USE OF GOLD-GRAPHENE PARTICLE NANOCOMPOSITES FOR THE DETECTION OF HYDROGEN PEROXIDE AND GLUCOSE IN FLUIDS AND METHOD OF PREPARATION

Abstract

The use of pristine graphene nanoplatelet (NPG) nanocomposites decorated with gold nanoparticles (NPAu) as electrochemical measurement materials for hydrogen peroxide and glucose content in fluids is described. Methods for preparing the nanocomposites by treating NPG suspensions to generate the NPAu in situ are detailed.

Description

DESCRIPTION OBJECT OF THE INVENTION The object of the present invention is to describe the use of graphene nanoplatelet hybrids decorated with gold nanoparticles in the electrochemical determination of hydrogen peroxide contents at neutral pH and glucose in basic fluids and the methods used to synthesize them. Background Gold is frequently used in the fabrication of materials that mimic enzyme activity (biozymes) and in various sensing methods that have historically employed enzymes as detection substrates. One of the first reports of the use of gold nanoparticles as a biozyme for the amperometric determination of glucose content was published by Jena and Retna in 2006. They described the fabrication of a three-dimensional silicate network deposited on a gold (Au) electrode and the self-assembly of gold nanoparticles onto the terminal thiols present in the silicate network (1). The material demonstrated glucose measurement capability with a sensitivity of 0.179 nAcm'2nm-1.Cheng et al. reported an electrochemical gold deposition method on carbon electrodes through which they synthesized different metal nanostructures (2); electrodes with gold nanocoral structure deposits showed the highest sensitivity, reaching values ​​of 22.6 pA / mMcm2 in PBS buffer at pH 7.4. Chang et al. reported the direct electrodeposition of gold nanoparticles on glassy carbon (GCE) electrodes and their use in glucose detection (3); the researchers showed a glucose content measurement sensitivity of 87.5 pA / mMcm2, with a detection limit of 0.05 mM. In a similar study published by Shu et al., which describes the electrodeposition of gold dendritic nanostructures obtained by electrodeposition of the metal on GCE, the study demonstrates the ability to electrochemically measure glucose content using PBS buffer at pH 7.4; the reported sensitivity is 190.7 μA / mMcm2(4). In 2016, Hebié et al. published an article showing the influence of the size of spherical gold nanoparticles (NPs) (4-15 nm) deposited on an ECV; electrochemical determinations of glucose content were made using a 0.1 M sodium hydroxide electrolyte, demonstrating that the smaller NPs, 4.2 nM, had greater electrocatalytic capacity (5). The construction and use of an impedance sensor made by depositing polyaniline on an ECV followed by the deposition of gold NPs on the polymer was reported by Ahammad et al. (6); the electrode showed good sensitivity for glucose detection with the help of ferricyanide ([Fe(CN)6]2q) as an electron transfer mediator.The deposition of gold nanotubes or nanowires on ECVs, fabricated by electrostatic deposition of gold salts on an aluminum oxide template, was described by Tian et al. (7); the electrode showed a glucose content measurement sensitivity of 44.2 μA / mM cm2 at pH 7.2. The formation of Au-CuO hybrids by in situ generation of gold nanoparticles in the presence of cupric oxide sheets, and their use on ECVs for the electrochemical determination of glucose in a 0.1 M NaOH solution, was described by Felix et al. (8); the electrodes revealed a glucose measurement sensitivity of 3126.76 μA / mM cm2. A gold-cuprite core-shell material (Au@Cu2O) was synthesized by Su et al. and used as a sensing material after deposition on an ECV (9); The electrodes were used in the measurement of glucose contents using an alkaline electrolyte (pH 12).6) of sodium hydroxide solution, the sensitivity achieved was 715 pA / mM cm2. On the other hand, Xu and collaborators demonstrated the use of gold nanocomposites on Ni(OH)2 sheets as an electrochemical glucose sensing material using a 0.1 M NaOH solution as the electrolyte (10); the authors reported a measurement sensitivity of 82.71 pA / mM cm2 and a detection limit of 0.66 pM. Just as the use of gold nanomaterials has been demonstrated in the electrochemical sensing of glucose, they have also been used in the measurement of hydrogen peroxide content. One of the first articles on the subject is that of Li et al., who in 2010 reported the preparation of gold compounds with manganese dioxide (11); the materials, deposited on ECV, showed a sensitivity for measuring H2O2 content of 5.35 x 105 AM “1 cm “2. Won's group published the fabrication of printed electrodes onto which gold nanospheres or nanocylinders were deposited, with which they measured H2O2 content (12), reporting measurement sensitivities of 11.13, 54.53, and 58.51 pA / mM for the nanosphere and nanocylinder materials with aspect ratios of 1:3 and 1:5, respectively. The use of gold nanoboxes for H2O2 sensing was reported by Zhang and collaborators (13), the authors showed a peroxide measurement sensitivity of 273.83 pA / mM cm2.The use of gold nanostars, synthesized by a growth method aided by gold seeds in the presence of poly(diallyldimethylammonium chloride) as a stabilizer, was described by Li et al. for the measurement of hydrogen peroxide in a neutral PBS buffer (14). The preparation and use of bimetallic AuM nanocrystals (M = Pd, Rh, Pt) was described by Han's group; the highest reported sensitivity was 195.3 μA / mM cm² at a potential of 0.25 V vs. SCE (15). The use of porous gold dendritic materials electrochemically deposited on a polycrystalline gold electrode was described by Sukeri and Bertoti (16), who reported an electrode reading sensitivity of 1176 pA / mM cm². The fabrication of ECV with nanocomposite deposits of SiO2 rods decorated with gold, platinum, or bimetallic compounds of both was described by Liu et al. (17); the measurement sensitivity of the Pt compounds showed to be 110.3 pA / mM cm2, while that of the PtAu compounds was 46.7 pA / mM cm2. The preparation of gold nanocubes, functionalized with the cytochrome cy protein deposited on a crosslinked chitosan-β-cyclodextrin hydrogel was published by Manickam et al. (18), the electrochemical determination of peroxide using the material showed a sensitivity of 1.2 mA / mM cm2 (1,200 pA / mM cm2). In all the previous examples, the use of nanostructures and compounds of bare gold or gold in combination with some inorganic or organic materials was demonstrated. It should be noted that the field of manufacturing gold-composite biosensors expanded substantially after the isolation of graphene and the demonstration of its high electrical conductivity. Since then, the sensing properties of graphene-gold composite materials have been evaluated, taking advantage of synergies between the properties of both. In an early example of the use of graphene-gold materials, Narang and colleagues fabricated polyaniline electrodes (PANI) onto which they deposited oxidized multi-walled carbon nanotubes (MWCNTs) (H2SO4 and HNO3, 