Fig 2: Schematic of fabrication and working of developed electrode: (A) GO; (B) one-step synthesised rGO; (C) activation of rGO via EDC-NHS carbodiimide coupling chemistry coated on the surface of FTO; (D) immobilization of BACE1 Ab onto activated rGO; (E) Alzheimer’s disease BACE1 biomarker protein sample; (F) capture of target BACE1 Ag upon interaction with immobilized BACE1 Ab; (G) electrochemical detection of the current output upon Ab–Ag interaction.

Fig 3: DPV of varying BACE 1 Ag concentrations in buffer samples: (Ai). testing of varying BACE1 Ag concentrations ranging from 1 µM to 1fM at 10-fold dilutions; (Aii). standard calibration graph of log of BACE1 Ag concentrations in buffer vs. I/µA = peak current/blank current; DPV of varying BACE 1 Ag concentrations in spiked serum samples: (Bi). testing of varying BACE1 Ag concentrations ranging from 1 µM to 1fM at 10-fold dilutions; (Bii). standard calibration graph of log of BACE1 Ag concentrations in serum vs. I/µA = peak current/blank current.

Fig 4: Specificity of the developed immunosensor: Cross-reactivity studies with BACE1 and NFL Ag in spiked buffer, serum and artificial CSF.

Fig 5: Modified FTO electrode optimization: (A) DPV of rGO-immobilized FTO sensor, where the rGO concentration was decreased from 1, 0.5, 0.25 to 0.1 mg/ml, showed maximum signal at 0.5 mg/ml; (B) DPV of Ab-immobilized FTO/rGO electrode where BACE1 Ab concentration was decreased from 1.5, 1, 0.5 to 0.25 µg, showed optimum signal at 1 µg; (C) DPV of FTO/rGO/BACE1Ab electrode where pH was increased from 6, 6.5, 7, 7.5 to 8, and pH 7.5 gave maximum current output; (D) DPV of FTO/rGO/BACE1Ab electrode where temperature was increased from 4°C, RT, 37°C to 45°C, and room temperature showed the highest current output.