Electrochemically reduced graphene–gold nano particle composite on indium tin oxide for label free immuno sensing of estradiol

• Label free immunosensing of estradiol is demonstrated using graphene–AuNP composite fabricated on ITO transducer.
• Continuous potential cycling reduction method selectively reduces the acid groups of the graphene oxide at pH 6.5.
• The AuNP deposition induces change in the graphene orientation on the ITO surface and enhances the charge transport.

Electro reduced graphene and gold nano particle (ErG/AuNP) composite is prepared on indium tin oxide (ITO) surface. Characterization by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Raman spectroscopy (RS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques reveals the formation of vertical and flat oriented ErG films on the ITO. The AuNP deposition changes the flat oriented ErGs into vertical orientation indicated by the FESEM. Coherent interactions between the ITO, ErG and AuNPs are responsible for the discrete formation of vertical oriented hetero structures of ErG–AuNP composite on the ITO. Electrochemical properties are investigated using [Fe(CN)6]3−/4− and [Ru(NH3)]2+/3+ redox probes using cyclic voltammetry (CV). While the [Fe(CN)6]3−/4− shows fast reversible behavior, the [Ru(NH3)]2+/3+ reveals very slow charge transport on both ErG and ErG/AuNP films indicating the multi and compact graphene layer posses positive charge at pH 6.5 used for preparing these composites. Immuno sensing of breast cancer inducing hormone 17β-estradiol (E2) is demonstrated in presence of [Fe(CN)6]3−/4−. Estrone (E1) and estriol (E3) antigens are used as the controls. The near vertical immobilization of anti-estradiol-antibody enhances the lowest detection limit of 0.1 fmol and dynamic range of 1 × 10−3–0.1 × 10−12 M without any signal amplifiers. These results prove that the acid group of the GO is reduced selectively in controlled way by simple potential cycling method which could not be achieved by other chemical reduction methods. Hence, the protocol is an alternative, simple and inexpensive technique for producing few layered vertical graphene and ErG/AuNP composite than the solution based chemical synthesis methods reported.

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