Lab-on-Chip for In Situ Analysis of Nutrients in the Deep Sea

Abstract

Microfluidic reagent-based nutrient sensors offer a promising technology to address the global undersampling of ocean chemistry but have so far not been shown to operate in the deep sea (>200 m). We report a new family of miniaturized lab-onchip (LOC) colorimetric analyzers making in situ nitrate and phosphate measurements from the surface ocean to the deep sea (>4800 m). This new technology gives users a new low-cost, highperformance tool for measuring chemistry in hyperbaric environments. Using a combination of laboratory verification and fieldbased tests, we demonstrate that the analyzers are capable of in situ measurements during profiling that are comparable to laboratorybased analyses. The sensors feature a novel and efficient inertialflow mixer that increases the mixing efficiency and reduces the back pressure and flushing time compared to a previously used serpentine mixing channel. Four separate replicate units of the nitrate and phosphate sensor were calibrated in the laboratory and showed an average limit of detection of 0.03 μM for nitrate and 0.016 μM for phosphate. Three on-chip optical absorption cell lengths provide a large linear range (to >750 μM (10.5 mg/L-N) for nitrate and >15 μM (0.47 mg/L-P) for phosphate), making the instruments suitable for typical concentrations in both ocean and freshwater aquatic environments. The LOC systems automatically collected a series of deep-sea nitrate and phosphate profiles in the northeast Atlantic while attached to a conductivity temperature depth (CTD) rosette, and the LOC nitrate sensor was attached to a PROVOR profiling float to conduct automated nitrate profiles in the Mediterranean Sea.

Two chemistries on a single lab-on-chip: Nitrate and orthophosphate sensing underwater with inlaid microfluidics

“…However, the fluid consumption rate (i.e., the volume of fluid consumed per measurement) limits the total possible number of samples before servicing; therefore, many sensors utilize microfluidics to maximize fluid efficiency. A wide array of microfluidic sensors have Frontiers in Sensors frontiersin.org been presented in recent literature, applied to measure nutrients (Clinton-Bailey et al, 2017;Beaton et al, 2022;Morgan et al, 2022), pH (Yin et al, 2021), silicate (Cao et al, 2018), or various other key ocean variables. Furthermore, these microfluidic platforms have been demonstrated to deep ocean depths (> 4,800 m) (Beaton et al, 2022), have performed thousands of samples per deployment (Grand et al, 2017), and present significant potential towards widespread ocean monitoring (Fukuba and Fujii, 2021;Li et al, 2022).…”

“…A wide array of microfluidic sensors have Frontiers in Sensors frontiersin.org been presented in recent literature, applied to measure nutrients (Clinton-Bailey et al, 2017;Beaton et al, 2022;Morgan et al, 2022), pH (Yin et al, 2021), silicate (Cao et al, 2018), or various other key ocean variables. Furthermore, these microfluidic platforms have been demonstrated to deep ocean depths (> 4,800 m) (Beaton et al, 2022), have performed thousands of samples per deployment (Grand et al, 2017), and present significant potential towards widespread ocean monitoring (Fukuba and Fujii, 2021;Li et al, 2022). However, these analyzers are typically limited to a single species per instrument, and multiplexed data collection may suffer from challenges of sample synchronization spatially and temporally.…”

Real-Time Underway Mapping of Nutrient Concentrations of Surface Seawater Using an Autonomous Flow Analyzer

“…and system requirements (high reliability, low consumption, high frequency, etc. ). − Major advances in the development of devices utilizing different flow techniques (e.g., segmented continuous-flow analysis, , normal flow injection analysis, − reverse flow injection analysis, , sequential injection analysis, , microfluidic chips, − flow batch analysis, − programmable flow injection (pFI) in batch mode , ) to measure nutrients in seawater have been reported. Some of them have been applied for the underway measurement of specific single or dual-parameter nutrients in shipboard laboratories. ,− However, to the best of our knowledge, studies on the simultaneous underway analysis of all five key nutrients in estuarine and coastal waters are not available.…”

High-Pressure Microfluidics for Ultra-Fast Microbial Phenotyping

“…Nevertheless, microreactors have been already used to study environmental soil microbiology ( Pucetaite et al, 2021 ) but also marine microbiology, under normal conditions (i.e., non-extremophilic) using droplet-based microfluidics ( Girault et al, 2019 ). Meanwhile, technological developments have been made to use microfluidics for geochemical and microbiological investigations in deep-sea waters, considering microreactors as in situ (bio)chemical sensors/detectors ( Wang et al, 2009 ; Beaton et al, 2022 ). In that case, the microreactor undergoes isostatic pressure both externally and internally, therefore not requiring mechanically resistant materials for its fabrication.…”