Au-decorated electrochemically synthesised polyaniline-based sensory platform for amperometric detection of aqueous ammonia in biological fluids

Abstract

Ammonia (NH3) present in biological fluids is biomarker for several disease states. In this work the well-known interaction between polyaniline (PANI) and NH3 was used for the fabrication of an amperometric sensory platform to detect aqueous NH3 at neutral i.e. biological pH. Understanding PANI's electrochemical synthesis and redox behaviour in acidic and neutral media was used to determine the NH3 detection mechanism. The latter is based on the PANI deprotonation reaction, NH4+ oxidation and follow-up PANI reduction and oxidation. Chronoamperometry was applied as an NH3-detection method in a 50 µL background electrolyte in which a 1 µL sample was injected, triggering instantaneous changes to the current. The sensory platform's detection limit, based on pure electrochemically synthesised PANI (PANIel) (24.64 µM), was reduced 17 times (1.44 µM) with the addition of 20 nm Au nanoparticles. This Au-decorated PANIel sensory platform showed excellent reversibility, reusability and the possibility for continuously cycled NH3 measurements, with a recovery rate of 90–99.5% for artificial saliva samples of different pHs. This demonstrates its suitability for more complex samples. The developed sensory platform presents potential from the industry point of view, as a base for an NH3 batch injection analysis and for preventive home medical self-care.