Evaluation of Nanomaterials-biomolecule hybrids for signal enhancement of impedimetric biosensors

Five different Nano-materials (NMs) were used for making hybrid conjugates with Protein-A (PrA), a biomolecule that binds specifically with antibodies (Abs). The choice of NMs (Gold, CdS, SrTiO₃, Graphene Oxide and Polystyrene) exhibit both inorganic and organic NMs, with a wide range of electrical characteristics i.e., from metal, semiconductor to non conducting dielectric materials. The NMs-PrA conjugates prepared were characterized using UV-visible spectroscopy and fluorescence microscopy before use for biosensor application. These hybrids were than compared for their relative efficacy in enhancing the biosensor signal as recorded using faradaic electrochemical impedance spectroscopy (EIS). A nanogap interdigitated electrodes array (IDEA) sensor was coated with rabbit IgG antibodies and the binding signal from NM-PrA was compared with that of PrA binding alone. The EIS signal was analyzed by fitting the data to a Randles equivalent circuit. Values of two prime circuit elements i.e., charge transfer resistance (R-Ct) and double layer capacitance (C-dl) were determined from the best fit. The difference between the two signals provided the insight into the mechanisms for different NMs and the relative efficiency in signal enhancement.