Paper-Based Screen-Printed Ionic-Liquid/Graphene Electrode Integrated with Prussian Blue/MXene Nanocomposites Enabled Electrochemical Detection for Glucose Sensing

As glucose biosensors play an important role in glycemic control, which can prevent the diabetic complications, the development of a glucose sensing platform is still in needed. Herein, the first proposal on the in-house fabricated paper-based screen-printed ionic liquid/graphene electrode (SPIL-GE) modified with MXene (Ti3C2Tx), prussian blue (PB), glucose oxidase (GOx), and Nafion is reported. The concentration of PB/Ti3C2Tx was optimized and the optimal detection potential of PB/Ti3C2Tx/GOx/Nafion/SPIL-GE is −0.05 V. The performance of PB/Ti3C2Tx/GOx/Nafion modified SPIL-GE was characterized by cyclic voltammetry and chronoamperometry technique. This paper-based platform integrated with nanomaterial composites were realized for glucose in the range of 0.0–15.0 mM with the correlation coefficient R2 = 0.9937. The limit of detection method and limit of quantification were 24.5 μM and 81.7 μM, respectively. In the method comparison, this PB/Ti3C2Tx/GOx/Nafion/SPIL-GE exhibits a good correlation with the reference hexokinase method. This novel glucose sensing platform can potentially be used for the good practice to enhance the sensitivity and open the opportunity to develop paper-based electroanalytical devices.


Introduction
Diabetes mellitus, a leading non-communicable disease-related health issue, is a risk factor for a variety of vascular illnesses [1]. By 2045, the predicted worldwide prevalence will reach 738.2 million cases [2]. This tremendous number led to the long-term health effects, mortality rate, and economic and financial burden. Regards to Diabetes self-management education and support from Centers for disease Control and prevention (CDC), the discipline in glycemic control can prevent and delay these serious health complications including diabetic retinopathy, peripheral neuropathy, chronic kidney disease, cerebrovascular disease, and heart disease [3]. As the vital demand of more than 420 million people with diabetes globally for the blood glucose control and monitoring result to rapidly growing in the glucose biosensor market [4]. This statistic emphasized the continuous development of glucose sensing along with good practice for effective diabetic management. The inspiring aspects of improving the performance of glucose sensor focus Herein, we are first proposed the in-house developed paper-based screen-printed ionic liquid/graphene electrode (SPIL-GE) modified with Ti 3 C 2 T x , PB, GOx, and Nafion. This proposed modified SPIL-GE was implemented to monitor glucose levels in real plasma samples. Ti 3 C 2 T x was modified to increase the enzyme loading capacity on the electrode surface [22] incorporated with the catalytic activity of PB toward H 2 O 2 [23]. This modification to paper-based SPIL-GE may increase sensitivity toward glucose detection. In addition, Nafion was also utilized to avoid the negatively charged interferences in sample matrices such as ascorbic acid, uric acid, and other proteins [24,25]. Firstly, GOx was loaded on MXene/PB layers to catalyzed glucose in the sample matrix to gluconolactone and hydrogen peroxide. Secondly, hydrogen peroxide, a by-product from the first reaction, can be catalyzed by PB at low potential. The response signal of the reaction can be monitored by amperometric measurement. In this study, Whatman No.1 was applied to assist the delivery of sample by capillary force to the working electrode area which allows portable measurement. This paper-based SPIL-GE was characterized and tested with real sample matrices. This study may enhance the knowledge on the modification of paper-based electrodes. This integrated paper-based sensor for glucose sensing may be wirelessly connected to a smart phone for monitoring and providing personal health information to medical staff, which could improve the efficacy of diabetes management in remote areas and be useful for portable in-field analysis [26,27].

