# Highly Sensitive Non-Enzymatic Detection of Glucose at MWCNT-CuBTC Composite Electrode
## 1 Introduction  
The determination of glucose concentration is extremely important clinically in the diagnosis and treatment of diabetes, but also in areas such as biotechnology and food industry [1]. Since the first enzyme electrode was reported by the pioneering work of [PERSON] and [PERSON] in 1962 [2], researchers have generated considerable interest in the development of glucose sensors, and a variety of improvements regarding the optimization of glucose sensors, the immobilization of enzymes, and the design of redox systems have been reported [3; 4; 5]. The most well-known amperometric glucose sensors are based on the immobilization of enzymes such as glucose oxidase (GOx), which catalyzes the oxidation ofglucose in the presence of oxygen to hydrogen peroxide. Another category of glucose sensors with promising results is based on the use of redox mediators [6; 7].  
Electrochemical detection of glucose using GOx exhibits a low detection limit and high sensitivity and selectivity, but due to the intrinsic nature of enzymes, such sensors have serious stability issues [5; 8; 9]. Indeed, the activity of GOx can be easily affected by temperature, humidity, and toxic chemicals. Moreover, several disadvantages of the enzyme-modified electrodes (e.g., high cost of the enzyme, a complicated procedure required for the immobilization of the enzyme on solid electrode, and a critical operating situation) may decrease their exploitation [5; 10; 11]. Therefore, to overcome these drawbacks, considerable attention has been paid to the development of non-enzymatic electrodes based on the direct electro-oxidation of glucose, considered to belong to the fourth generation of glucose sensors [12]. These sensors were fabricated by incorporating nanostructured metal [13; 14] or metal oxides [15; 16; 17] on the electrode surface, achieved by using inert metals, metal alloy, or metal dispersed in carbon nanotubes (CNTs), in which the inert metal or metal alloy are mixed with CNTs to form nanocomposites [13; 18; 19; 20; 21]. Among these, copper-based materials and nanomaterials have been attracting attention for glucose detection due to the Cu\({}^{+}\)/Cu\({}^{2+}\) and Cu\({}^{2+}\)/Cu\({}^{3+}\) redox pair system, considered to act as an electrocataly in glucose detection [14; 15; 16; 17; 22; 23; 24]. However, the morphobstructural, electroactive surface area and electrochemical properties of the copper-based electrodes determine their performance in glucose electrooxidation and detection [23].  
The aim of this study is to synthesize a multiwall carbon nanotube (MWCNT)-based composite with a good stability and long lifetime for the non-enzymatic detection of glucose in aqueous solutions. The utilization of nanotubes in epoxy resin composites allowed for enhanced mechanical properties and an electrical conductivity suitable for electrochemical sensor development [25]. Nanostructured copper benzene tricarboxylate (CuBTC), which was one of the first reported metal-organic frameworks (MOFs) in 1999 and was named HKUST1, was selected to modify the MWCNT-based composite electrode for two main reasons: the multiple application potential of this material, especially in sensing [24], and the presence of copper in its structure which, as mentioned before, is well known as a good electrocatalyst for glucose oxidation.  
In the present work, the electrochemical methodologies for the direct determination of glucose using a MWCNT-CuBTC composite electrode by cyclic voltammetry (CV), differential pulsed voltammetry (DPV), linear sweep voltammetry (LSV), chronoamperometry (CA), and multiple pulse amperometry (MPA) are described.