3:1 v / v); allowing the formation of amide bonds between the nitrogen atoms of PAÑI with the carboxylic groups of the MWCNTs, the functionalized materials were subsequently decorated with gold NPs (19). The electrodes showed hydrogen peroxide sensing capability with a sensitivity of 3.3 mA / mM. The effect of the amounts of rGOAu on the electrochemical response of ECV with deposits of the compounds and subsequent coating of chitosan mixtures with glucose oxidase (GOD) was reported by Bai et al. (20); in the absence of the enzyme, the electrodes showed sensitivities from 2.9 to 9.5 pA / mM cm2. Yuan et al. reported the fabrication of graphene oxide (GO) coated ECVs and their functionalization with polyethyleneimine (PEI) via amide bond formation and subsequent decoration of the materials by electrodeposition of gold NPs (21); the electrodes displayed an H2O2 measurement sensitivity of 460 pA / mM cm2.Jia et al. reported on electrocatalytic electrodes (ECVs) on which they placed commercial graphene sheets suspended in chitosan, subsequently depositing gold nanoparticles (NPs) electrochemically (22). The electrodes showed measurement sensitivity over a wide H2O2 concentration range and a detection limit of 1.6 pM. A comparative study of the electrocatalytic properties of nitrogen-doped graphene and reduced graphene compounds decorated with gold NPs, published by Pogacean et al. (23), demonstrated the greater electrocatalytic activity of nitrogen-doped graphene. The fabrication of a three-dimensional material manufactured by treating GO with cysteine ​​and decorated with gold nanocylinders was described by Xue et al. (24); electrodes made with this compound showed good H2O2 measurement sensitivity.Lv's group disclosed a non-enzymatic sensor prepared by electrodeposition of gold nanoparticles (NPs) on a reduced graphene oxide (rGO) coated ECV. The electrodes showed electrocatalytic activity and good H2O2 sensing sensitivity of 574.8 pA / mM cm2 (25). The layer-by-layer deposition of a GO paper interleaved with gold nanoparticles containing gold-Prussian blue heart-shell nanoparticles was described by Zhang et al. (26). Electrodes manufactured with these materials showed a hydrogen peroxide sensing sensitivity of 5 A / M cm2. Thanh et al. published the preparation of copper electrodes decorated with gold-palladium (AuPd) alloys on which graphene sheets were grown by chemical vapor deposition (27). These electrodes showed H2O2 sensing capability with a sensitivity of 186.86 pA / mM cm2.An electrode fabricated by the one-step reduction of GO, gold salt, and hemin, generating a ternary mixture of rGO-hemin-gold nanoparticles, was developed by Gu's group (28); ECVs prepared with the nanocomposite showed the ability to determine hydrogen peroxide content in various fluids. The synthesis of rGO-Au compounds by reducing GO mixtures with gold (Au III) salts was published by Dhara et al. (29); screen-printed electrodes containing the nanocomposites showed a peroxide measurement sensitivity of 1238 μA / mM cm². An electrode with an H₂O₂ measurement sensitivity of 47.4 pA / mM cm² was described by Wang et al. (30); the material was prepared by chemical vapor deposition of graphene on a nickel foam, followed by electrophoretic deposition of gold nanoparticles.Gold electrodes coated with gold nanocomposites on graphene sheets encapsulated in cerium oxide (GS@CeO2) were reported by Yang's group (31); these electrodes showed good electrolytic capacity for H2O2 reduction. The use of GO functionalized with silver or gold nanoparticles coated with nanostructured polyaniline and superimposed on glass coated with fluorinated tin oxide (FTO) was demonstrated by Gupta et al. (32) for the detection of ascorbic acid. A tin oxide (ITO) electrode modified with a Nafion / gold GONP mixture was used in the electrochemical measurement of hydrogen peroxide content by Jin's group (33). In this method, the authors used 3,3,5,5-tetramethylbenzidine (TMB) as a redox mediator, showing a high detection limit of 1.9 nM.Liu's group described the synthesis of an rGO-gold aerogel by reducing GO-HAuCl4:4H2O mixtures and subsequent heat treatment of the suspension; using a cut sheet of gel, they constructed an electrode that showed the ability to measure H2O2 in a range of 1.5 to 7.6 mM (34). Peng et al. demonstrated a method for synthesizing flexible GO fibers decorated with gold foils and fabricating microelectrodes with which they measured hydrogen peroxide and glucose concentrations with sensitivities of 378.1 and 1045.9 μA / mM cm2 respectively (35). Ko et al. described the fabrication of microfluidic devices for measuring hydrogen peroxide concentrations made with APTES-modified agarose microspheres, functionalized with GO and finally decorated with gold-platinum heart-shell nanoparticles (Au@PtNP) (36); The functionalized microspheres showed high electrochemical detection capacity of H2O2.The measurement of hydrogen peroxide with a high sensitivity of 51.28 pA / pM-cm2 was described by Thi et al. using mulberry-shaped gold nanoparticles deposited on an rGO-coated nickel foam (37). The electrochemical co-deposition of GO and gold NP suspensions on ITO-PET substrates was published by Patella et al. (38); electrodes fabricated with rGO-Au compounds showed good hydrogen peroxide detection capability (64.1 μA / mM-cm2). A commercially available nitrogen-doped graphene nanocomposite was sequentially treated with thionine and HAuCL-SfW under ultrasound to obtain the doped nanocomposite; H2O2 measurement electrodes obtained by depositing suspensions of the nanocomposite on ECV showed good capability and response sensitivity in a measurement range of 50 pM–10 mM (39). Just as a variety of gold nanocomposites with graphene materials have been evaluated in the electrochemical measurement of hydrogen peroxide content, similar materials have been used to determine glucose content in fluids. A method for depositing gold nanostructures generated by laser pulses onto carbon nanotubes was published by Gougis et al. in 2014 (40); electrodes fabricated with these materials were used to determine glucose content in a PBS buffer with a pH of 7.2. The voltammetric response to glucose oxidation was able to detect glucose content with a sensitivity of 25 pA / mM cm2.The decoration of gold nanoparticles (NPs) on GO nanoribbons was revealed by Ismail's group (41); the researchers described the fabrication of measuring electrodes by placing the oxidized nanoribbons on a carbon sheet, followed by the deposition of a gold NP suspension and heat treatment of the decorated sheets at 400 °C. The electrodes showed a glucose content measurement sensitivity of 59.1 pA / mM cm². Via the reaction of GO with pyrrole in acidic medium, Xue et al. prepared an rGO material functionalized with a pyrrole polymer (42); the PPy / rGO material was subsequently decorated by in situ reduction of HAuCl₂ with sodium borohydride. Glucose measuring electrodes were fabricated by placing AuNPs / PPy / rGO suspensions on ECV, achieving glucose determinations with a sensitivity of 123.8 μA / mM cm².The