Hyeonseok Yoon

Polypyrrole nanotubes conjugated with human olfactory receptors: high-performance transducers for FET-type bioelectronic noses.

Get a whiff of this: Human olfactory receptor (hOR)-conjugated polypyrrole (PPy) nanotubes were integrated into the field-effect transistor (FET) sensor platform for the fabrication of high-performance bioelectronic noses (see picture, S = source, D = drain). The device can translate and amplify hOR-odorant interaction into a detectable signal, and it showed highly sensitive and specific responses toward a target odorant.

Current Trends in Sensors Based on Conducting Polymer Nanomaterials

Conducting polymers represent an important class of functional organic materials for next-generation electronic and optical devices. Advances in nanotechnology allow for the fabrication of various conducting polymer nanomaterials through synthesis methods such as solid-phase template synthesis, molecular template synthesis, and template-free synthesis. Nanostructured conducting polymers featuring high surface area, small dimensions, and unique physical properties have been widely used to build various sensor devices. Many remarkable examples have been reported over the past decade. The enhanced sensitivity of conducting polymer nanomaterials toward various chemical/biological species and external stimuli has made them ideal candidates for incorporation into the design of sensors. However, the selectivity and stability still leave room for improvement.

Multidimensional Conducting Polymer Nanotubes for Ultrasensitive Chemical Nerve Agent Sensing

Tailoring the morphology of materials in the nanometer regime is vital to realizing enhanced device performance. Here, we demonstrate flexible nerve agent sensors, based on hydroxylated poly(3,4-ethylenedioxythiophene) (PEDOT) nanotubes (HPNTs) with surface substructures such as nanonodules (NNs) and nanorods (NRs). The surface substructures can be grown on a nanofiber surface by controlling critical synthetic conditions during vapor deposition polymerization (VDP) on the polymer nanotemplate, leading to the formation of multidimensional conducting polymer nanostructures. Hydroxyl groups are found to interact with the nerve agents. Representatively, the sensing response of dimethyl methylphosphonate (DMMP) as a simulant for sarin is highly sensitive and reversible from the aligned nanotubes. The minimum detection limit is as low as 10 ppt. Additionally, the sensor had excellent mechanical bendability and durability.

Kinetic Study of the Formation of Polypyrrole Nanoparticles in Water-Soluble Polymer/Metal Cation Systems: A Light-Scattering Analysis

A facile way to synthesize nanometer-sized polymer (polypyrrole, PPy) particles is explored on the basis of the formation of complexes between water-soluble polymers and metal cations in aqueous solution. The metal cation is used as an oxidizing agent to initiate the chemical oxidation polymerization of the corresponding monomer, and the water-soluble polymer effectively provides a steric stability for the growth of polymer nanoparticles during the polymerization process. Light-scattering analyses are performed to give insight into the behavior of the complexes in aqueous solution. In addition, major physical parameters affecting the formation of polymer nanoparticles are investigated, including hydrodynamic radius, radius of gyration, shape factor, and viscosity. By judicious control of these parameters, PPy nanoparticles with narrow size distribution can be readily fabricated in large quantities. It is also possible to control the diameter of the nanoparticles by changing critical synthetic variables. Importantly, PPy nanoparticles of approximately 20-60 nm in diameter can be prepared without using any surfactants or specific templates; this novel strategy offers great possibility for mass production of polymer nanoparticles.

A novel sensor platform based on aptamer-conjugated polypyrrole nanotubes for label-free electrochemical protein detection.

We first present a simple yet versatile strategy for the functionalization of polymer nanotubes in a controlled fashion. Carboxylic‐acid‐functionalized polypyrrole (CPPy) nanotubes were fabricated by using cylindrical micelle templates in a water‐in‐oil emulsion system, and the functional carboxyl groups were effectively incorporated into the polymer backbone during the polymerization by using pyrrole‐3‐carboxylic acid (P3CA) as a co‐monomer without a sophisticated functionalization process. It was noteworthy that the chemical functionality of CPPy nanotubes was readily controlled in both qualitative and quantitative aspects. On the basis of the controlled functionality of CPPy nanotubes, a field‐effect transistor (FET) sensor platform was constructed to detect specific biological entities by using a buffer solution as a liquid‐ion gate. The CPPy nanotubes were covalently immobilized onto the microelectrode substrate to make a good electrical contact with the metal electrodes, and thrombin aptamers were bonded to the nanotube surface via covalent linkages as the molecular recognition element. The selective recognition ability of thrombin aptamers combined with the charge transport property of CPPy nanotubes enabled the direct and label‐free electrical detection of thrombin proteins. Upon exposure to thrombin, the CPPy nanotube FET sensors showed a decrease in current flow, which was probably attributed to the dipole–dipole or dipole–charge interaction between thrombin proteins and the aptamer‐conjugated polymer chains. Importantly, the sensor response was tuned by adjusting the chemical functionality of CPPy nanotubes. The efficacy of CPPy nanotube FET sensors was also demonstrated in human blood serum; this suggests that they may be used for practical diagnosis applications after further optimization.

Facile fabrication of polypyrrole nanotubes using reverse microemulsion polymerizationElectronic supplementary information (ESI) available: FTIR spectrum and TEM images of PPy nanotubes. See http://www.rsc.org/suppdata/cc/b2/b211716a/

Polypyrrole (PPy) nanotubes have been fabricated by reverse microemulsion polymerization in an apolar solvent, and factors affecting the formation of PPy nanotubes have also been investigated.

