Electroanalytical Detection of Indigo Carmine in Presence of Tartrazine Using a Poly(dl-phenylalanine) Modiﬁed Carbon Nanotube Paste Electrode

: Certain dyes are deleterious to the biological system, including animals and plants living in the water sources, soil sources, and so on. Thus, the analysis of these dyes requires a potent, quick, and cost-effective approach to the environmental samples. The present research work shows a modest, low-cost, and eco-friendly electrochemical device based on poly(dl-phenylalanine)-layered carbon nanotube paste electrode (P(PAN)LCNTPE) material for indigo carmine (ICN) detection in the presence of tartrazine. The cyclic voltammetric, ﬁeld emission scanning electron microscopy, and electrochemical impedance spectroscopic methods were operated for the detection of the redox nature of ICN and electrode material surface activities, respectively. In better operational circumstances, P(PAN)LCNTPE provided better catalytic activity for the redox action of ICN than the bare carbon nanotube paste electrode. The P(PAN)LCNTPE showed good electrochemical activity during the variation of ICN concentrations ranging from 0.2 µ M to 10.0 µ M with improved peak current, and the limit of detection was about 0.0216 µ M. Moreover, the P(PAN)LCNTPE material was performed as a sensor of ICN in a tap water sample and shows adequate stability, repeatability


Introduction
Dyes or colorants are important organic compounds, used as artificial dyeing mediators in various industries including food, pharmaceutical, paper, photographic, paint, leather, and electronic industries. Numerous assessments reported that over 10,000 of various dyes are operated in several industrial products and over 700,000 tons of synthetic dyes are industrialized in the global market. Regrettably, 10.0-50.0% of colorants are wasted in the dyeing process and that massive quantity of colorants is directly liberated to environmental sources like water, soil, and so on. Here, most of the dyes are toxic, which formulates some harmful effects on nature such as decreasing photosynthesis action, oxygen lack, dissimilarity in BOD, the salinity of the soil, chemical oxygen demand, and so on. Additionally, less than 1 mg of colorant in 1 L of water is harmful to the plants and animals living in water resources [1].
Indigo carmine (ICN) is a water-soluble hydrophilic coloring agent (dye), naturally obtained during the indigo sulfonation process. ICN exhibits some significant applications during the detection of superoxide and ozone, redox reactions as a pH indicator, in the formulation of pharmaceutical pills, and coloring of food products, fabric materials, and beverages [2]. Likewise, ICN is extensively utilized during the treatments of gastric cancer

Chemicals and Reagents
ICN (electroactive compound under study), dl-phenylalanine (PAN) (surface activator), CNTs (electrode base material), and silicone oil (binder) were bought from Molychem, Mumbai, India. TN and potassium chloride (supporting electrolyte) were bought from Nice Chemicals, Kochin, India. Sodium salts (supporting electrolytes: Na 2 HPO 4 ·2H 2 O and NaH 2 PO 4 ·H 2 O) and potassium ferrocyanide (electroactive compound) were procured from Sisco Research Laboratories Pvt. Ltd., Maharashtra, India. These chemical compounds are analytical reagents graded and operated without extra purification. The solutions of know concentration were made by dissolving an estimated amount of chemical compound in a known amount of distilled water. The complete ICN analysis in the present work was done at the lab temperature of 25 • C.

Instrumentation
The CV and electrochemical impedance spectroscopic (EIS) methods were operated using z CHI-6038E instrument. The CHI-6038E (CHI Instrument, Austin, TX, USA) was used as a potentiostat for ICN in phosphate buffer (PB). Here, the mentioned potentiostat was connected to the electrochemical cell with three electrodes (three-electrode system), the P(PAN)LCNTPE and bare carbon nanotube paste electrode (BCNTPE) were used as a working electrode, the platinum wire was operated as a counter-electrode, and the saturated calomel electrode is used as a reference electrode. The field emission scanning electron microscopy (FE-SEM) characterization of the bare and modified electrode materials was conducted at DST-PURSE Laboratory, Mangalore University, Mangalore, India.