preparation of a hydrogel made with an rGO-Au nanohybrid was reported by Ruiyi et al. (43). The hydrogel was prepared by mixing gold nanoparticles (NPs) with gold (GO), reducing them with ascorbic acid, and unidirectionally freezing the mixture to obtain a hydrogel after lyophilizing it. To increase the gold content in the hydrogel, a suspension of gold NPs was added, and the resulting material was repeatedly frozen and lyophilized, followed by a final heat treatment at 180 °C. Suspensions of the nanohybrids were deposited onto ECVs, which were used to measure glucose content with very high sensitivity, although the glucose levels were not revealed.Duy et al. described the fabrication of ITO electrodes coated with pristine graphene made by chemical vapor deposition and their modification by nitrogen doping (immersion in HNO3 and subsequent treatment in a nitrogen atmosphere at 180 °C for 5 hours) and subsequent decoration with gold NPs made by a two-step method, by initial deposition of Au seeds followed by their growth into metal NPs (44); the electrodes showed a sensitivity of 0.25 μA / mM cm2. Kawde et al. published a method of depositing pre-formed gold NPs (reduction of chloroauric acid with ascorbic acid) onto a graphite core and using this as a glucose detection cathode (45); the electrode showed a measurement sensitivity of 52.61 μA / mM cm2, in 0.1 M NaOH electrolyte.The fabrication of a non-enzymatic glucose sensor was revealed by Jeong et al., who created a three-dimensional network of nitrogen-doped graphene sheets and carbon nanotubes by hydrothermal treatment (180 °C, 12 hours) of GO mixtures with the oxidized nanotubes in the presence of urea; the materials were decorated with gold NPs synthesized by reduction of HAuCL with sodium citrate (46). Glucose measurement, with a sensitivity of 0.9824 pA / mM cm2, was achieved using glassy carbon electrodes onto which suspensions of the prepared nanocomposites were placed. The fabrication of ECVs coated with graphene monolayers (made by chemical vapor deposition) decorated with spark-generated gold NPs and with subsequent deposition of glucooxidase and 6-(ferrocenyl)hexanethiol (Fc-CeH^-SH) as an electron transfer mediator MA. a. ZUZU U Ί ÓU I Ί was described by Yuan et al. (47); the electrodes showed a very low detection limit of 0.1 nM (S / N % 3). Electrochemical detection of glucose at physiological pH was revealed by Branagan et al., who described the fabrication and use of gold nanoparticle nanocomposites deposited on functionalized-walled carbon nanotubes (48); a suspension of the compounds was deposited on ECVs, and these were used to measure glucose content, revealing a sensitivity of 2.77 ± 0.14 μA / mM and a detection limit of 4.1 μM. An electrochemical sensor based on ECVs with a deposit of graphene nanofibers decorated with gold NPs was reported by Shamsabadi et al. (49); the measurement of glucose content in an acidic electrolyte showed a sensitivity of 1.1437 pA / mM.The use and manufacture of modified ECVs with gold NP deposits attached to carboxylated graphene oxide was reported by Dilmac et al. (50); the electrodes revealed glucose detection sensitivities of 20,218 pA / mM cm2. The synthesis of gold NPs deposited on rGO, by reduction with sodium borohydride of GO and chloroauric acid mixtures, was published by Chaandini et al. (51); suspensions of the nanocomposite were deposited on screen-printed electrodes with which the glucose content was determined at neutral pH with a sensitivity of 245 pA / mM cm2. A summary of what has been reported in the scientific literature listed above is found in Tables 1, 2, and 3. These tables show the variety of approaches to manufacturing sensing nanocomposites, deposition methods, and electrodes used, as well as the responses and measurement performance achieved. Electrode Applied Potential Detection Limit (μM) Linear Range (mM) Sensitivity pA / mM cm2 Electrolyte Reference H2O2. Electrodes with gratenes PANI-MWCNT NP Au (immersing a MWCNT / PANI electrodeposited Au electrode into AuNPs colloids oxidation peaks, +0.8 V and +0.5 V (due to the oxidation of H2O2) 0.3 pM 3.0 pM at 600.0 pM 3.3 mA / mM 0.1 M PBS buffer (pH 7.0) 19 rGO-NP Au ECV -0.3 V vs. Ag|AgCI 5 pM 0.025-41.5 mM 2.9 - 9.5 pA / mM cm2 20 Grafting PEI to GO (EDC / NHS) on GC, electrodeposition Au NPs reduction peak appeared at 0.2 V 0.2 pM 0.5 pM at 1.68 mM 460 pA / mM cm2 pH 7.2 PBS 21 Commercial graphene / chitosan sheets. Electrodeposition Au 1.6 pM 5.0 pM to 35 mM 190.7 pA / mMcm2 PBS at pH 7.2 22 G doped (GO+urea+heating) N spherical NPs on ECV (GO+auric+sodium ascorbate) No data No data No data 23 3D layer by layer GOcysteine ​​nanocylinders Au (modified active carbon electrode) CV voltage range of -0.2 to 1.2 V vs Ag / AgCI voltage sean rate of 0.1 V / s.reduction peaks appeared at 0.3 V for the GNR and GO-Cys-GNR electrodes 2.9 pM 0.648 pA / mMcm2 PBS 24 GO on ECV electrodeposition Au NPs 2 pM 0.02-23 mM 574.8 pA / mM cm2 25 Layer-by-layer GO intercalated NPs gold heartshell@Prussian blue 100 nM 1-30 pM 5000 pA / mMcm2 (5 A / M cm2) 0.1 M NaOH 26. Table 1. Table of graphene-gold composite materials and their electrochemical hydrogen peroxide measurement response. Electrode Applied potential Detection limit (µΜ) Linear interval (mM) Sensitivity µΑ / mM cm2 Electrolyte Reference Copper foil decorated with AuPd followed by chemical vapor deposition G. Deposit on ITO 1 µΜ 5 µΜ11.5mM 186.86 µΑ / mM cm2 PBS, pH 7.4 27 rGO-Au-hemin (One step reduction mixtures GOsalt gold hemin) 0.18V vs Ag / AgCI - 30 nM. 0.1 μΜ at 40 μΜ No data 0.1 M PBS (pH 7.0) 28 rGO-Au silkscreened electrode -0.4 V Ag / AgCI 0.1 μΜ 20 μΜ at 10 mM 1238 μΑ / mM cm2 0.1 M PBS 29 AuNPs@Gr / foam Nickel -0.2 V (vs.Ag / AgCI electrode) 1 μΜ 0.05-1.75 mmol L-1 47.4 μΑ / mM cm2 PBS 30 NP Au over GS@CeO2 -0.3V 0.26 μΜ 1.0 μΜ at 10.0 mM PBS pH 7 31 N-doped PANi-AuNP-GF over fluorinated ITO <1 pM / L Detection of AA 10-10000 μΜ 10,000 μΑ / mM cm2 32 nafion / GO-NP on ITO assisted by 3,3,5,5,tetramethylbenzidine 1.9 nM 10 nM to 10 mM 33 rGO-gold airgel 19 μΜ 1.5 to 7.6 mM 34 GO fiber foil Au -0.25 V 1.62 µΜ 378.1 y µΑ / mM cm2 for H2O2 0.05M PBS 35 GO fiber foil Au 0.2 V 1.15 µΜ 1045.9 µΑ / mM cm2 for glucose 0.1M NaOH 35 APTES functionalized Agarose microsphere GOAu@PtNP 1.62 µΜ) 1µΜ at 3 mM 36 Electrodeposition of blackberry-shaped Au NPs on rGO-coated Ni foam 1.06 µΜ, 1-296 µΜ 51.28 µΑ / mM cm2 37 Electrochemical deposition of GOAu on ITO-PET 6.55 µΜ 64.1 µΑ / mM cm2 38 G doped Nthionine-Au on ECV 50 µΜ- 10 mM 39. Table 2. Table of graphene-gold composite materials and their electrochemical measurement response of hydrogen peroxide. Electrode Applied Potential Detection Limit (pM) Linear Range (mM) Sensitivity μA / mM cm2 Electrolyte Reference Glucose. Electrodes with CNT graphene on Ni gold deposited by laser pulses -0.28 V vs. Ag / AgCl 0.1 mM 25 μA / mM cm2 PBS pH 7.2 40 Carbon electrode; NPs on GO nanoribbons followed by heat treatment 400 °C +0.209 V vs. NHE at 298.2 K) pAmM cm2 42 Precast Au NPs; GO Hydrogel freezing followed by Thermal Treatment 0.004 mM 0.01 to 16 mM pH 7.0 PBS containing 1.0 mM of K4Fe(CN)6in 0.1 M KCl by CVD N-doped Au NPs deposition on ITO 12 μΜ 40 μΜ. 16.1mM 0.25 pA / mM cm2 EIS in 0.1M Fe(CN)6] (5mM). 