Fabrication of Ultrafine Metal-Oxide-Decorated Carbon Nanofibers for DMMP Sensor Application

Ultrafine metal-oxide-decorated hybrid carbon nanofibers (CNFs) were fabricated by a single-nozzle co-electrospinning process using a phase-separated mixed polymer composite solution and heat treatment. To decorate metal oxides on the CNF surface, core (PAN) and shell (PVP) structured nanofibers (NFs) were fabricated as starting materials. The core-shell NF structure was prepared by single-nozzle co-electrospinning because of the incompatibility of the two polymers. Ultrafine hybrid CNFs were then formed by decomposing the PVP phase, converting the metal precursors to metal oxide nanonodules, and transforming the PAN to CNFs of ca. 40 nm diameter during heat treatment. The decoration morphology of the metal oxide nanonodules could be controlled by precursor concentration in the PVP solution. These ultrafine hybrid CNFs were applied to a dimethyl methylphosphonate (DMMP) chemical sensor at room temperature with excellent sensitivity. The minimum detectable level (MDL) of hybrid CNFs was as low as 0.1 ppb, which is 10-100 times higher than for a chemical sensor based on carbon nanotubes. This is because the metal oxide nanonodules of hybrid CNFs increase the surface area and affinity to DMMP vapor. Our new synthetic methodology promises to be an effective approach to fabricating hybrid CNF/inorganic nanostructures for future sensing technologies.

Size control of magnetic carbon nanoparticles for drug delivery

Carbonized polypyrrole nanoparticles with controlled diameters were readily fabricated by the pyrolysis of polypyrrole nanoparticles. The carbonized polypyrrole nanoparticles showed narrow size distribution, large micropore volume, and high surface area. Magnetic phases were introduced into the carbon nanoparticles during the pyrolysis without sophisticated process, which resulted in useful magnetic properties for selective nanoparticle separation. Field emission scanning electron microscopy, Raman spectrometer, N(2) adsorption/desorption, X-ray diffraction, and superconducting interference device were employed for characterizing the carbonized polypyrrole nanoparticles. Hydrophobic guest molecules were incorporated into the carbonized polypyrrole nanoparticles by surface adsorption, pore filling, and surface covalent coupling. The carbonized polypyrrole nanoparticles exhibited embedding capability using pyrene as a typical hydrophobic fluorescent molecule. In addition, ibuprofen was incorporated into the carbon nanoparticles, and drug-loaded carbon nanoparticles sustained release property. In addition, the carbonized polypyrrole nanoparticles revealed low toxicity at concentrations below 100 microg mL(-1) via cell viability test and were uptaken inside the cells. These results suggest a new platform for the drug delivery using carbonized polypyrrole nanoparticles.

Field-effect-transistor sensor based on enzyme-functionalized polypyrrole nanotubes for glucose detection.

We describe the detection of glucose based on a liquid-ion gated field-effect transistor configuration in which enzyme-functionalized polypyrrole nanotubes are employed as the conductive channel. First of all, carboxylated polypyrrole nanotubes (CPNTs) were successfully fabricated by the chemical polymerization of an intrinsically functionalized monomer (pyrrole-3-carboxylic acid, P3CA) without degradation in major physical properties. The CPNTs possessed not only well-defined functional groups but also electrical properties comparable to nonsubstituted polypyrrole. Importantly, the carboxylic acid functional group can be utilized for various chemical and biological functionalizations. A liquid-ion gated FET sensor was readily constructed on the basis of the chemical functionality of CPNTs. In the first stage, the CPNTs were immobilized onto a microelectrode substrate via covalent linkages. It was noteworthy that the covalent immobilization allowed high-quality contact between the nanotubes and the microelectrodes in the liquid phase. The second stage involved the covalent binding of glucose oxidase (GOx) enzyme to the nanotubes. The covalent functionalization generally provides excellent enzymatic activity and thermal stability. The fabricated FET sensor provided real-time response (an increase in source-drain current) and high sensitivity toward the various concentrations (0.5-20 mM) of glucose. The enzymatic reaction product, hydrogen peroxide, played pivotal roles in modulating the charge transport property of CPNTs.

Shape-dependent cytotoxicity and proinflammatory response of poly(3,4-ethylenedioxythiophene) nanomaterials.

Poly(3,4-ethylenedioxythiophene) (PEDT) is recognized as one of the most promising conducting polymers for future applications in the fields of electronics, optics, energy storage/conversion, and biomedical science. The toxicity of PEDT could be considered to affect the potential for its widespread application. Herein, the cytotoxicity and proinflammatory response of PEDT nanomaterials of three different shapes toward human lung fibroblast (IMR90) and mouse alveolar macrophage (J774A.1) cells are investigated. The shape-dependent toxicity of the PEDT nanomaterials is evaluated by examining cell morphological change, cytotoxicity, apoptosis/necrosis, oxidative stress, and immune response. The cytotoxicity and apoptosis of the nanomaterials increase with their decreasing aspect ratio in both cell lines. The formation of reactive oxygen species in cells treated with PEDT nanomaterials is dependent on the shape and concentration of the nanomaterial. Proinflammatory cytokines, such as interleukin-1, interleukin-6, and tumor necrosis factor alpha from macrophages, are induced by PEDT nanomaterial-treated cells.