Field-deployable microfluidic sensor for phosphate in natural waters

A microfluidic sensor for long-term monitoring of phosphate levels has been developed incorporating sampling, reagent and waste storage, detection, and wireless communication into a compact and portable device. The sensor is based on the yellow method for phosphate determination, a simple colorimetric technique involving the formation of vanadomolybdophosphoric acid when a phosphate-containing sample is mixed with an acidic reagent containing ammonium molybdate and ammonium meta vanadate. The sensor has been applied to on-site analysis of effluent from a wastewater treatment plant. The data was validated by comparison with the plant´s existing online monitor, and a good correlation between the two sets of data was achieved, showing that the phosphate sensor is capable of operating satisfactorily at low mg L^-1 levels over extended periods.