0.1 M NaOH 44 Graphite lead with preformed Au NPs -0.27 V 12 μΜ 0.05 to 5.0 mM 52.61 pA / mM cm2 0.1 M NaOH 45 N-GRCNTs / AuNPs (GO+CNT+Urea 180 °C12h) + HAuCI4 sodium citrate 500 nM 2 μΜ at 19.6 mM 0.9824 pA / mM cm2 (EIS) 0.1 M KCI containing 5.0 mM K4[Fe(CN)6]. Amperometric 0.1 M NaOH 46 G by CVD + Au NPs by sparking. GOD deposit 0.1 nM 47 Electrode (ECV) with functionalized CNTs + Au NPs 4.1 μΜ 0.1 mM at 25 mM 2.77 pA / mM cm2 0.1 M PBS 48 ECV of graphene nanofibers (of GO) + Au NPs 0.45 V vs Ag / AgCI 55 μΜ 0.5-9.0 mM 1.1437 pA / mM Acidic electrolyte 49 GOCOOAu / GCE (carboxylated GO-Au) 6 µΜ 0.02 to 4.48 mM 20.218 pA / mM cm2 0.15 M NaOH 50 rGO Au nanocubes (GO + chloroauric acid + NaBH4) on electrode silkscreened 69 and 245 μΑ / mM cm2 for reduction and oxidation respectively PBS pH 7.4 51. Table 3. Table of graphene-gold composite materials and their electrochemical glucose measurement response. It should be noted that the examples reported above detail the determination of H2O2 or glucose content, and that only one example describes the use of materials to measure both hydrogen peroxide and glucose (35). It should also be noted that most examples use graphene oxide as the raw material for fabricating the sensor nanocomposites or employ graphene obtained by chemical vapor deposition and its subsequent functionalization with gold nanomaterials; only one report (22) describes the use of a commercially available, non-functionalized graphene material. In general, the cited examples refer to relatively complex preparative methods for obtaining the sensing nanomaterials and / or complicated manufacturing procedures that do not facilitate the fabrication of the measuring electrodes.Considering the above, it is desirable to have composite materials capable of electrochemically sensing both H2O2 and glucose and to have simple methods for preparing and using them. In this proposal, we describe previously unreported methods for synthesizing graphene-gold nanoparticle nanocomposites. We also demonstrate that the synthesized materials can be advantageously used in the fabrication of electrodes for measuring hydrogen peroxide and glucose content in liquids. The use of a method for manufacturing pristine graphene nanoplatelets, their decoration with gold nanoparticles, and the application of the nanocomposites to determine hydrogen peroxide and glucose content highlight the novelty of both the materials and the methods used to prepare them. Bibliografía .- Enzyme-Free Amperometric Sensing of Glucose by Using Gold Nanoparticles; Bikash Kumar Jenaand C. Retna Raj;Chem. Eur. J.2006, 12,2702-2708. DOI: 10.1002 / chem.200501051 2,- (110)-Exposed Gold Nanocoral Electrodo as Low Onset Potential Selective Glucose Sensor; TaMing Cheng, Ting-Kai Huang, Huang-Kai Lin, Sze-Ping Tung, Yu-Liang Chen, Chi-Young Lee, and Hsin-Tien Chiu; Applied Materials Interfaces VOL. 2 NO. 10, 2773-2780, 2010. 3,- Gold nanoparticles directly modified glassy carbón electrode for non-enzymatic detection of glucose; Gang Chang, Honghui Shu, Kai J¡, Munetaka Oyama, Xiong Liu, Yunbin He; Applied Surface Science 288 (2014) 524- 529. .- Direct Electrodeposition of Gold Nanostructures onto Glassy Carbón Electrodes for Nonenzymatic Detection of Glucose; Honghui Shu, Leilei Cao, Gang Chang, Hanping He, Yuting Zhang, Yunbin He; Electrochimica Acta 132 (2014) 524-532. http: / / dx.doi.Org / 10.1016 / j.electacta.2014.04.031 .- Size-Dependent Electrocatalytic Activity of Free Gold Nanoparticles for the Glucose Oxidation Reaction; Seydou Hebié, Teko W. Napporn, Claudia Moráis, and K. Boniface Kokoh; ChemPhysChem 2016, 17, 1454- 1462. DOI : 10.1002 / cphc.201600065 .- Enzyme-free impedimetric glucose sensor based on gold nanoparticles / polyaniline composite film; A. J. Saleh Ahammad, Abdullah Al Mamun, Tania Akter, M. A. Mamun, S. Faraezi, F. Z. Monira; J Solid State Electrochem 2016. DOI 10.1007 / s10008-016-3199-2 .- Direct electrodeposition of highly ordered gold nanotube arrays for use in non-enzymatic amperometric sensing of glucose; Taolei Tian, Junping Dong, Jiaqiang Xu; Microchim Acta 2016. DOI 10.1007 / s00604-016-1835-2 .- Sensitive electrochemical detection of glucose based on Au-CuO nanocomposites; Sathiyanathan Félix, Andrews Nirmala Grace, Ramasamy Jayavel; Journal of Physics and Chemistry of Solids 122 (2018) 255-260. https: / / doi.Org / 10.1016 / j.jpcs.2018.06.038 .- Au@Cu2O core-shell structure for high sensitivo non-enzymatic glucose sensor; Ya Su, Hua Guo, Zuoshang Wang, Yumei Long, Weifeng L¡, Yifeng Tu; Sensors and Actuators B 255 (2018) 2510-2519. https: / / doi.Org / 10.1016 / j.snb.2017.09.056 .- The hybrid of gold nanoparticles and Ni(OH)2 nanosheet for non-enzymatic glucose sensing in food; Jinqiong Xu, Tingting Chen, Xiujuan Qiao, Qinglin Sheng, Tianli Yue, Jianbin Zheng; Colloids and Surfaces A 561 (2019) 25-31. .- Gold nanoparticles medíate the assembly of manganese dioxide nanoparticles for H2O2 amperometric sensing; Yali L¡, Jia Zhang, Huí Zhu, Fan Yang, Xiurong Yang; Electrochimica Acta 55 (2010) 5123-5128. ,- Au nanospheres and nanorods for enzyme-free electrochemical biosensor applications; Yu-Ho Won, Keon Huh, Lia A. Stanciu; Biosensors and Bioelectronics 26 (2011) 4514- 4519. do¡:10.1016 / j.bios.2011.05.012 .- Au nanocages for highly sensitive and selective detection of H2O2; Yue Zhang, Yujing Sun, Zhelin Liu, Fugang Xu, Kang Cui, Yan Shi, Zhiwei Wen, Zhuang L¡; Journal of Electroanalytical Chemistry 656 (2011) 23-28. doi:10.1016 / j.jelechem.2011.01.037 .- Synthesis of gold nanostars with tunable morphology and their electrochemical application for hydrogen peroxide sensing; Yanxiao Li, Jie Ma, Zhanfang Ma; Electrochimica Acta 108 (2013) 435440. .- Monodisperse AuM (M = Pd, Rh, Pt) bimetallic nanocrystals for enhanced electrochemical detection of H2O2; Tingting Han, Yuan Zhang, Jiaqiang Xu, Junping Dong, Chung-Chiun Liu; Sensors and Actuators B 207 (2015) 404-412. .- Electrodeposited honeycomb-like dendritic porous gold surface: An efficient platform for enzyme-free hydrogen peroxide sensor at low overpotential; Anandhakumar Sukeri, Mauro Bertotti; Journal of Electroanalytical Chemistry 805 (2017) 18-23. http: / / dx.doi.Org / 10.1016 / j.jelechem.2O17.10.004 7,- Pt and Au bimetallic and monometallic nanostructured amperometric sensors for direct detection of hydrogen peroxide: Influences of bimetallic effect and silica support; Wei Liu, Karl Hiekel, René Hübner, Hanjun Sun, Adriana Ferancova,Mika Sillanpáá; Sensors and Actuators B 255 (2018) 1325-1334. http: / / dx.doi.Org / 10.1016 / j.snb.2017.08.123 .- Gold nanocubes embedded biocompatible hybrid hydrogels for electrochemical detection of H2O2; Pandiaraj Manickam, Arti Vashist, Sekar Madhu, Mohanraj Sadasivam, Arunkumar Sakthivel, Ajeet Kaushik, Madhavan Nair; Bioelectrochemistry 131 (2020) 107373. https: / / doi.Org / 10.1016 / j.bioelechem.2019.107373 .