CN110243910A - A solid-bonded ion-selective electrode based on thiolated redox graphene - Google Patents

Abstract

The invention provides a fixed ion selective electrode based on mercapto-redox graphene, the electrode uses mercapto-redox graphene as an ion-electron conducting layer, and the conducting layer is covered with an ion-selective sensing membrane . The covalent linkage of thiolated redox graphene on the gold electrode surface forms a stable conducting layer. The resulting electrodes have Nernstian responses and low detection limits with good selectivity. More importantly, when simulating the external environment, the immobilized ion-selective electrode based on thiolated redox graphene exhibited better performance than redox graphite after placing the electrode in a continuous flowing solution using a peristaltic pump for up to two weeks. Alkene-bonded ion-selective electrodes for longer life. These advantages make thiolated redox graphene promising as a versatile and reliable ion-electron conducting layer for the development of durable bonded ion-selective electrodes.

Description

A solid-bonded ion-selective electrode based on thiolated redox graphene

technical field

The invention relates to the technical field of ion detection, in particular to a fixed ion selective electrode based on mercapto-redox graphene.

Background technique

Ion-selective electrodes (ISEs) are used to analyze ions, which have the advantages of high sensitivity, good selectivity, portability, and low cost, and thus are widely used in the analysis of complex biological and environmental samples. Stationary ion selective electrodes (SC-ISEs), as a new generation of ion selective electrodes, directly coat ion selective membranes on metal conductors, which have the advantages of low detection limit and easy miniaturization. The initial SC-ISEs were prepared in the form of coated wire electrodes, that is, the ion-selective sensing membrane was directly wrapped on the metal electrodes. However, the lack of a thermodynamically well-defined electrochemical interface between ion-sensing membranes and electronic conductors results in potential shifts that limit their long-term applications. In addition, a water film is formed between the ion-sensing membrane and the electronic conductor, which is another important factor causing potential instability. Therefore, in order to improve the electrode performance, components with high ion-electron conductivity can be added directly into the conductive film or as an intermediate layer to improve this problem.

On the one hand, conductive polymers (CPs) such as polypyrrole (PPy), poly-3-octylthiophene (POT), and poly-3,4-ethylenedioxythiophene (PEDOT) are the most commonly used as ion-electron sensors. Organic materials, they can facilitate charge transfer at the electrode interface. However, under certain conditions, CPs-based SC-ISEs may be disturbed by light, redox species, or the unavoidable water layer. To solve this problem, hydrophobic organic materials with high redox ability have been developed, such as polypyrrole perfluorooctane sulfonate (PPy-PFOS, water contact angle: 97±5°) and polyethylene 3,4-ethylene Dioxythiophene carbon 14 (water contact angle: 136±5°). The results show that the SC-ISEs based on PPy-PFOS and PEDOT-C14 have excellent E ⁰ repeatability (±0.7mV) and long-term stability (0.02±0.03mV/day). On the other hand, inorganic materials, especially carbon-based materials, such as carbon nanotubes and graphene, are excellent alternatives to conducting polymers due to their high electrical conductivity and inertness to light and redox species. Currently, graphene has attracted extensive attention due to its excellent electronic and electrochemical properties, such as inherent hydrophobicity and easy modification. Typically, electrochemically reduced graphene oxide (CRGO) is coated as an intermediate layer on the entire interface of the electrode by a drop-casting method. Then some SC-ISEs will slowly form water film after continuous use due to the existence of unstable interlayer. Fibbioli et al. report a seminal work on the use of thiolated fullerenes (ethyl(8-sulfamooctyl)1,2-methoxy[60]fullerene-61,61dicarboxylic acid) Prepare SC-ISEs as anchor layer. Thiolated fullerenes self-assemble onto gold electrodes via strong Au-S interactions. The results show that the prepared SC-ISEs have good stability and resistance to oxygen and redox species. However, the authors failed to show the lifetime of thiolated fullerene-based SC-ISEs based on self-assembly. Thiolated graphene oxide derivatives have been widely used as anchoring media for noble metal nanoparticles (AuNPs, AgNPs and PtNPs). For example, the strong Au-S interaction in the hybrid material prevents the aggregation of AuNPs and enhances their catalytic activity. Furthermore, hexadecanethiol- and thiophenol-functionalized graphene oxide was reported to self-assemble supramolecularly on the surface of the columnar interlayer of discotic liquid crystals via strong Au-S interactions. To the best of our knowledge, 2-aminoethanethiol-functionalized redox graphene has not been reported for use in SC-ISEs as ion-electron conducting layers.

