A chemiresistive nanosensor

Abstract

The invention relates to a chemiresistive nanosensor based on polyglycerol-modified graphene oxide and bromophenol blue.

Description

[0001] DESCRIPTION

[0002] A CHEMIRESISTIVE NANOSENSOR

[0003] Technical Field of the Invention

[0004] The present invention discloses a chemiresistive nanosensor based on polyglycerol-modified graphene oxide and bromophenol blue for detecting ammonia gas at ppb levels.

[0005] State of the Art of the Invention (Prior Art)

[0006] With the development of productivity and the improvement of people's quality of life, people's requirements for industrial production and living conditions are getting higher and higher, which leads the increase in the demand for gas sensors. The research and development of gas sensors, especially the research of toxic and harmful gas sensors, has increased rapidly. Ammonia is a toxic and irritating gas pollutant that is commonly used as a solvent, catalyst and raw material in industrial production. At present, gas sensors for detecting ammonia gas have been widely used in production and life. Metal oxide materials such as tungsten oxide, molybdenum oxide, tin oxide, etc. are commonly used for gas sensors, but their detection limits are high. The detection of ammonia in air stipulated by the US Occupational Safety and Health Administration (Occupational Safety and Health Administration), and there is a significant gap in the detection capability below 10 ppm. Improving the sensitivity of ammonia gas detectors and reducing the detection limit is important in the research of ammonia gas sensors.

[0007] CN114624288A discloses a method for detecting ammonia gas by using a sensor, which is characterized in that graphene-doped polypyrrole is used as a sensing film, and the graphene- doped polypyrrole is obtained by polymerizing pyrrole monomers on the surface of graphene under an acidic condition through an in-situ polymerization method.

[0008] WO2008153593A1 discloses a harmful gas sensor capable of simultaneously performing electrical sensing and optical sensing and a manufacturing method. This invention relates to the high-performance gas sensor, capable of simultaneously performing electrical and optical detection of harmful gas by using reduced graphene oxide (R-GO) and bromophenol blue (BPB).

[0009] WO2023272666A1 discloses a polymer-modified graphene composite material and a sensor and application thereof. The polymer-modified graphene composite material comprises molybdenum disulfide, graphene, graphene quantum dots, and a polymer. Specifically, the surface of a composite material of molybdenum disulfide, graphene, and graphene quantum dots is modified with the polymer to obtain the polymer-modified graphene composite material. The problem of an existing molybdenum disulfide sensor requiring heating to detect nitrogen dioxide has been solved, nitrogen dioxide can be detected at room temperature.

[0010] Brief Description and Objects of the Invention

[0011] The object of this invention is to manufacture a sensitive chemiresistive nanosensor to detect trace amounts of ammonia (NH3) gas at <50 ppb levels.

[0012] In line with this purpose, the invention discloses the modification of graphene oxide with hyperbranched polyglycerol and this polyglycerol-modified graphene oxide.

[0013] The invention also discloses a chemiresistive nanosensor comprising the mentioned polyglycerol-modified graphene oxide and bromophenol blue and the manufacturing method of this chemiresistive nanosensor.

[0014] The invention provides a solution for the challenging problem of measuring NH3 at trace concentrations (at ppb level) since the low concentrations of the target analyte present a key role in diagnostic applications.

[0015] The amount of ammonia gas, which is widely integrated into industrial applications, needs to be constantly monitored to avoid its toxic effects on the environment and human health. In the scope of invention, instant, continuous, and faster measurement of ammonia gas at low concentrations will contribute to human health, the environment, and the economy. Definitions of Figures Describing the Invention

[0016] The figures and related descriptions used to better explain the chemiresi stive nanosensor developed by this invention are as follows:

[0017] Figure 1: The current change behavior against ammonia for samples A) 1 : 1, and B) 1 :2.

[0018] Figure 2: The sensor response against ammonia for samples A) 1 : 1, and B) 1 :2.

[0019] Figure 3: Fifth-order polynomial fitting of Sample S16 measurement data for ammonia.

[0020] Figure 4: Linear fitting the measurement data of Sample 1 :1.

[0021] Figure 5: The current change diagrams of samples against time for relative humidity (RH). Figure 6: The sensor response values of the samples against time for relative humidity (RH). Figure 7: Current- Voltage (I-V) characterization of Sample 1 : 1 and Sample 1 :2.

[0022] Detailed Description of the Invention

[0023] The invention is related to the modification of graphene oxide with hyperbranched polyglycerol and this polyglycerol-modified graphene oxide.

