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

Copper ion (Cu(2+)) 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 Cu(2+) and CySH in live rat brains with AD. N,N-di-(2-picoly)ethylenediamine (DPEA) is first synthesized for specific recognition of Cu(2+) to form a DPEA-Cu(2+) complex. This complex shows high selectivity for CySH owing to the release of Cu(2+) from the complex through CySH binding to Cu(2+) 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 Cu(2+) and CySH in the live rat brains with AD. To our knowledge, this is the first report on the accurate concentrations of Cu(2+) and CySH in live rat brains with AD.