COPPER-GRAPHENE OXIDE NANOCOMPOSITES AS MATERIALS FOR MEASURING GLUCOSE AND HYDROGEN PEROXIDE CONTENT

Abstract

Manufacturing methods for copper hydroxide, cuprous oxide, and cupric oxide nanocomposites with graphene nanoplatelets are described, using high-intensity or ultrasonic mixing treatments of graphite and copper hydroxide precursor salts in water. Intermediate copper hydroxide reaction compounds are modified to cupric oxide-graphene, and this is further modified to cuprous oxide-graphene. The resulting binary compounds are successfully used as materials for measuring glucose and hydrogen peroxide content in aqueous solutions, serving as non-enzymatic biosensors for these molecules.

Description

Copper oxide-graphene nanocomposites as materials for measuring glucose and hydrogen peroxide content DESCRIPTION OBJECT OF THE INVENTION The object of the present invention is the development of manufacturing methods for cuprous oxide-graphene and cupric oxide-graphene nanocomposites and their use as materials for the detection and measurement of glucose and hydrogen peroxide contents in aqueous medium. BACKGROUND Diabetes mellitus is a condition affecting a growing number of people worldwide. It is a debilitating disease that, if left untreated, can lead to blindness, gangrene, limb loss, and eventually death. The condition arises from either a lack of insulin production (type 1 diabetes) or insufficient insulin production (type 2 diabetes). Insulin, a hormone produced in the pancreas, metabolizes sugars, helping to generate energy at the cellular level; however, insufficient levels of this enzyme are increasingly common, resulting in high glucose levels in the bloodstream. Patients with type 2 diabetes can manage the disease by changing their eating habits, exercising more frequently, and using medications that help regulate blood glucose levels.People with type 1 diabetes do not produce insulin and must obtain it, usually through insulin injections. To reduce the risks associated with high blood glucose levels, people with diabetes must monitor their blood sugar frequently. Portable glucose meters are now available that can be easily used by those with diabetes. They work by placing a small drop of blood on a strip containing materials that react with glucose and generate an electrical current. These strips are placed inside the meter, a simple potentiostat that relates the intensity of the electrical signal to the glucose level. Although the device is very easy to use, it is not widely accepted because blood is drawn via finger pricks. CJ LP Ln / A Lnz / E / Yli are uncomfortable and often painful. Another weakness of the system is that the strips rely on the use of enzymes, unstable organic materials with a limited lifespan, the use of which can lead to inaccurate measurements. Although enzyme-based sensing materials are currently the most widely used, the last decade has seen attempts to replace them with other raw materials that do not present the aforementioned drawbacks. Among the first materials studied were noble metal nanoparticles, such as platinum, gold, and silver, capable of catalyzing the oxidative conversion of glucose to gluconolactone, a reaction that releases electrons whose quantity can be measured electrochemically (1). Given the high cost of noble metals, research is underway to replace them with less expensive metals or their oxides. Notable examples include copper(I) and copper(II) oxides, cuprous oxide (Cu₂O) and cupric oxide (CuO), respectively, from which nanomaterials have been prepared for measuring glucose content by electrochemical methods.More recently, composite materials of graphene decorated with metal nanoparticles or their oxides have been successfully developed; in this combination, graphene acts as a support substrate for the particles and, due to its high electrical conductivity, as a transport medium for the electrons released during oxidation. One of the first published examples of the use of Cu2O particles for glucose determination is that of Ni's group in 2009 (2); the researchers describe the synthesis of porous cuprite cubes approximately 800 nm on each side, which electrochemically detect both hydrogen peroxide and glucose, with sensitivities of 50.6 pA / mM and 70.8 pA / mM, respectively. The following year, Hameed et al. reported the preparation of a compound by depositing cuprite, prepared by reducing cupric chloride with sodium borohydride, onto Vulcan XC-72 carbon. The material deposited on a glassy carbon electrode (GCE) is capable of measuring glucose content with a sensitivity of 629 pA / mM (3). Zhao and colleagues describe the use of cuprite nano-flowers and nano-boxes obtained by reducing cupric oxide precursors with hydrazine; the solids proved useful in the determination of glucose (4).Liu and colleagues report the synthesis of cuprite nano cubes. CJ LP Ln / A Lnz / E / Yli wrapped in reduced graphene oxide (rGO) sheets are used to measure glucose content with good sensitivity (5). The electrocatalytic detection capacity (121.7 μA / mM) of cuprite deposited on an ECV was reported by Félix et al. in 2012; the cuprite was obtained by treating cupric chloride with soda and subsequently reducing the intermediate with ascorbic acid (6). The hydrothermal treatment (80 °C for two hours) of CuCl2-2H2O mixtures in the presence of polyvinylpyrrolidone (PVP), potassium carbonate, and sodium citrate, to which glucose was subsequently added as a reducing agent, was described by Khan et al.; the cuprite showed a glucose measurement sensitivity of 933 μA mM'1cm·2 (7).The preparation and use of approximately 100 nm diameter cuprous oxide nanospheres in glucose biosensing, prepared by reducing copper nitrate mixtures with PVP and hydrazine, was reported by Cao et al. These nanospheres, when placed on a glucose-sensing device, showed a glucose measurement sensitivity of 2038.2 pA mM⁻¹ cm² (8). The use of carbon quantum dot nanocomposites with cuprite in glucose measurement has been described by Li's group; these nanocomposites showed a detection sensitivity of 298 pA mM⁻¹ cm² (9). The synthesis of rGO-Cu₂O nanocomposites and their use for glucose measurement has been reported by Ding's group, who prepared the materials by mixing graphene oxide (GO) with copper salts in the presence of sodium lauryl sulfate and subsequently reducing the suspensions by adding sodium ascorbate (10).The nanocomposites were prepared with GO to copper salt weight ratios of 1:20, 1:40, 1:60, and 1:80. The compound made with the last weight ratio demonstrated the greatest sensing capacity. The fabrication of rGO-Cu₂O composites has been described by Yan et al. This group begins by heating mixtures of GO and cupric acetate in diethylene glycol. During the initial treatment at 140 °C, the GO is reduced to rGO, and cuprite nanoparticles (NPs) form on its surface. Subsequently, the mixtures are heated to 180 °C. The NPs decrease in size as the initial heating time from 140 °C is prolonged. The researchers demonstrated