Electrodeposited Nickel-Iron Clusters Onto Glassy Carbon for the Detection of Methylene Blue
Authors: Bahrololoomi Arash , Podlaha Elizabeth J. 
Published: December 2020

Methylene blue (MB) is a redox-active molecule, which is used for biochemical studies as a redox indicator,1-3 and as a comparable model for pyocyanin, a bacteria metabolite.4 Electrochemical detection of MB has been demonstrated through adsorption on gold electrodes,5 enhanced with a gold modified alkanethiol layer,5-7 and with carbon nanotube modified gold electrodes.8 In this study, a low-cost approach was used to develop a novel Ni-Fe/glassy carbon (GC) composite electrode to detect methylene blue. Ni-Fe microstructures were deposited from a sulfate-boric acid electrolyte at a pH of 3 by a pulse galvanostatic method. A three-electrode cell was used, containing a glassy carbon disk (GC) working electrode, a platinum counter electrode and a silver chloride reference electrode (Ag/AgCl). Deposition was carried out with and without electrode rotation. Field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray spectroscopy (EDX) and x-ray fluorescence analyzer (XRF) were used to characterize the surface morphology and the composition of the Ni-Fe clusters. The redox and adsorption behavior of MB were characterized with cyclic voltammetry and chronoamperometry/coulometry in a phosphate buffer solution (PBS) containing variable μM amounts of MB.
The electrodeposition results showed interesting morphology and composition that impacted the MB electrochemistry, Fig. 1. The average composition of Ni-Fe clusters with a 2 s deposition time and without rotation was Ni-rich, 84 wt% Ni, 16 wt% Fe, and the morphology of the microscale clusters was composed of nanoscale nuclei in a circular shape with a hole in its center, attributed to gas evolution from the side reaction. The average size of the clusters was roughly 50 µm with different hole diameters (Fig. 1a). The average composition of Ni-Fe clusters with a 6 s deposition time and 400 rpm rotation rate had a contrasting composition, Fe-rich, 38 wt% Ni, 62 wt% Fe, and the morphology demonstrated microscale clusters with cracks. The average size of the microscale clusters was between 10 and 20 µm (Fig. 1b). The cyclic votammograms of the MB electrolyte, under quiescent conditions, were quasi-reversible, showing a single oxidation peak and a reduction peak. The Ni-Fe clusters impacted methylene blue (MB) chronoamperometry and coulometry, enhancing the response particularly for low concentrations of MB. Deviations from linearity in a plot of it1/2 vs. tunder reduction conditions, at a constant applied potential, indicated that the response was not diffusion controlled at times below 100 s, where the Ni-Fe/GC composite electrode had a significantly larger current signal, but with diffusion behavior observed at long times (Fig. 1c), with little to no improvement in the current in this region using the Ni-Fe/GC composite electrode compared to GC. The results show that the Ni-Fe/GC composite electrode can enhanced the electrochemical detection of MB at low MB concentration.
Acknowledgement
The authors wish to thank H. Bilan at the Center of Advanced Materials Processing (CAMP) at Clarkson University for SEM help.
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Figure 1