Wide range optical studies on transparent SWNT films

We present transmission spectra from the far infrared through the ultraviolet region on freestanding SWNT films at temperatures between 40 and 300 K. Several interesting features are observed in the low-frequency part of the spectrum: the Drude-like frequency dependence of the metallic tubes as well as a (sample-dependent) peak in the conductivity around 0.01 eV. We also studied the accidental nitrate doping of the SWNT samples during purification by nitric acid. Asprepared purified samples exhibit increased metallic absorption and decreased interband transitions; these features disappear on heating in vacuum

Study of charge dynamics in transparent single-walled carbon nanotube films

We report the transmission over a wide frequency range (far infrared - visible) of pristine and hole-doped, free-standing carbon nanotube films at temperatures between 50 K and 300 K. Optical constants are estimated by Kramers-Kronig analysis of transmittance. We see evidence in the far infrared for a gap below 10 meV. Hole doping causes a shift of spectral weight from the first interband transition into the far infrared. Temperature dependence in both the doped and undoped samples is restricted to the far-infrared region.Comment: 6 pages, 4 figures, submitted to Phys. Rev. B v3: Fig. 2 replaced, changes in caption of Table II, minor changes in tex

In-situ measurements of the optical absorption of dioxythiophene-based conjugated polymers

Conjugated polymers can be reversibly doped by electrochemical means. This doping introduces new sub-bandgap optical absorption bands in the polymer while decreasing the bandgap absorption. To study this behavior, we have prepared an electrochemical cell allowing measurements of the optical properties of the polymer. The cell consists of a thin polymer film deposited on gold-coated Mylar behind which is another polymer that serves as a counterelectrode. An infrared transparent window protects the upper polymer from ambient air. By adding a gel electrolyte and making electrical connections to the polymer-on-gold films, one may study electrochromism in a wide spectral range. As the cell voltage (the potential difference between the two electrodes) changes, the doping level of the conjugated polymer films is changed reversibly. Our experiments address electrochromism in poly(3,4-ethylene-dioxy-thiophene) (PEDOT) and poly(3,4-dimethyl-propylene-dioxy-thiophene) (PProDOT-Me$_2$). This closed electrochemical cell allows the study of the doping induced sub-bandgap features (polaronic and bipolaronic modes) in these easily oxidized and highly redox switchable polymers. We also study the changes in cell spectra as a function of polymer thickness and investigate strategies to obtain cleaner spectra, minimizing the contributions of water and gel electrolyte features

All-plastic electrochemical transistor for glucose sensing using a ferrocene mediator.

We demonstrate a glucose sensor based on an organic electrochemical transistor (OECT) in which the channel, source, drain, and gate electrodes are made from the conducting polymer poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS). The OECT employs a ferrocene mediator to shuttle electrons between the enzyme glucose oxidase and a PEDOT:PSS gate electrode. The device can be fabricated using a one-layer patterning process and offers glucose detection down to the micromolar range, consistent with levels present in human saliva

Applications of poly (3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) transistors in chemical and biological sensors

The application of transistors based on poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS) in chemical and biological sensing is reviewed. These devices offer enormous potential for facile processing of small, portable, and inexpensive sensors ideally suited for point-of-care analysis. They can be used to detect a wide range of analytes for a variety of possible applications in fields such as health care (medical diagnostics), environmental monitoring (airborne chemicals, water contamination, etc.), and food industry (smart packaging). Organic transistors are excellent candidates to act as transducers because they have the ability to translate chemical and biological signals into electronic signals with high sensitivity. Furthermore, fuctionalization of PEDOT:PSS films with a chemical or biological receptor can lead to high specificity. The advantages of using PEDOT:PSS transistors are described, and applications are presented for sensing analytes in both gaseous and aqueous environments. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc

Enzymatic sensing with organic electrochemical transistors

Since their development in the 1980's organic electrochemical transistors (OECTs) have attracted a great deal of interest for biosensor applications. Coupled with the current proliferation of organic semiconductor technologies, these devices have the potential to revolutionize healthcare by making point-of-care and home-based medical diagnostics widely available. Unfortunately, their mechanism of operation is poorly understood, and this hinders further development of this important technology. In this paper glucose sensors based on OECTs and the redox enzyme glucose oxidase are investigated. Through appropriate scaling of the transfer characteristics at various glucose concentrations, a universal curve describing device operation is shown to exist. This result elucidates the underlying device physics and establishes a connection between sensor response and analyte concentration. This improved understanding paves the way for rational optimization of enzymatic sensors based on organic electrochemical transistors. © The Royal Society of Chemistry

Simple glucose sensors with micromolar sensitivity based on organic electrochemical transistors

A simple glucose biosensor with micromolar sensitivity is reported. The sensor utilizes a conducting polymer transistor, with a channel made out of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and a Pt gate electrode. Glucose oxidase is used to confer specificity. It is shown that the sensor's response to glucose is well within the clinical range of glucose levels in human saliva. The sensitivity and range of detection of the sensor can be tuned by adjusting the magnitude of the gate bias. © 2006 Elsevier B.V. All rights reserved

Flexible, organic light-pen input device with integrated display

We report a light-pen input device with an integrated electrochromic display. The former is a photosensor array, based on a blend of bacterioRhodopsin (bR) and the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), while the latter is based on PEDOT:PSS. The use of organic materials allows the entire device to be deposited on a thin, mechanically flexible plastic substrate. The operation and characteristics of this device are discussed. © 2008 Elsevier B.V. All rights reserved