that the smaller NPs have greater sensitivity (11). He. and collaborators reported the synthesis of cuprous oxide nano-hedgehogs by microwave treatment of copper chloride mixtures in polyethylene glycol with TMHA (tetramethylenehexamine), the hedgehogs showed a sensitivity 1231.7 μA mM1cm2 in the electrochemical evaluation of glucose (12). A hydrothermal synthesis procedure (3 hours at 100 °C) of cuprite. CJ LP Ln / A Lnz / E / Yli on rGO has been published by Yazid et al.; they used the formation of copper hydroxide, its transformation into the copper tetramonium complex, mixing this solution with GO, and adding sodium carbonate, finally heating the mixture for two hours in a hydrothermal pump. The nanocomposites showed a sensitivity of 1,330.05 pA mM-1cm-2 to glucose (13). Other examples describing the manufacture of cuprites of different morphologies have been reported; these are generally based on the formation of spongy particles or aerogels with a large surface area, which is partially responsible for their high sensitivity (14-19). It should be noted that the reported cuprite-graphene materials use GO as a raw material, and therefore the nanocomposites obtained are cuprite-rGO.The use of cupric oxide (CuO) in glucose detection predates the use of cuprite for this purpose; one of the first examples was reported in 2008 when Leí's group described the hydrothermal synthesis of CuO spheres several hundred nanometers in diameter, from whose surface tiny wires of the oxide were projected (20). The spheres showed an electrochemical glucose measurement sensitivity of 404.53 pA mM⁻¹ cm⁻². Wang et al. have reported the electrospinning of cupric acetate solutions in PVA and the pyrolysis of the resulting meshes; the heat treatment generates three-dimensional CuO fiber structures with a glucose detection sensitivity of 431.3 pA mM⁻¹ cm⁻² when using glassy carbon electrodes (GCE) to deposit the measurement material and carry out the electrochemical measurement of the carbohydrate (21).In 2011, Bai et al. demonstrated the formation of CuO nanocomposites by deposition on macroporous carbon through 24-hour hydrothermal treatment at 120 °C of a mixture of mesoporous carbon with cupric nitrate and NaOH. The compounds showed a sensitivity of 1.43 μA / mM (22). Luo et al. reported the preparation of CuO nanocube composites with rGO. The rGO was synthesized by reducing GO with hydrazine, and the reduced material was deposited on a cyclic voltammetry electrode (CVE). Copper was electrochemically deposited onto this surface, and the electrode, immersed in a sodium hydroxide solution, was repeatedly treated by cyclic voltammetry to convert the copper to cupric oxide. The electrode thus manufactured demonstrated the ability to electrochemically measure glucose with a sensitivity of 1,360 pA mM1cm2 (23). Ye et al published a procedure similar to the above, mixing rGO with carbon nanofibers and depositing the mixture. CJ I Γ Ln / A mz / E / Yi on an ECV, copper was electrodeposited on it and subsequently oxidized to CuO by electrochemical treatment; the electrode showed a sensitivity of 912.7 μA mM'1cm-2 in glucose measurement (24). The preparation of CuO nano-hedgehogs and their use in glucose sensing was reported by Sun et al. (25), the oxides showed a sensitivity in the electrochemical measurement of glucose of 2,682 μA mM'1cm-2. The deposition of CuO on mesoporous carbon (26) or carbon nanofibers (27) has been described by two groups of researchers; The oxide compound on mesoporous carbon gives a sensitivity of 1,154.1 μA mM'1cm2, while when placed on nanofibers, the sensitivity found is 2,739 μA mM'1cm·2. The hydrothermal synthesis of CuO-rGO by treatments of 10 hours at 120, 150 and 180 °C has been reported, the compounds show a sensitivity of 262.52 μA mM'1cm-2 in the measurement of glucose (28).Another hydrothermal synthesis by treating copper nitrate in the presence of urea at 130 °C for 5 hours has been described. The materials, with a morphology of spheres of various sizes formed by the joining of nano-bricks, show a sensitivity of 164.25 μA mM-1cm-2 in glucose measurement at biological pH (29). Ahmad et al. have described the synthesis of CuO nanoseeds prepared by heating copper nitrate, triethylamine, and sodium hydroxide at 80 °C for 3 hours; the ECVs manufactured with them showed a glucose measurement sensitivity of 1,101 μA mM1cm2 (30). A composite material of CuO deposited on multi-walled carbon nanotubes was prepared by Alizadeh et al. After optimizing the weight ratio of the oxide with the nanotubes, the researchers report that the nanocomposites exhibit a sensitivity of 3,968.42 μA mMol-1cm-2 in glucose measurement (31).The preparation of CuO by hydrothermal treatment of copper salts with glucose (180 °C for 24 hours) followed by calcination of the intermediate material at 550 °C for 4 hours has been reported by Saraf et al.; the materials show an electrochemical glucose detection sensitivity of 26.59 μA mM1cm-2(32). Another hydrothermal preparation of cupric oxide by treatment with cupric chloride in the presence of glycine for 2 hours at 200 °C has been presented by Baloach et al.; the authors indicate that the materials, CuO agglomerates of multiple micron sizes, exhibit sensitivities of 464,285.7 μA mM-1cm-2(33). The synthesis of a CuO-rGO nanocomposite by microwave heating at 130 °C for 10 minutes has been published. CJ LP Ln / A Lnz / E / Yli preparation uses a mixture of cupric chloride in ethanol-ethylene glycol and the three-block polymer P123. After pre-treatment with ammonia and subsequently with soda, the reaction mixture generates spheres of about 1 µm in diameter which, when placed on an ECV, allow glucose content to be measured with a sensitivity of 52.1 μA mM-1 (34). The preparation of PDDA-graphene mixtures with CuO has been reported to show a sensitivity of 4,982.2 μA mM'1cm'2; the compound is synthesized by ultrasonic mixing of poly(dimethyldiallylammonium) chloride suspensions with GO followed by reduction of the mixture with hydrazine. This compound is finally mixed with CuO to generate the sensor material (35). Unfortunately, the authors do not clarify the amount of material deposited on the ECV, so it is not easy to assess the actual sensitivity.The preparation of a graphene oxide aerogel with CuO has been described by Yang et al.; the three-dimensional structure of CuO-rGO is obtained by a 12-hour hydrothermal treatment at 180 °C followed by lyophilization and calcination of the intermediate sponge at 300 °C for 4 hours. The product shows a sensitivity of 223.1 μA mM-1cm-2 (36). The preparation of faceted and unfaceted copper oxide has been reported by Sahoo et al., who use hydrothermal or microwave treatments to synthesize the oxides. The authors demonstrate that faceted oxides provide a better response for glucose measurement, reporting a sensitivity of 412 μA mM-1cm-2 (37). As with the cuprite-graphene composites previously described, the copper oxide-graphene composites are also prepared from GO, and are