Apparatus
All electrochemical characterization was carried out using a portable PalmSens4 (Palm-Sens, Houten, The Netherlands) ( Figure S1a). For the electrochemical detection of blood glucose, chronoamperometry was tested by using USB-C Sensit Smart (PalmSens, Houten, The Netherlands) with PStouch app for Android smart phone as showed in Figure S1b. A CO 2 laser cutting machine (60 Watt.) (Cnmanlaser, model MAN-6090, Qingdao, China) was purchased from the MIT group, Thailand. Field emission scanning electron microscope (FESEM) analysis were performed at the National Science and Technology Development Agency, Thailand. HITACHI SU8030 FESEM (Tokyo, Japan) were used to study the morphology of the modified electrode.
The electrochemical properties of PB/Ti 3 C 2 T x /GOx/Nafion on SPIL-GE were characterized by cyclic voltammetry (CV) with 5 mM ferri/ferrocyanide in 0.1 M KCl solution. The chronoamperometry technique was used for characterization to find the optimal concentration of modified nanomaterial and selection of optimal detection potential conditions for quantitative determination of glucose.

Fabrication of Screen-Printed IL/Graphene Electrodes (SPIL-GEs) on Paper Based
To Fabricated of SPIL-GEs on paper based, The commercial ionic liquid graphene ink (IL-GP ink) was composed of a conductive carbon paste, exfoliated graphene powder in poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) solution and 3-methyl-1-propylpyridinium bis(trifluoromethyl sulfonyl)imide (PMPlm) as a weight ratio of 100:2.5:1 [21]. In Figure 1a, the IL-GP ink was screened through the pattern stencil mesh on the A4 card paper with a thickness of 230 g for the fabrication of the working electrode (WE with a diameter of 4 mm.) and counter electrode (CE) by using a screen printer (DEK version 03ix). Next, silver/silver chloride paste (Ag/AgCl) and insulator paste was also screened on the same electrode for the fabrication of a references electrode (RE) and detection area, respectively. Each screened layer was dried to remove solvent by baking at 60 • C about 5 min and storage at room temperature for this application. concentration of modified nanomaterial and selection of optimal detection potential conditions for quantitative determination of glucose.

Fabrication of Screen-Printed IL/Graphene Electrodes (SPIL-GEs) on Paper Based
To Fabricated of SPIL-GEs on paper based, The commercial ionic liquid graphene ink (IL-GP ink) was composed of a conductive carbon paste, exfoliated graphene powder in poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) solution and 3methyl-1-propylpyridinium bis(trifluoromethyl sulfonyl)imide (PMPlm) as a weight ratio of 100:2.5:1 [21]. In Figure 1a, the IL-GP ink was screened through the pattern stencil mesh on the A4 card paper with a thickness of 230 g for the fabrication of the working electrode (WE with a diameter of 4 mm.) and counter electrode (CE) by using a screen printer (DEK version 03ix). Next, silver/silver chloride paste (Ag/AgCl) and insulator paste was also screened on the same electrode for the fabrication of a references electrode (RE) and detection area, respectively. Each screened layer was dried to remove solvent by baking at 60 °C about 5 min and storage at room temperature for this application.

Preparation of Modified PB/Ti3C2Tx/GOx/Nafion on Paper-Based Screen-Printed Ionic Liquid/Graphene Electrode (SPIL-GE) Glucose Sensor
To prepared Ti3C2Tx flakes, Ti3C2Tx were synthesized by the modified minimally intensive layer delamination (MILD) method using in situ HF formation from HCl and LiF to prepare both etchant and intercalation in exfoliation process which is less hazardous and provides an easier step than using HF where the flakes are isolated by manual shaking without further intercalation [28,29]. The in situ HF etchant was prepared by adding 1.0 g of LiF to 20 mL of 9 M HCl under continuous stirring to acquire homogeneous mixture. Next, a total of 1.0 g of Ti3AlC2 (MAX phase) powder was then slowly added to the etchant and allowed the reaction to run under continuous stirring at 50 °C for 50 h. The

