A Low-Cost and Environmentally Friendly Electrochemical Biosensor for the Determination of Estradiol

Estradiol is a natural estrogen belonging to the group of natural steroid hormones. This paper presents new electrochemical biosensors-simple and low-cost tools for the determination of β-estradiol. The receptor layer of the sensor is the enzyme laccase, which was immobilized on the substrate surface using the soft plasma polymerization technique. This technique is innovative and environmentally friendly as it allows for the effective deposition of the enzyme onto unmodified and modified electrode substrates. Three types of substrates were used: an unmodified glassy carbon electrode and two electrodes modified with composite layers-multi-walled carbon nanotubes combined with CuO nanoparticles and multi-walled carbon nanotubes combined with carbon nanofibers, respectively. Biosensors modified with such materials have not been described previously. In the course of the study, electrochemical measurement conditions (composition, concentration and pH of the base electrolyte, sensor response time, and interference effects) were optimized, and sensor parameters were determined. It was found that the modification of the substrate electrode increased the sensitivity of the sensor by more than 25 times in both cases and led to a lower detection limit for the sensor modified with the carbon nanotubes/carbon nanofiber composite. The best performance was achieved with the sensor containing the carbon nanotube/carbon nanofiber composite layer, which showed a linearity range of 0.1-5 µM, a sensitivity of 7.32 ± 0.22 µA/µM, and a limit of quantification of 0.078 µM. The analytical utility of this biosensor was confirmed by its successful application in the determination of estradiol in pharmaceutical preparations and river water samples.