Krystyna Jackowska

New trends in the electrochemical sensing of dopamine

Since the early 70s electrochemistry has been used as a powerful analytical technique for monitoring electroactive species in living organisms. In particular, after extremely rapid evolution of new micro and nanotechnology it has been established as an invaluable technique ranging from experiments in vivo to measurement of exocytosis during communication between cells under in vitro conditions. This review highlights recent advances in the development of electrochemical sensors for selective sensing of one of the most important neurotransmitters—dopamine. Dopamine is an electroactive catecholamine neurotransmitter, abundant in the mammalian central nervous system, affecting both cognitive and behavioral functions of living organisms. We have not attempted to cover a large time-span nor to be comprehensive in presenting the vast literature devoted to electrochemical dopamine sensing. Instead, we have focused on the last five years, describing recent progress as well as showing some problems and directions for future development.

Template synthesis of polyaniline and poly(2-methoxyaniline) nanotubes: comparison of the formation mechanisms

The process of polyaniline (PANI), poly(2-methoxyaniline) (POMA) nanotubes formation was investigated. Polyaniline and poly(2-methoxyaniline) nanotubes were prepared by chemical in situ deposition within the pores of polycarbonate membranes. It was found that the formation of polyaniline and poly(2-methoxyaniline) proceeds by two substantially different mechanisms. In the case of PANI, the polymer is first formed in the polymerization solution (the solution containing the monomer and oxidant, where the polycarbonate substrate is placed), and then it precipitates on/into the membrane. In the case of POMA, the oxidized 2-methoxyaniline molecules are first adsorbed on polycarbonate surface, and then, as a consequence of their accumulation, they recombine to form the polymer.

SERS of 1,8-diaminonaphthalene on gold, silver and copper electrodes polymerisation and complexes formed with the electrode material

Abstract Oxidation of 1,8-diaminonaphthalene (1,8DAN) on gold, silver and copper electrodes has been studied by SERS spectra. SERS results have been compared with Raman spectra of poly-1,8DAN thin film deposited on the platinum support. Oxidation of 1,8DAN on gold and silver electrodes leads to polymerisation. The pretreatment of the silver electrode influences the polymerisation: exposing the silver electrode to day light during the ORC procedure encourages growth of the polymer layer. In the case of a copper electrode the Cu 2+ -(1,8DAN) n complex is formed.

Effect of anions on the electrosynthesis, electroactivity and molecular structure of poly(o-methoxyaniline)

Abstract The effect of different anions (Cl − , ClO 4 − ) on the electrooxidation of o -methoxyaniline ( o -MA), on the electroactivity of poly( o -methoxyaniline) (POMA) and on the molecular structure of the polymer has been studied. It has been found that the rate of o -MA oxidation is much higher in HCl than in HClO 4 solution. It was also found that the nucleation and growth mechanisms of POMA films depend on anions being diffusion-controlled progressive nucleation with three-dimensional growth in HCl solution and two-dimensional growth in HClO 4 . It was shown that the electroactivity of POMA depends on the composition of the polymerization bath and that the ability of POMA degradation increases in HCl solution.

Sensitivity of poly 1,8-diaminonaphthalene to heavy metal ions — electrochemical and vibrational spectra studies

Abstract The sensitivity of poly(1,8-diaminonaphthalene) [poly(1,8-DAN)] to heavy metal ions (Ag + , Hg 2+ , Cu 2+ ) was studied by means of electrochemical (open circuit potential (oep), cyclic voltammetry) and spectroscopic methods (IR, Raman spectra). Changes of the open circuit potential of the polymer electrode indicate that (Ag + and Hg 2+ ions are able to oxidise poly(1,8-DAN), while Cu 2+ ions do not influence the oep of the polymer. Cyclic voltammograms of poly(1,8-DAN) give direct evidence that Ag + ions are reduced at the polymer surface whereas Hg 2+ or Hg 2 2+ ions are bonded by the polymer matrix, IR and Raman spectra indicate that Cu 2+ and Hg 2+ or Hg 2 2+ ions are complexed by the amino groups of the polymer.

In situ Raman studies of polypyrrole and polythiophene films on Pt electrodes

Abstract In situ Raman spectra of polypyrrole and polythiophene films were studied in order to describe the processes which occur during their electrochemical reduction and oxidation. It was shown that for both polymers these processes are influenced by the medium in contact with the film. The results obtained indicate that the molecular properties of the conducting polymers at various stages of an oxidation are better revealed by in situ Raman spectra than by ex situ studies.

Electrooxidation of O-methoxyaniline as studied by electrochemical and SERS methods

Abstract The electrooxidation of o -methoxyaniline ( o -MA) has been studied by electrochemical and surface-enhanced Raman scattering (SERS) methods. The electrochemical measurements showed that the early stages of o -MA electropolymerization were affected by both the monomer to acid concentration ratio and by the acid concentration. The SERS experiments demonstrated the C-N coupling mechanism of o -MA dimerization or oligomerization. The results of both methods indicate that the intermediate redox couple observed in electrochemical response of poly ( o -methoxyaniline) can be assigned to the incorporated dimer probably having the cyclic structure.

Spectroelectrochemical and EPR determination of the number of electrons transferred in redox processes in electroactive polymers. Polyindole films

Abstract The spectroelectrochemical (visible range—VIS) and in situ electron paramagnetic resonance (EPR) measurements were carried out for electroactive polyindole films. Both EPR and absorption VIS spectra were analyzed using the Nernst equation. The number of electrons transferred per monomer unit during the redox process in the polymer ( n ) as determined from both types of spectra is equal to 0.14 (VIS spectra) or 0.16 (EPR). The applicability of EPR data to determine the n value was verified by measurements for polypyrrole film. It seems that EPR spectra provide more credible values of the number of transferred electrons in redox reactions in the polymer matrix.

SERS spectra as evidence of pyrrole and thiophene polymerization on silver electrodes

Abstract Raman spectroscopic (SERS) evidence is given for the formation of polypyrrole, oligomeric units of thiophene and, probably, polythiophene on a rough silver electrode. Electrochemical experiments indicated that they are promoted by an unreduced product of silver oxidation (a small amount of AgCl) remaining on the electrode surface after its roughening by an oxidation-reduction cycle. A mechanism for the oxidation of pyrrole and thiophene by photochemical reduction of AgCl is suggested.

In situ Raman studies of polypyrrole formation on a silver electrode

Abstract Raman spectroscopic evidence is given for the formation of polypyrrole on some silver electrode surfaces. Oxidation of pyrrole and its subsequent polymerisation is merely promoted by the electrode surface illuminated by daylight during oxidation—reduction cycle. For the silver electrode roughened under neonlight conditions SERS spectrum of adsorbed pyrrole molecules was only observed.