Silk fibroin based impedance biosensor using interdigitated array microelectrode

Silk fibroin, a protein polymer, has emerged as a potential biomaterial for sensing applications due to its biocompatibility, mechanical strength, and ease of chemical modification. By a suitable degumming process, silk fibroin was functionalized with a synthetic epitope specific to -actin antigen, [NH2]-DNGSGMCKAGFAGDDAPRA-[OH], and applied as thin films onto interdigitated array microelectrode (Fig. 1). Using impedance spectroscopy, the antigen-antibody interaction was monitored as a function of the antibody concentration onto fibroin-antigen films. The biosensors were sensitive down to a few ng/ml of the antibody concentration. The detection mechanism takes advantage of the fibroin structure, a natural dielectric, providing insulation to the individual gold contacts. The antigen-antibody interaction results in a change of the relaxation frequency in the admittance spectrum with increasing antibody concentration. For a non-specific antibody there is no change in impedance with antibody concentration. Nyquist plots for the real and imaginary part of the impedance are modeled by an equivalent circuit comprising a resistor and constant phase elements (CPE). One of the CPE elements that describe the electrode-electrolyte interface capacitance becomes more resistive upon antibody-antigen binding. This same model was used with PSA L. infantum antigen. The epitope used was [NH2]-CTSSAPVARAAGTGDFTEEQRTNTL-[OH], and the antigen-antibody interaction was also observed in the admittance spectrum.