Contents of the invention

The object of the present invention is to provide a durable fixed-type ion-selective electrode based on mercapto-redox graphene.

The second object of the present invention is to provide the application of thiolated redox graphene in the preparation of the ion-electron conducting layer of the fixed-type ion-selective electrode.

In order to achieve the above object, the present invention provides a fixed-type ion-selective electrode based on mercaptolated redox graphene, characterized in that, the electrode uses mercaptolated redox graphene as the ion-electron conducting layer, and the The ion-selective sensing membrane is covered on the conducting layer.

As a preferred solution, the conductive layer adopts a fixed-point deposition method to cover the gold conductor part of the electrode interface.

As a preferred solution, the mercaptolated redox graphene is 2-aminoethanethiol functionalized redox graphene.

As a preferred solution, the ion selective sensing membrane is a K ⁺ selective sensing membrane or an NO ₃ ⁻ selective sensing membrane.

In order to achieve the second purpose of the present invention, the present invention provides the application of mercaptolated redox graphene in the preparation of the ion-electron conducting layer of the above-mentioned fixed ion-selective electrode based on mercaptolated redox graphene.

As a preferred solution, the mercaptolated redox graphene is 2-aminoethanethiol functionalized redox graphene.

The advantage of the present invention is that the present invention proposes SC-ISEs with 2-aminoethanethiol functionalized redox graphene as the intermediate layer, using X-ray energy spectrometer (EDS), Raman spectroscopy (Raman), X-ray The prepared 2-aminoethanethiol-functionalized redox graphene was characterized by photoelectron spectroscopy (XPS) and other methods. Using a facile site-directed deposition method, TRGO was self-assembled on gold-sputtered copper electrodes as an ion-electron conducting layer. Using K ⁺ as the cation model and NO ₃ ^- as the anion model to study the obtained electrode, the response slope, detection limit and selectivity isoelectric performance of the method were studied. In addition, the possibility of film formation at the interface can also be explored through the potential test of the water layer. We also present lifetime data collected using TRGO-based SC-ISEs and compare their performance characteristics with graphene oxide-based SC-ISEs. Based on the above experimental results, TRGO is expected to be fabricated as a general-purpose ion-electron conducting layer for micro-ISEs with the same performance as large electrodes.

Description of drawings

Fig. 1 TEM image of thiolated redox graphene TRGO.

Fig. 2 EDS spectrum of TRGO.

Fig. 3 Raman spectra of TRGO and unmodified graphene oxide GO.

Fig. 4 Fourier transform infrared spectra of TRGO and unmodified graphene oxide GO.

Fig. 5 XRD patterns of TRGO and unmodified graphene oxide GO.

Fig.6 XPS spectra of C _1s , N _1s and S _2p of TRGO.

Fig. 7 Potential responses of K ⁺ -TRGO-ISEs (A) and NO ₃ ^- -TRGO-ISEs (B) and calibration curves of K ⁺ -TRGO-ISEs (C) and NO ₃ ^- -TRGO-ISEs (D).

Fig. 8 Water layer experiments of K ⁺ -TRGO-ISEs (A) and NO ₃ ^- -TRGO-ISEs (B).

Figure 9 Comparison of the standard curves of K ⁺ -TRGO-ISEs (A) and NO ₃ ^- -TRGO-ISEs (B) on the first day and after two weeks.

Fig. 10 The selectivity coefficients of K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs and the comparison between the reported K ⁺ -ISEs and NO ₃ ^- -ISEs.

Detailed ways

Hereinafter, the technology of the present invention will be described in detail in conjunction with specific embodiments. It should be known that the following specific embodiments are only used to help those skilled in the art understand the present invention, rather than limiting the present invention.

