Poly (Orange CD) sensor for paracetamol in presence of folic acid and dopamine

In the present work, Orange CD was chosen as an intriguing modifier for the electropolymerization on the surface of CPE by the CV technique. A novel, sensitive, and cost-effective poly (Orange CD) MCPE (PoOCD/MCPE) sensor was utilized for the selective detection of paracetamol (PA) in 0.2 M phosphate buffer solution (PBS) of pH 7.4. The oxidation peak current of PA was vastly enhanced at the sensor. The scan rate study is suggested that electro-oxidation of PA was adsorption-controlled. The pH study testifies the redox pathways transport with the same quantity of electrons and protons. The detection limit of PA is found to be 2.64 µM. DPV results show that substantial peak separation between PA, folic acid (FA), and dopamine (DA) could be facilitating their individual and simultaneous determination on the sensor. The decorated sensor demonstrates high sensitivity, stability, reproducibility, repeatability and has been successfully exploited for the detection of PA in a tablet with promising results.

Preparation of paracetamol tablet sample. In a mortar, a 500 mg of Calpol pill was acquired from local drug stores (Shivamogga, India) was finely pulverized. In a 100 ml flask, an adequate amount of homogenous white powder was dissolved in water. The solution was thoroughly agitated to get the appropriate concentration before being utilized in pharmaceutical sample analysis.
Working electrode construction. The bare CPE was prepared as described in the literature 40 . The PoOCD/MCPE was constructed by dipping bare CPE into 1 mM aqueous Orange CD with NaOH (0.1 M) as a supporting electrolyte. The electrochemical polymerization was performed at the potential between − 0.6 and 1.6 V with a scan rate (SR) of 100 mVs −1 using ten cycles. Then obtained electropolymerized electrode was rinsed in the DDW to eliminate unreacted molecules.

Results and discussion
Electrochemical polymerization of Orange CD on bare CPE. Figure 1 shows the CVs of electrochemical polymerization of 1 mM aqueous orange CD with NaOH (0.1 M) on the bare CPE surface in the potential cycling between − 0.6 and 1.6 V with SR of 100 mVs −1 using ten cycles. The examination of voltammograms by gradually increasing the progressing electropolymerization procedure reveals accumulation and growth of orange CD film on the surface of bare CPE 41 . The polymer film thickness affects the electrochemical response of the modified electrode. The film thickness was easily managed by regulating the number of voltammetric scans from 5 to 25 during electropolymerization. The experimental results analogous to it were obtained for the PA as shown in Fig. 2. As the current response achieves a maximum at ten multiple cycles, the optimum cycle number of ten was selected for the construction of PoOCD/MCPE and further voltammetric measurements.
Characterization of PoOCD/MCPE. For investigation of electrocatalytic activity of the MCPE, a potassium ferrocyanide system was used. Figure 3 displays the electrochemical activity of K 4 [Fe(CN) 6 ] (freshly prepared) at bare CPE (A) and PoOCD/MCPE (B) containing 1 M KCI as supporting electrolyte obtained at an SR of 100 mVs −1 was recorded by CV method. The small redox peak current signal corresponds to bare CPE while PoOCD/MCPE shows enhanced peak current showing the dramatic increase in the rate of electron transfer 33 . According to Randles-Sevick's Eq. (1), the electrocatalytic surface area of both bare CPE and MCPE was calculated 42 .   www.nature.com/scientificreports/ The area of bare CPE (0.0295 cm 2 ) is less than PoOCD/MCPE area (0.0499 cm 2 ) which indicates that Orange CD acts as an effective modifier contributing a large surface and promotes the electron transfer between the electrode and the solution.
The surface morphological features of bare CPE and PoOCD/MCPE were characterized by SEM. The SEM of bare CPE (Fig. 4a) appears to be a rough surface with irregularly shaped and PoOCD/MCPE (Fig. 4b) appears to be a smooth with consistent ordering of the polymer film of Orange CD on the CPE surface. The remarkable distinction in the surface structure of both electrodes confirms the remarkable modification of the CPE surface by electropolymerized Orange CD.

Voltammetric measurements. The electrochemical response of PA was studied on the bare CPE (A) and
PoOCD/MCPE (B) in 0.2 M PBS (pH 7.4) at an SR 100 mVs −1 by CV method as displayed in Fig. 5. An irreversible voltammogram was obtained at bare CPE for PA with an anodic peak potential of 0.357 V indicating the poor response as well as the occurrence of only oxidation. But at the same condition, PoOCD/MCPE exhibited a significant increase in the current signals giving a sharp reversible voltammogram. The anodic and cathodic peak potential for PA were found to be 0.349 V and 0.320 V respectively reveals the occurrence of both oxidation and reduction at proposed PoOCD/MCPE.
(3) and (4) 6,46 for PA were found to be 2.64 µM and 8.81 µM respectively. The LOD of this modified electrode for the estimation of PA in comparison to other reported electrodes is given in Table 2 where S is the standard deviation, M is the slope.
The pH plays a remarkable role in asses the number of participating electrons and protons in the oxidation mechanisms of the PA. The increase of pH (6.2-7.8) over PA (10 µM) oxidation at PoOCD/MCPE shifts Epa towards a more negative direction as analyzed by CV are shown in Fig. 12. Figure 13 illustrates the Epa vs pH values of PA graph that are linear with a slope of 0.0601 V/pH (R 2 = 0.995). This suggests that during the oxidation of the PA, the same number of protons and electrons are participated 3,47 and the possible electrooxidation was shown in Scheme 2.
Simultaneous resolution of analytes PA, FA and DA. This study aimed to utilize the developed sensor for the selective and sensitive estimation of PA in the existence of FA and DA. Figure 14 illustrates the CVs       www.nature.com/scientificreports/ Interference studies. Studies were conducted by the DPV method in the solution mixture containing PA, FA, and DA at PoOCD/MCPE. The concentration of one analyte was varied, whereas the others were kept constant. Figure 15 illustrates the DPVs of PA by increasing the concentration of PA from 10 to 60 µM when holding the concentration of FA and DA constant. The oxidation peak current of PA increased linearly with increasing PA concentration from 10 to 60 µM and anodic peak current for FA and DA remaining constant. Similarly, it was also observed that the peak potentials remain unaltered with any enhancement in the peak current for the other  Repeatability, reproducibility and stability study.