Preparation of BCNTPE
The preparation of the BCNTPE was performed with the optimum composition like 60% CNTs and 40% silicone oil based on the previous literature [19]. Here, the powder of CNTs (60%) and silicone oil (40%) were mixed well for about 15 to 20 min in an agate mortar using a pestle to accomplish a homogeneous paste of CNT and silicon oil. A bit part of the resulting CNTP was filled into the void (3.0 mm width) of the Teflon tube and a copper wire was inserted to provide an electrical connection. The surface of the electrode was smoothened attentively utilizing soft paper and rinsed with distilled water. The finally obtained material is called BCNTPE.

Preparation of P(PAN)LCNTPE
The P(PAN)LCNTPE was prepared using the electrochemical polymerization of PAN (1.0 mm) in PB (0.2 M & 7.0 pH) at the surface of fresh CNTPE through cycling 10 CV cycles at the scan rate of 0.1 Vs −1 and the potential window of −1.0 V to 1.5 V. After the completion of 10 CV cycles the modified electrode surface was rinsed with distilled water to achieve a fresh sensitive electrode surface called P(PAN)LCNTPE.

FE-SEM and EDX Analysis of BCNTPE and P(PAN)LCNTPE
FE-SEM is an innovative characterization technique operated to capture and analyze the microstructure picture of the material surfaces. FE-SEM is characteristically operated in a high vacuum, since gas molecules tend to interrupt the electron beam and the emitted secondary and backscattered electrons used for imaging and morphological observations. In this study, FE-SEM and EDX techniques are used for the analysis of surface morphology and elemental analysis of BCNTPE and P(PAN)LCNTPE, and the data are shown in Figure 1. Here, Figure 1a shows an unsystematically distributed tube-like shape with rough exterior, which signifies the presence of CNTs on the surface of BCNTPE material. Nevertheless, Figure 1b shows a surface structure of P(PAN)LCNTPE, here the electrode surface is surrounded by a film of Poly(PAN) on the CNTP surface. In addition, the characteristic elemental analysis was performed using the EDX technique to coincide with the elemental configuration of BCNTPE and P(PAN)LCNTPE. Figure 1c,d display the EDX images of BCNTPE and P(PAN)LCNTPE with different topographies. In Figure 1c, elements such as carbon (C), oxygen (O), and silicon (Si) appeared, and it indicates the material of unmodified electrode (BGPPE). Nonetheless, Figure 1d presents C, nitrogen (N), Si, and O elements. Hence, it indicates the modification of nitrogen-based moiety (amino acid: PAN) on the CNTPE surface.

EIS Study of BCNTPE and P(PAN)LCNTPE
EIS systems are functioned by computer programs specifically designed for EIS testing. Hence, before conducting EIS experimentation, all components of the arrangement must be accomplished. In this study, three electrodes were used (already explained in Section 2.2). The PB solution of known concentration and volume was prepared and transferred to the electrochemical cell and all three electrodes were connected to the potentiostat. Here, four leads were operated to assign the three electrodes to the EIS analyzer. Once all leads were connected, the EIS system was set up and ready for testing.
EIS is the simple method for the examination of charge transfer resistance (Rct) of the materials (BCNPE & P(PAN)LCNTPE). Here, EIS was performed for K 4 [Fe(CN) 6 ], and (1.0 mM) was used as a standard analytical sample in KCl (0.1 M) at the surface of BCNTPE (curve-a) and P(PAN)LCNTPE (curve-b). The EIS outcomes are displayed based on the Nyquist plots ( Figure 2). The described Nyquist plots show that the surface of BCNTPE material offers a greater semicircle size and the surface of P(PAN)LCNTPE material presents a smaller semicircle size. Also, the fitted equivalent circuit of R(CR(QR)) shows the parameters such as Rct, Q represents the constant phase element, C dl represents the double layer capacitance, R represents the internal resistance, and Rs represents the solution resistance. The data relating to Rs, Rct, Q, and C dl of bare and modified electrodes are tabulated in Table 1. These outcomes agree that the Rct of P(PAN)LCNTPE is lesser with a high charge transfer character than BCNTPE [27].

EIS Study of BCNTPE and P(PAN)LCNTPE
EIS systems are functioned by computer programs specifically designed for E testing. Hence, before conducting EIS experimentation, all components of the arrang ment must be accomplished. In this study, three electrodes were used (already explain in Section 2.2). The PB solution of known concentration and volume was prepared a transferred to the electrochemical cell and all three electrodes were connected to the p tentiostat. Here, four leads were operated to assign the three electrodes to the EIS an lyzer. Once all leads were connected, the EIS system was set up and ready for testing.

