A disposable cobalt-based phosphate sensor based on screen printing technology

Abstract

Screen printing is a promising technology because of its simplicity, low-cost, high reproducibility, and efficiency in large-scale production. In this work, a cobalt-based phosphate sensor was successfully fabricated using the screen printing technology for the determination of phosphate concentration in the aqueous solution. The disposable sensor consists of a fully integrated cobalt (Co) electrode, which is a layer of carbon conductive ink (C) physically doped with Co powder, and Ag/AgCl reference electrode. The SEM images show that the morphology of the Co electrode changes after exposure to the phosphate solution, indicating that the expendable reaction exists during the measurement. At the Co/C ratio of 1:99, the cobalt-based phosphate sensor shows phosphate-selective potential response in the range of 10⁻⁴ to 10⁻¹ mol/L, yielding a detection limit of 1×10⁻⁵ mol/L and a slope of over 30 mV/decade in acidic solution (pH 4.5) for H₂PO₄ ⁻. The proposed screen-printed sensor also exhibited significant reproducibility with a small repeated sensing deviation (i.e., relative standard deviation (R.S.D.) of 0.5%) on a single sensor and a small electrode-to-electrode deviation (i.e., R.S.D.<3.2%). The recovery study of H₂PO₄ ⁻ in real wastewater samples gave values from 95.4% to 101.8%, confirming its application potential in the measurement of phosphate in real samples. Apart from its high selectivity, sensitivity, and stability comparable with a conventional bulk Co-wire electrode, the proposed phosphate sensor still yields many other advantages, such as low price, compactness, ease of use, and the possibility of integration with other analytical devices such as flow injection analysis.