therefore CuO-rGO nanocomposites. Different copper oxide nanocomposites with graphene have been tested as useful materials for determining hydrogen peroxide content; sometimes, the compounds are capable of measuring both hydrogen peroxide and glucose. One of the first examples of using CuO to sense H2O2 was reported by Song et al., who surface-modified a copper sheet by generating a cupric oxide layer. The product was able to electrochemically detect H2O2 with a sensitivity of 88.4 μA mM-1cm-2 (38). The use of rGO compounds with Cu2O has been reported with a peroxide measurement sensitivity of 19.5 μA mM-1cm-2 (39), as well as the production of nanocomposites of cuprous oxide nanocubes encased by CJ Ln / A Lnz / E / Yli graphene oxide sheets with good glucose and hydrogen peroxide detection capability (40). The preparation of cuprous oxide compounds with carbon quantum dots has been described by L1 et al.; these materials have sensitivities of up to 298 μA mM-1cm-2 for the detection of H2O2 and are also capable of measuring glucose content (41). A nanocomposite of Cu2O microspheres with rGO has been reported for the detection of glucose and hydrogen peroxide (42), as well as a graphene-Cu(II) oxide compound for the detection of H2O2 (43). The hydrothermal synthesis of cuprous oxide compounds in a three-dimensional rGO structure for the measurement of hydrogen peroxide has been described, the latter with a sensitivity of 15.8 μA mM-1cm-2 (44). A heterostructured Cu2O / CuO@rGO material has been described by Wu et al., with which H2O2 is detected with a sensitivity of 431.65 μA mM-1cm-2 (45).The preparation of a three-dimensional network of two-dimensional rGO sheets decorated with Cu2O has been reported by Cheng et al., with the materials demonstrating the possibility of measuring the presence of H2O2 (46). The use of cuprous oxide nanocubes deposited on rGO and dispersed in a chitosan matrix has been described by Gopalakrishnan et al., with the materials showing a sensitivity of 330 μA mM-1cm-2 for measuring H2O2 (47). The fabrication of cupric oxide nanocomposites deposited on exfoliated graphite in the presence of guar gum by ultrasonic treatment followed by a three-hour hydrothermal treatment at 140 °C has recently been reported by Balu et al. (48); the composite materials, with a low amount of guar-graphene, show a hydrogen peroxide sensing capacity with a sensitivity of 259 μA mM-1cm-2. Studying the reported examples of Cu₂O-rGO, CuO-rGO, and CuO-G preparation reveals that the methods are complex and require small quantities of raw materials, hindering their potential scalability. Except for the last example, which relies on graphene oxide as a raw material, the proposed materials require the conversion of graphite to its oxide, with the associated cost in terms of time, materials, and the management of polluting waste. Furthermore, many of the aforementioned procedures employ hydrothermal treatments lasting several hours at high temperatures or calcination processes lasting several hours at temperatures of several hundred degrees Celsius. CJ LP Ln / A Lnz / E / Yli Given the above, it is desirable to have processes that avoid the aforementioned drawbacks, the most significant of which is the use of graphene oxide as a starting point for their production. Ideally, the materials should be prepared efficiently, with low energy consumption, using inexpensive and easy-to-use equipment, and, fundamentally, avoiding the use of polluting raw materials or procedures. Therefore, manufacturing processes for Cu₂O-graphene and CuO-graphene nanocomposites are presented here, avoiding all the drawbacks associated with previously used procedures. These processes are carried out using environmentally acceptable solvents, primarily water, at room temperature in a matter of minutes, and allow for the manufacture of multi-gram quantities of material using inexpensive, easy-to-use equipment, thus enabling industrial-scale production. In the described processes, the graphite used is first pretreated to generate graphene nanoplatelet suspensions by agitation in a high-shear mixer, using water as the suspension medium. Copper salts are added to the suspensions as oxide precursors, and the mixture is treated by adding hydroxide solutions. The CuO-graphene composite is obtained in minutes after the addition of sodium hydroxide.Alternatively, the Cu₂O-graphene compound is obtained by further reduction of the CuO-graphene by adding a reducing agent to the reaction mixture. As an alternative procedure, the nanoplatelet powder can be separated and subjected to decoration methods with the oxides using other mixing-decoration systems such as ultrasonic irradiation or by means of a high-speed homogenizer-disperser (Turrax). It has also been proven that the deposition of suspensions of CuO-graphene and CusO-graphene compounds on glassy carbon electrodes can be used to advantage for electrochemically determining glucose and hydrogen peroxide contents in aqueous solutions. REFERENCES .- Electrode Systems for continuous monitoring in cardiovascular surgery; LC Clark Jr, C. Lyons; Ann NY Acad Sci 1962, 102: 29-45. 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DOi: 10.103905ra04164c 43,- Graphene oxide-Cu(ll) composite electrode for non-enzymatic determination of hydrogen peroxide; S. Muralikrishna, Sarawut Cheunkar, Benchaporn Lertanantawong, T. Ramakrishnappa, D.H. Nagaraju, Werasak Surareungchai, R. Geetha Balakrishna, K. Ramakrishna Reddy; Journal of Electroanalytical Chemistry 776 (2016) 59-65. http: / / dx.doi.Org / 10.1016 / i.ielechem.2O16.06.034 44,- Facile preparation of a three-dimensional macroporous graphene wrapped cuprous oxide composite by one-step hydrothermal assembly for stable and sensitive hydrogen peroxide detection; Guangran Ma, Min Yang, Guochun Zhao, Yanping Zhang, Fugang Xu and L¡ Wang; Anal. Methods, 2016, 8, 7405. DPI: 10,1039 / c6ay02244h 45,- Cu2O / CuO@rGO heterostructure derived from metal-organic-frameworks as an advanced electrocatalyst for non-enzymatic electrochemical H2O2 sensor; Duoming Wu, Zhaodong Xu, Ting Zhang, Yubo Shao, Pinxian X¡, Hua L¡ and Cailing Xu; RSC Adv., 2016, 6, 103116. DOi: 10.1039 / c6ra23551 d .- 3D NetWork and 2D Paper of Reduced Graphene Oxide / Cu2O Composite for Electrochemical Sensing of Hydrogen Peroxide; Chunfeng Cheng, Chunmei Zhang, Xiaohui Gao, Zhihua Zhuang, Cheng Du, and Wei Chen; Anal. Chem. 2018, 90, 1983-1991. DOI: 10.1021 / acs.analchem.7'b04070 47,- Cuprous oxide nanocubes decorated reduced graphene oxide nanosheets embedded in chitosan matrix: A versatile electrode material for stable supercapacitor and sensing applications; arthi CJ LP Ln / A Lnz / E / Yli Gopalakrishnan, Nandimalla Vishnu, Sushmee Badhulika; Journal of Electroanalytical Chemistry 834 (2019) 187-195. .