Deposition of Gold Nano-Micro Islands on Electrochemically Reduced Graphene Oxide to Use in Combination with Molecularly Imprinted Polymers

Abstract

Molecularly imprinted polymers (MIPs) are known as an alternative for antibodies in immunosensors with high stability and low production cost. MIP approach relies on polymerization in the presence of a template molecule and subsequent template removal. In this process, the template molecule is exactly the same as the target molecule leading to a good selectivity for the biomimetic sensor [1]. The integration of MIPs with nanomaterials enables ultrasensitive sensors for various analytes. Besides, nanomaterials with uniform distribution and suitable morphology provide a wide linear range of detection for the sensor [1]. In particular, the controlled electrodeposition of gold can supply gold nano-micro islands (NMIs) with remarkable electrochemical behavior and high active surface area [2, 3]. However, it is found that the modification of an electrode surface using electrochemically reduced graphene oxide (ERGO), as a facile and fast method, not only increases the surface area but also improves its electrochemical behavior [4]. Herein, we describe a surface modification strategy based on indium tin oxide (ITO) electrode coated with ERGO to increase the surface active sites for nucleation and deposition of NMI. For this aim, we electrochemically reduced graphene oxide (GO) by one cycle in cyclic voltammetry (CV) with a scan rate of 100 mV s-1 in the range of -0.6 to -2 VAg/AgCl. The succeed of the electrochemical reduction was confirmed through ID/IG ratio in Raman spectroscopy and observing the enhanced electrochemical behavior in CV and electrochemical impedance spectroscopy (EIS) tests. The gold layers were deposited at 0 and -0.4 VAg/AgCl in 5, 50 and 100 mM HAuCl4 solutions for 50 and 300 s. The surface area of the resulted structures was also determined by integrating the reduction peak in CV tests in 50 mM H2SO4 solution [2]. The results showed that the gold structure deposited from 100 mM HAuCl4 at 0 VAg/AgCl for 50 s provided a significant surface area (0.47 cm2) on the electrode surface of 1 mm diameter, while this value for gold nanoparticles, as the common form of gold nanostructure in electrochemical biosensing, was determined only 0.063 cm2. This noticeable increase in surface area can result in a wide linear range of detection as well as excellent electrochemical behavior in biosensing applications. Scanning electron microscopy (SEM) of NMI structures deposited on both ITO and ERGO/ITO electrodes indicated a shrub-like structure because of the concentration polarization governed during gold deposition. Transmission scanning electron microscopy (TEM) of the NMI displayed Au (113) as the main crystalline plane. Based on the chronoamperometry plots, the gold deposition mechanism on the surface of both electrodes was according to the instantaneous deposition mode [2]. However, the electrode background surface indicated that the ERGO/ITO was uniformly covered by gold. This was attributed to the higher nucleation sites on the ERGO-modified electrode, which was confirmed by the increase of double-layer formation time (tmax). Accordingly, several nucleation stages on the chronoamperometry plot during NMI deposition on the ERGO/ITO electrode, were related to the formation of gold shrub-like structures with more needle-shaped structures. Finally, electropolymerization of a thin layer of o-phenylenediamine in the presence of Heart-fatty acid binding protein (H-FABP) as the template molecule and its subsequent removal was applied to make a biomimetic sensor. In this study, we demonstrated that the biomimetic developed electrode with high surface area, low production cost, and facile and fast synthesis method is acceptably selective to H-FABP against other cardiac biomarkers and serum proteins.KEYWORDS: Electrodeposition; Electrochemically reduced graphene oxide; Electrochemical sensors; Gold nano-micro islands; Molecularly imprinted polymers.