MWCNTs-COOH/GCE was 19.38, 38.87, 46.61 and 59.95 μA, respectively, indicating that the biosensors of Fe₃O₄/MWCNTs-COOH and Lac-Cu had a significant catalytic effect on the electrochemical oxidation of gallic acid, the oxidation peak current increased by 2.10 times compared to the glassy carbon electrode. The experimental conditions optimized by linear sweep voltammetry (LSV) were as follows: 0.1 mol/L citric acid at pH 3 as the electrolyte solution, 4:1 of MWCNTs-COOH to Fe₃O₄ ratio, 5 μL of the composite solution, 4 U of Lac-Cu hybrid nanoflowers, and 12 min of enrichment time. Under these conditions, the I_p exhibited a linear relationship with polyphenol concentration (C_pp) over the range of 7 to 118 μmol/L, described by the equation I_p = 0.6797 C_pp + 38.978 (R² = 0.9993). The limit of detection (LOD) was 1.5 × 10^-9 mol/L (signal-to-noise ratio, R_SN = 3). For the detection of oat polyphenols, this method outperformed the Folin phenol method in accuracy, with spiked recovery rates of 94.45% to 103.5%. With its advantages of rapidity, high accuracy, low LOD and good interference resistance, this method is practical for the rapid and sensitive determination of polyphenols in foods.

A nano-immunosensor for the rapid determination of 3-amino-5-methylmorpholino-2-oxazolidinone (AMOZ) in aquatic products was prepared by immobilizing anti-AMOZ antibodies onto a glass carbon electrode modified with a hybrid nanocomposite (Fe₃O₄@AuNPs/MWCNTs-COOH) consisting of magnetic ferric oxide (Fe₃O₄), gold nanoparticles (AuNPs), and carboxylated multi-walled carbon nanotubes (MWCNTs-COOH). The microstructure of the prepared nanoparticles of Fe₃O₄ and Fe₃O₄@AuNPs was analyzed using ultraviolet-visible (UV-vis) spectroscopy and infrared (IR) spectroscopy, and their microscopic morphology was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical performance of the prepared immunosensor was studied by cyclic voltammetry, electrochemical impedance spectroscopy, and the experimental conditions were optimized by differential pulse voltammetry using [Fe(CN)₆]^3-/4- as the probe. The optimized conditions were as follows: V(Fe₃O₄@AuNPs) to V(MWCNTs-COOH) ratio 1:2, electrolyte solution pH 7.0, antibody concentration 80 μg/mL, incubation temperature 37 ℃, and incubation time 30 minutes. Under these conditions, the current response of the immunosensor showed a good linear relationship with lg C_[AMOZ] in the range from 1.0 × 10^-10 to 8.0 × 10^-7 mol/L, with a detection limit of 2.4 × 10^-11 mol/L. The recovery rates of spiked crucian carp samples were between 92.78% and 102.61%, which was basically consistent with the results of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Furthermore, the immunosensor method has the advantages of simple pre-treatment and fast detection speed, and can be used for the rapid detection of AMOZ in actual aquatic products.

In this study, in order to establish an electrochemical method for the rapid and sensitive determination of benzo[a]pyrene (BaP) in barbecued meat products, a Fe₃O₄/multi-walled carbon nanotubes (MWCNTs)-COOH/Nafion/glassy carbon electrode (GCE) electrochemical sensor was prepared using magnetic ferric oxide (Fe₃O₄), MWCNTs-COOH and Nafion as composite modifying materials and a GCE as carrier. The optimal conditions were determined as follows: disodium hydrogen phosphate-potassium dihydrogen phosphate solution at pH 2.5 as electrolyte solution, 0.5% Nafion as dispersant, 6 µL of modifying solution (2 mg/mL), and enrichment time 15 min. Under these conditions, there was a good linear relationship between BaP concentration in the range of 0–100 nmol/L and peak current, with a determination coefficient (R²) of 0.9970. The detection limit of this method was 3.12 × 10^–10 mol/L, and the spiked recoveries ranged from 86.65% to 96.97%. In conclusion, the electrochemical sensor has good stability and reproducibility and is suitable for the rapid detection of BaP in barbecued meat products.