Example 1. An immobilized ion-selective electrode based on mercapto-redox graphene

Reagent

High molecular weight polyvinyl chloride (PVC), bis(2-ethylhexyl) sebacate (DOS), 2-nitrophenyl n-octyl ether (NPOE), valinomycin, nitrate ionophore, 30 Dialkylmethylammonium chloride (TDMACl) and tetrahydrofuran (THF) were purchased from Sigma-Aldrich (Switzerland). Sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB) was purchased from Dojindo Laboratories (Japan). Graphite powder was purchased from Nanjing Xianfeng Nano Material Technology Co., Ltd. All salts were purchased from Sigma-Aldrich and dissolved in fresh deionized water (DI water, impedance 18.25 MΩcm, Millipore, USA). All other chemicals used were of analytical grade and were used as received.

Synthesis and characterization of TRGO

TRGO was synthesized through three synthetic steps. In the first step, graphite powder is used as a raw material to prepare raw material graphene oxide through an improved Hummers method. Graphite powder (1 g) was oxidized with K ₂ S ₂ O ₈ (1 g) and P ₂ O ₅ (1 g) at 80° C. with continuous stirring in sulfuric acid (7 ml) for 6 h. After cooling to room temperature, the solution was diluted and filtered to obtain graphite oxide. Ultrasonic treatment in acetone for about 1 h can exfoliate graphite oxide into crude graphene oxide, and obtain crude graphene oxide after solvent evaporation. KMnO ₄ (3 g) was slowly added to concentrated sulfuric acid (23 ml) with crude graphene oxide (1 g), and stirred in an ice-water bath at 35° C. for 4 h to purify the crude graphene oxide. Then 30% H ₂ O ₂ was added to the suspension until the solution color changed to glass yellow. After centrifugation, the precipitate was repeatedly washed with dilute hydrochloric acid, deionized water, and N,N-dimethylformamide (DMF) to obtain the desired graphene oxide. In the second step, graphene oxide (0.1g) is mixed with 2-aminoethanethiol (0.1g) in 200ml DMF to carry out the vulcanization reaction of graphene oxide. After reacting at 60 °C for 10 h, the solution was filtered to obtain the solid product 2-aminoethanethiol-functionalized graphene oxide (SGO), and the SGO powder was washed with DMF several times. In the third step, reduction of SGO (0.1 g) with hydrazine hydrate (0.1 g) in 200 ml DMF was carried out at 90° C. for 24 h. Finally, the desired 2-aminoethanethiol-functionalized reduced graphene oxide (TRGO) was obtained by filtration, washing, and vacuum drying. Using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy ( XPS) characterized TRGO.

Preparation of sensors

A gold disc electrode (Au, 2 mm inner diameter) was pretreated to obtain a mirror-like surface, polished with a 0.3 μm alumina suspension, rinsed with deionized water, sonicated with ethanol and deionized water, respectively, and finally dried under nitrogen. A clean gold electrode was snugly inserted into the distal end of a length of PVC tubing (1 cm long, 5 mm inner diameter and 8 mm outer diameter).

In order to obtain a fixed-type gold electrode, 20 μl of 0.20 mg/ml TRGO dispersion agent solution was dripped on the surface of the bare electrode, covering the entire gold area. For comparison, a redox graphene (rGO)-modified gold electrode (0.20 mg/ml) was fabricated following the same procedure. After evaporating the solvent, the TRGO- and rGO-coated SC-ISEs were washed with copious amounts of deionized water and then dried under nitrogen.

To prepare the modified K ⁺ -selective or _NO3 ^- selective electrodes, 100 μL of the K ⁺ -selective or _NO3 ^- selective membrane mixture was drop-poured on the TRGO or redox graphene (rGO)-covered electrodes. 1.1 wt% valinomycin, 0.25 wt% NaTFPB, 32.8 wt% PVC and 65.8 wt% DOS were dissolved in 1 mL THF to prepare a mixture of K ⁺ selective membranes (total mass 200 mg). It was prepared by adding 2.0 wt% nitrate ionophore IV, 1.1 wt% TDMACl, 32.3 wt% PVC and 64.6 wt% NPOE into 1 ml THF. A mixture of NO ₃ ^-selective membranes (total mass 200 mg) was prepared. Subsequently, the solvent was evaporated completely at ambient temperature. The prepared SC-ISEs were placed in 0.01M KCl or _KNO3 solution overnight, respectively. When not in use, store in the above solution.

