A 433-MHz surface acoustic wave sensor with Ni-TiO₂-poly(L-lysine) composite film for dopamine determination

A ternary hybrid material composed of Ni nanoparticles (NPs), TiO₂ NPs, and poly(L-lysine) (Ply) was used as a sensing material. It was electrodeposited in situ onto a commercial 433-MHz surface acoustic wave (SAW) resonator to construct a Ni-TiO₂-Ply/SAW sensor. The Ni-TiO₂-Ply sensing layer fully covered the resonant cavity of the SAW resonator. As the sensing layer completely covers the interdigital transducer and piezoelectric substrate, the sensing area is significantly increased, and the resonator is protected from damage or contamination. To detect the level of dopamine (DA) in serum, the fabrication of the Ni-TiO₂-Ply sensing layer, distributions of various components in the sensing layer, and responses of the SAW biosensor to DA were investigated in detail. In addition, an electric field-assisted liquid-phase oxidation technique was developed for loading analytes onto the SAW sensors. After optimizing the pH value and L-lysine content of the sensing layer electrolyte and the pH value of the DA solution, the SAW biosensor responded to DA with a linear concentration range of 1 to 1000 nM, sensitivity of 5.77 MHz nM^-1 cm^-2, and limit of detection of 0.067 nM. Moreover, the sensor exhibited good selectivity, reproducibility, and stability at ambient temperature.Graphical abstract.