[0024] A method of producing polyglycerol-modified graphene oxide comprises the steps of mixing and sonication of glycidol and graphene oxide powders, magnetically stirring the obtained mixture first under a nitrogen atmosphere and then in an oil bath, dissolving the resulting black gel-like product in methanol, precipitating of the resultant mixture in acetone to remove monomers and oligomers, and finally obtaining polyglycerol-modified graphene oxide.

[0025] The invention is also related to a chemiresi stive nanosensor comprising the mentioned polyglycerol-modified graphene oxide and bromophenol blue and the manufacturing method of this chemiresi stive nanosensor.

[0026] A method of manufacturing a chemiresistive nanosensor for the detection of trace amounts of ammonia (NH3) gas at <50 ppb levels comprises the steps that provide the polyglycerol- modified graphene oxide, which is mentioned above, self-assembly of the polyglycerol- modified graphene oxide on the chemiresistive chips, drying of the polyglycerol-modified graphene oxide assembled chemiresistive chip, and then coating the dried polyglycerol- modified graphene oxide layer of the obtained chemiresi stive chip with a bromophenol blue solution, and finally obtaining of a chemiresi stive nanosensor.

[0027] The detailed method descriptions required for a better understanding of the polyglycerol- modified graphene oxide and the chemiresistive nanosensor comprising the mentioned polyglycerol-modified graphene oxide are given below.

[0028] 1. Modification of graphene oxide with hyperbranched poly lycerol (PG-GO)

[0029] Hyperbranched polyglycerol (PG) is covalently grafted on the surface of graphene oxide (GO) through the ring-opening polymerization of glycidol via a simple one-step procedure.

[0030] This method that is for producing polyglycerol-modified graphene oxide, comprises; mixing and sonication of glycidol and graphene oxide powders, magnetically stirring of the obtained mixture first under a nitrogen atmosphere and then in an oil bath, dissolving the resulting black gel-like product in methanol, precipitating of the resultant mixture in acetone to remove monomers and oligomers, and obtaining of polyglycerol-modified graphene oxide.

[0031] In an alternative embodiment of the invention, this method comprises the step of dialyzing of the obtained polyglycerol-modified graphene oxide in distilled water with a dialysis membrane to remove the solvent and impurities.

[0032] In an alternative embodiment of the invention, this method also comprises the step of centrifuging and then freeze-drying the obtained polyglycerol-modified graphene oxide.

[0033] In the preferred embodiment of the invention, 4.5 ml glycidol and 22.5 mg GO powder are mixed and sonicated in an ice-water bath for 2 h. Subsequently, the mixture is magnetically stirred under a nitrogen atmosphere for 30 min followed by another 20 h at 140°C in an oil bath. The resulting black gel-like product is cooled and dissolved in 10 ml methanol, and the resultant mixture is precipitated in 10 ml acetone to remove monomers and oligomers. Finally, PG-GO is dialyzed in deionized water with a dialysis membrane for 24 h to remove the solvent and impurities. Then, the product is centrifuged for 10 min at 4000 rpm and freeze-dried for 72 h. After surface modification by hyperbranched polyglycerol, graphene oxide maintains its excellent physicochemical characteristics while new functional groups give it new characteristics. The oxygen-containing groups (e.g., hydroxyl, carboxyl, and epoxy groups) on the surface of graphene oxide make covalent bond functionalization easier than that of graphene.

[0034] 2. Self-assembly of PG-GO on the chemiresistive chips

[0035] Chemiresistive chips produced in clean room are pre-treated in acetone and then rinsed in pure analytical grade acetone and dried at room temperature. The PG-GO sample can be dispersed in water by sonication or vortex. Self-assembly of PG-GO can be performed via drop-casting or spin-coating on the chemiresistive chips and then dried at room temperature.

[0036] In the preferred embodiment of the invention, chemiresistive chips produced in clean room (0.6 cm x 0.6 cm) are pre-treated in acetone at 70 °C each for 3 min in an open beaker under a hood and then rinsed in pure analytical grade acetone and dried at room temperature. The PG- GO sample is dispersed in water (1 mg / ml) by sonication for 1 h. Self-assembly of PG-GO is performed immediately via drop-casting (20 pl) on the chemiresistive chips and then dried at room temperature.

[0037] 3. Coating the samples with a bromophenol blue (BPB) solution to prepare BPB / PG-GO

[0038] The drop-casting method is used to prepare homogeneous layers in which an ethanolic solution of BPB dye is drop-casted on the dried PG-GO layer, resulting in a yellow color on the substrates. The resulting sensor surface is annealed in an oven to improve the adhesion and remove residual solvent.