- Sonochemical synthesis of gum guar biopolymer stabilized copper oxide on exfoliated graphite: Application for enhanced electrochemical detection of H2O2 in milk and pharmaceutical samples; Sridharan Balu, Selvakumar Palanisamy, Vijaylakshmi Velusamy, Thomas CK Yang; Ultrasonics Sonochemistry 56 (2019) 254-263. https: / / dpj..prg / W Brief description of the figures Figure 1. X-ray diffraction of Cu(OH)2 Figure 2. X-ray diffraction of CuO-graphene. Figure 3. X-ray diffraction of CU2O by high shear stress from a) graphite powder and b) exfoliated graphite powder. Figure 4. X-ray diffraction of Cu(OH)2-graphene. Figure 5. TEM image of Cu(OH)2-graphene. Figure 6. Ultrasonic X-ray diffraction of CuO-graphene. Figure 7. TEM image of Cu2O-graphene by ultrasound by 1:10 molar reduction of Cu+2 / ascorbic acid. Figure 8. Cyclic voltammetry at 20mV s-1 of GP-CuO + 0.25mM Dextrose aliquots in a pH 12 0.05M NaOH solution. Figure 9. Cyclic voltammetry at 20mV s-1 of GP-CuO + 0.2mM aliquots of H2O2 in a pH12 0.05M NaOH solution. Figure 10. Cyclic voltammetry at 20mV s-1 of GP-Cu2O + 0.2mM aliquots of H2O2 in a pH12 0.05M NaOH solution. CJ LP LIVA LAZ / B / Yli DETAILED DESCRIPTION OF THE INVENTION Based on the above, manufacturing processes of CuOgraphene and CuzO-graphene nanocomposites capable of measuring glucose and hydrogen peroxide contents in aqueous solutions are presented here. In general, the manufacturing method involves exfoliating graphite by treating graphite mixtures in distilled or deionized water using a high-shear mixer (HST). This procedure is performed without dispersants, surfactants, or other delamination aids. The HST exfoliation treatment can be carried out using different natural or synthetic graphites of varying sizes and chemical compositions, by modifying the graphite-to-solvent weight / volume ratio, the solvent used, the mixing time, and the mixing speed, which can range from 500 to 10,000 rpm, preferably 8,000 rpm. Under these conditions, graphene nanoplatelet (GNP) suspensions are obtained. Once the suspensions are prepared, copper salts, precursors of the oxide, are added, maintaining agitation of the reaction mixture between 500 and 10,000 rpm, preferably 8,000 rpm. The pH of the mixture is then adjusted until copper hydroxide forms. The formation of the nanocomposites occurs without adjusting the temperature of the suspensions, which can rise to 80 °C due to friction within the suspended material. Alternatively, oxide formation can also occur after cooling the suspensions to room temperature. The agitation time after copper hydroxide formation can vary from one minute to several hours, but is preferably between 1 and 10 minutes. Under agitation conditions, it has been determined that copper(II) hydroxide dehydrates and transforms into cupric oxide in situ. To obtain CuO-graphene nanocomposites with glucose measurement capabilities, the final weight ratio of graphene nanoplatelet to CuO can be varied over a wide range, from 1:0.01 to 1:2 and higher. Preferred weight ratios of NPG:CuO are in the range of 1:0.01 to 1:0.5 and can be modified to further expand the CJ LP Ln / A Lnz / E / Yli range at both lower and higher weight ratios. The materials obtained are filtered and the solid is dried at a temperature of 50 °C to 80 °C for several hours in an electric oven. In the formation of CuO, simple copper salts capable of reacting with hydroxide compounds can be used. The copper salts most commonly used and least expensive, such as copper chloride, sulfate, nitrate, and acetate, are preferred, although other copper salts capable of converting to the hydroxide can be used. The hydroxides used to generate copper hydroxide can be sodium, potassium, or ammonium hydroxides, or mixtures thereof; alternatively, raw materials that generate hydroxide under the treatment conditions, such as urea, can be used. In a variation of the procedure, it has been found possible to generate copper hydroxide ex situ and subsequently mix it with NPG suspensions. Ex situ preparation is carried out by mixing copper salt solutions with hydroxide solutions or compounds that generate it; under these conditions, copper hydroxide suspensions are formed. The reaction between the copper salt and hydroxide solutions can be achieved with any system that facilitates rapid mixing of the reagents and their conversion to the hydroxide. It has been determined that high-shear mixing systems, Turrax-type homogenization-dispersion systems, ultrasound (immersion of the sonotrode tip in the reaction medium or treatment in cleaning baths), and magnetic stirring can be used for this purpose. The copper hydroxide suspensions are then mixed with the NPG suspensions under agitation. Once mixed, the suspensions are kept under agitation for varying times, from 1 to 500 minutes, preferably 2 to 30 minutes. The same mixing systems used in the formation of the copper hydroxide and NPG suspensions can be used for this purpose. As in the first general example, the resulting product is filtered and washed sequentially with distilled water and ethanol, and finally dried at 50 °C to 100 °C for several hours in an electric oven. In the manufacture of cuprous oxide-graphene nanocomposites (CU2O-NPG), the procedure described above and its variations can be followed, adding a reducing agent at the end of the CuO-graphene nanocomposite preparation method. The addition of the reducing agent modifies the state of CJ LP Ln / A Lnz / E / Yli oxidation of Cu(II) to Cu(I), generating cuprous oxide nanocomposites. In this step, a wide variety of reducing agents can be used, such as hydrazine, sodium borohydride, sodium hypophosphite, ascorbic acid, glucose, and other reducing sugars. Given their safety, ease of handling, and low cost, ascorbic acid or reducing sugars are preferable in this transformation. It has been found that the fabrication of CuO-graphene and Cu₂O-graphene nanocomposites can also be carried out in a discontinuous manner, that is, first by isolating graphene nanoplatelets and then decorating them with cupric or cuprous oxide. This stepwise manufacturing process allows for manipulation of the morphology of the produced oxides, depending on the synthesis conditions of the copper hydroxide generated as a precursor to the cupric and cuprous oxides. In this variation, the advantage of synthesizing copper hydroxide by mixing copper precursor salts with hydroxide solutions under ultrasonic treatment, followed by the addition of NPG, while maintaining the ultrasonic irradiation treatment for varying durations, has been discovered.In this preparative sequence, which allows the fabrication of Cu(OH)₂-graphene nanocomposites, after the generation of copper hydroxide during a short US irradiation interval of 1 to 5 minutes, NPG is added, and the ultrasonic treatment continues for 1 to 10 minutes, preferably up to 5 minutes. Finally, the resulting solid is filtered, sequentially washed with water and ethanol, and dried for several hours at 70 °C in an electric oven. The X-ray diffraction patterns of the synthesized solid show signals corresponding to graphite and copper hydroxide, without any diffraction signals attributable to CuO, demonstrating the clean formation of the hydroxide. Observation of the