In this paper we describe interactions between neural cells and the conducting polymer poly(3,4-ethylenedioxythiophene (PEDOT) toward development of electrically conductive biomaterials intended for direct, functional contact with electrically-active tissues such as the nervous system, heart, and skeletal muscle. We introduce a process for polymerizing PEDOT around living cells and describe a neural cell-templated conducting polymer coating for microelectrodes and a hybrid conducting polymer-live neural cell electrode. We found that neural cells could be exposed to working concentrations (0.01 M) of the EDOT monomer for as long as 72 hours while maintaining 80% cell viability. PEDOT could be electrochemically deposited around neurons cultured on electrodes using 0.5-1 μA/mm 2 galvanostatic current. PEDOT polymerized on the electrode and surrounded the cells, covering cell processes. The polymerization was impeded in regions where cells were well-adhered to the substrate. The cells could be removed from the PEDOT matrix to generate a neural cell-templated biomimetic conductive substrate with cell-shaped features that were cell-attracting. Live cells embedded within the conductive polymer matrix remained viable for at least 120 hours following polymerization. Dying cells primarily underwent apoptotic cell death. PEDOT, PEDOT+live neurons, and neuron-templated PEDOT coatings on electrodes significantly enhanced the electrical properties as compared to the bare electrode as indicated by decreased electrical impedance of 1-1.5 orders of magnitude at 0.01-1 kHz and significantly increased charge transfer capacity. PEDOT coatings showed a decrease of the phase angle of the impedance from roughly 80 degrees for the bare electrode to 5-35 degrees at frequencies >0.1 kHz. Equivalent circuit modeling indicated that PEDOT-coated electrodes were best described by R(C(RT)) circuit. We found that an RC parallel circuit must be added to the model for PEDOT+live neuron and neurontemplated PEDOT coatings.
Conjugated polymers recently have drawn much attention as an emerging sensory material due to their meritorious signal amplification, convenient optical detection, readily tunable properties, and easy fabrication. We review the molecular design principles of sensory conjugated polymer recognition events, which can trigger conformational change of the conjugated polymer, induce intermolecular aggregation, or change the distance between the conjugated polymer as an energy donor and the reporter dye molecule as an energy acceptor. These recognition/detection mechanisms result in mainly three types of measurable signal generation: turn on or turn off fluorescence, or change in either visible color or fluorescence emission color of the conjugated polymer. In this article, we highlight recent advances in fluorescent and colorimetric conjugated polymer-based biosensors.
Hybrid bio/‐synthetic sensory conjugated polyelectrolytes were developed to achieve selective label‐free detection of target oligonucleotides with amplified fluorescence signal in solution. A completely water soluble and highly fluorescent conjugated poly(p‐phenyleneethynylene) (PPE) was rationally designed and synthesized as a signal amplifying unit and chemically modified with carboxylic functional groups at the ends of the polymer chains to bioconjugate with amine functionalized single‐stranded oligonucleotides as a receptor using carbodiimide chemistry. This approach allows the functional groups on the polymers to be effectively linked to DNA without any damage to the conjugated π‐system of the polymers. DNA detection results using the PPE‐DNA hybrid system confirmed large signal amplification by means of efficient Förster energy transfer from the energy harvesting PPE to the fluorescent dye attached to the complementary analyte DNA. To realize label‐free detection, we also connected a DNA molecular beacon to the newly developed conjugated polymer as a self‐signaling molecular switch. A DNA detection study by using the resulting PPE‐DNA beacon and single strand analyte DNAs showed not only signal‐amplification properties but also self‐signaling properties.
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