Lab-on-a-disc for simultaneous determination of nutrients in water

In this study, we describe a novel platform based on centrifugal microfluidics for simultaneous determination of nitrite, nitrate and nitrite, ammonium, orthophosphate, and silicate in water samples. All processes from sample metering to detection were integrated and automatically conducted on a rotating disc-shaped device. Fluid transfer was controlled by laser irradiation on the ferrowax-based microvalves. Liquid samples and reagents were pumped by centrifugal force in the rotating disc, and their positions and movements were controlled through a programmable light from a laser diode. This novel water analysis platform required only 500 μL of sample (100 μL for each nutrient) and 10-30 μL of reagents for colorimetric detection. In addition, the fully automated parallel processes and efficient mixing in the rotating disc allowed for a significant reduction in total analysis time (∼7 min 40 s) and increased accuracy. Validation with a seawater certified reference material indicated that the platform accurately measured nutrient concentrations in water samples. In addition, we showed that the nutrients in the seawater collected from Chunsu Bay in Korea measured by the proposed lab-on-a-disc and by a commercialized autoanalyzer are comparable.