A Flexible Optical pH Sensor Based on Polysulfone Membranes Coated with pH-Responsive Polyaniline Nanofibers

Abstract

Abstract:A new optical pH sensor based on polysulfone (PSU) and polyaniline (PANI) was developed. A transparent and flexible PSU membrane was employed as a support. The electrically conductive and pH-responsive PANI was deposited onto the membrane surface by in situ chemical oxidative polymerization (COP). The absorption spectra of the PANI-coated PSU membranes exhibited sensitivity to pH changes in the range of 4-12, which allowed for designing a dual wavelength pH optical sensor. The performance of the membranes was assessed by measuring their response starting from high pH and going down to low pH, and vice versa. It was found that it is necessary to precondition the sensor layers before each measurement due to the slight hysteresis observed during forward and backward pH titrations. PSU membranes with polyaniline coating thicknesses in the range of «100-200 nm exhibited fast response times of <4 s, which are attributed to the porous, rough and nanofibrillar morphology of the polyaniline coating. The fabricated pH sensor was characterized by a sigmoidal response (R 2 = 0.997) which allows for pH determination over a wide dynamic range. All membranes were stable for a period of more than six months when stored in 1 M HCl solution. The reproducibility of the fabricated optical pH sensors was found to be <0.02 absorption units after one month storage in 1 M HCl solution. The performance of the optical pH sensor was tested and the obtained pH values were compared with the results obtained using a pH meter device.

A magenta polypyrrole derivatised with Methyl Red azo dye: synthesis and spectroelectrochemical characterisation

“…Similar results were found for Polyaniline (PAni) [59,60] and PPy [60,61] prepared by different methodologies, such as PAni nanocomposites [62], PAni-polyvinyl alcohol composite membranes [63], PAni nanofibers [64] and PPybromophenol blue composites [65], for pH determination in aqueous solutions and/or acid vapours. In such cases the colour variation was from green at pH = 4 through blue at pH = 7 and purple at pH = 12 for PAni [64], and from yellow in acidic medium (pH = 2) to blue in basic medium (pH = 10) for PPy-bromophenol blue composites [65]. The behaviour observed for PPy-bromophenol blue according to the pH variation suggest that the dye (dopant) plays an important role in the optical properties of the PPy films.…”

“…This pH dependent changes have therefore been used to develop optical pH sensors for applications in chemistry, biochemistry, clinical chemistry and environmental sciences [64].…”

Near-Infrared pH Sensor Based on a SPEEK–Polyaniline Polyelectrolyte Complex Membrane

“…Aniline was distilled twice and stored in the dark at 5 °C before use. The phosphate-buffered saline PBS buffer system was prepared as reported in our previous work [21].…”

Flexible Sensors—From Materials to Applications

“…Common materials used for this end are PI [13][14][15][23][24][25]34,36], PET [17,18,40,70,73,109,169], PEN [9,20,26,204,311] and PDMS [16,21,22,89,168,[312][313][314][315]. However, there are several other examples of flexible substrates suitable for sensor applications reported in literature, including PU [96,316,317], PLA [293], polysulfone (PSU) [318], polyetheretherketone (PEEK) [319], polycarbonate (PC) [79], parylene [47], polyvinyl alcohol (PVA) [12], polyarylate (PAR) [239], Ecoflex™ [320,321], Dragon Skin™ [101,[321][322][323], Al foil [238], common paper [28,…”