Development of an Efficient Biosensor for the In Vivo Monitoring of Cu⁺ and pH in the Brain: Rational Design and Synthesis of Recognition Molecules

An efficient biosensor was created for the ratiometric monitoring of Cu⁺ and pH in the brain using both current and potential outputs. A series of N,N-bis(2-[2-(ethylthio)ethyl])-based (NS4s) derivatives was designed for the specific recognition of Cu⁺. After systematically evaluating the electrochemical parameters of Cu⁺ oxidation by tuning alkyl chain length, polyaromatic structure, and substitute group site of NS4, N,N-bis(2-[2-(ethylthio)ethyl])-2-naphthamide (NS4-C1) was finally optimized for Cu⁺ detection as it showed the most negative potential and the largest current density. At the same time, 9,10-anthraquinone was used as a selective pH sensor with 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) as an internal reference. This single biosensor with both current and potential signal outputs can simultaneously determine Cu⁺ concentrations from 0.5 to 9.5 μm and pH values ranging from 6.0 to 8.0. The efficient biosensor was applied to the simultaneous detection of Cu⁺ and pH in the live brain. The average levels of Cu⁺ were reported for the first time in the cortex, hippocampus, and striatum in a mouse model of Alzheimer's disease.