A Single Biosensor for Evaluating the Levels of Copper Ion and L -Cysteine in a Live Rat Brain with Alzheimer's Disease

Copper ion (Cu²⁺) and L-cysteine (CySH) are closely correlated with physiological and pathological events of Alzheimer's Disease (AD), however the detailed mechanism is still unclear, mainly owing to a lack of accurate analytical methods in live brains. Herein, we report a single biosensor for electrochemical ratiometric detection of Cu²⁺ and CySH in live rat brains with AD. N,N-di-(2-picoly)ethylenediamine (DPEA) is first synthesized for specific recognition of Cu²⁺ to form a DPEA-Cu²⁺ complex. This complex shows high selectivity for CySH owing to the release of Cu²⁺ from the complex through CySH binding to Cu²⁺ center. In parallel, 5′-MB-GGCGCGATTTTTTTTTTTTT-SH-3′ (HS-DNA-MB, MB=Methylene Blue) is designed as an inner-reference for providing a built-in correction to improve the accuracy. As a result, combined with the amplified effect of Au nanoleaves, our single ratiometric biosensor can be successfully applied in real-time detection of Cu²⁺ and CySH in the live rat brains with AD. To our knowledge, this is the first report on the accurate concentrations of Cu²⁺ and CySH in live rat brains with AD.