Active Surface Area of BCNTPE and P(PAN)LCNTPE
The study of the electrochemically active surface area supports the clarificatio the conductivity and sensitivity of the electrode materials. Figure

Active Surface Area of BCNTPE and P(PAN)LCNTPE
The study of the electrochemically active surface area supports the clarification of the conductivity and sensitivity of the electrode materials. Figure 6 ] with enhanced peak current and reduced peak potential in contrast to BCNTPE. These results are dependant on the electrochemically active surface area of the electrode materials. The active surface area of P(PAN)LCNTPE and BCNTPE was calculated using the following Randles-Sevcik equation [23,27,28], [28], and C (M) is the concentration of K 4 [Fe(CN) 6 ]. Primarily, in the bare electrode (before modification) the calculated electroactive surface area (geometric surface area) value was found to be 0.017 cm 2 , but after modification of CNTPE surface by P(PAN), the calculated active surface area was found to be 0.034 cm 2 .
These data indicate that the geometric surface area of the bare electrode is lesser than the modified electrode and it is due to the effect of the modification. The heterogeneous electron transfer rate constant (k) is calculated through the data of EIS and active surface area, and the rate constant relation are as follows: where n represents the number of electrons, and other terms have their traditional denotation. The calculated value of k for P(PAN)LCNTPE was 0.0013 cm/s and for BCNTPE 0.0017 cm/s. These results show that the development of the P(PAN) layer at the surface of CNTPE increases its catalytic activity with a high number of active sites.
The heterogeneous electron transfer rate constant (k) is calculated through th of EIS and active surface area, and the rate constant relation are as follows: k = RT/n 2 F 2 A C Rct where n represents the number of electrons, and other terms have their traditio notation. The calculated value of k for P(PAN)LCNTPE was 0.0013 cm/s and for BC 0.0017 cm/s. These results show that the development of the P(PAN) layer at the of CNTPE increases its catalytic activity with a high number of active sites.

Electrochemical Polymerization of PAN on CNTPE Surface
Inset Figure 4 shows the cyclic voltammograms for the PAN (1.0 mm) in PB and 7.0 pH) at the surface of CNTPE for the electrochemical polymerization and t of the number of cycles vs. peak current. Firstly, the effect of film thickness was s by varying the number of CV cycles from 5 to 20 ( Figure 4a). Here, 10 CV cycle better electrochemical peak current for ICN than 5, 15, and 20 cycles. Hence, 10 CV are selected as optimum for the polymerization of PAN on the surface of CNTPE tionally, the cyclic voltammograms were documented through the cycling of ten cles (twenty CV segments) having a potential window of −1.0 V to 1.5 V and a scan 0.1 Vs −1 . The achieved PAN cyclic voltammograms exhibited an improved anod current based on each CV cycle. This result authorized the alteration of the monom of PAN to the polymer film of PAN on the surface of CNTPE. Furthermore, the oped P(PAN) film probably expands the electrocatalytic activity, electrostatic in and sensitive electrochemical behavior. The possible electrochemically polym structure of PAN is shown in Scheme 1.

Electrochemical Polymerization of PAN on CNTPE Surface
Inset Figure 4 shows the cyclic voltammograms for the PAN (1.0 mm) in PB (0.2 M and 7.0 pH) at the surface of CNTPE for the electrochemical polymerization and the plot of the number of cycles vs. peak current. Firstly, the effect of film thickness was studied by varying the number of CV cycles from 5 to 20 ( Figure 4a). Here, 10 CV cycles show better electrochemical peak current for ICN than 5, 15, and 20 cycles. Hence, 10 CV cycles are selected as optimum for the polymerization of PAN on the surface of CNTPE. Additionally, the cyclic voltammograms were documented through the cycling of ten CV cycles (twenty CV segments) having a potential window of −1.0 V to 1.5 V and a scan rate of 0.1 Vs −1 . The achieved PAN cyclic voltammograms exhibited an improved anodic peak current based on each CV cycle. This result authorized the alteration of the monomer film of PAN to the polymer film of PAN on the surface of CNTPE. Furthermore, the developed P(PAN) film probably expands the electrocatalytic activity, electrostatic interface, and sensitive electrochemical behavior. The possible electrochemically polymerized structure of PAN is shown in Scheme 1.

