SPR immunosensor combined with Ti⁴⁺@TiP nanoparticles for the evaluation of phosphorylated alpha-synuclein level

A highly sensitive and specific surface plasmon resonance (SPR) method using one anti-alpha-synuclein antibody (anti-αS) and titanium phosphate nanoparticles (Ti⁴⁺@TiP) was developed for quantitative evaluation of phosphorylated αS level which was defined by the ratio of p-αS to total alpha-synuclein (t-αS) (p-αS/t-αS). The close affinities of anti-αS to αS (0.975 pM^-1) and p-αS (0.938 pM^-1) were obtained. Based on this fact , both αS forms were simultaneously captured and the t-αS was quantified using the anti-αS immobilized Au chip. With the selective recognition of Ti⁴⁺@TiP nanoparticles, the p-αS was quantified. The dynamic ranges of our method were 1.0~20.0 pg mL^-1 for the detection of t-αS and 0.1~10.0 pg mL^-1 for that of p-αS. The analysis of αS- and p-αS-spiked artificial cerebrospinal fluid samples revealed the high accuracy of the method. Furthermore, the concentrations of αS and p-αS in clinical CSF samples collected from three healthy donors were determined and displayed a high correlation with the results from a commercial ELISA kit, confirming the viability and of the proposed method. The method is convenient, economical, and practical for the evaluation of phosphorylated αS level with high sensitivity and selectivity. It is of great significance for the early diagnosis of PD and the evaluation of PD progression.Graphical abstract.