- A non-enzymatic sensor for hydrogen peroxide based on polyaniline, multiwalled carbón nanotubes and gold nanoparticles modified Au electrode; Jagriti Narang, Nidhi Chauhan and C. S. Pundir; Analyst, 2011,136, 4460. .- Investigation of the optimal weight contents of reduced graphene oxide-gold nanoparticles composites and theirs application in electrochemical biosensors; Xiaoyun Bai, Kwok-Keung Shiu; Journal of Electroanalytical Chemistry 720-721 (2014) 84-91. http: / / dx.doi.Org / 10.1016 / j.jelechem.2O14.03.031 21,- Polyethylenimine-bridged graphene oxide-gold film on glassy carbón electrode and its electrocatalytic activity toward nitrite and hydrogen peroxide; Baiqing Yuan, Chunying Xu, Lin Liu, Yunfeng Shi, Sujuan L¡, Renchun Zhang, Daojun Zhang; Sensors and Actuators B 198 (2014) 5561. http: / / dx.doi.Org / 10.1016 / j.snb.2O14.03.014 22,- A simple non-enzymatic hydrogen peroxide sensor using gold nanoparticles-graphene-chitosan modified electrode; Ningming Jia, Baozhen Huang, Lina Chen, Liang Tan, Shouzhuo Yao; Sensors and Actuators B 195 (2014) 165-170. http: / / dx.doi.Org / 10.1016 / j.snb.2014.01.043 .- Graphene based nanomaterials as Chemical sensors for hydrogen peroxide - A comparison study of their intrinsic peroxidase catalytic behavior; Florina Pogacean, Crina Socaci, Stela Pruneanu, Alexandru R. Biris, María Coros, Lidia Magerusan, Gabriel Katona, Rodica Turcu, Gheorghe Borodi; Sensors and Actuators B 213 (2015) 474-483. http: / / dx.doi.Org / 10.1016 / j.snb.2O15.02.124 .- Facile fabrication of 3D layer-by-layer graphene-gold nanorod hybrid architecture for hydrogen peroxide based electrochemical biosensor; Chenming Xue, Chih-Chien Kung, Min Gao, ChungChiun Liu, Liming Dai, Augustine Urbas, Quan L¡; Sensing and Bio-Sensing Research 3 (2015) 711. http: / / dx.doi.Org / 10.1016 / j.sbsr.2O14.10.008 25,- Electrochemically Reduced Graphene Oxide-nafion / Au Nanoparticle Modified Electrode for Hydrogen Peroxide Sensing; Yajie Lv, Fang Wang, Hui Zhu, Xiaorong Zou, Cheng-an Tao and Jianfang Wang; Nanomater Nanotechnol, 2016, 6:30 | doi: 10.5772 / 63519 .- Free-standing and flexible graphene papers as disposable non-enzymatic electrochemical sensors; Minwei Zhang, Arnab Halder, Chengyi Hou, Jens Ulstrup, Qijin Chi; Bioelectrochemistry 109 (2016) 87-94. http: / / dx.doi.Org / 10.1016 / j.bioelechem.2016.02.002 27,- Novel porous gold-palladium nanoalloy network-supported graphene as an advanced catalyst for non-enzymatic hydrogen peroxide sensing; Tran Duy Thanh, Jayaraman Balamurugan, Seung Hee Lee, Nam Hoon Kim, Joong Hee Lee; Biosensors and Bioelectronics 85 (2016) 669-678. .- Reduced graphene oxide-Hemin-Au nanohybrids: Facile one-pot synthesis and enhanced electrocatalytic activity towards the reduction of hydrogen peroxide; Chang-Jie Gu, Fen-Ying Kong, Zhi-Dong Chen, Da-He Fan, Hai-Lin Fang, Wei Wang; Biosensors and Bioelectronics 78 (2016) 300-307. http: / / dx.doi.Org / 10.1016 / j.bios.2015.11.035 .- Au nanoparticles decorated reduced graphene oxide for the fabrication of disposable nonenzymatic hydrogen peroxide sensor; Keerthy Dhara, T. Ramachandran, Bipin G. Nair, T.G. Satheesh Babu; Journal of Electroanalytical Chemistry 764 (2016) 64-70. http: / / dx.doi.Org / 10.1016 / j.jelechem.2O16.01.011 .- Au nanoparticles decorated graphene / nickel foam nanocomposite for sensitive detection of hydrogen peroxide; XiaojuanWang, Xinli Guo, Jian Chen, Chuang Ge, Hongyi Zhang, Yuanyuan Liu, Li Zhao, Yao Zhang, Zengmei Wang, Litao Sun; Journal of Materials Science & Technology 33 (2017) 246-250. http: / / dx.doi.Org / 10.1016 / j.jmst.2016.11.029 .- Size controllable preparation of gold nanoparticles loading on graphene sheets@cerium oxide nanocomposites modified gold electrode for nonenzymatic hydrogen peroxide detection; Xin Yang, Yuejun Ouyang, Feng Wu, Yangjian Hu, Yang J¡, Zhaoyang Wu; Sensors and Actuators B 238 (2017) 40-47. http: / / dx.doi.Org / 10.1016 / j.snb.2016.07.016 32,- Metal nanoparticles-grafted functionalized graphene coated with nanostructured polyaniline hybrid’ nanocomposites as high-performance biosensors; Sanju Gupta, Romney Meek; Sensors & Actuators: B. Chemical 274 (2018) 85-101. https: / / doi.Org / 10.1016 / j.snb.2018.07.131 .- Graphene oxide-gold nanozyme for highly sensitive electrochemical detection of hydrogen peroxide; Ga Hyun Jin, Euna Ko, Min Ki Kim, Van-Khue Tran, Seong Eun Son, Yanfang Geng, Won Hur, G¡ Hun Seong; Sensors & Actuators: B. Chemical 274 (2018) 201-209. https: / / doi.Org / 10.1016 / j.snb.2O18.07.160 .- Graphene / gold nanoparticle aerogel electrode for electrochemical sensing of hydrogen peroxide; Xiaoli Liu, Ting Shen, Zhiyong Zhao, Yujun Qin, Pu Zhang, Hongxia Luo, Zhi-Xin Guo; Materials Letters 229 (2018) 368-371. https: / / doi.Org / 10.1016 / j.matlet.2018.07.024 .- Flexible fiber-shaped non-enzymatic sensors with a graphene-metal heterostructure based on graphene fibres decorated with gold nanosheets; Yu Peng, Deqing Lin, J.Justin Gooding, Yuhua Xue, Liming Dai; Carbón 136 (2018) 329-336. .- Characterization of Au@PtNP / GO nanozyme and its application to electrochemical microfluidic devices for quantification of hydrogen peroxide; Euna Ko, Van-Khue Tran, Seong Eun Son, Won Hur, Hyun Choi, Gi Hun Seong; Sensors & Actuators: B. Chemical 294 (2019) 166-176. https: / / doi.Org / 10.1016 / j.snb.2O19.05.051 .- Novel nanohybrid of blackberry-like gold structures deposited graphene as a free-standing sensor for effective hydrogen peroxide detection; M.L.N. Thi, V.T. Pham, Q.B. Bul, P.H. Ai-Le, H.-T. Nhac-Vu; Journal of Solid State Chemistry 286 (2020) 121299. .- Electrochemical sensor based on r-GO / Au nanoparticles for monitoring H2O2 released by human macrophages; B. Patella, M. Buscetta, S. Di Vincenzo, M. Ferraro, G. Aiello, C. Sunseri, E. Pace, R. Inguanta, C. Cipollina; Sensors and Actuators September 2020. https: / / doi.Org / 10.1016 / j.snb.2020.128901 .- One-pot synthesis of nitrogen doped graphene-thionine-gold nanoparticles composite for electrochemical sensing of diethylstilbestrol and H2O2; Shasha Pang, Xianwen Kan; Microchemical Journal 157 (2020) 104924. https: / / doi.Org / 10.1016 / j.microc.2020.104924 .- Láser synthesis and tailor-design of nanosized gold onto carbón nanotubes for non-enzymatic electrochemical glucose sensor; Máxime Gougis, Amel Tabet-Aoul, Dongling Ma, Mohamed Mohamedi; Sensors and Actuators B 193 (2014) 363- 369. http: / / dx.doi.Org / 10.1016 / j.snb.2O13.12.008 .- Development of Non-enzymatic Electrochemical Glucose Sensor Based on Graphene Oxide Nanoribbon - Gold Nanoparticle Hybrid: Nur Syakimah Ismail, Quynh Hoa Le, Hiroyuki Yoshikawa, Masato Saito; Electrochimica Acta 146 (2014) 98-105. http: / / dx.doi.Org / 10.1016 / j.electacta.2O14.08.123 .- A novel amperometric glucose biosensor based on ternary gold nanoparticles / polypyrrole / reduced graphene oxide nanocomposite; Kaiwen Xue, Shenghai Zhou, Hongyan Shi, Xun Feng, Hua Xin, Wenbo Song; Sensors and Actuators B 203 (2014) 412-416. http: / / dx.doi.Org / 10.1016 / j .snb.2014.07.018 .