Core-shell magnetic MCM-41/guanidine nanocomposite-modified electrode for highly sensitive and selective detection of dopamine in some biological samples

A novel core-shell structured magnetic nanocomposite with carbon and mesoporous silica shells supporting guanidine (Fe 3 O 4 @C@MCM41-guanidine) was developed to modify a glassy carbon electrode (GCE) for highly sensitive dopamine (DA) detection. The nanocomposite was synthesized through a controlled sol-gel process, featuring a magnetic Fe 3 O 4 core (50 nm diameter), conductive carbon interlayer (8 nm thickness), and functionalized MCM-41 shell (15 nm thickness) with guanidine groups. Comprehensive characterization confirmed the hierarchical structure, superparamagnetic behavior (47 emu/g saturation magnetization), and thermal stability up to 350 °C. Electrochemical studies revealed the modified electrode's superior performance, exhibiting: (1) significant negative shift in oxidation potential at pH 4.0, (2) 7.3-fold current enhancement versus bare GCE, and (3) reduction in charge transfer resistance from electrochemical impedance spectroscopy analysis. Because enhanced surface area and electron transfer, catalytic activity toward DA oxidation. The sensor demonstrated exceptional analytical parameters, including a wide linear range (0.01–450 μM, R 2 = 0.9997), ultra-low detection limit (3.6 nM, S/N = 3), and excellent selectivity against interferences (1000-fold ascorbic acid). Real-sample validation in human serum and urine showed high accuracy (92.4–101.6 % recovery) and precision (RSD < 3.8 %). The Fe 3 O 4 @C@MCM41-guanidine/GCE demonstrated superior electrochemical behavior compared to both bare GCE and Fe₃O₄/GCE, as evidenced by three key observations including enhanced surface area and electron transfer, catalytic activity toward DA oxidation. • Novel Fe 3 O 4 @C@MCM41-guanidine/GCE sensor achieves record 3.6 nM dopamine detection limit. • Widest reported linear range (0.01–450 μM) covering physiological to pathological levels. • Triple-functional nanocomposite combines magnetic separation, enhanced conductivity, and molecular recognition. • Validated in real samples with high recoveries in human serum and urine samples (RSD < 3.8 %).