[0039] In the preferred embodiment of the invention, the drop-casting method is used to prepare homogeneous layers in which 10 pl of an ethanolic solution of BPB dye (Sigma Aldrich) is drop-casted on the dried PG-GO layer, resulting in a yellow color on the substrates. The resulting sensor surface is annealed in an oven at 80 °C for 5 min to improve the adhesion and remove residual solvent. The sensing measurements and measurement results of the manufactured chemiresistive nanosensors towards NH3 gas are described below.

[0040] During all measurements, the sensor operation temperature is maintained at room temperature and dry air is used as the carrier gas. To comprehensively investigate the ammonia sensing properties of the samples, sensors are exposed to target gas molecules in concentration ranges from 1.6 ppm to 11.6 ppm. Initially, 11.6 ppm ammonia gas is introduced into the sensor chamber three times to investigate repeatability. A clear sensor response signal against ammonia is observed at all measured concentration values. The limit of detection (LOD) value calculated / estimated based on the literature is 1.181826 ppb.

[0041] To study the effect of the thickness of the BPB layer on the sensing performance of the sensors, two types of sensors with 1 and 2 layers of BPB were prepared, which are referred to as 1 : 1 for BPB / PG-GO and 1 :2 for BPB / BPB / PG-GO representing the number of (PG- GO:BPB) layers throughout the text.

[0042] In preliminary studies, the response of the sensor under NH3 exposure, in visual detection mode on a glass substrate was tested, which provided a very fast response (3 s) and recovery (1 min) time for color changes of BPB upon NH3 vapor exposure (10 ppm), which is much faster than the responses in the electrical detection mode. The BPB@glass substrate showed a response time of 10 min and a recovery time of 30 min after exposure to NH3 vapor, which proves the role of PG-GO in capturing NH3.

[0043] The current change behavior against ammonia for the two samples of 1 : 1 and 1 :2 is given in Figure 1. To comprehensively investigate the ammonia sensing properties of the samples, sensors were exposed to target gas molecules in concentration ranges from 1.6 ppm to 11.6 ppm. Initially, 11.6 ppm ammonia gas was introduced into the sensor chamber three times to investigate repeatability. For calculating sensor response values, the average of these three peaks was used against 11.6 ppm. Subsequently, ammonia concentration was gradually reduced to 1.16 ppm, and a single peak was used at each concentration step. The sensors’ baseline signal was determined under dry airflow conditions, and after exposure to the target gas, the sensor was recovered back to baseline using dry airflow. Then, all current time data were transformed into sensor response, defined by Equation (1). SR = Al / Io (1)

[0044] In Equation (1), Al is the change in current value when the sensor is exposed to target gas molecules, I is the baseline current value of the sensors under dry airflow conditions. The sensor response charts of the samples against ammonia in the concentration range between 11.6 ppm and 1.6 ppm are given in Figure 2.

[0045] As seen in Figure 2, a clear sensor response signal was observed for both sensors against ammonia in all measured concentration values. The grey highlighted regions (i.e., response time) correspond to the gas exposure. The white area (i.e., recovery time) between the two grey highlighted regions is the recovery of the sensor under only dry airflow. Sample 1 : 1 exhibited the sensor response values as 0.44716 and 0.05506 against ammonia in the highest and lowest experimental concentrations, respectively. The sensor response values of 0.53843 and 0.0876 were obtained for sample 1 :2. A decrease in concentration from 11.6 ppm to 9.28 ppm resulted in decreased sensor response values for the sensors. However, the sensor response values increased again when sensors were exposed to ammonia at a concentration of 8.12 ppm. The correlation between ammonia concentration and sensor response values remained stable from 8.12 ppm to 1.16 ppm. The sensor response values for both samples against ammonia are detailed in Table 1.

[0046] Table 1. The sensor response values of both samples against ammonia in the concentration range between 1.16 ppm and 11.6 ppm.

[0047] The limit of detection (LOD) values of both samples were calculated based on literature [Li, J., et al., Carbon nanotube sensors for gas and organic vapor detection. Nano letters, 2003. 3(7): p. 929-933.]. In the first step, the sensor noise of samples was calculated using the variation in the relative current change in the baseline using root mean square deviation (rmsd). After plotting the data, a fifth-order polynomial fit (Figure 3), which gives the cure fitting Equation and the statistical parameters of the polynomial fit, was executed within the data point range. where - • is the measured data point and f is the corresponding value calculated from the curefitting Equation. The is calculated as: where N is the number of data points used in the curve-fitting.

[0048] The sensor noise is 0.00000123398 (1.23x^ ') for ammonia. Therefore, the detection limit was extrapolated from linear calibration curve (is given in Figure 4) when the signal equals 3 times the noise.

