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In this study, an innovative nanocomposite of multiwalled carbon nanotubes (MWCNTs), copper oxide nanoparticles (CuONPs) and lignin (LGN) polymer were successfully synthesized and used to modify the glassy carbon electrode for the determination of chlorogenic acid (CGA). Cyclic voltammetry (CV) emphasised a quasi-reversible, adsorption controlled and pH dependent electrode procedure. In cyclic voltammetry a pair of well distinct redox peaks of CGA were observed at the LGN-MWCNTs-CuONPs-GCE in 0.1 M phosphate buffer solution (PBS), at pH 2. The synthesized nanoparticles and nanocomposites were characterized by Fourier transformation infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and x-ray diffraction (XRD) analyses. Differential pulse voltammetry (DPV) was applied to the anodic peak and used for the quantitative detection of CGA. Under optimal conditions, the proposed sensor showed linear responses from 5 μM to 50 μM, the linear regression equation I pa (μA) = 2.6074 C-5.1027 (R 2 = 0.995), whilst the limit of detection (LOD) and limit of quantifications (LOQ) were found to be 0.0125 μM and 0.2631 μM respectively. The LGN-MWCNTs-CuONPs-GCE were applied to detect the CGA in real coffee samples with the recovery ranging from 97 to 106 %. The developed sensor was successfully applied for the analysis of CGA content in the coffee samples. In addition, electrophilic, nucleophilic reactions and chlorogenic acid docking studies were carried out to better understand the redox mechanisms and were supported by density functional theory calculations.

The present work involves the fabrication of glassy carbon electrode (GCE) with iron oxide nanoparticles (Fe 3 O 4 NPs) and multiwalled carbon nanotubes (MWCNTs) composite. Further it was immobilized with Coenzyme q (Co en-q/ Fe 3 O 4 NPs/MWCNTs/GCE) to enhance the electrochemical performance of the modified electrode for the determination of rifampicin (RIF). The designed sensor was successfully characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), thermo gravimetry (TGA) and x-ray diffraction (XRD) studies. The electrochemical oxidation of RIF has been studied by cyclic voltammetry (CV) and differential pulse voltammetric techniques (DPV). The enzyme immobilized sensor surface area was calculated and found to be 10.03 mm 2 . This larger surface area was responsible for the oxidation of more number of RIF molecules on the surface of sensor. The RIF shows two anodic peaks at + 0.10 V and + 0.72 V in phosphate buffer solution (PBS) pH 7.5. The cyclic voltammetric measurements reveals that the developed sensor exhibited an enhanced electrochemical platform with an approximately eight-fold increment in the anodic peak currents. Under the optimized conditions, a good linear relationship was observed between peak currents and RIF concentration. The studied linearity range (2 -20 µM) showed a limit of detection (LOD) of 0.032 µM, 0.413 µM and limit of quantification (LOQ) of 1.069 µM, 1.258 µM for anodic peaks I and peaks II respectively. The proposed sensor showed longstanding stability and high reproducibility. The method was successfully applied for the determination of RIF in pharmaceutical tablets without any sample pre-treatment.

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