- Novel graphene-gold nanohybrid with excellent electrocatalytic performance for the electrochemical detection of glucose; L¡ Ruiyi, Zhang Juanjuan, Wang Zhouping, L¡ Zaijun, Liu Junkang, Gu Zhiguo,Wang Guanglia; Sensors and Actuators B 208 (2015) 421-428. http: / / dx.doi.Org / 10.1016 / j.snb.2014.11.004 .- Effective seed-assisted synthesis of gold nanoparticles anchored nitrogen-doped graphene for electrochemical detection of glucose and dopamine; Tran Duy Thanh, Jayaraman Balamurugan, Seung Hee Lee, Nam Hoon Kim, Joong Hee Lee; Biosensors and Bioelectronics 81 (2016) 259267. http: / / dx.doi.Org / 10.1016 / j.bios.2016.02.070 .- Cathodized Gold Nanoparticle-Modified Graphite Pencil Electrode for Non-Enzymatic Sensitive Voltammetric Detection of Glucose; Abdel-Nasser Kawde, Md. Abdul Aziz, Manal El-Zohr¡, Nadeem Baig, and Nurudeen Odewunmi; Electroanalysis 2017, 29, 1 -9. DOI: 10.1002 / elan.201600709 .- N-doped graphene-carbon nanotube hybrid networks attaching with gold nanoparticles for glucose non-enzymatic sensor; Hun Jeong, Dang Mao Nguyen, Min Sang Lee, Hong Gun Kim, Sang Cheol Ko, Lee Ku Kwac; Materials Science and Engineering: C Volume 90, 1 September 2018, Pages 38-45. do¡:10.1016 / j.msec.2O18.04.039 .- Gold nanoparticles decorated on single layer graphene applied for electrochemical ultrasensitive glucose biosensor; Yawen Yuan, Yishi Wang, Hua Wang, Shifeng Hou; Journal of Electroanalytical Chemistry855 (2019) 113495. https: / / doi.Org / 10.1016 / j.jelechem.2019.113495 .- Electrochemical detection of glucose at physiological pH using gold nanoparticles deposited on carbón nanotubes; David Branagan, Carmel B. Breslin; Sensors & Actuators: B. Chemical 282 (2019) 490-499. https: / / doi.Org / 10.1016 / j.snb.2018.11.089 .- Electrochemical non-enzymatic sensing of glucose by gold nanoparticles incorporated graphene nanofibers; Amir Shahin Shamsabadi, Hossein Tavanai, Mehdi Ranjbar, Ameneh Farnood, Mehdi Bazarganipour; Materials Today Communications 24 (2020) 100963. .- Fabrication of non-enzymatic glucose sensor dependent upon Au nanoparticles deposited on carboxylated graphene oxide; Yusuf Dilmac, Muhammet Guler; Journal of Electroanalytical Chemistry 864 (2020) 114091. .- Gold nanoparticle decorated reduced graphene oxide for the nonenzymatic electrochemical sensing of glucose in neutral médium; J.P. Chaandini, Punathil Vasu Suneesh, T.G. Satheesh Babu; Materials Today: Proceedings Available Online 12 September 2020. https: / / doi.Org / 10.1016 / j.matpr.2020.08.072 BRIEF DESCRIPTION OF THE FIGURES Figure 1. X-ray diffraction (XRD) of graphene nanoplatelets (GNPs). Figure 2. Transmission electron micrograph (TEM) of graphene nanoplatelets decorated with gold NPs (NPGAu) by in situ reduction of NPG and HAuCI4 trihydrate suspensions in ethylene glycol and caustic soda by magnetic stirring. Figure 3. Cyclic voltammetry of graphene nanoplatelets decorated with gold NPs (NPGAu) by in situ reduction of NPG and HAuCI4 trihydrate suspensions in ethylene glycol and caustic soda by magnetic stirring for glucose sensing at pH 12. Figure 4. Cyclic voltammetry of graphene nanoplatelets decorated with gold NPs (NPGAu) by in situ reduction of NPG and HAuCI4 trihydrate suspensions in ethylene glycol and caustic soda by magnetic stirring for hydrogen peroxide sensing at pH 7. Figure 5. Thermogravimetry (TGA) of NPGAu by in situ reduction of NPG and HAuCI4 trihydrate suspensions in ethylene glycol and caustic soda by ultrasound treatment. MA / a / ¿U¿U / U1 ÓU I1 DETAILED DESCRIPTION OF THE INVENTION We describe the use of nanocomposites made from graphene nanoplatelets decorated with gold nanoparticles as electrocatalytic materials capable of measuring H2O2 and / or glucose content in fluids. Suspensions of the nanocomposites were deposited onto glassy carbon electrodes (GCEs), using different nanocomposite / solvent ratios, typically 5 to 10 mg / mL, depositing 5 pL of the suspensions onto the surface of 3 mm diameter GCEs. The electrochemical characterization of the materials, as well as their responses to the presence of hydrogen peroxide, 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 174 mmol hydrogen peroxide into 200 mL of electrolyte. The responses to the presence of glucose were also determined 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 into 200 mL of electrolyte. The sensing capacity of the materials was 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 hydrogen peroxide or glucose 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. To measure H₂O₂ content, a 0.1 M PBS electrolyte adjusted to pH 7 was introduced into the electrochemical cell; for glucose content determinations at pH 12, a 0.05 M NaOH solution was used. The working electrodes were 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 was varied from 1 to 10 mg / mL using distilled water as the dispersion medium or solutions of PEDOT-PSS in water (0.1 mg / mL). To one milliliter of these mixtures, varying volumes of Nafion solution were added at different weight percentages. The ink was treated for 10 minutes by immersion in an ultrasonic cleaning bath, and then varying volumes of ink were applied to the ECV (electrode vitreous vapor). The electrodes were subjected to a heat treatment of 60 °C for 20 minutes and then cooled to room temperature. The electrochemical measurement responses are very positive, in many cases equivalent to or better than those reported in the scientific literature. The fabricated materials compare favorably with those prepared by other methods because they can be used to determine both hydrogen peroxide and glucose content. Considering the potential of graphene-gold nanocomposites in the fabrication of electrodes for the electrochemical measurement of hydrogen peroxide and / or glucose content in liquid media, and taking into account the complexity of the reported preparative methods for manufacturing these nanocomposites, we explored alternative methods. Specifically, we evaluated the fabrication of pristine graphene nanoplatelets and their decoration with gold nanoparticles, avoiding the traditional methods of graphite oxidation to graphite oxide, its subsequent conversion to reduced graphene oxide (rGO), and its decoration with the metallic nanoparticles. In the procedures studied, pristine graphene nanoplatelets (NPGs) produced by exfoliating graphite in water were used, decorated with gold nanoparticles (NPs). The NPGs were obtained by high-shear mixing treatment of aqueous suspensions of natural or synthetic graphite, without the use of surfactants as exfoliation aids. The NPG-Au nanocomposites were obtained using two general preparation processes. In one, the isolated NPGs were decorated in a second step in which suspensions of the nanoplatelets were treated in situ with chloroauric acid trihydrate, generating gold nanoparticles that were deposited onto the NPGs. In the second, chloroauric acid and subsequently reducing agents were added to the suspensions formed during the high-shear mixing treatment, generating gold nanoparticles in situ that were deposited onto the NPGs.This variant makes it possible to synthesize nanocomposites in a container without resorting to a second