compound using a transmission electron microscope (TEM) shows the deposition of hydroxide wires intercalated between graphene sheets with a low number of layers.If the treatment of the mixture by US is prolonged up to 30 minutes, the hydroxide is converted into the oxide, resulting in CuOgraphene nanocomposites. It has also been established that the direct formation of CuO-graphene nanocomposites is possible by adding copper precursor salts to an NPG suspension subjected to ultrasound irradiation, followed by the addition of hydroxide solutions. That is, the modification of the order of CJ LP Ln / A Lnz / E / Yli mixing of copper salt solutions with hydroxide solutions and NPG suspensions enables the formation of copper hydroxide or oxide nanocomposites. Following the procedures described in the general example of CuzO-graphene preparation using high shear mixing systems, the copper hydroxide or copper oxide nanocomposites obtained by ultrasound can be transformed into cuprosographene oxide nanocomposites by adding reducing agents to aqueous suspensions of the former. The fabricated nanocomposites proved useful in the electrochemical determination of glucose and hydrogen peroxide content in aqueous media. The glucose or hydrogen peroxide concentration was measured using a Biologic SP-50 potentiostat, a 200 mL electrochemical cell equipped with three electrodes: a platinum counter electrode, a 3.5 M Ag / AgCl reference electrode, and a glassy carbon electrode used as a substrate for fabricating the working electrode. A 0.05 M NaOH solution was introduced into the electrochemical cell for measurements at pH 12, while a 0.05 M PBS electrolyte was used for measurements at pH 7.The working electrodes are prepared by depositing different volumes of aqueous suspensions of the nanocomposites (1 pL to 10 pL) onto the glassy carbon substrate. The solids content of the suspensions is varied from 1 to 10 mg / mL using distilled water as the dispersion medium or PEDOT-PSS solutions in water (0.1 mg / mL). Variable volumes of Nafion solution at different weight percentages are added to one milliliter of these mixtures. The ink is treated for 10 minutes by immersion in an ultrasonic cleaning bath, and then variable volumes of ink are placed onto the ECV. The electrodes are subjected to a heat treatment of 60 °C for 20 minutes and then cooled to room temperature. The electrochemical characterization of the materials, as well as their responses to the presence of glucose, were performed using cyclic voltammetry at a rate of 50 mV s⁻¹ and a measurement range of 478–1,120 mV vs. SHE, incorporating 200 pL aliquots of 200 mmol glucose in 200 mL of electrolyte. The responses to the presence of peroxide were also performed using cyclic voltammetry at a rate of 50 mV s⁻¹ and a measurement range of CJ I Γ I Π / AI n7 / E / Yl· measurement of -478 - 1,120mV vs SHE incorporating 200 pL aliquots of 174 mmol hydrogen peroxide in 200 mL of electrolyte. The sensing capacity of the materials is determined by linear regression of the current with respect to the concentration of glucose or hydrogen peroxide in solution, using the chronoamperometry technique at a potential of 810 mV vs SHE and a rotating disk system at 400 rpm. The following are examples of the methods used, which should be considered illustrative and not limiting of the procedures described and the variations that may arise from them. Example 1 Graphite exfoliation by high shear stress mixing in water One gram of Aldrich graphite powder is added to a 2 L beaker containing 500 mL of distilled water (DW). The suspension is then treated with a Ross high-shear mixer (HSTM) for one hour at 1,000 to 10,000 rpm, preferably 8,000 rpm. The suspension is filtered and subsequently dried overnight in an electric oven at 70 °C. The material is named graphene nanoplatelets (PNGs). Quantities of 5 to 15 g of graphite are treated in the same manner using 1 L of DW. Example 2 Cu(OH)2-graphene nanocomposite by high shear stress mixing In a 2 L beaker containing 500 mL of distilled water (DW), one gram of Aldrich graphite powder is added, and the suspension is stirred for one or more hours using a Ross high-shear mixer at a mixing speed of 1,000 to 10,000 rpm, preferably 8,000 rpm. Separately, 1 g of NaOH is dissolved in 500 mL of DW. To this solution, 128 mg of copper sulfate pentahydrate (0.51265 mM) is added and mixed for one minute at 1,000 to 10,000 rpm, preferably 8,000 rpm. The formation of a lumpy, white-turquoise precipitate is observed. The first NPG suspension is added to this second suspension, stirring for two minutes at a speed of 1,000 to 10,000 rpm, preferably 8,000 rpm. the solid filters through by gravity, CJ LP LO / A LAZ / B / Yli was washed with water and finally with acetone, and dried overnight at 70 °C in an electric oven. X-ray reflections (XRD, Figure 1) show the formation of Cu(OH)2. Example 3 CuO-graphene nanocomposite by high shear mixing from graphite In a 2 L beaker containing 500 mL of distilled water (DW), 2.5 g of GP are added and treated with an MAEC for 1 h at 1,000 to 10,000 rpm, preferably at 8,000 rpm. After this time, the mixture is allowed to cool to room temperature. Separately, in a 1 L beaker, 500 mL of water are mixed with 980 mg of copper sulfate pentahydrate (3.93 mM). A 1 M NaOH solution is added, adjusting the pH of the suspension to 10-11. The mixture is stirred for 1 minute with a Turrax at 5,000 rpm to form a copper hydroxide suspension. This is mixed with the NPG suspension and treated with an MAEC for 1 to 10 minutes, preferably 2 minutes. The solid is filtered by gravity and washed successively with distilled water and finally with acetone; it is then dried at 70 °C. The formation of CuO-graphene is demonstrated by observation of X-ray reflections (XRD, Figure 2). Example 4 Preparation of Cu2O-graphene nanocomposite by high shear mixing from graphite In a 2 L beaker containing 1 L mL of distilled water (DW), 5 g of GP are placed. The mixture is treated with a MAEC (a flask-burning electrophoresis) for 1 h at 1,000 to 10,000 rpm, preferably at 8,000 rpm. After this time, it is allowed to cool to room temperature. 1,960 mg (7.86 mM) of copper sulfate pentahydrate is added to the suspension, adjusting the pH to 10 by adding 1 M aqueous sodium hydroxide solution. Stirring continues for another 30 minutes. 