Polyaromatic hydrocarbons (PAHs) are typically present in environmental samples at very low concentrations. Therefore, extensive sample preparation is necessary to enhance the signal for analytical determination of these compounds by classical methods based on chromatography or spectroscopy. In this study an electrochemical sensor for anthracene based on polyamic acid- graphene oxide (PAA-GO) nanocomposite electrode was prepared for application in the direct analysis of small volumes of samples with minimal pre-treatment steps. Polyamic acid and graphene oxide (GO) are materials with well-defined electrochemistry of their own and both are readily synthesised under ambient laboratory conditions. The sensor was prepared by cyclic voltammetric co-deposition of PAA and GO onto a commercial screen printed carbon electrode (SPCE) in five voltammetric cycles with initial and switch potentials of -1000 mV and +1000 mV, respectively, at a potential scan rate of 50 mV/s. The sensor materials (GO, PAA and PAA-GO) were characterised by Fourier transform infrared spectroscopy (FTIR), high resolution scanning electron microscopy (HRSEM) and cyclic voltammetry (CV), while their corresponding screen printed electrode systems (GO/SPCE, PAA/SPCE and PAA-GO/SPCE) were evaluated as possible chemical sensors for anthracene.
The measurement of antibiotics in environmental water systems is increasingly becoming a top priority for global environmental watchdog organisations, as the looming threat of emerging contaminants moves to centre stage. A novel chemical sensor based on polyamic acid (PAA) semiconducting polymer and cobalt nanoparticles (CoNP) was developed and used to demonstrate proof of concept evidence for measurement of norfloxacin at trace concentrations in aqueous systems. Polyamic acid and cobalt nanoparticles were both chemically synthesised and characterised using Fourier transform infrared spectroscopy, transmission electron microscopy, cyclic voltammetry and small angle x-ray scattering. The polyamic acid and cobalt nanoparticles were electrodeposited onto screen printed carbon electrodes to produce novel composite sensors (SPCE/PAA/CoNP). The polymer composite chemical sensors were applied to the detection of norfloxacin in the micromolar concentration using square wave voltammetry, with a sensitivity of 18.0 � 6.59 μA/mM, calculated from the slope of the calibration curve and a limit of detection (LOD) of 0.979 � 0.419 mM, with LOD = 3.3(Sy/S). The SPCE/PAA/ CoNP sensor response to norfloxacin as measured by electrochemical impedance spectroscopy, yielded a sensitivity of 17.6 � 8.72 Ω/mM as and a limit of detection (LOD) of 0.228 � 0.0935 mM.
Polyamic acid (PAA) thin films were prepared by electrodepositing PAA onto indium tin oxide (ITO) electrode and characterized using electrochemical methods (cyclic voltammetry, square wave voltammetry), Ultraviolet Visible spectroscopy and Ultraviolet Visible/Spectro-electrochemistry (UV/vis Spectro-electrochemistry). The electrodeposited PAA thin films were observed to have two redox couples with a formal of 118 mV and 274 mV. The diffusion coefficient (De) determined from cyclic voltammetry was found to be 7.9x10-6 cm2/s and provide a measure of how fast charge is transported through the thin film. PAA showed a broad absorption peak at 214 nm due to the carbonyl chromophores within the polymer and shoulder peak at 293 nm from a quinoid-type chromophore. The calculated band gap of 4.23 eV suggested the polymer was optically transparent between 300 nm to 800 nm. This indicated that the PAA thin films has emerged as a very promising and cost effective alternative material to ITO with good transparent and conductive properties. PAA thin films were further applied for the detection of anthracene. The analytical response of anthracene was studied at the ITO/PAA using spectro-electrochemistry. The characteristic analytical absorbance signal for anthracene was clearly identified at 375 nm when ITO/PAA electrode was polarised at -800 mV (vs Ag/AgCl). The calibration curve for anthracene showed a linear response from 4.95x10-4 to 1.15x10-2 M. The ITO/PAA showed a low detection limit of (0.0068 g/L) and high sensitivity for anthracene, making it a suitable platform for spectro-electrochemical analysis of polycyclic aromatic hydrocarbons.
Polyamic acid (PAA) nanofibers produced by using the electrospinning method were fully characterized in terms of morphology and spectroscopy. A PAA nanofiber–modified screen-printed carbon electrode was applied to the detection of selected sulfonamides by following an electroanalytical protocol. The polyamic acid (PAA) nanofibers were characterized using Fourier transform infrared (FTIR) spectroscopy to study the integrity of polyamic acid functional groups as nanofibers by comparing them to chemically synthesized polyamic acid. A scanning electron microscope (SEM) was used to confirm the morphology of the produced nanofibers and 3D arrangement at the electrode interface. The Brunauer–Emmett–Teller (BET) method was used to determine the surface area of the nanofibers. Atomic force microscopy (AFM) was used to study the porosity and surface roughness of the nanofibers. Electrochemical evaluation based on diffusion-controlled kinetics was applied to determine the number of electrons transferred in the system, the surface concentration of the deposited PAA thin film (2.14 × 10−6 mol/cm2), and the diffusion coefficient (De) for the PAA nanofiber–modified screen-printed carbon electrode (9.43 × 10−7 cm−2/s). The reported LODs for sulfadiazine and sulfamethazine detection are consistent with requirements for trace-level monitoring by early warning diagnostic systems.
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