Label-free flexible immunosensor based on nitrogen-doped graphene with titanium dioxide for the determination of depression marker dendritic cell nuclear protein-1

In this work, a label-free flexible immunosensor for selective and sensitive detection of dendritic cell nuclear protein-1 (DCNP1), a newly discovered potential marker of depression, was successfully constructed. At first, a highly conductive nanomaterial nitrogen-doped graphene with titanium dioxide (NG/TiO2) was prepared using a one-pot method, and it was used as an electrode modification material in the construction of immunosensors for the first time. NG/TiO2 was functionalized with 1-pyrene-butyric acid N-hydroxysuccinimide ester (PSE), and then the DCNP1 antibody could be better immobilized on the surface of the modified indium tin oxide-polyethylene terephthalate (ITO-PET). Then bovine serum albumin (BSA) was used to block non-specific active sites, and the immunosensor (BSA/anti-DCNP1-PSE/NG/TiO2/ITO-PET) can be obtained. The fabricated NG/TiO2 and the construction process of the immunosensor were characterized by scanning electron microscopy, infrared spectroscopy, cyclic voltammetry, and electrochemical impedance methods. Differential pulse voltammetry (DPV) was used to measure different concentrations of DCNP1 after optimizing the ratio of NG and TiO2, the modification amount of NG/TiO2, the ratio of NG/TiO2 to PSE, the concentration of anti-DCNP1 and its immobilization time, the concentration of BSA, and the incubation time of DCNP1. The constructed sensor had a wide linear range of 1 similar to 10(4) pg mL(-1), and a low detection limit of 0.45 pg mL(-1) (S/N = 3). It had good reproducibility (RSD = 1.90 %), repeatability (RSD = 2.6 %), and selectivity. After storing it at 4 degree celsius for 15 days, its performance decreased to 92.37 %. And it had been successfully used to determine DCNP1 in the brain homogenate of mice with depression induced by chronic unpredictable mild stress (CUMS), providing a possible method for the rapid and accurate determination of DCNP1.