11.6 g (65.86 mM) of ascorbic acid is added to the suspension, and stirring continues for an additional 30 minutes. The suspension is filtered by gravity, and the filtered powder is washed thoroughly with DW and finally with acetone. The solid is dried at 70 °C for 14 hours in an electric oven. Using XRD (Figure 3a) it was determined that the material obtained exhibits reflections of graphite and cuprous oxide. Example 5 Preparation of Cu2O-graphene nanocomposite by high shear mixing from exfoliated graphite CJ lp lo / a laz / b / yl In a 2 L beaker, 1 L of distilled water is placed and 392 mg of copper sulfate is added. The pH of the solution is adjusted to 10 by adding 1 M sodium hydroxide solution. The mixture is then stirred for one minute at 1,000 to 10,000 rpm, preferably at 8,000 rpm. One g of exfoliated GP, prepared according to Example 1, is added to the mixture, and the suspension is stirred for another two minutes. After this time, a solution of 2.3 g of ascorbic acid in 50 mL of water, adjusted to 10 by adding 1 M sodium hydroxide, is added; the suspension is stirred for an additional two minutes. The suspension is filtered by gravity, and the filtered powder is washed thoroughly with AD and finally with acetone. The solid is dried at 70 °C for 14 hours in an electric oven. Using XRD (Figure 3b) it is determined that the material obtained has reflections of graphite and cuprous oxide. Example 6 Cu(OH)2-graphene nanocomposite by ultrasound treatment In a 250 mL beaker, 196 mg of copper sulfate pentahydrate were dissolved in 75 mL of distilled water. Using a Q Sonic sonotrode, model Q 700, the solution was sonicated from 10% to 70%, preferably at 60% intensity, for one minute after adjusting the pH to 10 by adding 1 M sodium hydroxide. Then, 500 mg of GP exfoliated according to Example 1 were added, and sonication continued for another 10 minutes. The suspension was gravity-filtered, and the filtered powder was thoroughly washed with AD and finally with acetone. The solid was dried at 70 °C for 14 hours in an electric oven. Figure 4 shows the XRD of the material. Figure 5 shows a TEM photograph. Example 7 CuO-graphene nanocomposite by ultrasound In a 250 mL beaker, 500 mg of exfoliated graphite powder obtained according to Example 1 were added and sonicated at 10% to 70% intensity, preferably at 60% intensity, for 10 minutes. A Q Sonica sonotrode, model Q 700, was used for sonication. Then, 1196 mg of copper sulfate pentahydrate, dissolved in 75 mL of distilled water, were added. After adjusting the pH of the suspension to 10 by adding 1 M sodium hydroxide, the mixture was sonicated for another ten minutes. The product was vacuum filtered, washed with AD, and finally with acetone. The solid was dried at 70 °C for 14 hours in an electric oven. The XRD of the material is shown in Figure 6. CJ LP Ln / A Lnz / E / Yli Example 8 Cu2O-graphene nanocomposite by ultrasonic reduction of 1:1 molar Cu+2 / ascorbic acid In a 250 mL beaker, 196 mg of copper sulfate pentahydrate are dissolved in 75 mL of distilled water. After adjusting the pH to 10 by adding 1 M sodium hydroxide, the solution is sonicated for one minute using a Q Sonic sonotrode, model Q 700. Then, 500 mg of GP exfoliated according to Example 1 is added, and sonication continues for another 10 minutes. After this time, a solution of 145 mg of ascorbic acid dissolved in 50 mL of AD, whose pH was adjusted to 10 by adding 1 M sodium hydroxide, is added, and sonication continues for 15 minutes. The product is vacuum filtered, washed with AD, and finally with acetone. The solid is dried at 70 °C for 14 hours in an electric oven. Example 9 Cu2O-graphene nanocomposite by ultrasonic reduction of 1:10 molar Cu+2 / ascorbic acid The procedure is the same as in Example 8, varying the amount of ascorbic acid. A solution of 1.2 g of ascorbic acid dissolved in 50 mL of AD, whose pH was adjusted to 10 by adding 1 M sodium hydroxide, is added to the previous mixture. The material is treated as in the previous example. Figure 7 shows a micrograph obtained using a transmission electron microscope (TEM). Example 10 Electrochemical measurement of glucose in alkaline medium (0.05 M NaOH) with Cu2O-graphene, or, CuO-graphene, or, Cu(OH)2-graphene Glucose measurement was performed by preparing inks as suspensions of 5 mg mL⁻¹ of Cu₂O-graphene, or CuO-graphene, or Cu(OH)₂ in 1 mL of distilled water, or suspensions of 0.1 mg mL⁻¹ PEDOT-PSS. 5 dL of 5% w / w Nafion were added to the mixtures. A Biologic SP-50 potentiostat, a 200 mL three-electrode electrochemical cell, a 0.05 M NaOH solution as electrolyte, a platinum counter electrode, a 3.5 M Ag / AgCl reference, and a glassy carbon electrode as substrate for fabricating the working electrodes were used to measure glucose content. 5 dL of ink, previously integrated by immersion in an ultrasonic bath for 10 minutes, was deposited onto the glassy carbon electrode. Once the ink was deposited, the electrode was... The sample C2 I Γ LO / A ι λζ / ε / υι was subjected to a heat treatment of 60 °C for 20 min and subsequently cooled to room temperature. Cyclic voltammetry was used (Figure 8) at a rate of 50 mV s⁻¹ and a measurement range of -778 to 1,120 mV vs. SHE, incorporating 200 DL aliquots of 200 mmol glucose in 200 mL of electrolyte. The sensing capacity of the materials was determined by linear regression of the peak oxidation current with respect to the glucose concentration in solution. Figure 8 shows a graph of the rate of change of the currents obtained at different glucose peroxide concentrations, at pH 12, using a GP-CuO compound with a weight ratio of 1:0.1. Example 11 Electrochemical measurement of hydrogen peroxide in alkaline medium with Cu2O-graphene, or, CuO-graphene, or, Cu(OH)2-graphene Hydrogen peroxide measurement was performed by preparing inks as suspensions of 5 mg mL⁻¹ of Cu₂O-Graphene, or CuO-Graphene, or Cu(OH)₂ in 1 mL of distilled water, or suspensions of 0.1 mg mL⁻¹ PEDOT-PSS. 5 DL of 5% w / w Nafion was added to the mixtures. For glucose content measurement, a Biologic SP-50 potentiostat, a 200 mL three-electrode electrochemical cell, a 0.05 M NaOH solution as electrolyte, a platinum counter electrode, a 3.5 M Ag / AgCl reference, and a glassy carbon electrode as a substrate for fabricating the working electrodes were used. 5 DL of ink, previously integrated by immersion in an ultrasonic bath for 10 minutes, was deposited onto the glassy carbon electrode. Once the ink was deposited, the electrode was subjected to a heat treatment of 60 °C for 20 min and subsequently cooled to room temperature.Cyclic voltammetry was used at a rate of 50 mV s⁻¹ and a measurement range of -778 to 1,120 mV vs. SHE, incorporating 200 DL aliquots of 174 mM hydrogen peroxide into 200 mL of electrolyte. The sensing capacity of the materials was determined by linear regression of the peak oxidation current with respect to the glucose concentration in solution. Figure 9 shows a graph of the rate of change of the currents obtained at different hydrogen peroxide concentrations, at pH 12, using a GP-CuO compound with a weight ratio of 1:0.1. CJ LP Ln / A Lnz / E / Yli Example 12 Electrochemical measurement of hydrogen peroxide in neutral medium with Cu2O graphene, or, CuO-graphene. The detection capability of hydrogen peroxide was carried out as described in Example 11, replacing the electrolyte solution with a solution of 0.1 M monobasic potassium phosphate (K2HPO4), 0.1 M dibasic potassium phosphate (KH2PO4) with a pH = 7. Figure 10 shows a graph of the rate of change of the currents obtained at different concentrations of hydrogen peroxide, at neutral pH, using a GP-CuiO compound with a weight ratio of 1:0.1.

