The incorporation and controlled release of dopamine from a sulfonated β–cyclodextrin–doped conducting polymer

Abstract

Pyrrole was electropolymerised in the presence of sulfonated β-cyclodextrin to give a conducting polypyrrole film doped with the anionic cyclodextrin, PPy-sβ-CD. On reduction of the polymer film at −0.80 V vs SCE, high concentrations of dopamine (DA) were incorporated and the DA was subsequently released at a potential of 0.10 V vs SCE. Much higher levels of DA were incorporated and released at PPy-sβ-CD compared to polypyrrole films doped with smaller anions and doped with the larger para-toluene sulfonic acid. In addition to releasing higher concentrations of DA, the DA was less prone to oxidation and degradation in the presence of the sulfonated β-cyclodextrin. This was attributed to the formation of an inclusion complex between the protonated DA molecule and the anionic CD. The higher release rates were explained in terms of the immobile nature of the large CD and the high charge density with approximately 9 sulfonated groups attached to the rim of the CD cavity, which facilitated the uptake of high levels of DA. Approximately 6.0 μmol cm −2 of DA was released at 0.10 V vs SCE over 60 min on reducing the PPy-sβ-CD film for 30 min at −0.80 V vs SCE. Higher levels of 9.6 μmol cm −2 were obtained on increasing the reduction period to 60 min, while levels of 14.0 μmol cm −2 were achieved with thicker polymer films.

The selective electrochemical sensing of dopamine at a polypyrrole film doped with an anionic β−cyclodextrin

“…1, where the logarithm of the current is presented as a function of time, while a typical chargeÀtime plot recorded at a higher potential of 0.80 V vs SCE is shown in the inset. A near steadyÀstate current is observed within 30 s, indicating efficient polymerisation at the relatively low potential of 0.50 V in the presence of the anionic cyclodextrins without the presence of any other salts [26,27]. The chargeÀtime plot recorded at 0.80 V vs SCE shows a near linear increase in charge with increasing polarisation times, which is again consistent with efficient polymerisation and the deposition of conducting polymer layers.…”

“…Bidan and coÀworkers [23] and Temsamani et al [24] have elctrosynthesised polypyrrole doped with sulfonated βÀcyclodextrins, while Tamer et al [25] have prepared a threeÀdimensional network of branched fibres of polypyrrole doped with sulfonated βÀcyclodextrin through an interfacial polymerisation process. These anionic cyclodextrin doped polypyrrole films are particularly easy to prepare and they have been used to detect and uptake viologens [26] and in the controlled release of dopamine [27]. Also, polypyrrole has good biocompatibility properties [28] while cyclodextrins are well known in the drug delivery field [29], making these modified electrodes considerably more suitable for implantation compared to some of the more complex electrodes.…”

In Vivo Organic Bioelectronics for Neuromodulation

“…Over the decades, a variety of such controlled delivery electrodes have been demonstrated, all following the basic recipe of embedding bioactive substances in the redox-active conducting polymer film (as counterions in the PPy example above, or co-ions compensating the counterions) and releasing them into the adjacent electrolyte upon redox switching (Figure a). These devices have been extensively reviewed elsewhere − and have been utilized in a variety of recent in vitro neuromodulation demonstrations. − However, such controlled delivery electrodes have seen few neuromodulation demonstrations in vivo .…”

The formation and properties of polypyrrole doped with an immobile antibiotic

“…Another strategy is to incorporate antibiotic molecules as dopants within the polypyrrole film. A number of drug molecules, including glutamate, adenosine 5′-triphosphate (ATP), salicylate, dexamethasone, chlorpromazine and dopamine, have been successfully incorporated into polypyrrole and subsequently released using electrical stimulation [10][11][12][13][14][15][16]. The d r u g m o l e c u l e s , a s a n i o n s , a r e a d d e d t o t h e e l e c t r o p o l y m e r i s a t i o n s o l u t i o n , a n d d u r i n g electropolymerisation, they are doped within the growing polymer.…”

“…The anionic drugs are retained as dopants while the polymer films are maintained in an oxidised state, but in order to maintain charge neutrality, they are expelled from the polymer on reduction of the film. The incorporation and release of cationic drugs or molecules, such as dopamine [10], have also been achieved.…”