Toward an In Situ Phosphate Sensor in Natural Waters Using a Microfluidic Flow Loop Analyzer

Abstract

In this paper, we describe an automated microfluidic flow loop analyzer toward an in-situ phosphate measurement in natural waters. The system consists of a microfluidic chip and a setup for driving and detecting which form a microfluidic flow loop analyzer with one peristaltic micropump, seven microvalves, three inlets, one outlet and a loop channel which connects them together. The loop channel functions as a mixer, and the mixing process can be monitored continuously. Three reagents can be injected into the water sample at any time. The reagent consumption is 6 μL per sample for one measurement of the phosphate concentration, which would increase the in-situ usage time greatly because of the limited reagents. The analyzer is small, and its power consumption is low (343 mW), which increase the potential of the analyzer for monitoring phosphate in situ. The analyzer has been calibrated, and its performance has been quantified. Because of the continuous monitoring function of the microflow loop, we increase sample throughput to 10 samples per hour. The phosphate concentrations of the water samples have been measured using both normal method and rapid method we proposed. The results show there are no significant differences between our analyzer and reference procedures.

Colorimetric Phosphate Detection Using Organic DFB Laser Based Absorption Spectroscopy

“…A beam splitter is conventionally used to determine the initial intensity I 0 . Using a beam splitter increases the complexity of miniaturized setups, which is why the excitation energy of the emission source is often used as a measure of the emission intensity [8,22]. This approach simplifies the measurement setup but runs the risk that changes in the emission source intensity will lead to measurement errors.…”

“…Based on this, it is possible to use the emitted pulse energy Q instead of intensity for further calculations. According to Equation (8), the energy Q of a pulse is proportional to the intensity I integrated over the pulse duration. The solid angle Ω is defined by the distances and the active area of the photodiode.…”

“…Electrochemical sensors are highly suitable for miniaturization and can therefore be manufactured inexpensively, and the energy requirement can also be reduced. However, electrochemical sensors often suffer from low selectivity or low sensitivity [6][7][8]. Spectrophotometric methods usually require complex, expensive and bulky equipment and are typically not amenable to field measurements [6].…”

“…Spectrophotometric sensors use color-forming reactions and thus, generate special waste. This waste has to be collected and can become a problem, especially in small, stand-alone systems [8,9]. Spectroscopic detection is a photometric measurement of absorption at a small spectral bandwidth.…”

“…A possible remedy is the use of an emission source with a narrow spectral emission bandwidth. This is often achieved by the integration of inorganic emission sources, such as light-emitting diodes or laser diodes, which have a limited emission bandwidth due to their discrete optical transitions [8,10]. Furthermore, organic emission sources are also used [11,12], which can cover the entire visible spectrum (and beyond) [12][13][14].…”