Nan-Rong Chiou

Growth and alignment of polyaniline nanofibres with superhydrophobic, superhydrophilic and other properties

Polyaniline nanofibres can be prepared by a number of methods based on chemical oxidative polymerization and in situ adsorption polymerization. However, the lack of alignment in these nanostructures makes them unsuitable for many applications. Here, we report a simple approach to chemical oxidative polymerization that can control the growth and simultaneous alignment of polyaniline nanofibres grown on a range of conducting and non-conducting substrates in a wide variety of sizes. The diameters of the tips of the nanofibres can be controlled within the range 10-40 nm, and the average length can be controlled within the range 70-360 nm. Moreover, the coatings display a range of properties including superhydrophilicity and superhydrophobicity. Such nanostructured coatings may be useful for applications such as anti-fog coatings, self-cleaning surfaces, DNA manipulation, transparent electrodes for low-voltage electronics, and chemical and biological sensors.

Design and testing of a microfluidic biochip for cytokine enzyme-linked immunosorbent assay

Enzyme-linked immunosorbent assay (ELISA) has been widely used in medical diagnostics, environmental analyses, and biochemical studies. To reduce assay time and lower consumption of reagents in cytokine ELISA analysis, a polymeric microfluidic biochip has been designed and fabricated via several new techniques: Polyaniline-based surface modification for superhydrophobic capillary valving and oxygen plasma-poly(ethyleneimine)-tyrosinase-protein A modification for high sensitivity protein detection. The proper flow sequencing was achieved using the superhydrophobic capillary valves. The burst frequency of each valve was experimentally determined and compared with two capillary force equations and the fluent finite element simulation. This fully automated microfluidic biochip with an analyzer is able to provide high fluorescence signal of ELISA with a wider linear detection range and a much shorter assay time than 96-well microtiter plates. It is applicable to a variety of nonclinic research and clinically relevant disease conditions. The modification technologies in this study can be implemented in other lab-on-a-chip systems, druggene delivery carriers, and other immunoassay biosensor applications.

Large Laterally Ordered Nanochannel Arrays from DNA Combing and Imprinting

One-dimensional nanostructures such as nanochannels (and nanotubes) are characterized by extremely small transverse size and resultant high degree of spatial confinement that endow them a unique set of properties. When patterned laterally, these nanostructures are widely used as critical transport devices for a variety of applications such as sensing, nanomanipulation, and information processing.[1–8] While numerous fabrication techniques have been developed, few can generate large and highly ordered arrays of both nanochannels and nanowires with no defects and low-cost. The most notable high-resolution lithographic techniques include electron beam lithography (EBL) and focused ion beam milling (FIB),[9–13] but they are associated with either low throughput or high-cost. Another lithographic technique, nanoimprint lithography (NIL), is of high throughput and relatively low-cost, but it requires the use of highly specialized equipment and molds prepared typically by EBL.[14– 17] Many inexpensive techniques have been developed, but they are inadequate in terms of high precision, low defect rate, or large area fabrication of both nanochannels/tubes and nanowires/strands.[7,18–25] Moreover, these nanostructures need to be connected to the micro/macroscale structures, such as reservoirs and channels, to form functional devices. This is not a trivial task and the lack of a low-cost solution to this problem significantly limits the applicability of many nanoconstructs.

Electric-field induced ion-leveraged metal–insulator transition in conducting polymer-based field effect devices

Abstract The field effect devices prepared completely from conducting polymers, especially poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonic acid) (PEDOT/PSS), were studied. Normally in a conductive “on” state, the transistor-like device has a transition to a substantially less conductive “off” state at an applied positive gate voltage, typically ∼15–25 V. The current ratio I off / I on can exceed 10 −4 at room temperature. We have found that the field effect is strongly temperature dependent and is substantially reduced upon decreasing the temperature by only a 10 °C. This loss of current reduction upon application of a gate voltage is not due to the temperature dependence of the electrical conductivity of polymers of which the devices are made. The temperature dependence of the dc conductivity of the PEDOT/PSS follows the variable range hopping law both before and after application of the gate voltage, though with an increased activation energy, T 0 . We suggest that the conducting polymer is near the metal–insulator transition and that the field effect in the device is related to the electric field modulating this transition in the region underneath the gate electrode. The transition is controlled and leveraged by ion motion. The time dynamics of the current with the gate modulation strongly supports our conjecture. We demonstrate the generality of the phenomena by presenting similar results for devices fabricated from the conducting polypyrrole doped with Cl.

Porous membrane controlled polymerization of nanofibers of polyaniline and its derivatives

A novel, simple, and scalable technique to control the formation of the nanofibers of polyaniline and its derivatives via porous membrane controlled polymerization (PMCP) is reported. Through appropriate synthesis conditions, there are nearly 100% nanofibers formed with diameters tunable from 20nm to 250nm via the selection of pore diameter, monomer, counterions, and polymerization conditions. The nanofiber lengths vary from sub-micrometre to several micrometres. A single nanofiber can be easily isolated from the agglomeration. X-Ray diffraction patterns show that doped polyaniline nanofibers are substantially crystalline.

Doped conducting polymer-based field effect devices

Field effect devices (FEDs) prepared completely from conducting polymers PEDOT/PSS (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) and polypyrrole doped with Cl - (PPy/Cl - ) are reported. In the on (conductive) state when the gate voltage V G is applied, these FEDs have threshold turn-off positive V g s of - 15 V (varying with polymer, geometry, and preparation conditions). The current ratio I on /I off can exceed 10 +4 at room temperature. We have found this field effect is strongly temperature dependent and nearly entirely disappears with decrease of temperature by as little as ten degrees. The conductance of the active channel has stronger temperature dependence when V G exceeds the threshold voltage. Time dynamics of drain current with gate voltage modulation and its temperature dependence supports that this transition is coupled with ion motion. We suggest that the conducting polymer is near the insulator-metal transition (IMT) and this field effect caused by positive V g in the FED may be related with this IMT in the region underneath the gate.