Electrochemical Strategy for Analyzing the Co-evolution of Cu²⁺ and ^•OH Levels at the Early Stages of Transgenic AD Mice

As more researchers have acknowledged that the aggregation of amyloid β (Aβ) peptides might only be a pathological phenomenon that appears during the course of Alzheimer’s disease (AD), it is therefore of great significance to have a preclinical or an early clinical diagnosis. Cu2+ dyshomeostasis and oxidative stress, such as hydroxyl radical (•OH), are found to be associated with peptide aggregations. However, we still do not know how the levels of Cu2+ and •OH are altered in the brain before massive Aβ plaques appear. Herein, we demonstrated the design and application of a sensitive electrochemical sensor to monitor Cu2+ and •OH simultaneously in one system without obvious cross-talk. The electrode was fabricated using black phosphorus-loaded Au (BP-Au) nanoparticles, which were then sequentially linked with DNA1, DNA2-labeled Au (Au-DNA2) nanoparticles, and methylene blue (MB). Cu2+ was first recognized and captured onto the sensor by BP with high selectivity and then produced a reduction current at around −0.01 V. The •OH quantification was established on the cleavage of the hybrid structure between DNA1 and BP-Au upon the appearance of •OH in the phosphate-buffered saline (PBS), leading to the depletion of the voltammetric response of MB around −0.25 V. Good linear correlations were obtained over concentrations of 0.5–127.5 μM for Cu2+ and 0.5–96.0 μM for •OH. Most importantly, the developed sensor was successfully applied to track the variations of the two species in brain tissues from APP/PS1 transgenic AD mice at the early stages before massive Aβ plaques appeared.