Dopamine, electropolymerization

Biogenic amines, such as histamine [131], adenine [132], dopamine [133] and melamine [134], have been determined using chemosensors combining MIP recognition and PM transduction at QCM. Electronically conducting MIPs have been used in these chemosensors as recognition materials. Initially, functional electroactive bis(bithiophene)methane monomers, substituted either with the benzo-18-crown-6 or 3,4-dihydroxyphenyl, or dioxaborinane moiety, were allowed to form complexes, in ACN solutions, with these amines as templates. Subsequently, these complexes were oxidatively electropolymerized under potentiodynamic conditions. The resulting MIP films deposited onto electrodes of quartz resonators were washed with aqueous base solutions to extract the templates. 

The histamine [131], adenine [132] and dopamine [133] amines are electroactive in the positive potential range, in which the thiophene is electropolymerized. Therefore, these amines could be oxidized at the electrode surface in the course of deposition of the MIP film. That way, products of these oxidations might be available in the electrode vicinity for imprinting rather than the desired pristine... 

An imprinted poly[tetra(o-aminophenyl)porphyrin] film, deposited on a carbon fibre microelectrode by electropolymerization, was used for selective determination of dopamine [208] in the potential range of —0.15 to 1.0 V. This chemosensor has been used successfully for dopamine determination in brain tissue samples. The dopamine linear concentration range extended from 10 6 to 10-4 M with LOD of 0.3 pM. However, this LOD value is very high compared to that of the dopamine voltammetric detection using polyaminophenol MIPs prepared by electropolymerization [209]. Dopamine was determined by CV and DPV at concentrations ranging from 2 x 10 s to 0.25 x 10 6 M with LOD of 1.98 nM. This LOD value is lower than that of PM dopamine detection [133]. 

A. Pietrzyk et al. reported an imprinted poly[bis(2,2 -bithienyl)methane] film for a piezoelectric microgravimetry of dopamine. The MIP film contained either a 3,4-dihydroxyphenyl or benzo-18-crown-6 substituent, for selective determination of dopamine and was electropolymerized on an imderlayer of poly(bithiophene) on a Pt/ quartz resonator. The detection limit of the method was reported to be 10 nM [401]. Kan et al, on the other hand, developed a composite of multiwalled carbon nanotube (MWCNTs) and MIP with dopamine templates using the copolymerization reaction of methacrylic acid and trimethylolpropane trimethacrylate (copoly(MAA-co-TRIM)) on the vinyl functionalized MWCNT surface and used the composite for the thermo-gravimetric analysis of the template. The composite was found to be selective towards dopamine in comparison with epinephrine and the response was linear in the range of 5.0 X 10 "-2.0 X 10 M [427]. 

Zhou et al. [1025] described a simple drug-release system based on a P(Py)-poly(styrene sulfonate) (P(Py)/PSS) film electropolymerized on a Pt electrode. Upon reduction of this as-prepared film in an aqueous solution containing dopamine hydrobromide (Dopa-HBr) or dimethyl-dopamine-hydrobromide (MeDopa-HBr), the dopamine was incorporated into the CP as a cationic dopant (the amine group of Dopa forms a substituted alkyl ammonium ion in aqueous solution). Electrochemical re-oxidation of this CP-Dopa complex then caused release of the Dopa. Controlled release could be effected via controlled, coulometric application of charge and controlling the CP film thickness between 0.35 and 2.8 /tm. Release was however slow, of the order of minutes Fig. 24-3 shows a typical release pattern, monitored optically via solution Absorbance. These authors also showed that the anesthetic BNA could also be bound and released reversibly in the same manner as Dopa. 

The electropolymerization of dopamine leads to conjugated polydopamine films, which can serve on electrodes as neural interfaces [559]. In some cases, the molecular design allowed the preparation of water sensors [549], Also, P-cyclodextrin can be electropolymerized with the formation of thin films [560]. Electropolymerized pyrrole served for actuating purposes [561-563] and films of electropolymerized monomers could be modified with polymer grafts (Fig. 49) [564, 565]. 

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