Claims

1. - Process of synthesizing materials to manufacture electrodes for measuring glucose content in aqueous solutions through electrochemical methods, comprising the use of graphene nanoplatelets decorated with copper oxide nanoparticles and metallic copper.

2. - Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 1, characterized by being carried out in the following steps: treatment of graphite to prepare suspensions in aqueous medium of graphene nanoplatelets (NPG); addition of copper precursor salts to these suspensions and conversion of the salts to cupric hydroxide, cupric oxide or cuprous oxide in the form of wires, wire agglomerates or nanoparticles, by adding hydroxide solutions or compounds that generate it under the reaction conditions.

3. - Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claims 1 and 2, characterized by being carried out in the following steps: preparation of graphene nanoplatelets by exfoliation of graphites in aqueous medium, according to the process described in patent applications MX-a-2017-013705 and MX-a-2017-013707; formation of suspensions of the nanoplatelets by treating aqueous mixtures by means of ultrasound; addition of copper precursor salt solutions and treatment of the mixtures with hydroxide solutions or compounds that generate it; subsequent addition of a reducing agent to the copper hydroxide or oxide suspensions to form copper(I) oxide materials.

4. A process for synthesizing materials for manufacturing electrodes for the electrochemical measurement of glucose content in aqueous solutions, according to claims 1-3, characterized by being carried out by the subsequent reduction of copper hydroxide, copper(II) oxide, or copper(I) oxide nanocomposites to metallic copper, using different reducing agents and reduction conditions. CJ LP LÍVA LAZ / B / Yli 5.- Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claims 1, 2 and 3, characterized in that under the treatment conditions the nanoplatelets are decorated with nanomaterials of copper (II) and copper (I) oxides.

6. - Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 5, characterized in that the decoration of the nanoplatelets is carried out using aqueous suspensions.

7. - Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 5, characterized in that the suspensions are prepared using process acceleration mixing systems such as high shear mixers, Turrax-type homogenizers or ultrasound systems.

8. - Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 6, characterized in that the MAEC or Turrax mixing systems can be operated in a revolution range of 1,000 to 10,000 rpm. 9 - Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 7, characterized in that the treatment times can vary from 1 minute to several hours, preferably from 1 to 60 minutes.

10. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claims 7, 8 and 9, characterized in that the weight / volume ratio of NPGs / solvent can vary in a range of 0.001 mg / mL to 20 mg / mL, preferably from 0.1 mg / mL to 10 mg / mL and more preferably from 0.5 mg / mL to 5 mg / mL. 11.- Process of synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 5, characterized in that CJ LP LA / A LAZ / E / Yli copper precursor salts are added to the NPG suspensions in solid form and more preferably as solutions prepared by dissolving the salts in the solvent used to prepare the suspensions. 12 - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 11, characterized in that aqueous solutions of hydroxides are added to the NPG suspensions with the copper salts, being treated for variable times under high shear stress mixing conditions or using a Turrax homogenization-dispersion system.

13. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 12, characterized in that after the addition of the salts the additional treatment time of the resulting suspensions can vary from a few minutes to several hours, preferably from 1 to 60 minutes and more preferably from 1 to 30 minutes. 14.- Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 13, characterized in that the mixing speeds with MAEC or Turrax can vary from 1,000 to 10,000 rpm.

15. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 7, characterized in that the ultrasound systems can comprise different irradiation frequencies and the mixtures can be treated by placing them inside the sonication baths or by immersing the tip of the sonotrode in the reaction medium, preferably by immersing the tip of the sonotrode in the reaction mixture.

16. A process for synthesizing materials for manufacturing electrodes for the electrochemical measurement of glucose content in aqueous solutions, according to claim 15, characterized in that the power intensity of the ultrasound systems can be varied from 10% to 100%, preferably from 40% to 60%. CJ LP LÍVA LAZ / B / Yli 17 - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claims 15 and 16, characterized in that the treatment times can vary from a few minutes to several hours, preferably from 1 to 60 minutes and more preferably from 1 to 30 minutes.

18. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 10, characterized in that the weight / volume ratio of NPGs / solvent can vary in a range of 0.001 mg / mL to 20 mg / mL, preferably from 0.1 mg / mL to 10 mg / mL and more preferably from 0.5 mg / mL to 5 mg / mL.

19. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 15, characterized in that copper precursor salts are added to the NPG suspensions in solid form and more preferably as solutions prepared by dissolving the salts in the solvent used to prepare the suspensions.

20. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 19, characterized in that after the addition of the salts the additional treatment time of the resulting suspensions can vary from a few minutes to several hours, preferably from 1 to 60 minutes and more preferably from 1 to 30 minutes.

21. - Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 20, characterized in that hydroxides are subsequently added to the resulting suspensions, either in solid form or in aqueous solution.

22. A process for synthesizing materials for manufacturing electrodes for the electrochemical measurement of glucose content in aqueous solutions, according to claim 21, characterized in that after the addition of the hydroxide, the mixtures are treated for a time from 1 minute to several hours, preferably from 1 to 60 minutes. CJ LP LÍVA LAZ / B / Yli 23. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claims 11 and 19, characterized in that the precursor salts can be any copper salt that is soluble in the solvent used in the preparation of the NPG suspensions. 24 - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claims 12 and 21, characterized in that the hydroxides can be sodium hydroxide, potassium hydroxide, ammonium hydroxide or any other hydroxide soluble in aqueous medium.

25. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 24, characterized in that the amount of hydroxides added can vary from the stoichiometric amount necessary to combine with Cu+2, to a molar excess.

26. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claims 4, 12 and 21, characterized in that after the treatment time of the NPG suspensions with copper precursor salts and hydroxides, a reducing agent is added to them in solid form or as a solution prepared in the treatment solvent.

27. A process for synthesizing materials for manufacturing electrodes for the electrochemical measurement of glucose content in aqueous solutions, according to claim 26, characterized in that the reducing agent can be any reducing agent, preferably one of those typically used in the reduction of metal cations to the transition metal; without limitation, the reducing agent can be sodium or potassium borohydride, hydrazine, sodium hypophosphite, ascorbic acid, reducing sugars, or mixtures of reducing agents. Preferably, the reducing agent should be non-polluting and, more preferably, of natural origin, such as ascorbic acid or reducing sugars. 28.- Process of synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 27, characterized in that CJ LP Ln / A Lnz / E / Yli the molar ratio of reducing agent to metal salt can vary from 0.5 to 20, preferably from 1 to 10 and more preferably from 1 to 5.

29. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 28, characterized in that the treatment time can vary from a few minutes to several hours, preferably from 1 to 90 minutes and more preferably from 1 to 20 minutes.

30. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 29, characterized in that the treatment temperature can be within the range of 0°C to 100°C, preferably between 20°C to 70°C and more preferably from 30°C to 50°C.

31. - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 4, characterized in that the NPG nanocomposites with copper hydroxide, cupric oxide or cuprous oxide obtained according to claims 2 and 3 are reduced to obtain the graphene-metallic copper nanocomposites. 32 - Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 31, characterized in that various reduction methods and reducing agents can be used to achieve the conversions of hydroxide and oxide nanocomposites to graphene nanocomposites with metallic copper. 33.- Process for synthesizing materials for manufacturing electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 31, characterized in that in the conversion to copper wet reduction methods can be employed using different reducing agents as well as the glycol-assisted polyol reduction method.

34. A process for synthesizing materials for manufacturing electrodes for the electrochemical measurement of glucose content in aqueous solutions, according to claim 33, characterized in that the reducing agents used in the wet methods can be those commonly employed in reductions such as hydrazine, sodium potassium borohydride, sodium hypophosphite, ascorbic acid, or reducing sugars. In the reduction, non-polluting reducing agents of natural origin are preferably used, and among these, ascorbic acid is preferred.

35. A process for synthesizing materials for manufacturing electrochemical measurement electrodes for glucose content in aqueous solutions, according to claim 34, characterized in that the reduction is carried out by adding the reducing agents dissolved in water to suspensions of the NPG nanocomposites with copper hydroxide, cupric oxide, or cuprous oxide. The reaction mixtures can be treated at room temperature or by heating up to 100 °C, room temperature being preferable. 10 36.- Process for synthesizing materials to manufacture electrodes for electrochemical measurement of glucose content in aqueous solutions, according to claim 35, characterized in that the reduction can be achieved by means of agitation (MAEC, Turrax, ultrasound) or without it; in the latter case, by simply mixing the nanocomposites with the reducing agent. 37.- Process of synthesis of materials for manufacturing electrochemical measuring electrodes of 15 glucose contents in aqueous solutions, according to claim 35, characterized in that the molar ratio of reducing agent-copper hydroxide copper oxides varies between 2-40, preferably 10-20.