Instruments and Measurements

TEM and SEM imaging were performed using an S-3400N II electron microscope (Hitachi) and a Zeiss EVO 50 analytical microscope (Germany). Raman spectroscopy was performed using a laser micro-Raman spectroscopy system (Renishaw) with a 532 nm Ar ion laser at room temperature. FTIR spectra were recorded in transmittance mode with a resolution of 4 cm ⁻¹ using a Nicolet Nexus 670 FTIR spectrometer. All binding energies are referenced to the C 1s peak at 284.8 eV on the surface adventitious carbon. Bruker D8 Advance X-ray diffractometer (Cu-Kα ₁ irradiation, ) collected XRD data.

The electrochemical response was completed on the 16-channel EMF interface of Lawson Labs, controlled by the PCI-6281 data processing system and LabView 8.5 software. The reference electrode used is a double-junction silver/silver chloride reference electrode produced by Metrohm Ion Meter (Switzerland), the internal reference solution is 3M KC1 solution, and the external reference is 1M CH ₃ COOLi solution. The activity of ions is related to the activity coefficient, which is calculated by the extended Debye-Hückel equation. The potential values of all SC-ISEs are the average value measured at room temperature with at least three parallel electrodes.

Before the aqueous layer experiment, the prepared TRGO-based K ⁺ selective or NO ₃ ^-selective electrode was soaked in 10 ^-2 MKCl solution (or 10 ^-2 M KNO ₃ ) for 2 hours. When carrying out the life test, the prepared electrode was placed in a continuous flow solution system (10 ^-2 M KCl solution or 10 ^-2 M ^KNO ₃ )middle.

Results and discussion

Characterization of TRGO

As shown in Fig. 1, the surface morphology of 2-aminoethanethiol-functionalized redox graphene (TRGO) was studied by transmission electron microscopy (TEM). The transparent nano-sized TRGO in the TEM image is characterized by slab creases. To evaluate the effect of thiol functionalization on reduced graphene oxide, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to study. The peaks of C, N and S can be observed on the EDS energy spectrum of Figure 2, which proves that 2-aminoethanethiol has been successfully modified on graphene oxide. The FTIR spectrum of Figure 3 also demonstrates the successful modification of 2-aminoethanethiol on redox graphene. The peaks related to thiol groups are as follows: SH stretching peak (2580cm ^-1 ), amide C=O (1630cm ^-1 ), CN stretching peak (1470cm ^-1 ), NH stretching peak (3420cm ^-1 ) and NH bending peak (1590cm -1 ^{) 1} ). The peaks at 2920 and 2850cm ^-1 are related to methylene [27]. In addition, Raman spectroscopy (Fig. 4) can also be used to identify functionalized graphite materials, because it can detect the changes in the graphite structure of carbon materials . Figure 4 shows the characteristic signals of nanocarbon materials, including the D band at 1354cm ^-1 , which is related to oxidation defects and edge effects in the unmodified region; the G band at 1592cm ^-1 , which is related to the C–C pull on the graphite structure Stretch related. The intensity ratio between _D -band and _G -band (ID/IG) is commonly used to evaluate the general defect nature of sp ² materials, and more specifically, is related to the degree of functionalization. As shown in Fig. ₄ , the ID/ _IG ratio of unmodified GO is _1.06 , while that of _TRGO is 1.20. The increase in the ID/ _{IG ratio} is associated with defects in redox graphene planes, indicating the successful modification of sulfhydryl groups. Furthermore, the comparative XRD patterns of TRGO and GO are shown in Fig. 5. Generally, graphene oxide shows a diffraction peak at 2θ of 11.4°, indicating that the interlayer spacing is The thiol-modified TRGO showed a sharp peak at 2θ of 23.7°, and the higher interlayer spacing was Corresponding to the thiol-modified graphene oxide interface. Moreover, the C _1s , N _1s and S _2p peaks in the XPS spectrum of Figure 6 demonstrate the successful modification of sulfhydryl groups. The peaks at 284.7eV, 286.2eV and 288.5eV correspond to CC, CO and -CONH of the C _1s nuclear energy spectrum, respectively. By curve fitting the N _1s nuclear energy level spectrum, the peak at 398.4eV corresponds to the NH functional group of the amide. Whereas the peak at 400.5 eV is associated with unreacted NH functional groups in 2-aminoethanethiol and hydrazine hydrate. The 2p _1/2 and 2p _3/2 dual orbital signals of the S _2p nuclear energy spectrum are fitted in Fig. 6C. The peak in the region of 163.8 eV confirms the presence of sulfhydryl groups in redox graphene. Whereas the peak in the 165.0 eV region is associated with the sulfhydryl peak in unreacted 2-aminoethanethiol.

