Porous graphene oxide based disposable non-enzymatic electrochemical sensor for the determination of nicotinamide adenine dinucleotide

Abstract

Accurate quantification of nicotinamide adenine dinucleotide (NADH) is crucial due to its inevitable role in biological systems. NADH is a pivotal coenzyme identified in almost all living cells, which promotes energy production and consumption as well as involved in several metabolic reactions. An abnormal amount of NADH in living cells can cause diminished mental alertness, insomnia, Parkinson’s disease, anxiety, Alzheimer’s dementia, attention deficit disorder in humans [1,2]. Hence, there is a compelling need to develop an effective methodology to detect NADH with high sensitivity and selectivity. Until now, many analytical approaches have been explored for the detection of NADH like colourimetry, fluorescence, liquid chromatography, electrochemical, and photoelectrochemical methods [3,4]. Among these approaches, the electrochemical methodology has received considerable attention, owing to its high sensitivity, selectivity, ease of analysis, rapid detection of analytes and miniaturization [5]. In electrochemical techniques, enzyme-based electrochemical sensors are highly preferred due to their excellent selectivity and high catalytic activity. However, it entails high cost, lacks stability and durability as well as cumbersome electrode fabrication. Consequently, the non-enzymatic electrochemical methods are simple, ease of fabrication, cost-effective, yields high stability and durability. Therefore, the non-enzymatic determination of NADH has grabbed immense attraction, and various materials have been explored as electrode modifiers, including metal nanoparticles, carbon nanomaterials, metal oxides/complexes, and other organic redox mediators. Among these materials, carbon nanomaterials offer high surface morphology, excellent electrical conductivity, great chemical and mechanical stability, which favours the electrochemical determination of target analytes. Besides, carbon nanomaterials have been broadly used to minimize the surface contamination effect and reduce the overpotential for electrocatalytic oxidation/reduction of analytes without the need for enzymes, protein, and redox mediators. However, the voltammetric behaviour of carbon nanomaterials displayed low sensitivity and inadequate anti-interference ability. Thus, it requires to be modified by incorporating functional groups or by including dopants or other surface defects and changes to further improve their nature and electronic properties for their utilization in the rapid and precise determination of target analytes. Graphene (GR) is considered to be the basis of all carbon nanomaterials due to the fact that it can be rolled to form carbon nanotubes, wrapped to form fullerenes, stacked to form graphite sheets, and further, it can be functionalized by oxidation and reduction processes. Moreover, GO is hydrophilic in nature and has improved electrical conductivity, intense internal porosity, which facilitates further surface modification. Another crucial advantage of GO and its derivatives such as doped (with heteroatom) GO, reduced GO (chemically or electrochemically), porous GO are that it can be utilized as a substrate to host a wide variety of functional nanomaterials for different applications [6,7]. Therefore, the rational architect of multifaceted materials for electrode assembly is becoming prevalent in today’s modern era. Herein, we have synthesized porous GO (PGO) and fabricated a low-cost disposable sensor using PGO modified screen printed electrode (SPE) for the electrochemical sensing of NADH. PGO has received growing attention owing to its high internal porosity, large surface area, good electrical conductivity, excellent stability, improved active sites, and hence it is expected to show excellent electrocatalytic activity than graphene and other derivatives of carbon. The PGO was prepared by creating pores on the GO sheets through a sequential simple base reduction and acidification process. Thus formed PGO was confirmed by Fourier-transform infrared, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction, adsorption-desorption isotherms, and transmission electron microscopy. The synthesized PGO was immobilized on the surface of the pre-anodized SPE to form PGO/SPE, which was utilized for the non-enzymatic electrochemical sensing of NADH (Fig. 1). To compare the performance of the developed sensor, unmodified SPE, GO/SPE, and ERGO/SPE were also fabricated in a similar manner and investigated their electrocatalytic behaviour under the aforementioned conditions. Interestingly, the fabricated PGO/SPE has shown excellent electrocatalytic activity with high sensitivity and selectivity towards the oxidation of NADH compared to other modified electrodes, which could be ascribed to their improved surface area, excellent porosity, and enhanced electrocatalytic activity. Moreover, the PGO/SPE has exhibited high stability, excellent reproducibility, broad linear range, and low limit of detection towards NADH sensing.