A Lab-on-Chip Analyzer for in Situ Measurement of Soluble Reactive Phosphate: Improved Phosphate Blue Assay and Application to Fluvial Monitoring.

Here, we present a new in situ microfluidic phosphate sensor that features an improved "phosphate blue" assay which includes polyvinylpyrrolidone in place of traditional surfactants-improving sensitivity and reducing temperature effects. The sensor features greater power economy and analytical performance relative to commercially available alternatives, with a mean power consumption of 1.8 W, a detection limit of 40 nM, a dynamic range of 0.14-10 µM, and an infield accuracy of 4 ± 4.5%. During field testing, the sensor was continuously deployed for 9 weeks in a chalk stream, revealing complex relations between flow rates and phosphate concentration that suggest changing dominance in phosphate sources. A distinct diel phosphorus signal was observed under low flow conditions, highlighting the ability of the sensor to decouple geochemical and biotic effects on phosphate dynamics in fluvial environments. This paper highlights the importance of high resolution in situ sensors in addressing the current gross under-sampling of aquatic environments.

A high performance microfluidic analyser for phosphate measurements in marine waters using the vanadomolybdate method.

We report a high performance autonomous analytical system based on the vanadomolybdate method for the determination of soluble reactive phosphorus in seawater. The system combines a microfluidic chip manufactured from tinted poly (methyl methacrylate) (PMMA), a custom made syringe pump, embedded control electronics and on-board calibration standards. This "lab-on-a-chip" analytical system was successfully deployed and cross-compared with reference analytical methods in coastal (south west England) and open ocean waters (tropical North Atlantic). The results of the miniaturized system compared well with a reference bench-operated phosphate auto-analyser and showed no significant differences in the analytical results (student's t-test at 95% confidence level). The optical technology used, comprising of tinted PMMA and polished fluidic channels, has allowed an improvement of two orders of magnitude of the limit of detection (52 nM) compared to currently available portable systems based on this method. The system has a wide linear dynamic range 0.1-60 µM, and a good precision (13.6% at 0.4 µM, n=4). The analytical results were corrected for silicate interferences at 0.7 µM, and the measurement frequency was configurable with a sampling throughput of up to 20 samples per hour. This portable micro-analytical system has a low reagent requirement (340 µL per sample) and power consumption (756 J per sample), and has allowed accurate high resolution measurements of soluble reactive phosphorus in seawater.