Functionalized magnetic nanomaterials for electrochemical biosensing of cholesterol and cholesteryl palmitate

Synthesis and functionalization of magnetite nanoparticles (Fe₃O₄) was achieved with the view to covalently bind both cholesterol oxidase and cholesterol esterase biorecognition agents for the development of free and total cholesterol biosensors. Prior to enzyme attachment, Fe₃O₄ was functionalized with 3-aminopropyltriethoxysilane (APTES) and polyamidoamine (PAMAM) dendrimer. Characterization of the material was performed by FT-IR and UV spectroscopy, SEM/EDX surface analysis and electrochemical investigations. The response to cholesterol and its palmitate ester was examined using cyclic voltammetry. Optimum analytical performance for the free cholesterol biosensor was obtained using APTES-functionalized magnetite with a sensitivity of 101.9 μA mM^-1 cm^-2, linear range 0.1-1 mM and LOD of 80 μM when operated at 37 °C. In the case of the total cholesterol biosensor, the best analytical performance was obtained using PAMAM dendrimer-modified magnetite with sensitivity of 73.88 μA mM^-1 cm^-2 and linear range 0.1-1.5 mM, with LOD of 90 μM. A stability study indicated that the free cholesterol biosensors retained average activity of 98% after 25 days while the total cholesterol biosensors retained 85% activity upon storage over the same period. Graphical abstract Schematic representation of cholesterol esterase and oxidase loaded magnetic nanoparticles (Fe₃O₄@APTES or Fe₃O₄@APTES-PAMAM) generating hydrogen peroxide from cholesterol palmitate.