Potential response based on TRGO electrodes

ISEs based on TRGO modification were modeled with potassium ions (K ⁺ -TRGO-ISEs) and nitrate ions (NO ₃ ^- -TRGO-ISEs) as cations and anions, respectively. The potential responses of K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs were recorded by continuously adding potassium ions and nitrate ion solutions, as shown in Fig. 7A and B, respectively. The Nernstian responses of K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs in the linear range were 60.0±0.4mV/decade and 60.0±0.5mV/decade, respectively. As shown in Fig. 7C, the detection limit of K ⁺ -TRGO-ISEs is 2.5×10 ^-6 M, which is consistent with that of the traditional potassium ion selective electrode without conductive layer. As shown in Fig. 7D, the detection limit of NO ₃ ⁻ -TRGO-ISEs was 5.0 × 10 ^-6 M, which was lower than that of the reported reduced graphene oxide-based electrodes (3 × 10 ^-5 M). The standard deviations of the standard curves for K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs were 2.6 and 4.8 mV from the intercepts of the Y axis, respectively. These results indicated that the introduction of TRGO did not affect the response performance of the electrode. As shown in the insets in Fig. 7A and B, the prepared electrode has a fast response time of less than 5 s.

Selectivity based on TRGO electrodes

The selectivity coefficients of TRGO-based electrodes were measured according to the separated solution method. The selectivity coefficients of K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs are shown in Fig. 10 and compared with the reported K ⁺ -ISEs and NO ₃ ^- -ISEs. K ⁺ -TRGO-ISEs are more selective to K ⁺ in the presence of Na ⁺ , Li ⁺ , NH ₄ ⁺ , Ca ²⁺ and Mg ²⁺ Potassium-ion printed electrodes with reduced graphene oxide have better selectivity. Moreover, the selectivity of NO ₃ ^- -TRGO-ISEs is higher than that of nitrate ion-selective electrodes based on electrochemical reduction of graphene oxide and carbon black.

water layer experiment

The formation of a water layer between the ion-sensing membrane and the metal conductor leads to potential instability, affecting the long-term application of the electrode. The key to this work is to eliminate the potential water layer between the surface of the gold electrode and the ion-sensing membrane. The TRGO-based ion-selective electrode was first placed in the main ion solution (0.01M KCl or KNO ₃ ), and then in the interfering ion solution (0.01M CaCl ₂ or K ₂ SO ₄ ). Figure 8A and B show the instantaneous potential shift (284 mV for K ^{+ -TRGO -} ISEs _; 91 mV for NO ₃ ⁻ The high selectivity of TRGO-ISEs is consistent. However, when the interfering ion solution was replaced by the main ion solution, the equilibrium was rapid, and the potential value returned to the initial value within 10s. The 27-hour continuous potential value recording results showed that K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs had good long-term stability, and the potential drift values were 1.75μV/h and 8.79μV/h, respectively. And previously reported based on three-dimensional porous carbon (C.Lai, MA Fierke, A.Stein, P.Bühlmann, Ion-selective electrodes with three-dimensionally ordered macroporous carbon as solid contact, Anal.Chem.79(2007)4621–4626.) and four (4-chlorophenyl) borate anion-doped nanoclusters (M.Zhou, S.Gan, B.Cai, F.Li, W.Ma, D.Han, L.Niu, Effective solid contact for ion-selective electrodes: tetrakis (4-chlorophenyl) borate (TB ^- ) anions doped nanocluster films, Anal. Chem. 84 (2012) 3480–3483.) respectively as the solid-type electrode of the conductive layer has a larger potential The drift values are 9.17μV/h and 10.1μV/h respectively. The low potential shift value is mainly attributed to the covalent attachment of the high-capacitance TRGO and the disappearance of the interfacial water layer.