Electrochemical Nature of ICN
The electrochemical redox action of 0.01 mM ICN on the surface-bare and modified electrodes was analyzed using the CV method. Cyclic voltammograms for the presence and absence (blank: curve-b) of 0.1 mM ICN in 0.2 M PB (pH 6.5) at the surface of P(PAN)LCNTPE (curve-c) and BCNTPE (curve-a) with a scan rate of 0.1 Vs −1 ( Figure 5). Here, P(PAN)LCNTPE provided higher electrocatalytic activity for the redox action of ICN with more improved redox peak current than the BCNTPE. Additionally, the absence of ICN (only PB of 6.5 pH) at P(PAN)LCNTPE (curve-b) did not show any electrochemical behavior. From the recorded information, the greater ICN electrochemical redox activity at P(PAN)LCNTPE as compared to BCNTPE was due to the faster electron transfer among electrode and analyte interface, higher electrochemical heterogeneous rate constant, high active surface area, stronger interactions like electrostatic, hydrogen bonding, electronic, covalent, and so on, among the interface of the modified electrode surface and ICN.

Electrochemical Nature of ICN
The electrochemical redox action of 0.01 mM ICN on the surface-bare and modified electrodes was analyzed using the CV method. Cyclic voltammograms for the presence

Effect of pH on ICN Electrochemical Activity
ICN is very sensitive to pH, oxidation, and reduction effects. Under normal co tions the ICN is in its oxidized form since it is always in interaction with oxygen in air. ICN is pH-sensitive and at strongly basic conditions it has a yellow-greenish co The ICN is in its blue form that dominates when the pH of the solution is less than ab eleven points. Hence, the analysis of the pH effect on the redox activity of ICN at surface of the modified electrode is essential. The influence of 0.2 M PB solution pH the redox reaction of 0.1 mM ICN at P(PAN)LCNTPE was inspected using the method. Figure 6a shows the cyclic voltammograms recorded for the redox activit ICN at the surface of P(PAN)LCNTPE in altered 0.2 M PB solution pHs ranging from 8.0 with the scan rate of 0.1 Vs −1 . Figure 6b represents the plot of Epa vs. pH, here movement of ICN peak potential (Epa) towards the negative path as the increase of from 5.5 to 8.0 was noticed with an effective linear relationship among Epa and pH (Ep = 0.716 -0.054 pH (V/pH) & R 2 = 0.988). Here, the slope value of Epa vs. pH was −0 V/pH was nearer to the hypothetical value of −0.059, suggesting that the redox reactio ICN was conducted through an equal number of protons and electrons (1:1 ratio). S portive of this, the number of protons in the electro-redox reaction of ICN P(PAN)LCNTPE was verified using the slope of Epa vs. pH and the Nernst relat ΔEp/ΔpH = −2.303 mRT/nF. Here, m is the number of protons, n is the number of e trons, ΔEp is the change in potential, F is the Faraday constant, T is the temperature, the universal gas constant, and ΔpH is the change in pH. The calculated value of number of electrons (n) was found to be 2.190 (almost two), signifying that the ICN e tro-redox reaction in P(PAN)LCNTPE probably continues through the transmissio two electrons and two protons. Additionally, Figure 6c shows that the 6.5 pH pres

