Abstract
A 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.
Highlights
Microfluidic platforms are useful tools for studying organic reactions [1], enzyme kinetics [2,3,4] and cells [5,6,7,8] at microor nanoscale
The used computerized numerical control (CNC) airbrush spraying set-up can be programmed which is a helpful step for obtaining reproducible sensor layers
We report a powerful measurement-set up for microfluidic applications consisting of NIR-emitting optical oxygen sensors and an inexpensive and robust readout via commercially available oxygen meters adapted with gradient index lenses to enhance the signal intensities
Summary
Microfluidic platforms are useful tools for studying organic reactions [1], enzyme kinetics [2,3,4] and cells [5,6,7,8] at microor nanoscale. The integration of luminescent chemical sensors into microfluidic devices can be one useful technique for obtaining online and real-time analytical data at this miniaturized scale [9,10]. Luminescent oxygen sensors are highly suited for microfluidic applications due to their high sensitivity, ability of contactless readout, ease of miniaturization, ease of integration and their low cost [11]. Ground state triplet oxygen is transformed into reactive excited state singlet oxygen during the quenching process of the luminescent oxygen sensors [12,13,14]. The excited state singlet oxygen can react with its surrounding environment and can bias the investigated system in the microscale [15]
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