[0049] Using Equation (4), the detection limit of ammonia is calculated to be 0.0722611 ppb. Moreover, the linear concentration fitting slope, noise level, and the limit of detection values for both samples are outlined in Table 2. Sample 1 :2 exhibited the lower detection limit, calculated at 0.129518 ppb compared to 1.181826 for sample 1 : 1.

[0050] Table 2. Limit of detection (LOD) of samples 1 : 1 and 1 :2 against ammonia.

[0051] As previously mentioned, sensor response values remained stable from 8.12 ppm to 1.16 ppm for the two samples. This phenomenon can be attributed to the chemical characteristics of the sensing layer. When sensor response data between 8.12 ppm and 1.16 ppm were analyzed, a more stable concentration behavior became evident. Sensor signals of sample 1 :2, which has a higher sensor response against ammonia in all concentration values, are clear, but the noise level is higher than the other sample (1 : 1). The noise level of a sensor is directly related to the detection limit, as mentioned previously. Therefore, the theoretical limit of the detection value of sample 1 :2 is lower than sample 1 : 1.

[0052] The current change diagrams of sensors against time (Figure 5) and sensor response diagram (Figure 6) are given. After the analysis of the current time diagrams of each sample, sensor response values against relative humidity (RH) were calculated according to Equation (1). The sensor response charts of the samples against relative humidity in the concentration range between 80% and 8% are given in Figure 5 and the sensor response values of the samples are given in Table 3. The sensor response values are correlated with the concentration of RH. However, when the concentration decreased under 48%, sample 1:2 was transformed into a more sensitive layer against relative humidity. During the measurements, very clear response signals were observed for each concentration of RH.

[0053] Table 3. The sensor response values of the samples against relative humidity (RH) in the concentration range between 8% and 80%.

[0054] While investigating all data detailed in the previous sections to select the better-performing sensor between 1 : 1 and 1 :2, there are many criteria to be considered, such as sensitivity, cross-selectivity against RH, detection limit, and noise level. Sample 1 :2 has a higher sensor response against ammonia in all experimental concentration ranges between 1.16 ppm and 11.6 ppm. Moreover, it has a lower LOD of 0.129518 ppb for ammonia compared to 1.181826 ppb for sample 1 : 1. However, its noise level and RH sensitivity are very high compared to sample 1 : 1. Therefore, there could be some potential issues in the real-time- applications regarding the noise level and the cross-sensitivity against RH. On the other hand, sample 1 :1 has lower measurement noise levels of 1.89896 x 10'5. Moreover, the sensor response of sample 1 : 1 against 80% RH is only 1068.84021. Therefore, sample 1 : 1 is more efficient for cross-sensitivity against RH. According to our primary goal for LOD, 50 ppb is the threshold value for the breath analysis. Regarding this concentration, both sensors are adequate for this purpose.

[0055] However, sample 1 : 1 is proposed for the selectivity measurements due to its clear sensor signal characteristics. Moreover, it could be a possible candidate for real-time applications and competitors for commercial ones. Moreover, understanding the sensing mechanism is also important for the development of novel sensors and for optimizing device performance. The sensing mechanism of BPB / PG-GO sensing material can be related to the ambipolar behavior of the transfer characteristics in chemiresistive devices, which enables charge transfer, trapping, doping, and so on. Generally, the charge transfer between the adsorbed molecule and GO governs the nanosensing mechanism. The revealed cross-sensitivity in such devices can also enhance the electrical sensing performance toward NH3.

[0056] Sensing measurements are performed on a calibrated hand-made measurement system. First, I-V characterizations are conducted for each sample at room temperature. Subsequently, sensors are tested against ammonia in concentrations ranging from 11.6 ppm to 1.16 ppm and relative humidity in concentrations ranging from 80% to 8%.

[0057] Before investigating sensing properties, I-V characterization was performed for each sample to determine bias voltage at room temperature (Figure 7). Thus, to assess the sensing properties of the produced chemiresistive sensors towards NH3 gas, the conductivity of the sensing materials of BPB / PG-GO (1 : 1) and BPB / BPB / PG-GO (1 :2) was first tested. When the applied bias voltage was increased from 0 to 10 V, the electrical conductivity of the samples increased. At the bias voltage of 10 V, electrical conductivity was 0.183 pA and 0.037 pA for 1 : 1 and 1 :2 sensors, respectively. The lower value due to the higher thickness of the 1 :2 layer causes more noise in the NH3 sensing response signals.

