(62ar) Synthesis and Characterization of Polyaniline-Polymer Acid Complexes for Use in Biosensing Applications

Conducting polymers have the potential to be used for biosensor applications because they can be made to exhibit a measurable change in their conductivity in response to the presence of biomolecules. The concentration of the biomolecule determines the extent of the change in conductivity, thereby providing the basis for a sensing mechanism.

We have targeted polyaniline (PANI) because it has been shown to become conductive when doped with poly(2-acrylamido-2-methylpropane sulfonic acid) (PAAMPSA). A method has been developed for the template synthesis of in-situ PANI-PAAMPSA films that are deposited on glass substrates with gold electrodes. The use of a polymer acid means that polyaniline can now be incorporated into aqueous solutions without losing its conductivity, which increases its versatility and the ease with which it can be used in a sensing device. Going hand in hand with this achievement is the development of a method for the deposition of PANI-PAAMPSA films on a substrate, which is of great importance because even if PANI-PAAMPSA maintains its conductivity in aqueous solutions, it cannot be used as a sensor because it will be dissolved into the solution. By mounting the film on a substrate, it can be exposed to an aqueous solution without being dissolved and thus function as an effective biosensor.

PANI-PAAMPSA nanofilms with thicknesses of approximately 500 nm have been formed on glass substrates with thermally evaporated gold electrodes through the use of in situ methods, which have produced thinner films than those made previously by using drop or spin-coating methods, and are more ideal for achieving a fast sensor response. The homogeneity of the films has been increased by treating the substrates with 3-triethoxysilylpropylamine prior to exposure to the PANI-PAAMPSA reaction solution.

The change in conductivity of the PANI-PAAMPSA films after exposure to pH levels ranging from 4.5 to 8.80 has been measured and found to show a linear response. Biomolecular sensing capabilities of PANI-PAAMPSA films have also been evaluated using 10 mg/ml solutions of lysozyme and bovine serum albumin (BSA) in a 150 mM sodium phosphate buffer. The conductivity of the films exposed to only the buffer, lysozyme and BSA was found to be 0.109, 0.362 and 0.788 S/cm respectively. The change in the conductivity of the films has been shown to occur within five minutes. The results of both the pH and biomolecule studies have been supported by UV-VIS spectroscopy, which shows appropriate shifts in absorbance peaks either towards the non-conductive pernigraline form of polyaniline or its conductive emeraldine form. The films from the pH studies have also been shown to re-dope when rinsed in water.

These results support the notion that PANI-PAAMPSA is a promising platform for a biosensing device.