Development of Bimetallic Film with Electrocatalytic Activity in Non-Enzymatic Glucose Oxidation

Abstract

Fast and reliable detection of glucose is of great scientific and technological importance both in clinical diagnostics and analytical practices industrial applications. Besides the necessity of glucose detection and quantization as an application in environmental pollution monitoring, biotechnology, and food industry, it is essential for the detection and regular monitoring of diabetes mellitus in clinical diagnostics. This metabolic disorder results from the deficiency of insulin and hyperglycemia and results in the fluctuation of blood glucose level with a value falling outside the normal range of 4.4 – 6.6 mM. In detail, blood sugar concentration for healthy people range between 4.0 and 5.4 mM in fasting and up to 7.8 mM in postprandial glucose. A prolonged increase in the blood glucose concentration, will cause severe damage to essential human body organs. Thus affordable, efficient and regular monitoring of blood glucose level is necessary to avoid major health complications.Presently, enzyme-based glucose sensors are the most widely distributed and commercially produced devices for monitoring glucose level at home and clinics. Despite the prompt sensitivity and selectivity, enzymatic glucose sensors suffer from drawbacks due to denaturization of enzymes, higher cost, lesser reproducibility, and lack of stability from temperature fluctuations, pH variation, and humidity. These drawbacks were overcome by the non-enzyme sensors, particularly, the metal based amperometric sensors with direct detection of glucose, owing to its good stability, simplicity, and reproducibility. However, detection of glucose using non-enzymatic metal-based sensors via direct oxidation have their own set of challenges. Precious metal-based sensors, besides being expensive, have recorded narrow linear current response ranges, limited sensitivity and selectivity, and surface poisoning from the adsorbed intermediates and interferences from chloride ions.In this work fabrication of non-enzymatic transition metal-based glucose sensors with good stability, linear range of response covering the normal glucose levels of human, lower detection limit, faster response, workable sensitivity and low cost, were studied. Here, we have researched thin film electrodes of single transition metal as well as bimetallic nanostructures to enhance the surface area, catalytic active sites and electrochemical properties via synergic effects. A two-stage electrochemical deposition technique was used to fabricate bimetallic thin films. A uniform film of nickel (Ni) crystals were formed on the titanium (Ti) cathode. Post the deposition of Ni coating, another two set of samples were prepared with a second-stage electrochemical reduction of silver (Ag) and copper (Cu) nanoparticles on the surface on Ni-coated Ti plate. Scanning electron microscopy images revealed a uniform film of transition-metal nanocrystals with varying diameter depending on the deposition conditions.The electrochemical behavior and the electrocatalytic properties of the as-prepared bimetallic films towards glucose oxidation were studied using cyclic voltammetry and amperometric techniques. The three metallic films investigated, namely, Ni, NiAg, and NiCu showed a fast response towards non-enzymatic glucose oxidation and detected amperometric signals that were linearly proportional in the 0.2-1.8 mM, 0.2-6.4 mM, and 0.2-12.2 mM ranges, respectively and with sensitivity values of 110 μm mM-1 cm-2, 320 μm mM-1 cm-2, and 420 μm mM-1 cm-2, respectively. The sensitivity of the bimetallic films was recorded higher than the monolayer of Ni nanocrystals due to higher surface area and low detection limits were recorded for all the samples. Besides that, for all the three samples, both the cathodic reduction peak current (Ipc) and anodic oxidation peak current (Ipa) increased linearly with the square root of the scan rate between 10 mV/s and 100 mV/s signifying that the electrocatalytic reaction is limited by the diffusion of the glucose molecules into the electrode/electrolyte interface. The as-fabricated bimetallic films are thus promising candidates for electrocatalytic glucose oxidation reaction with wide linear detection range covering the physiological levels of glucose.