Development and validation of microfluidic lab-on-chip analyzers for the in situ quantification of dissolved iron and manganese species in seawater

There has been an increasing demand over the last decades for autonomous in situ measurement systems for the quantification of physical and chemical parameters in the marine environment. The demand is largely linked to the need to address the present undersampling of the world’s oceans. The need for reliable and well resolved time series, both on a temporal and spatial scale, cannot be satisfied with conventional approaches involving collection of discrete samples during ship campaigns followed by their analysis in a land-based laboratory. This PhD project investigates whether the well-established spectrophotometric approaches for Fe and Mn using Ferrozine (FZ) and 1-(2-pyridylazo)-2-naphthol (PAN) as complexing agents, respectively, can be utilized for reliable and accurate in situ quantification of dissolved Fe and Mn species in an autonomous wet chemical analyzer based on lab-on-chip (LoC) technology. Those systems are based around a microfluidic chip and integrate all steps of analysis (sampling, sample treatment, chemical reaction, detection, data processing) into a single instrument

Evaluation of a ferrozine based autonomous in situ lab-on-chip analyzer for dissolved iron species in coastal waters

The trace metal iron (Fe) is an essential micronutrient for phytoplankton growth and limits, or co-limits primary production across much of the world's surface ocean. Iron is a redox sensitive element, with Fe(II) and Fe(III) co-existing in natural waters. Whilst Fe(II) is the most soluble form, it is also transient with rapid oxidation rates in oxic seawater. Measurements of Fe(II) are therefore preferably undertaken in situ. For this purpose an autonomous wet chemical analyzer based on lab-on-chip technology was developed for the in situ determination of the concentration of dissolved (<0.45 μm) Fe species (Fe(II) and labile Fe) suitable for deployments in a wide range of aquatic environments. The spectrophotometric approach utilizes a buffered ferrozine solution and a ferrozine/ascorbic acid mixture for Fe(II) and labile Fe(III) analyses, respectively. Diffusive mixing, color development and spectrophotometric detection take place in three separate flow cells with different lengths such that the analyzer can measure a broad concentration range from low nM to several μM of Fe, depending on the desired application. A detection limit of 1.9 nM Fe was found. The microfluidic analyzer was tested in situ for nine days in shallow waters in the Kiel Fjord (Germany) along with other sensors as a part of the SenseOCEAN EU-project. The analyzer's performance under natural conditions was assessed with discrete samples collected and processed according to GEOTRACES protocol [acidified to pH < 2 and analyzed via inductively coupled plasma mass spectrometry (ICP-MS)]. The mechanical performance of the analyzer over the nine day period was good (consistent high precision of Fe(II) and Fe(III) standards with a standard deviation of 2.7% (n = 214) and 1.9% (n = 217), respectively, and successful completion of every programmed data point). However, total dissolved Fe was consistently low compared to ICP-MS data. Recoveries between 16 and 75% were observed, indicating that the analyzer does not measure a significant fraction of natural dissolved Fe species in coastal seawater. It is suggested that an acidification step would be necessary in order to ensure that the analyzer derived total dissolved Fe concentration is reproducible and consistent with discrete values

A versatile optode system for oxygen, carbon dioxide, and pH measurements in seawater with integrated battery and logger

Herein, we present a small and versatile optode system with integrated battery and logger for monitoring of O-2, pH, and pCO(2) in seawater. Three sensing materials designed for seawater measurements are optimized with respect to dynamic measurement range and long-term stability. The spectral properties of the sensing materials were tailored to be compatible with a commercially available laboratory oxygen logger that was fitted into a pressure housing. Interchangeable sensor caps with appropriate "sensing chemistry" are conveniently attached to the end of the optical fiber. This approach allows using the same instrument for multiple analytes, which offers great flexibility and minimizes hardware costs. Applications of the new optode system were demonstrated by recording depth profiles for the three parameters during a research cruise in the Baltic Sea and by measuring surface water transects of pH. The optode was furthermore used to monitor the concentration of dissolved oxygen in a seagrass meadow in the Limfjord, Denmark, and sensor packages consisting of pO(2), pH, and pCO(2) were deployed in the harbors of Kiel, Germany, and Southampton, England, for 6 d. The measurements revealed that the system can resolve typical patterns in seawater chemistry related to spatial heterogeneities as well as temporal changes caused by biological and tidal activity