Preparation of Modified PB/Ti 3 C 2 T x /GOx/Nafion on Paper-Based Screen-Printed Ionic Liquid/Graphene Electrode (SPIL-GE) Glucose Sensor
To prepared Ti 3 C 2 T x flakes, Ti 3 C 2 T x were synthesized by the modified minimally intensive layer delamination (MILD) method using in situ HF formation from HCl and LiF to prepare both etchant and intercalation in exfoliation process which is less hazardous and provides an easier step than using HF where the flakes are isolated by manual shaking without further intercalation [28,29]. The in situ HF etchant was prepared by adding 1.0 g of LiF to 20 mL of 9 M HCl under continuous stirring to acquire homogeneous mixture. Next, a total of 1.0 g of Ti 3 AlC 2 (MAX phase) powder was then slowly added to the etchant and allowed the reaction to run under continuous stirring at 50 • C for 50 h. The resulting mixture was centrifuged and washed with deionized water to remove the acidic supernatant ( Figure S2a) and repeat washing cycles until the pH of supernatant reached to pH 5-6. After being washed, the black Ti 3 C 2 T x layer and a grey layer of Ti 3 AlC 2 /Ti 3 C 2 T x mixture were settle at the bottom of the centrifuge tube as showed in Figure S2b [29]. The Ti 3 C 2 T x clay was transferred to a glass petri dish and dried at 65 • C for 12 h to obtain the Ti 3 C 2 T x film ( Figure S2c). Ti 3 C 2 T x film was kept under argon gas in a sealed aluminum foil bag for further use.
For PB/Ti 3 C 2 T x , the composite was synthesized via the in situ reduction process as described in previous studies [30]. The PB nanoparticles were produced by reduction of the Fe(III) and Fe(CN) 6 3− mixture with Ti 3 C 2 T x , where Fe(III) was reduced to Fe(II) and Fe(CN) 6 3was reduced to Fe(CN) 6 4− . To synthesize, the total amount of 13.5 mg of FeCl 3 and 16.5 mg of K 3 [Fe(CN) 6 ] were dissolved in 10 mL of 0.1 M KCl (pH 1.5) for 30 min. A total 10 mL of 2 mg/mL Ti 3 C 2 T x suspension was slowly added into the mixture solution of FeCl 3 and K 3 [Fe(CN) 6 ]. After continuous stirring for 30 min, the precipitated PB/Ti 3 C 2 T x were filtrated by vacuum assisted filtration and washed with deionized water for 5 times. The resulting PB/Ti 3 C 2 T x nanocomposites were obtained after being dried at 60 • C for 12 h.

Fabrication of the Paper-Based Glucose Sensor
To fabricate the devices, paper-based SPIL-GEs were electrochemically cleaned to remove contaminants on electrode surfaces [21]. Briefly, 80 µL of 0.1 M PBS solution (pH 7.4) was dropped onto the electrode surface and applied the voltage between−0.3 and +0.6 at a scan rate of 50 mV/s for 5 scans by using the cyclic voltammetry (CV) technique. After being cleaned, paper-based SPIL-GEs were carefully washed with deionized water and dried at 60 • C for 15 min. Before applying PB/Ti 3 C 2 T x nanocomposites on the electrode surface, 3 mg/mL PB/Ti 3 C 2 T x was dispersed in deionized water and the suspended solution was sonicated for 90 min to acquire a homogeneous mixture. In Figure 1b, total 8 µL of PB/Ti 3 C 2 T x mixture was then dropped cast on paper-based SPIL-GE and dried at 60 • C for 30 min. After the electrode was cooled for 10 min, 6 µL of 10 mg/mL GOx in sodium acetate (pH 5.1) was dropped and dried at 25 • C for 2 h. Subsequently, 2 µL of 0.5% Nafion was dropped at room temperature for 1 h. Finally, the designed Whatman No.1 was cut by using CO 2 laser cutting machine and applied on the working electrode area with transparent adhesive tape to assist the delivery of sample by capillary force, as showed in Figure 1a. The modified paper-based microfluidic glucose sensor was store in sealed aluminum foil bag at 4 • C before use.

