# Potentiometric Biosensor Based on Artificial Antibodies for an Alzheimer Biomarker Detection
## 3 Results and Discussion
### Sensory Surfaces  
The materials MIP and NIP were incorporated into the PVC membrane and tested as sensing materials with potentiometric transduction. The effect of membrane composition on the potential response was investigated and the results are shown in Table 1.  
Overall, the membranes were prepared by dispersing the active compounds (MIP or NIP) in a high dielectric constant plasticizer, oNPOE and PVC. The type of plasticizer employed is important to the analytical performance of PVC-based sensors. Some plasticizers cause leakage or migration from the membrane, which limits the lifetime of sensor materials based on plasticized membranes. [PERSON] and co-authors have previously described the effects of the plasticizer dielectric constant on the analytical performance of sensors. When oNFOE was used as plasticizing solvent, the detection limit of the sensor was lower due to the higher dielectric constant compared to other conventional solvents [70].  
PH Effect  
ISEs were calibrated in the MOPS buffer, 1.0 \(\times\) 10\({}^{-1}\) mol/L, pH 6.0 and 8.0. Under these conditions, the peptide is slightly negatively charged because its isoelectric point is 5.5 [64]. However, all electrodes exhibited cationic slopes, and an opposite behavior was expected. A possible explanation for this behaviour is related to the presence of several ionizable functional groups on the amyloid surface that can interact with the PVC membrane, causing the protein to approach the MIP binding sites within the PVC membrane by its positively charged groups. At pH 6, the MIP showed linear behavior after 1.23 \(\upmu\)g/mL, a cationic slope of 62.1 mV/dec and a detection limit of 1.20 \(\upmu\)g/mL. The NIP showed a nonlinear behavior with an R\({}^{2}\) of 0.92, indicating that the (re)binding mechanism  
Figure 4: SEM images of oxidized SWCNT and MIP materials.  
of the peptide in the imprinted material dominates the potentiometric response (Table 1). Overall, the ISEs with the MIP material showed the best operating characteristics in terms of the slope and R\({}^{2}\).  
For the calibration curve at pH 8.0, the MIP sensor showed overernrstian slopes of 75.0 mV/decade and an NIP material of 44.0 mV/decade, respectively. The MIP showed a linear response after 1.20 ug/mL and LOD after 0.97 ug/mL (Figure 5). The particles of NIP showed acceptable properties in terms of LOD, but a lower Nernstian slope compared to the MIP material, indicating that the binding sites of MIP led to the analytical response.  
Overall, the best results in terms of the analytical performance were obtained for the membranes with MIP as an ionophore at pH 8.0. These conditions were used for further studies.  
The analytical performance of the biosensor was compared (Table S2) with previously reported electrochemical biosensors with different recognition elements for A\(\beta\)-42 detection. Overall, these methods show a better analytical performance compared to this approach. However, to our knowledge, this research demonstrates for the first time a simple approach based on potentiometric transduction. We are aware that improvements should be made in terms of the analytical performance. However, we present a low-cost and simple system based on two electrodes made of graphite carbon electrode (reference and working electrode).