Enhanced Middle Convolution

Recently, D'Agnolo and Kashiwara established a Riemann--Hilbert correspondence for holonomic D-modules, introducing the concept of enhanced ind-sheaves for the construction of the target category. In subsequent work, they endowed the category of R-constructible enhanced ind-sheaves with a self-dual generalized t-structure, which naturally gives rise to the notion of enhanced perverse sheaves. In our thesis, we use this framework to define and investigate an enhanced version of Katz' middle convolution operation for classical perverse sheaves. We also reflect on the compatibility of our construction with Arinkin's version of the middle convolution for connections on P^1 via the enhanced Riemann--Hilbert correspondence.Vor Kurzem entwickelten D'Agnolo und Kashiwara eine Riemann--Hilbert-Korrespondenz für holonome D-Moduln, wobei die Konstruktion der Zielkategorie auf dem Konzept der zu diesem Zweck eingeführten enhanced ind-sheaves basiert. In einer darauffolgenden Arbeit versahen sie die Kategorie der R-konstruierbaren enhanced ind-sheaves mit einer selbstdualen verallgemeinerten t-Struktur, was auf natürliche Weise einen Begriff von perversen enhanced ind-sheaves liefert. In unserer Arbeit verwenden wir diese Theorie, um eine Version von Katz' middle convolution für perverse enhanced ind-sheaves zu definieren und zu untersuchen. Dabei gehen wir auch auf die Kompatibilität unserer Konstruktion mit Arinkins middle convolution für Zusammenhänge auf P^1 unter der Riemann--Hilbert-Korrespondenz ein

Enhanced Middle Convolution

Recently, D'Agnolo and Kashiwara established a Riemann--Hilbert correspondence for holonomic D-modules, introducing the concept of enhanced ind-sheaves for the construction of the target category. In subsequent work, they endowed the category of R-constructible enhanced ind-sheaves with a self-dual generalized t-structure, which naturally gives rise to the notion of enhanced perverse sheaves. In our thesis, we use this framework to define and investigate an enhanced version of Katz' middle convolution operation for classical perverse sheaves. We also reflect on the compatibility of our construction with Arinkin's version of the middle convolution for connections on P^1 via the enhanced Riemann--Hilbert correspondence.Vor Kurzem entwickelten D'Agnolo und Kashiwara eine Riemann--Hilbert-Korrespondenz für holonome D-Moduln, wobei die Konstruktion der Zielkategorie auf dem Konzept der zu diesem Zweck eingeführten enhanced ind-sheaves basiert. In einer darauffolgenden Arbeit versahen sie die Kategorie der R-konstruierbaren enhanced ind-sheaves mit einer selbstdualen verallgemeinerten t-Struktur, was auf natürliche Weise einen Begriff von perversen enhanced ind-sheaves liefert. In unserer Arbeit verwenden wir diese Theorie, um eine Version von Katz' middle convolution für perverse enhanced ind-sheaves zu definieren und zu untersuchen. Dabei gehen wir auch auf die Kompatibilität unserer Konstruktion mit Arinkins middle convolution für Zusammenhänge auf P^1 unter der Riemann--Hilbert-Korrespondenz ein

Enhanced Middle Convolution

Recently, D'Agnolo and Kashiwara established a Riemann--Hilbert correspondence for holonomic D-modules, introducing the concept of enhanced ind-sheaves for the construction of the target category. In subsequent work, they endowed the category of R-constructible enhanced ind-sheaves with a self-dual generalized t-structure, which naturally gives rise to the notion of enhanced perverse sheaves. In our thesis, we use this framework to define and investigate an enhanced version of Katz' middle convolution operation for classical perverse sheaves. We also reflect on the compatibility of our construction with Arinkin's version of the middle convolution for connections on P^1 via the enhanced Riemann--Hilbert correspondence.Vor Kurzem entwickelten D'Agnolo und Kashiwara eine Riemann--Hilbert-Korrespondenz für holonome D-Moduln, wobei die Konstruktion der Zielkategorie auf dem Konzept der zu diesem Zweck eingeführten enhanced ind-sheaves basiert. In einer darauffolgenden Arbeit versahen sie die Kategorie der R-konstruierbaren enhanced ind-sheaves mit einer selbstdualen verallgemeinerten t-Struktur, was auf natürliche Weise einen Begriff von perversen enhanced ind-sheaves liefert. In unserer Arbeit verwenden wir diese Theorie, um eine Version von Katz' middle convolution für perverse enhanced ind-sheaves zu definieren und zu untersuchen. Dabei gehen wir auch auf die Kompatibilität unserer Konstruktion mit Arinkins middle convolution für Zusammenhänge auf P^1 unter der Riemann--Hilbert-Korrespondenz ein