Immobilization of tyrosinase on Fe3o4@Au core-shell nanoparticles as bio-probe for detection of dopamine, phenol and catechol.

An optical bio-probe based on the immobilized tyrosinase on the surface of Fe3O4@Au was described for the detection of dopamine, phenol and catechol. The prepared bio-probe (Fe3O4@Au@tyrosinase) was characterized by means such as TEM, SEM, VSM, DLS and TGA. In the presence of the bio-probe, the phenol, catechol and dopamine were converted to benzoquinone, o-quinone and dopaquinone, and the fluorescence spectra appeared at 308 nm, 329 nm and 336 nm with ex = 270 nm, respectively. However, by increasing the concentration of phenolic compounds in the bio-probe, the amount of products (benzoquinone, o-quinone and dopaquinone) was increased which was the reason for the increase in fluorescence intensity. Using this mechanism, a bio-probe was designed such that the intensity of the fluorescence spectra increased proportionally with the increase of the substrate concentrations after different time periods. The 0.003 mg/mL of tyrosinase was loaded on 1.65 mg/mL of the Fe3O4@Au. The highest performance for a bio-probe was demonstrated at room temperature and pH 6.8. By investigating the characteristics of the response of the bio-probe to different phenolic compounds, it was found that the bio-probe had a linear response in the concentration range 5.0-75.0 µM, 10.0-100.0 µM for phenol and dopamine and 50.0-500.0 M for catechol. The Michaelis-Menten constant (Km) of the bio-probe was calculated as 0.6 µM. Finally, the bio-probe seems to be stable and efficient even after about 2 months. A novel and easy method for the detection of dopamine, phenol and catechol by florescence that uses oxide capability to identify the phenolic compounds was introduced.