A highly explicit electrochemical biosensor for catechol detection in real samples based on copper-polypyrrole

Abstract

Catechol is a pollutant that can lead to serious health issues. Identification in aquatic environments is difficult. A highly specific, selective, and sensitive electrochemical biosensor based on a copper-polypyrrole composite and a glassy carbon electrode has been created for catechol detection. The novelty of this newly developed biosensor was tested using electrochemical techniques. The charge and mass transfer functions and partially reversible oxidation kinetics of catechol on the redesigned electrode surface were examined using electrochemical impedance spectroscopy and cyclic voltammetry scan rates. Using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry, the characteristics of sensitivity (8.5699 μA cm^-2), LOD (1.52 × 10^-7 μM), LOQ (3.52 × 10^-5 μM), linear range (0.02-2500 μM), specificity, interference, and real sample detection were investigated. The morphological, structural, and bonding characteristics were investigated using XRD, Raman, FTIR, and SEM. Using an oxidation-reduction technique, a suitable biosensor material was produced. In the presence of interfering compounds, it was shown that it was selective for catechol, like an enzyme.

Scheme 1. (a) Formation of polypyrrole (PPy) in the presence of an oxidizing agent (ammonium persulfate). (b) Formation of polypyrrole incorporated around Cu NPs dispersed in pyrrole. Dotted lines show the interaction between π electrons, N–H, and copper NPs.

Fig. 1. Electrochemical responses of bare GCE and modified electrodes in 0.1 M PBS/1.0 M KCl: (a) comparative voltammograms of bare GCE, GCE@Cu, GCE@PPy, and GCE@Cu-PPy; (b) scan rate voltammograms from 5 mV s⁻¹ to 100 mV s⁻¹; (c) pH study showing CV plots at various pH values (pH 5 to 13) against current (μA).

Fig. 2. Data plots of Cu NPs, PPy, and Cu-PPy: (a) XRD spectra of Cu NPs, PPy, and Cu-PPy; (b) Raman shift spectra of Cu NPs, PPy, and Cu-PPy; (c) FTIR absorbance spectra of (a) Cu NPs, (b) PPy, and (c) Cu-PPy.

Fig. 3. Surface morphology of PPy, Cu NPs, and Cu-PPy; SEM micrographs: (a) PPy, (b) Cu NPs, (c) Cu-PPy composite. (d) EDX: energy dispersive spectra of Cu NPs.

Scheme 2. Oxidation of catechol at the surface of GCE@Cu-PPy.

Fig. 4. Electrochemical responses of GCE@Cu-PPy as a CAT sensor: (a) CV voltammograms of GCE@Cu-PPy at different concentrations of CAT (100–1100 μL), (b) DPV plots at different concentrations of CAT (100–2500 μL).

Fig. 5. (a) EIS (Nyquist plot) comparison of CAT with bare GCE and modified GCE@Cu-PPY working electrode in the blank solution and in the presence of 100 μL of CAT. (b) Nyquist plots with varying [CAT], GCE@Cu-PPy as working electrode at different concentrations of CAT (100–1300 μL); inset: equivalent circuit (CPE; constant phase element with diffusion).

Fig. 6. (a) Chronoamperometry plot of a standard solution of CAT (5 mM) with injection at 100 μL/50 s, (b) chronoamperometry of CAT in a real sample with injection at 100 μL/100 s.

Fig. 7. (a) DPV plots after four weeks in the presence of 500 μL (5 mM) of CAT with four electrodes stored at room temperature. (b) Oxidative current (I_pa) vs. square root of scan rate (ν^1/2) and reduction current (I_pc) vs. square root of scan rate (ν^1/2) plots. (c) I_pavs. pH. (d) Amperogram interference study with GCE@Cu-PPy biosensor in the presence of interfering species injected at a rate of 100 μL/100 s CAT solution.

Fig. 8. (a) Comparison regression (R²) vs. techniques used in the electrochemical study of GCE@Cu-PPy. (b) SEM image of the Cu-PPy composite after testing.