Effect of pH on ICN Electrochemical Activity
ICN is very sensitive to pH, oxidation, and reduction effects. Under normal conditions the ICN is in its oxidized form since it is always in interaction with oxygen in the air. ICN is pH-sensitive and at strongly basic conditions it has a yellow-greenish color. The ICN is in its blue form that dominates when the pH of the solution is less than about eleven points. Hence, the analysis of the pH effect on the redox activity of ICN at the surface of the modified electrode is essential. The influence of 0.2 M PB solution pH on the redox reaction of 0.1 mM ICN at P(PAN)LCNTPE was inspected using the CV method. Figure 6a shows the cyclic voltammograms recorded for the redox activity of ICN at the surface of P(PAN)LCNTPE in altered 0.2 M PB solution pHs ranging from 5.5-8.0 with the scan rate of 0.1 Vs −1 . Figure 6b represents the plot of E pa vs. pH, here the movement of ICN peak potential (E pa ) towards the negative path as the increase of pH from 5.5 to 8.0 was noticed with an effective linear relationship among E pa and pH (E pa (V) = 0.716 -0.054 pH (V/pH) & R 2 = 0.988). Here, the slope value of E pa vs. pH was −0.054 V/pH was nearer to the hypothetical value of −0.059, suggesting that the redox reaction of ICN was conducted through an equal number of protons and electrons (1:1 ratio). Supportive of this, the number of protons in the electro-redox reaction of ICN in P(PAN)LCNTPE was verified using the slope of E pa vs. pH and the Nernst relation: ∆E p /∆pH = −2.303 mRT/nF. Here, m is the number of protons, n is the number of electrons, ∆E p is the change in potential, F is the Faraday constant, T is the temperature, R is the universal gas constant, and ∆pH is the change in pH. The calculated value of the number of electrons (n) was found to be 2.190 (almost two), signifying that the ICN electro-redox reaction in P(PAN)LCNTPE probably continues through the transmission of two electrons and two protons. Additionally, Figure 6c shows that the 6.5 pH presents the maximum ICN redox peak current in comparison with the remaining pHs (5.5, 6.0, 7.0, 7.5, and 8.0). The Chemosensors 2022, 10, 461 9 of 15 maximum electrochemical response of ICN at 6.5 is probably due to the stronger interactions such as electrostatic, hydrogen bonding, electronic, covalent, and so on. Therefore, 6.5 pH was selected as the optimum pH value for the current research.
Chemosensors 2022, 10, x FOR PEER REVIEW 9 of 15 and so on. Therefore, 6.5 pH was selected as the optimum pH value for the current research.

Simultaneous and Interference Analysis
The CV method was used for the inspection of 0.01 mM ICN in presence of 0.1 mM TN at the surface of BCNTPE (curve-a) and P(PAN)LCNTPE (curve-b) in PB (0.2 M and 6.5 pH) at 0.1 Vs −1 scan rate. In Figure 8a, BCNTPE reveals lower electrochemical activity with a low redox peak for ICN and low oxidation peak for TN. Nonetheless,

Simultaneous and Interference Analysis
The CV method was used for the inspection of 0.01 mM ICN in presence of TN at the surface of BCNTPE (curve-a) and P(PAN)LCNTPE (curve-b) in PB (0.2 6.5 pH) at 0.1 Vs −1 scan rate. In Figure 8a, BCNTPE reveals lower electrochemical with a low redox peak for ICN and low oxidation peak for TN. None

Simultaneous and Interference Analysis
The CV method was used for the inspection of 0.01 mM ICN in presence of 0.1 mM TN at the surface of BCNTPE (curve-a) and P(PAN)LCNTPE (curve-b) in PB (0.2 M and 6.5 pH) at 0.1 Vs −1 scan rate. In Figure 8a, BCNTPE reveals lower electrochemical activity with a low redox peak for ICN and low oxidation peak for TN. Nonetheless, P(PAN)LCNTPE displays a good and well-defined redox peak for ICN and an oxidation peak for TN. These results clarify that the elevated catalytic nature of P(PAN)LCNTPE for the redox action of ICN with TN (presence and absence) is approximately similar. Additionally, the interference effect on the surface of the modified electrode was tested for the electrochemical behavior of ICN in the presence of different organic molecules such as alizarin red (AR), erythromycin (ECN), methyl orange (MO), riboflavin (RF), TN, sucrose (SR), and Congo red (CR). The results are shown in Figure 8b. Here, only less than ±5.0% of signal change in ICN electrochemical oxidation is observed with respect to the base potential of ICN at P(PAN)LCNTPE. Therefore, the proposed P(PAN)LCNTPE shows acceptable anti-interferent and is good for simultaneous analysis even in the presence of different organic interferents.
Chemosensors 2022, 10, x FOR PEER REVIEW 11 of 15 P(PAN)LCNTPE displays a good and well-defined redox peak for ICN and an oxidation peak for TN. These results clarify that the elevated catalytic nature of P(PAN)LCNTPE for the redox action of ICN with TN (presence and absence) is approximately similar. Additionally, the interference effect on the surface of the modified electrode was tested for the electrochemical behavior of ICN in the presence of different organic molecules such as alizarin red (AR), erythromycin (ECN), methyl orange (MO), riboflavin (RF), TN, sucrose (SR), and Congo red (CR). The results are shown in Figure 8b. Here, only less than ±5.0% of signal change in ICN electrochemical oxidation is observed with respect to the base potential of ICN at P(PAN)LCNTPE. Therefore, the proposed P(PAN)LCNTPE shows acceptable anti-interferent and is good for simultaneous analysis even in the presence of different organic interferents.

