A disposable on-chip phosphate sensor with planar cobalt microelectrodes on polymer substrate

Disposable microsensors on polymer substrates consisting of fully integrated on-chip planar cobalt (Co) microelectrodes, Ag/AgCl reference electrodes, and microfluidic channels have been designed, fabricated, and characterized for phosphate concentration measurement in aqueous solution. The planar Co microelectrode shows phosphate-selective potential response over the range from 10^-5 to 10^-2 M in acidic medium (pH 5.0) for both inorganic (KH₂PO₄) and organic (adenosine 5′-triphosphate (ATP) and adenosine 5′-diphosphates (ADP)) phosphate compounds. This microfabricated sensor also demonstrates significant reproducibility with a small repeated sensing deviation (i.e. relative standard deviation (R.S.D.) < 1%) on a single chip and a small chip-to-chip deviation (i.e. R.S.D. < 2.5%). Specifically, while keeping the high selectivity, sensitivity, and stability of a conventional bulk Co-wire electrode, the proposed phosphate sensor yields advantages such as ease of use, cost effectiveness, reduced analyte consumption, and ease of integrating into disposable polymer lab-on-a-chip devices. The capability to sense both inorganic and organic phosphate compounds makes this sensor applicable in diverse areas such as environmental monitoring, soil extract analysis, and clinical diagnostics.