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An overview of ionophore-based electrodes for ammonium sensing critically analyzing contributions in the last 20 years and with focus in analytical applications.

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The growth of (bio)­sensors in analytical chemistry is mainly attributable to the development of affordable, effective, portable, and user-friendly analytical tools. In the field of sensors, paper-based devices are gaining a relevant position for their outstanding features including foldability, ease of use, and instrument-free microfluidics. Herein, a multifarious use of filter paper to detect copper ions in bodily fluids is reported by exploiting this eco-friendly material to (i) synthesize AuNPs without the use of reductants and/or external stimuli, (ii) print the electrodes, (iii) load the reagents for the assay, (iv) filter the gross impurities, and (v) preconcentrate the target analyte. Copper ions were detected down to 3 ppb with a linearity up to 400 ppb in standard solutions. The applicability in biological matrices, namely, sweat and serum, was demonstrated by recovery studies and by analyzing these biofluids with the paper-based platform and the reference method (atomic absorption spectroscopy), demonstrating satisfactory accuracy of the novel eco-designed analytical tool.