Solvent-induced microstructure changes and consequences for electrochemical activity of redox-active conducting polymers

An ionic liquid-modified PEDOT/Ti3C2TX based molecularly imprinted electrochemical sensor for pico-molar sensitive detection of L-Tryptophan in milk

L-Tryptophan (L-Trp) is essential for the human body and can only be obtained externally. It is important to develop a method to efficiently detect L-Trp in food. In this work, ionic liquid (IL) modified poly(3,4-ethylendioxythiophene)/ Titanium carbide (PEDOT/Ti3C2TX) was used as a substrate material to improve detection sensitivity. Molecular imprinted polymers (MIP) film for specific recognition of L-Trp was fabricated on the surface of modified electrodes using electrochemical polymerization. The monitoring results showed that the molecularly imprinted electrochemical sensors (MIECS) exhibited good linearity ranges (10-6 - 0.1 μM and 0.1-100 μM) with a low detection limit (LOD) of 2.09 × 10-7 μM. In addition, the MIECS exhibited remarkable stability, reproducibility, and immunity to interference. A good recovery (93.54-99.59%) was demonstrated in the detection of milk. The sensor was expected to be developed as a highly selective and sensitive portable assay, and applied to the detection of L-Trp in food.

Solvent effects on electrosynthesis, morphological and electrochromic properties of a nitrogen analog of PEDOT

A new nitrogen analog of 3,4-ethylenedioxythiophene (EDOT), N-methyl-3,4-dihydrothieno[3,4-b][1,4]oxazine (MDTO), was electropolymerized in different solvents (deionized water, acetonitrile, and propylene carbonate) using LiClO4 as the electrolyte. The structure and performance of as-prepared PMDTO polymers were systematically studied by cyclic voltammetry, UV-vis spectroscopy, FT-IR, SEM, thermogravimetry, spectroelectrochemistry and electrochromic techniques. To our surprise, solvents had a major influence on the electropolymerization of MDTO and properties of the resultant polymers, including morphology, electrochemistry, electronic and optical properties, and electrochromics, etc. In aqueous solution, MDTO revealed the lowest onset oxidation potential (0.19 V) than in acetonitrile (0.48 V) and propylene carbonate (0.49 V). However, PMDTO films showed rather poor cycling stability in water, while outstanding stability in acetonitrile and propylene carbonate. Films prepared in propylene carbonate displayed a rather smooth morphology, lower band gap (1.65 eV), higher transparency (97.3%) and a contrast ratio (44.6%) at λ = 466 nm. PMDTO films obtained in acetonitrile showed significantly higher coloration efficiency (169.5 cm(2) C(-1)) than in other two solvents (∼ 97.6 cm(2) C(-1)) with a moderate contrast ratio (24.5%).

A Label-Free, Sensitive, Real-Time, Semiquantitative Electrochemical Measurement Method for DNA Polymerase Amplification (ePCR)

Oligonucleotide hybridization to a complementary sequence that is covalently attached to an electrochemically active conducting polymer (ECP) coating the working electrode of an electrochemical cell causes an increase in reaction impedance for the ferro-ferricyanide redox couple. We demonstrate the use of this effect to measure, in real time, the progress of DNA polymerase chain reaction (PCR) amplification of a minor component of a DNA extract. The forward primer is attached to the ECP. The solution contains other PCR components and the redox couple. Each cycle of amplification gives an easily measurable impedance increase. Target concentration can be estimated by cycle count to reach a threshold impedance. As proof of principle, we demonstrate an electrochemical real-time quantitative PCR (e-PCR) measurement in the total DNA extracted from chicken blood of an 844 base pair region of the mitochondrial Cytochrome c oxidase gene, present at ∼1 ppm of total DNA. We show that the detection and semiquantitation of as few as 2 copies/μL of target can be achieved within less than 10 PCR cycles.

Highly functionalisable polythiophene phenylenes

The synthesis and properties of novel conducting polymer monomers, and their polymers, based on poly(thiophene phenylenes) (PThP) is described.

Reversible electrochemical switching of polymer brushes grafted onto conducting polymer films

We demonstrate the electrochemical switching of conformation of surface-bound polymer brushes, by grafting environmentally sensitive polymer brushes from an electrochemically active conducting polymer (ECP). Using atom transfer radical polymerization (ATRP), we grafted zwitterionic betaine homopolymer and block copolymer brushes of poly(3-(methacryloylamido)propyl)-N,N'-dimethyl(3-sulfopropyl)ammonium hydroxide) (PMPDSAH) and poly(methyl methacrylate)-b-PMPDSAH, from an initiator, surface-coupled to a poly(pyrrole-co-pyrrolyl butyric acid) film. The changes in ionic solution composition in the surface layer, resulting from oxidation and reduction of the ECP, trigger a switch in conformation of the surface-bound polymer brushes, demonstrated here by electrochemical impedance spectroscopy (EIS) and in a change of wettability. The switch is dependent upon temperature in a way that is analogous to the temperature-dependent solubility and aggregation of similar betaine polymers in aqueous solution but has a quite different dependence on salt concentration in solution. The switch is fully reversible and reproducible. We interpret the switching behavior in terms of a transition to a "supercollapsed" state on the surface that is controlled by ions that balance the charge state of the ECP and are adsorbed to the opposite charges of the zwitterionic graft, close to the graft-ECP interface. The behavior is significantly modified by hydrophobic interactions of the block copolymer graft. We speculate that the synergistic combination of properties embodied in these "smart" materials may find applications in electrochemical control of surface wetting and in the interaction with biomolecules and living cells.

Developing Polypyrrole-Based Oligonucleotide Biosensors

Many medical, forensic science, environmental and general scientific difficulties may be aided by the existence of suitable biosensors such as gene sensors, body fluid detection DNA sensors, disease detection DNA sensors etc. The sensor technology described here uses the conducting polymer polypyrrole (PPy) as both sensing element and transducer of sensing events. Stability and reproducibility are necessary characteristics of practical biosensors. The stability of polymers can be investigated using electrical impedance spectroscopy (EIS). This work discusses research focused towards creating a stable, reproducible sensor surface for oligonucleotide detection. The effect of electropolymerisation conditions (electropolymerisation method, solvent and electrolyte used), post-growth treatment (cycling and EIS experiments), and the sensing-environment conditions on sensor stability and applicability will be discussed.