When considering new sensory technologies one should look to nature for guidance. Indeed, living organisms have developed the ultimate chemical sensors. Many insects can detect chemical signals with perfect specificity and incredible sensitivity. Mammalian olfaction is based on an array of less discriminating sensors and a memorized response pattern to identify a unique odor. It is important to recognize that the extraordinary sensory performance of biological systems does not originate from a single element. In actuality, their performance is derived from a completely interactive system wherein the receptor is served by analyte delivery and removal mechanisms, selectivity is derived from receptors, and sensitivity is the result of analyte-triggered biochemical cascades. Clearly, optimal artificial sensory sys-

Conjugated polymer-based chemical sensors.

Immobilization of horseradish peroxidase onto polyaniline polymers

In this study, emeraldine base (EB)-form polyaniline (PANI) powder was chemically prepared in 1M HNO3 aqueous solution. The thermal characteristics and chemical structures of this powder were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). A polarizing optical microscope was also used to examine the crystalline morphology of this sample. The results indicated that the EB-form PANI powder had a discernible moisture content. Moreover, in the first run of DSC thermal analysis, the exothermic peak at 170–340°C was due to the crosslinking reaction occurring among the EB-form PANI molecular chains. FTIR and XRD examinations further confirmed the chemical crosslinking reaction during thermal treatment. TGA results illustrated that there were two major stages for weight loss of the EB-form PANI powder sample. The first weight loss, at the lower temperature, resulted from the evaporation of moisture. The second weight loss, at the higher temperature, was due to the chemical structure degradation of the sample. The degradation temperature of the EB-form PANI powder was around 420–450°C. The degradation temperature of emeraldine salt (ES)-form PANI powder was lower (around 360–410°C) than that of the EB form (around 420–450°C). From the TGA results, I roughly estimated that 2.74 aniline repeat units, on average, were doped with 1 HNO3 molecule in the ES-form PANI. I found a single crystalline morphology of EB-form PANI, mostly like a conifer leaf. More complex, multilayered dendritic structures were also found. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2142–2148, 2003

Thermal and morphological studies of chemically prepared emeraldine‐base‐form polyaniline powder

Immobilization of Aspergillus niger glucoamylase onto a polyaniline polymer

Properties of horseradish peroxidase immobilised onto polyaniline

A Flow Injection Analysis (FIA) for glucose using glucose oxidase (E.C.1.1.3.4) was developed. The enzyme was immobilised on polyaniline chemically synthetized on internal surface of silicon tube (2.0 mm of diameter and length from 1 to 5 meters), using glutaraldehyde as a bifunctional agent. The system was able to measure glucose at levels from 5 to 500mM with a response time of 2min using 250μl of sample. The system has been operated satisfactorily for one month with more than 300 assays with loss of 60% of activity.

Increasing glucose determination range by flow injection analysis (FIA) using glucose oxidase immobilised on polyaniline

A Flow Injection Analysis (FIA) for sucrose using invertase (E.C. 3.2.1.26), mutarotase (E.C.5.1.3.3) and glucose oxidase (E.C.1.1.3.4) was developed. The enzymes were immobilised on glass beads using glutaraldehyde. The sucrose concentration was related to oxygen saturation. Fall in O2 concentration, as a result of sucrose oxidation, was detected by a low cost, home-made O2 electrode. The system was able to measure sucrose from 0.025 to 100mM with a response time of 6min using 200 μl of sample, with an apparent Km of 42mM of sucrose. The system has been operated satisfactorily for 50 days without loss any initial activity.

V. Leite

Papers

Increasing glucose determination range by flow injection analysis (FIA) using glucose oxidase immobilised on polyaniline

Simple and inexpensive Flow Injection Analysis for determination of sucrose using invertase and glucose oxidase immobilised on glass beads