An insight into impedimetric immunosensor and its electrical equivalent circuit

We report the effect of multi-component film, formed during fabrication of nanoparticles modified label-free impedimetric immunosensor, on its physico-chemical properties and the electrical equivalent circuit designing. As a model system, we fabricated an immunosensor by modifying the screen printed electrode with gold nanoparticles followed by anti-TSH antibody immobilization and blocking the electrode surface with BSA. Randles equivalent circuit fails to mimic the impedimetric response of the immunosensor, with error as high as 6%. We have proposed an open finite diffusion element to incorporate the diffusive behaviour within the Nernst Layer formed by complex nanoparticle-antibody-blocking agent layer, in addition to the Cole-Cole element for addressing the suppressed impedimetric curves with lesser curvature exhibited by immunosensor. This equivalent circuit reduces the error to 1.5-2%, making it suitable for usage in EIS based diagnostic device development.