Abstract
AbstractThe measurement of low concentrations of ammonia in small sample volumes is required in biological, biomedical and environmental measurement applications. However, achieving this without instrumentation remains challenging. Here, sensor devices for the measurement of ammonia in a liquid were developed. These were based on the fabrication of polyaniline nanoparticle films onto screen printed interdigitated electrodes using inkjet printing and their integration into a polymer microfabricated device with polytetrafluroethylene membrane and air flow path between the membrane and the sensor. Samples of ammonia in phosphate buffered saline of 52 μL were measured using electrochemical impedance. While water vapour and ions from the buffer did result in a decrease in sensor impedance, this was eradicated by displacement of the headspace above the sensor with air. This, in combination with the adjustment of the sample to pH to 11 allowed the quantification of ammonia from 0 to 200 μM with a limit of detection of 25 μM. The device has the potential to be used for sensitive, low volume measurement applications of ammonia at point‐of‐test and point‐of‐care.
Highlights
200^^μM with a limit of detection of 25^^μM
The principle feature of polyaniline as an ammonia sensor material lies in the emeraldine salt (ES) form’s affinity with ammonia due to a distinct similarity of the coordinative roles of nitrogen atoms in polyaniline and ammonia
An optical detector in combination with polyaniline-coated silica micro-capillaries was used for the detection of aqueous ammonia [37]
Summary
The measurement of low concentrations of ammonia in small sample volumes is required in biological, biomedical and environmental measurement applications. We present the measurement of aqueous ammonia in low sample volumes (52^^μL) at low concentrations (25 to 200^^μM) using a printed polyaniline nanoparticle sensor integrated into a microfabricated microfluidic device. The development and optimisation of a simple, low cost, printed disposable sensor device for the sensitive detection of ammonia in low volume liquid samples was demonstrated. While use of the PTFE membrane allowed measurement of ammonia from liquid using an impedimetric, two-electrode interdigitated configuration, interference from water vapour and dissolved ions remained an issue. The resulting sensor device was capable of the measurement of ammonia in a 52^^μL sample in the range from 0 to 200^^μM with an LOD of 25^^μM (R2 of 0.9868, a slope of 0.0043, an intercept of 0.9562 and RSDs in the range of 0.8 to 4.2^%), making it widely suitable for environmental, biological, biomedical and point-of-care diagnostic applications. Table^^1 Analytical performance of a range of aqueous ammonia sensing systems.
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