Simultaneous Monitoring of Amyloid-ß (Aß) Oligomers and Fibrils for Effectively Evaluating the Dynamic Process of Aß Aggregation.

Herein, we provide a proof of concept for a novel strategy that targets the assessment of the aggregation of amyloid-ß (Aß) by simultaneously determining its oligomers (Aßo) and fibrils (Aßf) in one analytical system. By fabricating and combining two immunosensors for Aßo and Aßf, respectively, we constructed a two-channel electrochemical system. The ratio of Aßf to Aßo was calculated and taken as a possible criterion for evaluating the extent of aggregation. Thereby, the presence of and transformation between oligomers and fibrils were accurately probed by incubating the Aß monomer for different times and then calculating the ratios of Aßf to Aßo. The applicability of this method was further validated by tracking the dynamic progress of Aß aggregation in the cerebrospinal fluid and tissues of Alzheimer's disease (AD) rats, which revealed that the ratio of Aßf to Aßo in rat brain gradually increased with the progression of AD, which was indicative of the severity of peptide aggregation during this process. Overall, this study represents the first example of a quantitative strategy for precisely evaluating the aggregation process that is related to pathological events in AD brain.

Combined determination of copper ions and ß-amyloid peptide by a single ratiometric electrochemical biosensor.

Copper ions (Cu2+) play a critical role in biological processes and are directly involved in ß-amyloid peptide (Aß) aggregation, which is responsible for the occurrence and development of Alzheimer's disease (AD). Therefore, combined determination of Cu2+ and Aß in one analytical system is of great significance to understand the exact nature of the AD event. This work presents a novel ratiometric electrochemical biosensor for the dual determination of Cu2+ and Aß1-42. This unique sensor is based on a 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulphonate) (ABTS) and poly(diallyldimethylammonium chloride) (PDDA)-bi functionalized single-walled carbon nanotubes (ABTS-PDDA/CNTs) composite. The inclusion of ABTS not only enhanced the sensitivity, but it also acted as an inner reference molecule to improve detection accuracy. The specific recognition of Cu2+ was realized by neurokinin B (NKB) coatings on the ABTS-PDDA/CNTs surface to form a [CuII(NKB)2] complex with Cu2+. The ABTS-PDDA/CNTs-NKB modified electrode also displayed an excellent electrochemical response toward the Aß1-42 monomer, when a certain amount of the Aß1-42 monomer was added to Cu2+-contained PBS buffer, which was due to the release of Cu2+ from the [CuII(NKB)2] complex through Aß binding to Cu2+. Meanwhile, our work showed that Cu2+ bound Aß1-42 was concentration-dependent. Consequently, the presented electrochemical approach was capable of quantifying two important biological species associated with AD by one single biosensor, with the detection limits of 0.04 µM for Cu2+ and 0.5 ng mL-1 for Aß1-42, respectively. Finally, the ratiometric electrode was successfully applied for monitoring Cu2+ and Aß1-42 variations in plasma and hippocampus of normal and AD rats.

Functionalized poly (ionic liquid) as the support to construct a ratiometric electrochemical biosensor for the selective determination of copper ions in AD rats.

An efficient ratiometric electrochemical biosensor for Cu2+ determination was constructed using dual hydroxyl-functionalized poly (ionic liquid) (DHF-PIL) as the catalyst support. The DHF-PIL exhibited typical macroporous structure, which provided a high surface area of 39.31m2/g for the sufficient loading of biomolecules. The specific recognition of Cu2+ was accomplished by employing neurokinin B (NKB) for the first time, which could bind to Cu2+ to form a [CuII(NKB)2] complex with high specificity. Meanwhile, a common redox mediator, 2, 2'-Azinobis-(3-ethylbenzthiazoline-6-sulfonate) (ABTS) was modified into DHF-PIL by electrostatic interactions to act as an inner reference molecule, which provided a built-in correction for environmental effects and improving the detection accuracy. With this strategy, the developed electrochemical biosensor was capable of determining Cu2+ with a linear range between 0.9 and 36.1µM and low detection limit (LOD) and quantification limit (LOQ) of 0.24 and 0.6µM, respectively. The sensor also displayed a satisfactory selectivity against a series of interferences in the brain, including metal ions, amino acids and other endogenous compounds. Accordingly, the present biosensor was successfully applied to evaluate Cu2+ levels in normal and AD rats.