[0058] The sensing mechanism of BPB / PG-GO sensing material can be related to the ambipolar behavior of the transfer characteristics in chemiresistive devices, which enables charge transfer, trapping, doping, and so on. Generally, the charge transfer between the adsorbed molecule and GO governs the nanosensing mechanism. The revealed cross-sensitivity in such devices can also enhance the electrical sensing performance toward NH3.

[0059] The areas where the invention can be applied are exemplified as follows: o Detection and monitoring of NH3 in exhaled human breath for disease diagnosis causing peptic, duodenal, and gastric ulcer or cancer (e.g., helicobacter pylori diagnosis < 50 ppb), o Detection of NH3 from fertilizer degradation (e.g., ammonium phosphate <100 PPm), o Detection of NH3 released from chemical plants (e.g., using NH3 as a coolant), o Detection of NH3 released by degradation of protein-rich foods, o Detection of NH3 released from motor vehicles, o In the defense and security industry, most conventional military explosives contain nitrogen, of which ammonia is the primary nitrogen source.

Claims

CLAIMS1. A method of producing polyglycerol-modified graphene oxide, the method comprising the steps of: a) mixing and sonication of glycidol and graphene oxide powders, b) magnetically stirring of the obtained mixture first under a nitrogen atmosphere and then in an oil bath, c) dissolving the resulting black gel-like product at step b in methanol, d) precipitating of the resultant mixture at step c in acetone to remove monomers and oligomers, e) obtaining of the polyglycerol-modified graphene oxide.

2. A method of according to Claim 1, the method further comprising the step of dialyzing of the obtained polyglycerol-modified graphene oxide in distilled water with a dialysis membrane to remove the solvent and impurities.

3. A method of according to Claim 1, the method further comprising the step of centrifuging and then freeze-drying the obtained polyglycerol-modified graphene oxide.

4. A method of according to Claim 1, the method comprising sonication of 4.5 ml glycidol and 22.5 mg graphene oxide powders in an ice-water bath for 2 hours, in the step a.

5. A method of according to Claim 1, the method comprising magnetically stirring of the obtained mixture under a nitrogen atmosphere for 30 min followed by another 20 h at 140°C in an oil bath, in the step of b.

6. A method of according to Claim 1, the method comprising dissolving the resulting black gel-like product at step b in 10 ml methanol, in the step of c.

7. A method of according to Claim 1, the method comprising precipitating of the resultant mixture at step c in 10 ml acetone to remove monomers and oligomers, in the step of d.

8. A method of according to Claim 2, the method comprising dialyzing of the obtained polyglycerol-modified graphene oxide in distilled water with a dialysis membrane for 24 h to remove the solvent and impurities.

9. A method of according to Claim 3, the method comprising centrifuging for 10 min at 4000 rpm and then freeze-drying the obtained polyglycerol-modified graphene oxide for 72 h.

10. A polyglycerol-modified graphene oxide obtained by a method according to any one of Claims 1-9.

11. A method of manufacturing a chemiresi stive nanosensor for the detection of trace amounts of ammonia (NH3) gas at <50 ppb levels, the method comprising the steps of: i. providing the polyglycerol-modified graphene oxide according to Claim 10, ii. self-assembly of the polyglycerol-modified graphene oxide on a chemiresistive chips, iii. drying of the polyglycerol-modified graphene oxide assembled chemiresistive chip, iv. coating the dried polyglycerol-modified graphene oxide layer of the obtained chemiresistive chip in the step of ii., with a bromophenol blue (BPB) solution v. obtaining a chemiresistive nanosensor.

12. A method of according to Claim 11, the method further comprising the step of pretreating of chemiresistive chip in acetone at 70 °C for 3 minutes in an open beaker under a hood and then rinsing in pure analytical grade acetone and drying at room temperature.

13. A method of according to Claim 11, the method further comprising the step of dispersing the polyglycerol -modified graphene oxide according to Claim 10 in water by sonication for 1 hour.

14. A method of according to Claim 11, the method comprising performing self-assembly of the polyglycerol-modified graphene oxide on the chemiresi stive chips via dropcasting, in the step ii.

15. A method of according to Claim 11, the method comprising coating the dried polyglycerol-modified graphene oxide layer of the obtained chemiresi stive chip in the step of ii., with a 10 pl of ethanolic solution of bromophenol blue dye with the dropcasting method, in the step iii.

16. A method of according to Claim 11, the method further comprising the step of annealing of the obtaining a chemiresistive nanosensor in an oven at 80 °C for 5 minutes.

17. A chemiresistive nanosensor manufactured by a method according to any one of Claims 11-17.

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