Real Sample Analysis and Interference Studies
The paper-based SPIL-GE device was used to determine blood glucose level by using human blood plasma (n = 10) and compared with enzymatic glucose assay (Hexokinase) using automated analyzer ARCHITECT ci4100 (Abbott, IL, USA). The concentration of ascorbic acid (0.1 mM), uric acid (0.1 mM), and hemoglobin (0.06 mM) in PBS were used to study the effects of the main interferences in human blood plasma.
To verify the electrochemical method for real sample analysis, the prepared paperbased PB/Ti 3 C 2 T x /GOx/Nafion/SPIL-GE was used to measure blood glucose concentration. In this work, separated blood plasma was carefully collected from sodium fluoride (NaF) containing tube after drawing the whole blood sample from volunteers and centrifuged at 3000 rpm for 10 min. The human blood plasma was then determined to have glucose concentration in plasma using paper-based PB/Ti 3 C 2 T x /GOx/Nafion/SPIL-GE that was connected to Sensit Smart. In the process of real sample assay, the sample matrix is one of the crucial factors that effects the obtained signal because it contains lots of interference, including ascorbic acid, and uric acid. To minimize the sample matrix effects, we diluted the plasma sample with PBS at a ratio of 1 to 3. Furthermore, the Nafion was utilized to trap the negatively charged interference species that may affect the real sample of plasma glucose measurements.

Electrochemical Characterization of the Modified Electrodes
The electrochemical behavior of modified electrodes in this work was investigated in the presence of a 5 mM redox probe [Fe(CN) 6 ] 3−/4− in 0.1 M KCl by cyclic voltammetry (CV) at a potential range between −0.5 to +1.0 V/s with a scan rate of 50 mV/s. As shown in Figure 2a, after the electrode was modified, the redox peak current response of modified PB/Ti 3 C 2 T x nanocomposites on SPIL-GE was distinctly enhanced due to the excellent electroactivity of PB nanoparticles and the multilayer of Ti 3 C 2 T x sheets. Furthermore, the redox peak currents of PB/Ti 3 C 2 T x /GOx/Nafion/SPIL-GEs were also studied. Immobilized GOx and Nafion on PB/Ti 3 C 2 T x showed a significant decrease in the redox peak currents, which may be affected by the fact that GOx is a protein and Nafion also has an insulation property that may block the electron transfer between the redox probe and electrode surfaces [25,31]. To characterize modified PB/Ti 3 C 2 T x on SPIL-GEs, the electrochemical behavior property was investigated. The ∆Ep values obtained for bare SPIL-GE, PB/Ti 3 C 2 T x /SPIL-GE, and PB/Ti 3 C 2 T x /GOx/Nafion/SPIL-GE were 279, 239, and 299 mV, respectively. When the SPIL-GE was modified with PB/Ti 3 C 2 T x , the ∆Ep value decreased due to the high surface area and excellent electrical conductivity of MXene. However, when PB/Ti 3 C 2 T x /SPIL-GE was modified with GOx/Nafion, the ∆Ep value again increased due to the insulating nature of GOx and nafion. Since the behavior of PB does produce a redox peak signal, PB/Ti 3 C 2 T x modified electrode have been studied with 0.1 M KCl to verify the redox process of PB. In Figure S3, CV of PB/Ti 3 C 2 T x /SPIL-GE showed the resulting of clear redox peak current compare with bare-SPIL-GE and Ti 3 C 2 T x modified SPIL-GE. Figure 2b, the cyclic voltammograms (CVs) of PB/Ti 3 C 2 T x modified SPIL-GEs (PB/Ti 3 C 2 T x /SPIL-GEs) at different scan rates in range of 10-100 mV/s with 5 mM [Fe(CN) 6 ] 3−/4− in 0.1 M KCl solution showed a pair of redox peaks which were the oxidation and reduction peak currents. To investigate the electrochemical behaviors, Figure 2c showed the relationship between the square root of scan rate and redox peak currents. The electroactive properties of the oxidation peak currents and reduction peak currents were linearly related to the square root of the scan rate between 10 to 100 mV/s with the linear correlation (R 2 ) of 0.9743 and 0.9948, respectively. Indicating the diffusion control behavior.

