Refine
Document Type
Language
- English (7)
Keywords
- Electropolymerization (2)
- Gas sensor (2)
- Chemoresistor (1)
- Conductometric chemosensor (1)
- Fire detector (1)
- Four-point technique (1)
- HCI sensors (1)
- Poly-(N-methyl-aniline) (1)
- Poly-(N-methylaniline) (1)
- Surface plasmon resonance (1)
Institute
A step-by-step ‘all-electrochemical’ approach has been presented to develop a multilayer structure of conducting polymers for gas sensors. The integrated structure includes a sensitive layer (polyaniline, PANI) and a conductive bridge consisting of poly(3,4-ethylenedioxythiophene) (PEDOT). Good sensitivity, stability, and response of the multilayer material to gaseous HCl indicate a possible application of conductive polymers to provide a binding of sensitive elements in sensors or other fields. The conducting multilayer material, Au/pATP/PANI/PEDOT, was synthesized electrochemically.
Combinatorial electropolymerization with electrical addressing was realized on the array of 96 electrode groups, each from four electrodes. The polymer synthesis was combined with subsequent high-throughput investigation of analytical properties of synthesized polymers. Two-and four-point techniques were applied simultaneously to measure electrical properties of synthesized polymers and contact resistances between electrodes and polymers and modifications of these parameters on addition of analyte. The system was used for development of sensitive materials for detection of gaseous hydrogen chloride.
The optical properties of electrochemically polymerized N-methylaniline are changed in the presence of gaseous hydrogen chloride. This effect was used for preparation of chemical sensors with transduction based on surface plasmon resonance. The interaction of hydrogen chloride with a two nm layer of poly-(N-methylaniline) on gold leads to the shift of the surface plasmon resonance. The analysis of the resonance spectra demonstrates that the effect is caused by an increase of the imaginary component of the refractive index; a minor contribution is also provided by film condensation leading to an increase of the real component of the refractive index and a decrease in the thickness. The effect is selective and quasi-reversible. The concentration dependence of the gas effect obeys Langmuir's adsorption isotherm with a reciprocal value of the binding constant of 850 ± 160 ppm.
A conventional resistance measured by two-point technique includes bulk and contact components. The contact resistance can be excluded by a four-point technique. A simultaneous use of the two- and four-point techniques allows to separate the total resistance between two electrodes for the contact and bulk parts. This approach has been used to analyze electrical coupling between metal electrodes of interdigitated structures and chemically sensitive coating formed by polyaniline (PANI). The polymer layers were deposited by electropolymerization on bare gold and platinum electrodes as well as on gold electrodes precoated by a self-assembled monolayer of 4-aminothiophenol. An exposure of the PANI films formed on interdigitated structures to gaseous HCl displays proportional changes of resistance measured by the two- and four- point techniques for platinum electrodes and for the precoated gold electrode, while a strong deviation from this proportionality was observed for the gold electrodes without precoating. The results demonstrate a high contribution of the contact resistance between PANI and bare gold electrodes into the resistance measured by the two-point technique. This contribution is small and therefore not measurable for bare platinum electrodes or for gold electrodes coated by 4-aminothiophenol.
The influence of polymerization conditionson the morphology of thin films of poly-(N-methylani-line) (PNMA) was studied. The films were prepared byelectropolymerization on gold and platinum electrodesand studied by optical and electron microscopy. It wasdemonstrated that the film morphology does notdepend on the polymerization rate or on the electrodemetal.However,itissensitivetothekindofcounterionofPNMA.Thepolymerscontainingacetate orchloridedo not form stable films. Polymer films containingphosphate or sulfate display inhomogeneous struc-tures. A formation of sprouts and ‘‘nanotubes’’ wasobserved for PNMA sulfate. The films formed byPNMA perchlorate are smooth and transparent(glass-likestructure).Asublayerof4-aminothiophenolincreases the adhesion of polymers to the gold surface.
High throughput characterization of combinatorial libraries demands a compromise between completeness of the study and reasonable investigation time. This compromise can be found by the development of test protocols consisting of the minimal number of the most informative measurements. Multiparameter high throughput characterization of sensitive materials is described. The parameters include response time, regeneration time, reversibility, reproducibility, sensitivity, linearity. The approach was applied for characterization of conductometric gas-sensitive polymer materials. Chemical microarrays prepared by electrochemical synthesis of polymers on platinum electrodes.