An electrochemical sensor for phosphate detection in body fluids was developed based on the hydration transition of magnesium hydrogen phosphate (newberyite, MgHPO4·3H2O). The sensor was fabricated through incubation of a multi-walled carbon nanotube/Nafion (MWCNT/Nafion) modified glassy carbon electrode (GCE) in magnesium phosphate solution, where MgHPO4·3H2O was self-assembled on the electrode surface (denoted as MgP/MWCNT/Nafion). An electrooxidation peak at 1.0 V vs. Ag/AgCl was observed when the as-prepared electrode was subjected to a differential pulse voltammetry (DPV) scan in the presence of phosphate in acetate solution. When the DPV scan was performed in 0.4 - 1.3 V vs. Ag/AgCl, a linear relationship was observed between the peak height and the phosphate concentration in the range from 0.01 to 25 μM in the presence of 0.1 mM Mg2+ in the acetate solution with a limit of detection of 32 nM. And the sensor was successfully applied for phosphate detection in human urine and saliva samples with recoveries of 94.7 - 104.4 and 96 - 103.3%, respectively.
Keywords: Electrochemical sensor; body fluids; hydration; magnesium phosphate; phosphate ion.