Electrochemical Characterization of the Modified Electrodes
The electrochemical behavior of modified electrodes in this work was investigated in the presence of a 5 mM redox probe [Fe(CN)6] 3−/4− in 0.1 M KCl by cyclic voltammetry (CV) at a potential range between −0.5 to +1.0 V/s with a scan rate of 50 mV/s. As shown in Figure 2a, after the electrode was modified, the redox peak current response of modified PB/Ti3C2Tx nanocomposites on SPIL-GE was distinctly enhanced due to the excellent electroactivity of PB nanoparticles and the multilayer of Ti3C2Tx sheets. Furthermore, the redox peak currents of PB/Ti3C2Tx/GOx/Nafion/SPIL-GEs were also studied. Immobilized GOx and Nafion on PB/Ti3C2Tx showed a significant decrease in the redox peak currents, which may be affected by the fact that GOx is a protein and Nafion also has an insulation property that may block the electron transfer between the redox probe and electrode surfaces [25,31]. To characterize modified PB/Ti3C2Tx on SPIL-GEs, the electrochemical behavior property was investigated. The ∆Ep values obtained for bare SPIL-GE, PB/Ti3C2Tx/SPIL-GE, and PB/Ti3C2Tx/GOx/Nafion/SPIL-GE were 279, 239, and 299 mV, respectively. When the SPIL-GE was modified with PB/Ti3C2Tx, the ∆Ep value decreased due to the high surface area and excellent electrical conductivity of MXene. However, when PB/Ti3C2Tx/SPIL-GE was modified with GOx/Nafion, the ∆Ep value again increased due to the insulating nature of GOx and nafion. Since the behavior of PB does produce a redox peak signal, PB/Ti3C2Tx modified electrode have been studied with 0.1 M KCl to verify the redox process of PB. In Figure S3, CV of PB/Ti3C2Tx/SPIL-GE showed the resulting of clear redox peak current compare with bare-SPIL-GE and Ti3C2Tx modified SPIL-GE. Figure 2b Figure 2c showed the relationship between the square root of scan rate and redox peak currents. The electroactive properties of the oxidation peak currents and reduction peak currents were linearly related to the square root of the scan rate between 10 to 100 mV/s with the linear correlation (R 2 ) of 0.9743 and 0.9948, respectively. Indicating the diffusion control behavior. In addition, A plot of logarithm of redox peak currents vs. logarithm of scan rate were investigated. Figure 2d shows a good linear correlation with the slope of 0.456 which indicating that the reduction reaction has a diffusion control behavior.  The elemental mapping analysis was carried out using EDS analysis to study elemental distribution in Ti3C2Tx and PB/Ti3C2Tx nanocomposites. Figure 3c show distinctly demonstrates of the existence and distribution of Ti, C, O, and F elements in Ti3C2Tx after delamination and further confirmed the elemental analysis of Fe and N elements in In addition, A plot of logarithm of redox peak currents vs. logarithm of scan rate were investigated. Figure 2d shows a good linear correlation with the slope of 0.456 which indicating that the reduction reaction has a diffusion control behavior.

The Topographical Analysis of Ti 3 C 2 T x and PB/Ti 3 C 2 T x
FESEM was employed to investigate the morphological analysis of Ti 3 C 2 T x and PB/Ti 3 C 2 T x . The micrographs of Ti 3 C 2 T x and PB/Ti 3 C 2 T x were recorded under the accelerating voltage of 5.0 kV and magnifications of 50,000× as showed in Figure 3a In addition, A plot of logarithm of redox peak currents vs. logarithm of scan rate were investigated. Figure 2d shows a good linear correlation with the slope of 0.456 which indicating that the reduction reaction has a diffusion control behavior.  The elemental mapping analysis was carried out using EDS analysis to study elemental distribution in Ti3C2Tx and PB/Ti3C2Tx nanocomposites. Figure 3c show distinctly demonstrates of the existence and distribution of Ti, C, O, and F elements in Ti3C2Tx after delamination and further confirmed the elemental analysis of Fe and N elements in PB/Ti3C2Tx nanocomposites as showed in Figure 3d. The elemental mapping analysis was carried out using EDS analysis to study elemental distribution in Ti 3 C 2 T x and PB/Ti 3 C 2 T x nanocomposites. Figure 3c show distinctly demonstrates of the existence and distribution of Ti, C, O, and F elements in Ti 3 C 2 T x af-ter delamination and further confirmed the elemental analysis of Fe and N elements in PB/Ti 3 C 2 T x nanocomposites as showed in Figure 3d.

