Electrochemical nitrite nanosensor developed with amine- and sulphate-functionalised polystyrene latex beads self-assembled on polyaniline

Aniline doped with polyvinyl sulphonate (PV-SO₃⁻) was electropolymerised on screen printed carbon (SPCE) and glassy carbon (GCE) electrodes. Then nano-structured polystyrene (PS_NP) latex beads functionalised with amine (PS_NP-NH₂) and sulphate (PS_NP-OSO₃⁻) were self-assembled on the modified SPCE and GCE. The resultant polyaniline nanocomposites (PANI|PS_NP-NH₂ or PANI|PS_NP-OSO₃⁻) were characterised by cyclic voltammetry (CV), UV-vis spectroscopy and scanning electron microscopy (SEM). Brown-Anson analysis of the multi-scan rate CV responses of the various PANI films gave surface concentrations of the order of 10⁻⁸ mol cm⁻². UV-vis spectra of the PANI films dissolved in dimethyl sulphoxide showed typical strong absorbance maxima at 480 and 740 nm associated with benzenoid π-π* transition and quinoid excitons of polyaniline, respectively. The SEM images of the PANI nanocomposite films showed cauliflower-like structures that are <100 nm in diameter. When applied as electrochemical nitrite sensor, sensitivity values of 60, 40 and 30 μA/mM were obtained for electrode systems containing PANI|PS_NP-NH₂, PANI and PANI|PS_NP-SO₃⁻, respectively. The corresponding limits of detection of the sensors were 7.4, 9.2 and 38.2 μM NO₂⁻.     

Electrochemical studies of the nickel catecholate complexes for detection of sulphur dioxide gas

Nickel catecholate complexes, bis(diphenylphosphino)ethanenickelcatecholate [(dppe)NiO₂C₆H₃4-R₁] R₁ = CH₃ (1), C(CH₃)₃ (2), H (3) and F (4)] were studied using CV and SWV techniques between −1.5 and +1.5 V at 50 mV s⁻¹ in cathodic and anodic sweeps. Glassy carbon electrode was used with 0.1 M tetrabutylammonium tetrafluroborate (TBATFB) in CH₂Cl₂. Complexes 1-4 before addition of SO₂, showed approximately reversible behaviour (i_pa/i_pc ≈ 1 and ΔE ≈ 77-88 mV); oxidation peaks observed between +313 and +524 mV, reduction peaks between +225 and +436 mV, depending on the substituent on the ligand. Detection limit 0.01 ppm, linear range 0.01-20 ppm, sensitivity 0.02 ppm/mV (with SWV) were obtained. The complexes 1 and 2 could be used as voltammetric sensors while complexes 3 and 4 would be suitable as amperometric sensors, for monitoring industrial SO₂ emissions.     

Spectroscopic and microscopic evaluation of immobilized cytochrome c interaction with cyanide/arsenic ligands in quantitative analysis

The electrochemical, spectroscopic and microscopic analyses of cytochrome c and its immobilization on bare glassy carbon (GC) and platinum (Pt) electrodes were performed. Cytochrome c interaction was examined by studying cyanide and arsenic as model compounds for these types of behavior. Subtractively normalized interfacial Fourier transform infrared (SNIFTIR) spectroscopy, fluorescence and electrochemical methods, Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM) were used to characterize the protein in the immobilized state and to confirm that the protein was not denatured upon binding to the pre-treated bare GC and Pt electrodes. The spherical morphology of the immobilized protein, which is typical of native cytochrome c, was observed using AFM. The protein binding was monitored as a decrease in peak currents (by CV) for the immobilized protein. Under analysis was also a decrease in emission intensities by fluorescence in solution, by the FTIR and SNIFTIR spectroscopies. Fluorescence and AFM proved the existence of the binding process between the protein and the analytes. This behavior was confirmed by the FTIR and SNIFTIR spectroscopies, which gave evidence that the binding event took place at the amino acids side chain of the protein.