Limit of Detection and Quantification
The electrochemical-based redox nature of ICN was examined by changing its concentration in the range of 0.2 µM to 10.0 µM in PB (0.2 M & 6.5 pH) at the modified electrode surface (P(PAN)LCNTPE) using the CV method (0.1 Vs −1 scan rate) and the recorded cyclic voltammograms are displayed in Figure 9a. Here, the concentration of ICN and Ipa and Ipc of ICN are proportional to each other, and they provide a good linear relationship. In this contrast, we considered anodic peak current as an analytical signal to plot a calibration curve and the results are noticed in the plot of Ipa vs.
[ICN] shown in Figure 9b. The linear relation among Ipa vs.
[ICN] is shown as Ipa (A) = 9.265 × 10 −7 + 0.096 [ICN] (M) & R 2 = 0.999. The ICN-detecting ability of P(PAN)LCNTPE was studied using the limit of detection (LOD) and limit of quantification (LOQ). The values of LOD and LOQ are calculated using the relations of LOD = 3 (Standard deviation of the blank/Slope of the calibration curve) and LOQ = 10 (Standard deviation of the blank/Slope of the calibration curve). The calculated value of LOD and LOQ were found to be 0.021 µM and 0.072 µM, correspondingly. The attained LOD and prepared electrode were contrasted with the earlier ICN electrochemical sensors, and the assessment data is documented in Table 2 [27,[30][31][32][33].

Limit of Detection and Quantification
The electrochemical-based redox nature of ICN was examined by changing its concentration in the range of 0.2 µM to 10.0 µM in PB (0.2 M & 6.5 pH) at the modified electrode surface (P(PAN)LCNTPE) using the CV method (0.1 Vs −1 scan rate) and the recorded cyclic voltammograms are displayed in Figure 9a. Here, the concentration of ICN and I pa and I pc of ICN are proportional to each other, and they provide a good linear relationship. In this contrast, we considered anodic peak current as an analytical signal to plot a calibration curve and the results are noticed in the plot of I pa vs. [ICN] shown in Figure 9b. The linear relation among I pa vs.
[ICN] is shown as I pa (A) = 9.265 × 10 −7 + 0.096 [ICN] (M) & R 2 = 0.999. The ICN-detecting ability of P(PAN)LCNTPE was studied using the limit of detection (LOD) and limit of quantification (LOQ). The values of LOD and LOQ are calculated using the relations of LOD = 3 (Standard deviation of the blank/Slope of the calibration curve) and LOQ = 10 (Standard deviation of the blank/Slope of the calibration curve). The calculated value of LOD and LOQ were found to be 0.021 µM and 0.072 µM, correspondingly. The attained LOD and prepared electrode were contrasted with the earlier ICN electrochemical sensors, and the assessment data is documented in Table 2 [27,[30][31][32][33].

Stability, Repeatability and Reproducibility
The stability, repeatability, and reproducibility of the proposed electrochemical sensor (P(PAN)LCNTPE) were inspected by recording the cyclic voltammograms for a redox reaction of 0.01 mM ICN in PB (0.2 M & 6.5 pH) at a scan rate of 0.1 Vs −1 . The P(PAN)LCNTPE stability was analyzed by recording cyclic voltammograms by driving 25 CV cycles (fifty CV segments) at a scan rate of 0.1 Vs −1 . Here, the stability of the sensor was calculated using the initial and final electrochemical peak currents and the value was about 92.22%, which proposes acceptable P(PAN)LCNTPE stability. P(PAN)LCNTPE repeatability was verified based on five successive CV cycles for ICN analyte (changed at the end of each cycle) at the surface of constantly fixed P(PAN)LCNTPE. Here, all five cyclic voltammograms show a nearer oxidation peak current for ICN at P(PAN)LCNTPE with the relative standard deviation value of 0.544%, which proposes an adequate P(PAN)LCNTPE repeatability. P(PAN)LCNTPE reproducibility was confirmed with re-

