Development of a highly sensitive CNT-metal graphene hybrid nano-IDA electrochemical biosensor for the diagnosis of Alzheimer's disease†

The blood-based detection of Alzheimer's disease (AD) is becoming challenging since the blood–brain barrier (BBB) restricts the direct circulation of AD molecules in the blood, thereby precluding the detection of AD at an early-stage. Herein, we report the development of a novel CNT-metal-porous graphene hybrid (CNT-MGH) nano-interdigitated array (n-IDA) electrochemical 8-well biosensor for the successful early-stage diagnosis of AD from blood. Laser-induced graphene (LIG) technology has been used to fabricate the proposed CNT-MGH n-IDA 8-well sensor. Firstly, the electrochemical characterization (i.e., electrode gap, material composition, etc.) of the proposed sensor was demonstrated by measuring p-aminophenol (PAP) with a limit of detection (LOD) of 0.1 picomole. Subsequently, the CNT-MGH n-IDA 8-well sensor was then used to diagnose AD via novel blood biomarkers p-Tau 217 and p-Tau 181 using an electrochemical enzyme-linked immunosorbent assay (e-ELISA) enzyme by-product PAP. During e-ELISA, the alkaline phosphatase enzyme (IgG-AP) tagged to the detection antibody produced an electroactive ELISA by-product PAP by reacting with the enzyme–substrate 4-aminophenyl phosphate (PAPP). Finally, the CNT-MGH n-IDA 8-well sensor was then used to measure the current generated by the redox reaction via the e-ELISA by-product PAP. While quantified, the proposed CNT-MGH n-IDA 8-well sensor successfully detected p-Tau 217 and p-Tau 181 proteins in blood with LODs of 0.16 pg ml⁻¹ and 0.08 pg ml⁻¹, respectively.