transformation step. In the aqueous exfoliation process, mixtures of synthetic or natural graphite and water were used, subjected to varying high-shear mixing treatment times, from 1 / 2 to 4 hours, with mixing speeds of 6,000 to 10,000 rpm. The graphite / water weight / volume ratio was evaluated within a range of 0.1 g / mL to 20 mg / mL. After the exfoliation treatment, the suspension was filtered and the solid (NPG) was dried overnight at 70 °C in an electric oven. In the general two-step preparation method, NPG suspensions were prepared in different solvents. Chlorauric acid trihydrate was added to these suspensions, which were then mixed magnetically or by sonotrode tip immersion ultrasonic treatment. Gold nanoparticles were then generated in situ via different reduction methods for the Au(III) present. After varying reduction times, the suspensions were vacuum filtered, and the solid was thoroughly washed with water, ethanol, and acetone, then dried for several hours at 70 °C in an electric oven. NPG suspensions were prepared in ethylene glycol (EG) or water by mixing them with different proportions of chloroauric acid trihydrate, in sufficient quantities to generate, after reduction of the Au(III) present in the reaction medium, hybrids with NPG-Au weight contents of 1:0.05 to 1:0.5. The solvent / NPG weight ratios (mL / mg) were varied from 10:1 to 2:1, preferably 4:1. The NPG / HAuCk trihydrate suspension mixtures were treated by magnetic stirring or ultrasonic treatment (immersion of the sonotrode tip in the reaction medium) for varying times, and subsequently a reducing agent was added, allowing the reduction to take place over different time intervals. Once the reduction was complete, the suspensions were vacuum filtered and the solid was washed repeatedly (water, ethanol, acetone) and finally dried for several hours at 70 °C in an electric oven. The following are some specific examples of the general procedures described above. EXAMPLE 1. Preparation of graphene nanoplatelets (NPG) by high shear stress treatment in water Ten grams of synthetic graphite (Aldrich < 320 pm) were placed in a 2 L beaker with 1 L of distilled water. The mixture was subjected to high-shear mixing using a Ross mixer operated at 8,000 rpm. After stirring for one hour, the suspension was gravity-filtered, and the solid was dried at 70 °C for 12 hours in an electric oven. Figure 4 shows the X-ray diffraction (XRD) of the resulting graphene nanoplatelets. EXAMPLE 2. Preparation of graphene nanoplatelets decorated with gold NPs (NPGAu) by in situ reduction of suspensions of NPG and HAuCL trihydrate in ethylene glycol and caustic soda by magnetic stirring. In a 125 mL flask, 200 mg of NPG exfoliated graphite powder obtained in Example 1 and 35 mg of HAuCL are placed; 50 mL of ethylene glycol (EG) is added, and the mixture is magnetically stirred (300 rpm) for one hour. 500 µL of a sodium hydroxide solution in ethylene glycol (EG) is then added to the suspension. The solution is prepared by dissolving 200 mg of NaOH in 10 mL of EG. Mixing is continued for an additional 60 minutes; the suspension is vacuum filtered, and the solid is sequentially washed with hot water, ethanol, and acetone. The solid is dried for 12 hours at 70 °C in an electric oven. A TEM micrograph of the nanocomposite is shown in Figure 5. ECVs on which 5 pL of an ink made by suspension of 2 mg / mL of the nanocomposites in 0.1 mg / mL of PEDOT PSS in water were deposited were used in the determination of glucose contents at pH 12. The electrochemical response detected was ip= 786 pA @ 370 mV R2~ 0.9980.Using the same ink to determine hydrogen peroxide content, measurements of ip= 208 pA @ -200mV R2~ 0.9787 and ip= 226 pA @700mV R2~ 0.9670 are obtained. Figure 6 and Figure 7 show the cyclic voltammetry of the measurements. EXAMPLE 3. Preparation of NPGAu by in situ reduction of suspensions of NPG and HAuCL trihydrate in ethylene glycol and caustic soda by ultrasound treatment. In a 125 mL flask, 200 mg of exfoliated graphite powder (NPG) obtained in Example 1 and 35 mg of HAuCI4 are placed; 50 mL of ethylene glycol (EG) is added. The mixture is treated for 10 minutes by ultrasound at 60% intensity, introducing the tip of a QSonica Model Q700 sonotrode into the suspension. 500 pL of sodium hydroxide solution in EG (200 mg / 10 mL) is added, and the ultrasound treatment continues for an additional 10 minutes. The suspension is vacuum filtered, and the solid is sequentially washed with hot water, ethanol, and acetone. The solid is dried for 12 hours at 70 °C in an electric oven. The TGA of the NPGAu sample is shown in Figure 8. ECVs on which 5 pL of an ink made by suspension of 2 mg / mL of the nanocomposites in 0.1 mg / mL of PEDOT PSS in water were deposited were used in the determination of H2O2 contents in PBS buffer solution at pH 7.4. The electrochemical response detected was ip= 58 pA @-400mV Rz~ 0.9808 and ip= 60 pA @800mV R2~ 0.9993. EXAMPLE 4.- Preparation of NPGAu by in situ reduction of suspensions of NPG and HAuCI4 trihydrate and ascorbic acid in water by ultrasound treatment. In a 125 mL flask, 200 mg of NPG exfoliated graphite powder obtained in Example 1 and 21 mg of HAuCI4 are placed, and 50 mL of water is added. The mixture is treated for 10 minutes by ultrasound at 60% intensity, introducing the tip of a QSonica Model Q700 sonotrode into the suspension. 9.4 mg of ascorbic acid are added in a 1:1 molar ratio (Au(III):ascorbic acid). The ultrasound treatment is continued for an additional 10 minutes. The suspension is vacuum filtered, and the solid is washed sequentially with hot water, ethanol, and acetone. The solid is dried for 12 hours at 70 °C in an electric oven. ECVs on which 5 pL of an ink made by suspension of 2 mg / mL of the nanocomposites in 0.1 mg / mL of PEDOT PSS in water were deposited were used in the determination of H2O2 contents in PBS buffer solution at pH 7.4. The detected electrochemical response was ip= 165 pA @-400mV R2~ 0.9800 and ip= 143 pA @700mV R2~ 0.9987. EXAMPLE 5.- Preparation of NPGAu in one step by graphite treatment by high shear mixing in water and in situ reduction of HAuCI4 trihydrate by addition of ascorbic acid. In a 1 L flask, 500 mg of graphite powder and 500 mL of distilled water are placed; the suspension is treated by high-shear mixing at 8,000 rpm for 50 minutes using a Ross mixer. After this time, 52.5 mg of HAuCk trihydrate are added, and stirring continues for an additional 10 minutes. Then, 262.5 mg of ascorbic acid (Au(III):ascorbic acid molar ratio of 1:5) is added to the suspension, and stirring continues for another 10 minutes. The suspension is vacuum filtered, and the solid is washed sequentially with hot water, ethanol, and acetone. The solid is dried for 12 hours at 70 °C in an electric oven. ECVs on which 5 pL of an ink made by suspension of 2 mg / mL of the nanocomposites in 0.1 mg / mL of PEDOT PSS in water were deposited were used in the determination of H2O2 contents in PBS buffer solution at pH 7.4. The electrochemical response detected was ip= 102.42 pA @800mV R2~ 0.9981.