Stability, Repeatability and Reproducibility
The stability, repeatability, and reproducibility of the proposed electrochemical sensor (P(PAN)LCNTPE) were inspected by recording the cyclic voltammograms for a redox reaction of 0.01 mM ICN in PB (0.2 M & 6.5 pH) at a scan rate of 0.1 Vs −1 . The P(PAN)LCNTPE stability was analyzed by recording cyclic voltammograms by driving 25 CV cycles (fifty CV segments) at a scan rate of 0.1 Vs −1 . Here, the stability of the sensor was calculated using the initial and final electrochemical peak currents and the value was about 92.22%, which proposes acceptable P(PAN)LCNTPE stability. P(PAN)LCNTPE repeatability was verified based on five successive CV cycles for ICN analyte (changed at the end of each cycle) at the surface of constantly fixed P(PAN)LCNTPE. Here, all five cyclic voltammograms show a nearer oxidation peak current for ICN at P(PAN)LCNTPE with the relative standard deviation value of 0.544%, which proposes an adequate P(PAN)LCNTPE repeatability. P(PAN)LCNTPE reproducibility was confirmed with respect to five successive CV cycles for a constantly fixed ICN analyte at the surface of P(PAN)LCNTPE (changed at the end of each cycle). Here, all the recorded cyclic voltammograms showed a closer oxidation peak current value for ICN at P(PAN)LCNTPE with a relative standard deviation value of 1.025%, which suggests decent P(PAN)LCNTPE reproducibility. The results related to stability, repeatability, and reproducibility are shown in Figure 10. Here, all the recorded cyclic v ammograms showed a closer oxidation peak current value for ICN at P(PAN)LCNT with a relative standard deviation value of 1.025%, which suggests dec P(PAN)LCNTPE reproducibility. The results related to stability, repeatability, and producibility are shown in Figure 10.

Analysis of Water Sample
To authenticate the resolution of the projected P(PAN)LCNTPE by examining I in a water sample (the tap water is used as a real sample and it was collected from municipality water tank, Madikeri, India). The operated CV method was used for I inspection in a tap water sample in PB (0.2 M & 6.5 pH) at a scan rate of 0.1 Vs −1 at surface of the projected P(PAN)LCNTPE. Here, the tap water sample did not give voltammetric response for ICN, hence the ICN investigation was completed in the water sample using the typical spike recovery method with three trials for each addit The P(PAN)LCNTPE provided decent recovery for ICN in tap water samples under standard addition method ranging from 97.80 ± 0.0005% to 100.40 ± 0.001%, and the stitute outcomes are tabulated in Table 3.

Analysis of Water Sample
To authenticate the resolution of the projected P(PAN)LCNTPE by examining ICN in a water sample (the tap water is used as a real sample and it was collected from the municipality water tank, Madikeri, India). The operated CV method was used for ICN inspection in a tap water sample in PB (0.2 M & 6.5 pH) at a scan rate of 0.1 Vs −1 at the surface of the projected P(PAN)LCNTPE. Here, the tap water sample did not give the voltammetric response for ICN, hence the ICN investigation was completed in the tap water sample using the typical spike recovery method with three trials for each addition. The P(PAN)LCNTPE provided decent recovery for ICN in tap water samples under the standard addition method ranging from 97.80 ± 0.0005% to 100.40 ± 0.001%, and the institute outcomes are tabulated in Table 3.

Conclusions
In this research, the simple, responsive, and low-priced electrochemical sensors: P(PAN)LCNTPE and BCNTPE were prepared using an eco-friendly procedure for the sensitive and selective ICN electrochemical analysis in presence of TN. The surface of CNTPE was effectively activated by developing an active layer of P(PAN) through a simple electrochemical polymerization approach. The enhanced electrochemical surface area of P(PAN)LCNTPE developed a faster rate of electron transference during the ICN redox reaction with elevated electrocatalytic action and more active spots than the BCNTPE. The surface features of P(PAN)LCNTPE and BCNTPE were confirmed successfully by means of FE-SEM, CV, and EIS approaches. The P(PAN)LCNTPE frames an improved electrochemical response with good linear correlation, lower LOD, higher stability, repeatability, and reproducibility toward the analysis of the redox nature of ICN. Furthermore, the projected P(PAN)LCNTPE and the CV technique retain superb ICN recapture in a tap water sample with fine recovery in the range of 97.80% to 100.40%.