A simple hydrothermal one-step synthesis of 3D-MoS₂/rGO for the construction of sensitive enzyme-free hydrogen peroxide sensor

Highlights

• We synthesized MoS₂ with a lattice spacing of 0.62 nm using a simple method.

• The constructed MoS₂/rGO sensor can achieve high sensitivity detection of H₂O₂.

• Fully exposed MoS₂ active sites greatly improve the sensitivity of the sensor.

Abstract

Hydrogen peroxide (H₂O₂) is an important intermediate in biological and environmental systems, which is widely used in pharmaceutical, environmental protection, fuel cell and other fields. It is also the most important signal conducting molecule, second messenger and growth factor in Reactive Oxygen Species (ROS). The increase of intracellular H₂O₂ level is closely related to cancer and neurodegenerative diseases. Therefore, the detection of H₂O₂ is an important goal of clinical research. Herein, we synthesized molybdenum disulfide (MoS₂) with a lattice spacing of 0.62 nm using a simple method, maintaining the excellent characteristics of MoS₂ itself, and performing sensitive detection of H₂O₂. In this work, we use graphene oxide as the precursor, and use one-step hydrothermal method to synthesize three-dimensional molybdenum disulfide/reduced graphene oxide composite (MoS₂/rGO). Graphene not only provides a support structure for the growth of MoS₂, but also forms large number of pores in it. These channels greatly increase the specific surface area of the MoS₂/rGO composite and provide a sufficient reaction environment for the reaction of H₂O₂ on the composite. Its greatly improves the sensitivity of the MoS₂/rGO enzyme-free sensor. We have calculated that the enzyme-free sensor composed of this electrode has a good linear dependence on the H₂O₂ concentration in the range of 2 μM to 23.18 mM, and the detection limit is 0.19 μM. The enzyme-free sensor with simple preparation method is expected to be greatly developed in the clinical application of hydrogen peroxide sensor.

Introduction

Hydrogen peroxide (H₂O₂), as an important signal transducer, second messenger and growth factor are closely related to many physiological functions of the body and the occurrence of various diseases [1], [2], [3]. Studies have shown that when the organism is invaded by pathogens, the macrophage environment will produce H₂O₂ to eliminate external invasion, it’s the innate activation of immune function. In addition, excessive accumulation of H₂O₂ in cells can cause damage to lipids, proteins, and DNA [4]. Therefore, the detection of hydrogen peroxide is of great significance in both clinical diagnosis and neurophysiology. Although traditional detection methods, such as chromatography and fluorescence methods, can also detect hydrogen peroxide well, they have the disadvantages of expensive equipment, large scale, long time-consuming, and complicated operation methods. Electrochemical methods are commonly used to detect the content of H₂O₂ [5], [6].The main reason is that H₂O₂ has electrochemical activity, it can be directly analyzed and detected based on the size of the electrical signal. However, the traditional electrode has a low catalytic activity and a complex preparation process, which makes it difficult to detect highly sensitive hydrogen peroxide. Therefore, it is necessary to modify the traditional electrochemical interface to achieve rapid and specific detection of hydrogen peroxide[7], [8], [9], [10], [11], [12].

Molybdenum disulfide nanomaterials are often used as the main part of biosensing platforms and can be used to detect proteins[13], [14], nucleic acids[15], [16], [17], cancer cells[18], and intracellular metabolites[19], [20]. However, the conventional molybdenum disulfide cannot meet the needs of sensing because the bulk molybdenum disulfide has a small specific surface area and low surface activity, which makes the detection sensitivity low[21], [22]. In many studies for detecting hydrogen peroxide, it is common to load highly active enzymes on molybdenum sulfide, or combine molybdenum sulfide with precious metals to enhance the sensitivity of the material in the detection[23], [24]. Enzymes composed of proteins are extremely sensitive to temperature, acidity and alkalinity, and precious metals are prone to deactivate protein poisoning, so the stability of such composite materials is usually poor[25]. Molybdenum disulfide nanoflow has an optimized sandwich and electronic configuration, especially in the detection of hydrogen peroxide, which is expected to meet the requirements of high sensitivity and high selectivity at the same time. [26].

As the most representative 2-D nano material, graphene is a kind of hexagonal honeycomb, which is a single-layer graphite mixed with carbon atom sp2[27]. The thickness of graphene monolayer is about 0.345 nm, the surface area of graphene monolayer is 2600 m² g⁻¹ theoretically, and the mobility of carrier at room temperature is about 15000 cm² V⁻¹ s⁻¹ [28]. Because of its unique physical and chemical properties, such as extremely high specific surface area, excellent conductivity and heat conductivity, excellent mechanical and optical properties, graphene has broad application prospects in materials science, energy, micromachining device and biomedicine, and is the most influential material in the 21st century[29], [30], [31], [32], [33]. However, compared to 2D-G, the three-dimensional graphene (3D-G) structure can effectively prevent the graphene nanolayer from agglomerating to exhibit more excellent properties. 3D-G is considered as an excellent material for sensor because of its unique three-dimensional porous network structure, good conductivity, high specific surface area and fast charge mobility[34].

The non-enzymatic material sensor can greatly improve the current signal response of the oxidation–reduction reaction of the target molecule at the electrochemical oxidation/reduction point, and realizes signal amplification of the small molecule marker by simulating enzyme. Studies have shown that the edge sites of MoS₂ have a catalytic effect on the electrochemical reduction process of H₂O₂, so the activity and abundance of the edge sites of MoS₂ have an important impact on the electrochemical detection of H₂O₂[35]. Here, by utilize that interaction between the molybdenum disulfide monolayer and the reduced graphene oxide, molybdenum disulfide (MoS₂) with the lattice space of 0.62 nm is prepare through a one-step hydrothermal method, which not only maintains the excellent characteristics of MoS₂, but also strengthens the bin ability of *OH and the edge active site of MoS₂, thereby promoting the speed control step of electrochemical reduction of H₂O₂ and finally improving the sensitivity of MoS₂ to the H₂O₂ electrochemical sensor. In addition, its good anti-interference ability enables MoS₂/rGO to maintain high sensing activity and stability in a variety of interfering samples. The morphology and size of MoS₂ nanoflowers and three-dimensional MoS₂/rGO composites were observed by SEM, and the elemental analysis of EDS was also conducted. XRD phase analysis and TEM analysis were carried out respectively. The morphology and crystal structure of MoS₂/rGO composite were determined. After the 3D-MoS₂/rGO composite electrode was modified, the electrocatalytic reaction of H₂O₂ was studied by cyclic voltammetry and time current method.