## 1 Introduction  
Recently, interest in the production of biopharmaceuticals has grown due to their high sensitivity, specificity, low risk and adverse effects for the patient [1]. Biopharmaceuticals are mostly therapeutic recombinant proteins obtained by biotechnological processes [2]. L-asparaginase (ASNase) (EC 3.5.1.1) is an example of a biopharmaceutical with extensive use in the treatment of acute lymphoblastic leukemia (ALL), which is the most frequent type of leukemia in children up to 14 years old [3]. ASNase circulates in the blood system for only a short time before being hydrolyzed by native proteases. This property can lead to a restriction of enzyme effectiveness. They are also primarily unstable and thermolabile enzymes. Therefore, to prolong its lifetime, reduce its potential side effects, and enhance drug effects in blood, the native ASNase is often immobilized on various supports. It is reported that this process can reduce immunity, toxicity and improve the resistance to proteolysis [4]. The commercial approved PEG-asparaginase is an example of a confined enzyme obtained from an _Escherichia coli_-derived ASNase that is subsequently covalently linked to polyethylene glycol. It is reported to cause 18% of hypersensitivity reactions, compared with 32% for native ASNase [5]. ASNase application in the food industry is also very relevant since it can promote acrylamide mitigation without flavor changes. Acrylamide is considered a probable carcinogen to humans, formed by Maillard reaction between L-asparagine and reducing sugars of starch foods [6]. Nevertheless, ASNase must be more stable during all the processing steps in the food industry. ASNase immobilization is a technique that can overcome the hindrances of its application in the pharmaceutical and food industries, increasing enzyme stability and half-life without activity loss [6]. Over the last twenty years, carbon-based nanomaterials, such as carbon nanotubes (CNTs), have started to be used to immobilize enzymes [5; 7; 8]. CNTs are carbon allotropes constituted by sheets of graphene with cylinder form. When multiple concentric graphitic tubes are wrapped around a single axis, they are designated multi-walled carbon nanotubes (MWCNT). CNTs have excellent mechanical, chemical, optical, and electrical properties, presenting a high loading capacity [7; 9]. These characteristics, together with their biocompatibility, makes CNTs appropriate nanomaterials for the use in the pharmaceutical industry [10; 11]. Additionally, CNTs' surface can be easily functionalized, tuning their properties towards precise applications and improving their efficacy as enzymes support [12]. Immobilizing biomolecules onto CNTs can be carried out by different methods, explicitly non-covalent processes, such as direct physical adsorption, physical adsorption onto CNTs functionalized with biomolecules, polymers, or surfactants and layer-by-layer deposition, and covalent attachment, either with or without crosslinkers [13; 14; 15]. Adsorption is the preferred method for enzyme immobilization onto CNTs since it is a conservative and straightforward method concerning the conformational structure of the biomolecules and CNTs properties [16]. However, the main disadvantage of this method concerns the detachment of the biomolecules from the CNTs surface [17]. This can be battled by CNTs functionalization by introducing different surface groups such as carboxyl, amine, glycol, among others [18; 19]. Moreover, the surface modification increases the CNTs' compatibility with biomolecules, such as enzymes, by permanent or reversible modifications that change their chemical properties [4]. Although promising results using modified CNTs can be found, only a few works reporting the immobilization of ASNase onto functionalized CNTs are published [20; 21]. Studies on MCWNTs still lack key parameters, such as their structure, size, surface chemistry, charge, and shape, determinant for the nanomaterials' biocompatibility.