Selection the Optimal Concentration of PB/Ti 3 C 2 T x Modified on Paper-Based SPIL-GE
To optimize the modified PB/Ti 3 C 2 T x on paper-based SPIL-GE, varying concentrations of PB/Ti 3 C 2 T x nanocomposites were prepared as mentioned above. (Section 2.5) To select the optimal concentration of PB/Ti 3 C 2 T x for further experiments, chronoamperometry was selected to test the difference concentration of modified PB/Ti 3 C 2 T x /SPIL-GE with 1.0 mM glucose in 0.1 M PBS (pH 7.4). As shown in Figure 4a, the result showed that, the more concentration of PB/Ti 3 C 2 T x on SPIL-GE the current response was increases until the concentration reaches to 4 mg/mL. However, the background and standard deviation (error bar) at a concentration of 4 mg/mL PB/Ti 3 C 2 T x were also increased. While the concentration of 3 mg/mL PB/Ti 3 C 2 T x gives the highest signal/background ratio as showed in Figure 4b. Therefore, the concentration of 3 mg/mL was chosen as the optimal concentration of PB/Ti 3 C 2 T x for modified SPIL-GE due to the lower in standard deviation and the highest current of signal/background ratio.

Selection the Optimal Concentration of PB/Ti3C2Tx Modified on Paper-Based SPIL-GE
To optimize the modified PB/Ti3C2Tx on paper-based SPIL-GE, varying concent tions of PB/Ti3C2Tx nanocomposites were prepared as mentioned above. (Section 2.5) select the optimal concentration of PB/Ti3C2Tx for further experiments, chronoamperom try was selected to test the difference concentration of modified PB/Ti3C2Tx/SPIL-GE w 1.0 mM glucose in 0.1 M PBS (pH 7.4). As shown in Figure 4a, the result showed that, t more concentration of PB/Ti3C2Tx on SPIL-GE the current response was increases until t concentration reaches to 4 mg/mL. However, the background and standard deviation ( ror bar) at a concentration of 4 mg/mL PB/Ti3C2Tx were also increased. While the conce tration of 3 mg/mL PB/Ti3C2Tx gives the highest signal/background ratio as showed Figure 4b. Therefore, the concentration of 3 mg/mL was chosen as the optimal concent tion of PB/Ti3C2Tx for modified SPIL-GE due to the lower in standard deviation and t highest current of signal/background ratio.

Selection the Optimal Detection Potential of PB/Ti3C2Tx/GOx/Nafion/SPIL-GE
After optimizing the concentration of PB/Ti3C2Tx on SPIL-GE with chronoampero etry, the detection potential for determining glucose concentration was also optimized. select the optimal detection potential for acquiring the lowest detection limit, the high current response with the lowest background current was considered. Therefore, the fin concentration of 0.5 mM glucose in 0.1 M PBS pH 7.4 was added and measured at fix different potentials of 0.00, −0.05, −0.10, −0.15, and −0.20 V (vs Ag/AgCl) compared w 0.1 M PBS pH 7.4 as the background current response. In Figure 5a, it can be seen that t applied potential of −0.05V (vs. Ag/AgCl) shows a high current response than the re Therefore, the −0.05 V was chosen due to the lowest applied potential to avoid interferen from applying the high potential and give the highest signal/background ratio as show in Figure 5b.

Selection the Optimal Detection Potential of PB/Ti 3 C 2 T x /Gox/Nafion/SPIL-GE
After optimizing the concentration of PB/Ti 3 C 2 T x on SPIL-GE with chronoamperometry, the detection potential for determining glucose concentration was also optimized. To select the optimal detection potential for acquiring the lowest detection limit, the highest current response with the lowest background current was considered. Therefore, the final concentration of 0.5 mM glucose in 0.1 M PBS pH 7.4 was added and measured at fixed different potentials of 0.00, −0.05, −0.10, −0.15, and −0.20 V (vs Ag/AgCl) compared with 0.1 M PBS pH 7.4 as the background current response. In Figure 5a, it can be seen that the applied potential of −0.05V (vs. Ag/AgCl) shows a high current response than the rest. Therefore, the −0.05 V was chosen due to the lowest applied potential to avoid interference from applying the high potential and give the highest signal/background ratio as shown in Figure 5b.

