The fabrication and characterisation of a highly sensitive polypyrrole sensor and its electrical responses to amines of differing basicity at high humidities

Ammonia is a common feedstock for many chemical processes involving nitrogen compounds. It is a poisonous, colourless gas with a pungent smell and a fairly low odour threshold of approximately 5 ppm. The recommended threshold limit value for human exposure is 25 ppm (18 mg/m3 of air). The detection of ammonia gas is of interest in many technological fields such as industrial processes, clinical diagnosis and environmental monitoring. we describe a methodology for producing cheap, disposable, highly sensitive ammonia/amine sensors with particular regard to detecting ammonia in mouth air from patients and/or amines in headspace urine from patients. Ammonia is a potential diagnostic marker for H. pylori infections, a stomach bacterium known to be implicated in stomach ulcers. Amines, such as trimethylamine, are known to be emitted by Proteus species in some cases of urinary tract infection (UTI). Pyrrole was chemically polymerised on poly(etheretherketone) (PEEK) with a solution of ferric nitrate nonahydrate as the oxidant. The resulting films were used as gas sensors and tested to a range of amines including ammonia. The sensors exhibited high sensitivity towards low concentrations of ammonia and other amines in air, as low as 1 ppm at 100% humidity with reproducible and reversible resistance changes. Films of polypyrrole on PEEK were found to be considerably more stable in air than films of polypyrrole on poly(methylmethacrylate) (PMMA). Treatment with acids increased the polypyrrole films sensitivity to ammonia. The polymer surface morphology and surface analysis were studied by ESEM and XPS.