High-Capacity Conductive Nanocellulose Paper Sheets for Electrochemically Controlled Extraction of DNA Oligomers
Nyholm L (2011) High-Capacity Conductive Nanocellulose Paper Sheets for Electrochemically Controlled
Extraction of DNA Oligomers. PLoS ONE 6(12): e29243. doi:10.1371/journal.pone.0029243
High-Capacity Conductive Nanocellulose Paper Sheets for Electrochemically Controlled Extraction of DNA Oligomers
Aamir Razaq 0
Gustav Nystro m 0
Maria Strmme 0
Albert Mihranyan 0
Leif Nyholm 0
Nikolai Lebedev, US Naval Reseach Laboratory, United States of America
0 1 The A ngstro m Laboratory, Department of Engineering Sciences , Nanotechnology and Functional Materials , Uppsala, Sweden, 2 The A ngstro m Laboratory, Department of Materials Chemistry Uppsala , Sweden
Highly porous polypyrrole (PPy)-nanocellulose paper sheets have been evaluated as inexpensive and disposable electrochemically controlled three-dimensional solid phase extraction materials. The composites, which had a total anion exchange capacity of about 1.1 mol kg21, were used for extraction and subsequent release of negatively charged fluorophore tagged DNA oligomers via galvanostatic oxidation and reduction of a 30-50 nm conformal PPy layer on the cellulose substrate. The ion exchange capacity, which was, at least, two orders of magnitude higher than those previously reached in electrochemically controlled extraction, originated from the high surface area (i.e. 80 m2 g21) of the porous composites and the thin PPy layer which ensured excellent access to the ion exchange material. This enabled the extractions to be carried out faster and with better control of the PPy charge than with previously employed approaches. Experiments in equimolar mixtures of (dT)6, (dT)20, and (dT)40 DNA oligomers showed that all oligomers could be extracted, and that the smallest oligomer was preferentially released with an efficiency of up to 40% during the reduction of the PPy layer. These results indicate that the present material is very promising for the development of inexpensive and efficient electrochemically controlled ion-exchange membranes for batch-wise extraction of biomolecules.
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Funding: The work was financially supported by the Swedish Foundation for Strategic Research (SSF) (grant RMA08-0025), the Swedish Research Council (VR)
(grants 621-2008-3690 and 621-2009-4626) and the Higher Education Commission of Pakistan (HEC). The funders had no role in study design, data collection and
analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
The application of electronically conductive polymers, e.g.
polyaniline, polythiophene and polypyrrole, in biosciences has been
developing rapidly during more than two decades, particularly in
the fields of controlled drug delivery, biomedical engineering and
diagnostics [14]. One reason for the interest in these polymers
stems from the fact that they can extract and release ions upon their
oxidation and reduction. It is well-known [5] that the charge
compensation upon the oxidation of conducting polymers can be
taken care of either by anions entering the polymer or cations
leaving the polymer, or a combined movement of both anions and
cations, depending on the charge and size of the ions. In
electrochemically controlled solid-phase micro extraction [612],
this effect is used to perform batch-wise extraction and release of
charged species by applying an electrical potential/current to a
conducting solid phase extraction material in contact with the
solution containing the charged species. In another approach,
conducting polymer coated particles have been used as an
electrochemically controlled stationary phase in a chromatographic
separation system [1319]. The latter technique, (i.e.
electrochemically modulated liquid chromatography EMLC), has, however, not
yet found widespread use most likely due to the relatively complex
experimental set-up and problems associated with the packing of
efficient columns (the stationary phase should be composed of
uniform (210 mm) conductive particles with a sufficiently large (e.g.
150200 m2 g21) surface area.
Compared to conventional solid phase micro extraction (SPME)
[20], in which a material with a fixed number of exchange sites is
employed, electrochemically controlled SPME offers higher
flexibility since the properties of the material and thus the number
of exchange sites can be externally controlled by electrochemically
controlling the charge of the material. The applicability of
electrochemically controlled SPME has, however, so far been
limited by the relative low capacities [7] of the available extraction
materials. For conducting polymer films this problem generally
stems from mass transport limitations appearing when attempting
to increase the capacity of the films by increasing the film thickness
[7,21,22]. It has thus been reported [7] that only the outermost
layer of the polymer film on a planar electrode surface was active
in the extraction of ions when using electrodes coated with
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