Online analysis of oxygen inside silicon-glass microreactors with integrated optical sensors

AbstractA powerful online analysis set-up for oxygen measurements within microfluidic devices is presented. It features integration of optical oxygen sensors into microreactors, which enables contactless, accurate and inexpensive readout using commercially available oxygen meters via luminescent lifetime measurements in the frequency domain (phase shifts). The fabrication and patterning of sensor layers down to a size of 100μm in diameter is performed via automated airbrush spraying and was used for the integration into silicon-glass microreactors. A novel and easily processable sensor material is also presented and consists of a polystyrene- silicone rubber composite matrix with embedded palladium(II) or platinum(II) meso-tetra(4-fluorophenyl) tetrabenzoporphyrin (PdTPTBPF and PtTPTBPF) as oxygen sensitive dye. The resulting sensor layers have several advantages such as being excitable with red light, emitting in the near-infrared spectral region, being photostable and covering a wide oxygen concentration range. The trace oxygen sensor (PdTPTBPF) in particular shows a resolution of 0.06–0.22hPa at oxygen concentrations lower than 20hPa (<2% oxygen) and the normal range oxygen sensor (PtTPTBPF) shows a resolution of 0.2–0.6hPa at low oxygen concentrations (<50hPa) and 1–2hPa at ambient air oxygen concentrations. The sensors were integrated into different silicon-glass microreactors which were manufactured using mass production compatible processes. The obtained microreactors were applied for online monitoring of enzyme transformations, including d-alanine or d-phenylalanine oxidation by d-amino acid oxidase, and glucose oxidation by glucose oxidase

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

Ratiometric Oxygen Imaging to Predict Oxygen Diffusivity in Oak Wood During Red Wine Barrel Aging

Producción CientíficaAbstract In this work, we present a high-resolution oxygen imaging approach to study the two-dimensional oxygen dis- tribution inside an oak stave in contact with wine and that applies the series resistance model to explain the dynamic evolution of oak wood oxygen transfer rate (OTR). Oxygen flux throughout the oak stave has been studied by considering the wood as a permeable membrane with moisture content (MC) in a decreasing gradient from the wine-contacting side of the oak stave to the side in contact with atmospheric air in cellar conditions. The presence of different levels of liquid across the thickness of the wet stave modifies the oxygen diffusion flux, as the diffusion coefficient of oxygen in water is four orders of magnitude lower than in air. The stave resem- bles a multilayered membrane, where wood with an MC over the fiber saturation point represents a distinct layer. To that end, three simultaneous measurements were made, namely the MC profile of the wood within the thickness of the stave at different liquid-wood contact times, the OTR of the stave at those times, and finally the oxygen concentration profile with- in the thickness of the stave using planar optical sensors, a color camera, and ratiometric image analysis. The results show heat flux and oxygen flux that is analogous to that in a multilayer.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA124U14

Quantification of Arsenolipids in the Certified Reference Material NMIJ 7405‑a (Hijiki) using HPLC/Mass Spectrometry after Chemical Derivatization

Arsenic-containing lipids (arsenolipids) are novel natural products recently shown to be widespread in marine animals and algae. Research interest in these arsenic compounds lies in their possible role in the membrane chemistry of organisms and, because they occur in many popular seafoods, their human metabolism and toxicology. Progress has been restricted, however, by the lack of standard arsenolipids and of a quantitative method for their analysis. We report that the certified reference material CRM 7405-a (Hijiki) is a rich source of arsenolipids, and we describe a method based on HPLC-ICPMS/ESMS to quantitatively measure seven of the major arsenolipids present. Sample preparation involved extraction with DCM/methanol, a cleanup step with silica, and conversion of the (oxo)­arsenolipids originally present to thio analogues by brief treatment with H₂S. Compared to their oxo analogues, the thioarsenolipids showed much sharper peaks on reversed-phase HPLC, which facilitated their resolution and quantification. The compounds were determined by HPLC-ICPMS and HPLC-ESMS, which provided both arsenic-selective detection and high resolution molecular mass detection of the arsenolipids. In this way, the concentrations of two arsenic-containing hydrocarbons and five arsenosugar phospholipids are reported in the CRM Hijiki. This material may serve as a convenient source of characterized arsenolipids to delineate the presence of these compounds in seafoods and to facilitate research in a new era of arsenic biochemistry

Oxygen Management at the Microscale: A Functional Biochip Material with Long-Lasting and Tunable Oxygen Scavenging Properties for Cell Culture Applications

Oxygen plays a pivotal role in cellular homeostasis, and its partial pressure determines cellular function and fate. Consequently, the ability to control oxygen tension is a critical parameter for recreating physiologically relevant in vitro culture conditions for mammalian cells and microorganisms. Despite its importance, most microdevices and organ-on-a-chip systems to date overlook oxygen gradient parameters because controlling oxygen often requires bulky and expensive external instrumental setups. To overcome this limitation, we have adapted an off-stoichiometric thiol–ene-epoxy polymer to efficiently remove dissolved oxygen to below 1 hPa and also integrated this modified polymer into a functional biochip material. The relevance of using an oxygen scavenging material in microfluidics is that it makes it feasible to readily control oxygen depletion rates inside the biochip by simply changing the surface-to-volume aspect ratio of the microfluidic channel network as well as by changing the temperature and curing times during the fabrication process

Simultaneous Determination of Oxygen and pH Inside Microfluidic Devices Using Core–Shell Nanosensors

A powerful online analysis setup for the simultaneous detection of oxygen and pH is presented. It features core–shell nanosensors, which enable contactless and inexpensive read-out using adapted oxygen meters via modified dual lifetime referencing in the frequency domain (phase shift measurements). Lipophilic indicator dyes were incorporated into core–shell structured poly­(styrene-<i>block</i>-vinylpyrrolidone) nanoparticles (average diameter = 180 nm) yielding oxygen nanosensors and pH nanosensors by applying different preparation protocols. The oxygen indicator platinum­(II) meso-tetra­(4-fluorophenyl) tetrabenzoporphyrin (PtTPTBPF) was entrapped into the polystyrene core (oxygen nanosensors) and a pH sensitive BF₂-chelated tetraarylazadipyrromethene dye (aza-BODIPY) was incorporated into the polyvinylpyrrolidone shell (pH nanosensors). The brightness of the pH nanoparticles was increased by more than 3 times using a light harvesting system. The nanosensors have several advantages such as being excitable with red light, emitting in the near-infrared spectral region, showing a high stability in aqueous media even at high particle concentrations, high ionic strength, or high protein concentrations and are spectrally compatible with the used read-out device. The resolution for oxygen of the setup is 0.5–2.0 hPa (approximately 0.02–0.08 mg/L of dissolved oxygen) at low oxygen concentrations (<50 hPa) and 4–8 hPa (approximately 0.16–0.32 mg/L of dissolved oxygen) at ambient air oxygen concentrations (approximately 200 hPa at 980 mbar air pressure) at room temperature. The pH resolution is 0.03–0.1 pH units within the dynamic range (apparent p<i>K</i>_a 7.23 ± 1.0) of the nanosensors. The sensors were used for online monitoring of pH changes during the enzymatic transformation of Penicillin G to 6-aminopenicillanic acid catalyzed by Penicillin G acylase in miniaturized stirred batch reactors or continuous flow microreactors