Analytical Performance of Glucose Determination on PB/Ti3C2Tx/GOx/Nafion/SPIL-GE
To determine the analytical performance of the paper-based SPIL-GE biosensor, t different concentrations of glucose were prepared and measured by using chronoa perometry with an applied detection potential of −0.05 V (Figure 6a) and the determin tion result was recorded and constructed as a calibration curve by plotting between av

Analytical Performance of Glucose Determination on PB/Ti 3 C 2 T x /Gox/Nafion/SPIL-GE
To determine the analytical performance of the paper-based SPIL-GE biosensor, the different concentrations of glucose were prepared and measured by using chronoamperometry with an applied detection potential of −0.05 V (Figure 6a) and the determination result was recorded and constructed as a calibration curve by plotting between average amperometry current responses (t = 100-150 s) and the prepared standard glucose concentration in the range of 0.0-15.0 mM as shown in Figure 6b. The linear range of glucose determinations are 0.0-0.50 and 0.0-15.0 mM with the correlation coefficient R 2 = 0.9937 (LOD = 24.5 µM) and 0.9878 (LOD = 62.1 µM), respectively. These results indicate that, the paper-based PB/Ti 3 C 2 T x /Gox/Nafion/SPIL-GE showed an excellent electrochemical response for glucose determination.

Analytical Performance of Glucose Determination on PB/Ti3C2Tx/GOx/Nafion/SPIL-GE
To determine the analytical performance of the paper-based SPIL-GE biosensor, the different concentrations of glucose were prepared and measured by using chronoamperometry with an applied detection potential of −0.05 V (Figure 6a) and the determination result was recorded and constructed as a calibration curve by plotting between average amperometry current responses (t = 100-150 s) and the prepared standard glucose concentration in the range of 0.0-15.0 mM as shown in Figure 6b

Real Sample Analysis of the Paper-Based PB/Ti3C2Tx/GOx/Nafion/SPIL-GE and Interferences Study
In this study, blood samples with spiked glucose at different concentrations in the range of 4.28-12.61 mM (n = 10) were analyzed using diluted procedure as mentioned above. The results were compared with the reference hexokinase/glucose-6-phosphate dehydrogenase (G6PD) method using automated analyzer (Architect ci4100). As shown in