Lifetime based on TRGO electrodes

The lifetime of the TRGO-based ion-selective electrode was obtained by continuously recording the standard curve of the electrode, as shown in Figure 9. To simulate the external environment, the prepared electrodes were placed in a continuous flowing solution (0.01M KCl or KNO ₃ ) using a peristaltic pump when not in use. In addition, a fixed-type ion-selective electrode based on reduced graphene oxide was tested as a control group. Both K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs showed stable ion response performance up to 2 weeks, with little change in response slope and detection limit. As shown in Figure 9A, the response slopes decreased from 60.0±0.4 to 59.8±0.2mV/decade(K ⁺ -TRGO-ISEs), from 60.0±0.4 to 59.8±0.2mV/decade(NO ₃ ^- -TRGO-ISEs ); detection limit decreased from 2.5×10 ^-6 M to 5.0×10 ^-6 M (K ⁺ -TRGO-ISEs), from 2.5×10 ^-6 M to 6.3×10 ^-6 M (NO ₃ ^- -TRGO- ISEs). However, the linear range of the calibration curve of the fixed-type ion-selective electrode based on reduced graphene oxide showed a severe drop, as shown in FIG. 9B . From this, we can conclude that the ion-selective electrode based on TRGO has better repeatability and durability than the electrode based on reduced graphene oxide, and the main reason can be attributed to the fixed price of TRGO.

in conclusion

In summary, for the first time, using hydrazine hydrate as the reducing agent and DMF as the solvent, TRGO was prepared by mercaptolation and reduction of graphene oxide, which can be covalently attached to the upper surface of the gold electrode as a new sensing layer. Prepare durable SC-ISE. The results of EDS, Raman, XRD and XPS demonstrated the successful modification of the thiol functional groups on the reduced graphene oxide. The TRGO-based electrode was modeled by determining potassium ions and nitrate ions as cations and anions, respectively. The prepared K ⁺ -TRGO-ISEs and NO ₃ ^- -TRGO-ISEs both have Nernst slope, good potential stability and resistance to water layer. Most importantly, the TRGO-based electrodes have a longer lifetime than those based on reduced graphene oxide, proving that TRGO, as a conductive layer, is a better choice for making durable electrodes.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications should also be considered Be the protection scope of the present invention.

Claims (6)

1. a kind of monimostyly ion selective electrode based on sulfhydrylation redox graphene, which is characterized in that the electrode Using sulfhydrylation redox graphene as ionic-electronic conduction layer, ion selectivity sensing membrane is covered on the conducting shell.

2. a kind of monimostyly ion selective electrode based on sulfhydrylation redox graphene according to claim 1, It is characterized in that, the conducting shell covers the golden conductor part of electrode interface using the method for fixed point deposition.

3. a kind of monimostyly ion selective electrode based on sulfhydrylation redox graphene according to claim 1, It is characterized in that, the sulfhydrylation redox graphene is 2- aminoothyl mercaptan functionalization redox graphene.

4. a kind of monimostyly ion selective electrode based on sulfhydrylation redox graphene according to claim 1, It is characterized in that, the ion selectivity sensing membrane is K⁺Selective sensing membrane or NO₃ ^-Selective sensing membrane.

5. sulfhydrylation redox graphene monimostyly based on sulfhydrylation redox graphene described in preparation claim 1 Application in the ionic-electronic conduction layer of ion selective electrode.

6. application according to claim 5, which is characterized in that the sulfhydrylation redox graphene is 2- amino second sulphur Alcohol functionalized redox graphene.