Diagnosing Alzheimer's Disease through Detection of Tau Protein in Human Blood Using Ultrasensitive Nano-Gap Sensor: From CSF to Blood

Abstract

Background In nowadays, the importance of detecting biomarker in blood is dramatically increased. A-beta and tau are known as one of most important hallmark for diagnosing Alzheimer's disease in blood [1]. In case of Tau, various post-translational modification exists such as phosphorylated tau (p tau), O-glycosylated tau (O-g tau), and acetylated tau unlike A-beta. Recently, complementary relationship between p tau and O-g tau was revealed because tau pathology is regulated by O-GlcNAcylation and phosphorylation at same site [2]. Reference: [1] L.M. Ittner et al. Nature Reviews Neuroscience, 12 (2011) 67. [2] S. Lim et al. International journal of molecular sciences, 16 (2015) 20212-20224.

Methods (Figure 1) To detect ultra-low concentration of tau in plasma, novel type of electrochemical sensor with highly sophisticated structure was developed, which is composed of nanogap electrode and SU-8 microwell for loading single magnetic bead. We employed secondary antibody assay which makes possible to extract intrinsic signal from secondary antibody conjugations to compare the expression from phosphor site and of O-glycosylated site of tau.

Results Nanogap-based biosensor demonstrated high linearity when we measured total tau level from 50 fg/ml to 500 pg/ml (Figure 2a-b)). In case of plasmas from wildtype (WT) and transgenic (TG) mouse (tau p301L) as shown in Figure 2c-d, o-g tau was decreased and p-tau was increased with aging from 3 to 12 month. However, O-g tau is higher than p tau for WT while p tau is higher than O-g tau for TG. Furthermore, human CSF and plasma were also measured using our sensors. Figure 3 (b) shows a linear correlation between CSF and plasma even if the concentration of plasma is lower than that of CSF. Furthermore, human plasma from NC (n=9) and AD (n=11) were measured after observing a linearity according to the tau concentration. Compared to conventional diagnosis factor of p-tau/total-tau ratio (Figure 4a-b), our method shows much high sensitivity and specificity (Figure 4c-d).

Conclusions We successfully developed ultra-high sensitive nanogap based biosensor for detecting tau and its PTM. The suggested indicator of p-tau/O-g tau achieved more accurate diagnosis which demonstrates big possibility of diagnosis and prognosis.