Claims

1 - The use of nanocomposites of pristine graphene nanoplatelets decorated with gold nanoparticles as materials for the electrochemical measurement of hydrogen peroxide (H2O2) and glucose contents in aqueous solutions at neutral and basic pH respectively. 2 - Methods for preparing pristine graphene nanoplatelet compounds decorated with gold nanoparticles (NPGAu), according to claim 1, characterized by generating gold nanoparticles in the presence of NPG suspensions and depositing the metal nanoparticles onto the graphene sheets of the nanoplatelets. 3.- The methods for preparing pristine graphene nanoplatelet compounds decorated with gold nanoparticles (NPGAu), according to claim 2, characterized by obtaining pristine graphene nanoplatelets (NPG), by high shear stress treatment of graphite mixtures in water.

4. The procedure for preparing pristine graphene nanoplatelets, according to claim 3, is characterized in that synthetic or natural graphite can be used, subjecting mixtures of these in water to different mixing times (from V2 to 5 hours), at variable stirring speeds ranging from 5,000 to 10,000 rpm.

5. The procedure for preparing pristine graphene nanoplatelets, according to claim 4, characterized in that the nanoplatelets can be obtained from the resulting suspension by filtration and drying.

6. The procedure for preparing pristine graphene nanoplatelets, according to claim 4, characterized in that the nanoplatelet suspension can be treated in the mixing container generating in situ gold NPs, facilitating their deposition on the graphene sheets. 7 - Preparation procedures for pristine graphene nanoplatelets decorated with gold nanoparticles (NPGAu), according to claim 2, characterized in that the NPGs are suspended in ethylene glycol (EG) or protic solvents (alcohols or water) mixed with Au(lll) compounds, preferably chloroauric acid (HAuCI4) to subsequently produce gold NPs by reduction of the Au(111) compounds.

8. NPGAu preparation procedures according to claim 7, characterized in that the NPG suspensions with Au(III) compounds in ethylene glycol are magnetically stirred for 10 min to 2 hours, preferably 1 hour, subsequently adding variable amounts of sodium hydroxide solutions in ethylene glycol, continuing the stirring for 1 to 2 hours, filtering the suspensions, sequentially washing the solids with water, ethanol and acetone, and finally drying the obtained materials for several hours at 70 °C.

9. - NPGAu preparation procedures, according to claim 8, characterized in that the volume / weight ratio of EG / NPG (mL / mg) can be varied from 10:1 to 2:1, preferably from 4:

1. 10.- NPGAu preparation procedures, according to claim 8, characterized in that the weight ratio of NPGAu can be adjusted to contents from 1:0.01 to 1:1, preferably from 1:0.05 to 1:0.1 by modifying the amount of Au(lll) compounds added to the suspensions. 11.- NPGAu preparation procedures, according to claims 8 and 10, characterized in that the added volume of soda solution can be varied, adjusting the molar ratio of hydroxide ion to Au(II) ion from 1:1 to 10:

1. 12.- NPGAu preparation procedures, according to claim 7, characterized in that the NPG suspensions with Au(III) compounds in ethylene glycol are subjected for 5 to 60 minutes to sonotrode tip immersion ultrasound treatments, subsequently adding variable amounts of sodium hydroxide solutions in ethylene glycol, continuing the ultrasound treatment for an additional 5 to 60 minutes, and working the reaction mixtures by filtration, washing, and drying.

13. - NPGAu preparation procedures, according to claim 12, characterized in that: the weight ratio of NPG:Au can be adjusted to contents from 1:0.01 to 1:1, preferably from 1:0.05 to 1:0.1 and in that the added volume of soda solution can be varied, adjusting the molar ratio of hydroxide ion to Au(111) ion from 1:1 to 10:

1. 14.- NPGAu preparation procedures, according to claim 7, characterized in that the NPG suspensions with Au(lll) compounds are treated by adding reducing agents to generate gold nanoparticles in situ. 15.- NPGAu preparation procedures, according to claim 14, characterized in that the reducing agents can be ascorbic acid, glucose, sodium borohydride, sodium hypophosphite, preferably using ascorbic acid or glucose.

16. - NPGAu preparation procedures, according to claims 14 and 15, characterized in that the solvent / NPG volume / weight ratio (mL / mg) can be varied from 10:1 to 2:1, preferably from 4:

1.

17. NPGAu preparation procedures according to claims 14 and 15, characterized in that the NPG:Au weight ratio can be adjusted to contents from 1:0.01 to 1:1, preferably from 1:0.05 to 1:0.1 18. - NPGAu preparation procedures, according to claims 14 and 15, characterized in that the mixtures are magnetically stirred for 10 min to 2 hours, preferably 1 hour, and then variable amounts of reducing agent are added, continuing the stirring for an additional 5 to 60 minutes to finally separate, wash and dry the generated solids.

19. - NPGAu preparation procedures, according to claims 14 and 15, characterized in that the sonotrode tip immersion ultrasound treatments can be carried out for 5 to 60 minutes, then variable amounts of reducing agent are added, continuing the ultrasound treatment for an additional 5 to 60 minutes, and finally separating, washing and drying the generated solids.

20. - Preparation procedures for NPGAu nanocomposites, according to claim 2, characterized in that, without separating the generated NPGs, these are decorated with gold nanoparticles by adding gold salts to the suspensions to subsequently reduce the Au(lll) ions, using the reduction variations used previously.