Printed flexible bifunctional electrochemical urea-pH sensor based on multiwalled carbon nanotube/polyaniline electronic ink

Urea concentration and pH are two crucial parameters in food and clinical analysis. Traditional analytical methods of urea and pH determination are unsuitable for field and involve complex instrumentation or and enzyme-based assays. In this study, we used screen printing technology to prepare an electrochemical sensor with a carbon electrode modified by a multiwalled carbon nanotube/polyaniline (MWCNT/PANi) composite for the simultaneous detection of urea and pH. Urea was detected by a simple current–potential (I–V) experiment and its concentration level on the MWCNT/PANi-modified screen-printed carbon electrode (SPCE) surface was determined by cyclic voltammetry. The MWCNT/PANi-modified SPCE had a linear response (R² = 0.99902), lower detection limit, higher selectivity, and higher sensitivity than reported biosensors. Specifically, the detection limit was 10 µM and the sensitivity was 0.38 mA mM⁻¹ cm⁻² in the urea concentration range of 10–50 µM. Chronoamperometry was applied to investigate the changes in voltage on the MWCNT/PANi-modified SPCE with varying solution pH. The sensor exhibited excellent linearity (R² = 0.99089) and an average sensitivity of 20.63 mV/pH over a wide pH range of 2–11. Thus, the MWCNT/PANi-modified SPCE has a promising field application as a simple, bifunctional non-enzymatic sensor.