Real Sample Analysis of the Paper-Based PB/Ti 3 C 2 T x /Gox/Nafion/SPIL-GE and Interferences Study
In this study, blood samples with spiked glucose at different concentrations in the range of 4.28-12.61 mM (n = 10) were analyzed using diluted procedure as mentioned above. The results were compared with the reference hexokinase/glucose-6-phosphate dehydrogenase (G6PD) method using automated analyzer (Architect ci4100). As shown in Table 1, the determination results of glucose using both electrochemical method on paper-based PB/Ti 3 C 2 T x /Gox/Nafion/SPIL-GE and automated analyzer (Hexokinase method) were compared. The result demonstrated that no bias for measurement of glucose in any samples was obtained, since the difference between the two methods fell within the ±1.96 standard deviation (SD) as shown in Figure 7a. based PB/Ti3C2Tx/GOx/Nafion/SPIL-GE and automated analyzer (Hexokinase method) were compared. The result demonstrated that no bias for measurement of glucose in any samples was obtained, since the difference between the two methods fell within the ±1.96 standard deviation (SD) as shown in Figure 7a. A scatter plot of the results obtained from both methods was constructed in which a correlation coefficient of 0.9846 (Figure 7b) was obtained. To compare two population means with 95% confidence interval, the degree of freedom of 9 and the critical t-value (t0. 05,9) was calculated to be ±2.262. Paired sample statistical analysis revealed that the experimental value of |t| was 1.022, a significantly lower than the critical t-value so the null hypothesis assumed no differences in means between the results of the two methods. This implies that our proposed electrochemical paper-based device can be used in the application of glucose analysis with the portable electrochemical device. In addition, this research is the first to use screen-printed ionic liquid electrode on a paper substrate. The development is further studies of previous work on disposable screen-printed ionic liquid/graphene on polyethylene (PET) substrates [21]. A procedure used to prepare PB/Ti3C2Tx nanocomposites for easy electrode surface modification based on the process of reacting reeducation between Ti3C2Tx and Prussian Blue precursors [30], A scatter plot of the results obtained from both methods was constructed in which a correlation coefficient of 0.9846 (Figure 7b) was obtained. To compare two population means with 95% confidence interval, the degree of freedom of 9 and the critical t-value (t 0.05, 9 ) was calculated to be ±2.262. Paired sample statistical analysis revealed that the experimental value of |t| was 1.022, a significantly lower than the critical t-value so the null hypothesis assumed no differences in means between the results of the two methods. This implies that our proposed electrochemical paper-based device can be used in the application of glucose analysis with the portable electrochemical device.
In addition, this research is the first to use screen-printed ionic liquid electrode on a paper substrate. The development is further studies of previous work on disposable screen-printed ionic liquid/graphene on polyethylene (PET) substrates [21]. A procedure used to prepare PB/Ti 3 C 2 T x nanocomposites for easy electrode surface modification based on the process of reacting reeducation between Ti 3 C 2 T x and Prussian Blue precursors [30], which is a convenient procedure compared to other methods of nanocomposite preparation [32][33][34]. To compare the electrochemical performance of the proposed sensor, the limit of detection and the analytical range were evaluated and compared with the sensors for glucose monitoring that have been reported in the past, and the results are described in Table 2. It is clear that the newly created sensor has a wider detection range and more sensitive detection capabilities than the majority of other sensors. As a result, the newly designed sensor demonstrates very good detection capabilities for glucose across a wider linear range. Therefore, there is a possibility that the electrochemical sensor might be used for the sensitive detection of glucose. To investigate the selectivity of the proposed electrode toward glucose detection, the potential interferences in blood plasma including uric acid, ascorbic acid, and hemoglobin at their significant interfering concentration were added into 5 mM of glucose. The amperometric measurements were carried out and the % recoveries were reported as shown in Table 3. According to the obtained % recoveries, which are higher than 90%, these results verify that this designed electrode system is very selective for glucose detection in the existing of interferences. Table 3. Effects of interferences on the paper-based PB/Ti 3 C 2 T x /GOx/Nafion/SPIL-GE.

Conclusions
A novel paper-based screen-printed ionic liquid/graphene modified with PB/Ti 3 C 2 T x / GOx and Nafion was successfully fabricated for glucose sensing in real plasma samples. The use of ionic liquid/graphene ink to create an electrode on a paper substrate was described for the first time. With the simple modification process, the PB/Ti 3 C 2 T x /GOx/Nafion SPIL-GE can be applied to manufacture scale in the future. the advantageous properties of MXene such as good in conductivity and catalytic activity synergies with the outstanding properties of PB which can be measured glucose at low potential. This strategy has been applied in glucose determination to avoid the disturbed signal from interference species at high potential and enhance sensitivity. This promising platform can potentially be used for in-field analysis and applied to monitor other reactions that produce H 2 O 2 as a by-product.
Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/bios12100852/s1, Figure S1: The picture of the physical device for the electrochemical characterization using a portable Palm-Sens4 (a) and the electrochemical detection of plasma glucose using USB-C Sensit Smart connected to smartphone device (b). Figure S2: The resulting mixture of Ti 3 C 2 T x after the first washing cycle (a), the same Ti 3 C 2 T x sediment after washing with deionized water until the pH of supernatant was 5-6, showing the top black Ti 3 C 2 T x layer and grey layer of Ti 3 C 2 T x /Ti 3 AlC 2 mixture at the bottom of the centrifuge tube (b), and the resulting Ti 3 C 2 T x film (c). Figure