Abstract
The advanced and widespread use of microfluidic devices, which are usually fabricated in polydimethylsiloxane (PDMS), requires the integration of many sensors, always compatible with microfluidic fabrication processes. Moreover, current limitations of the existing optical and electrochemical oxygen sensors regarding long-term stability due to sensor degradation, biofouling, fabrication processes and cost have led to the development of new approaches. Thus, this manuscript reports the development, fabrication and characterization of a low-cost and highly sensitive dissolved oxygen optical sensor based on a membrane of PDMS doped with platinum octaethylporphyrin (PtOEP) film, fabricated using standard microfluidic materials and processes. The excellent mechanical and chemical properties (high permeability to oxygen, anti-biofouling characteristics) of PDMS result in membranes with superior sensitivity compared with other matrix materials. The wide use of PtOEP in sensing applications, due to its advantage of being easily synthesized using microtechnologies, its strong phosphorescence at room temperature with a quantum yield close to 50%, its excellent Strokes Shift as well as its relatively long lifetime (75 µs), provide the suitable conditions for the development of a miniaturized luminescence optical oxygen sensor allowing long-term applications. The influence of the PDMS film thickness (0.1–2.5 mm) and the PtOEP concentration (363, 545, 727 ppm) in luminescent properties are presented. This enables to achieve low detection levels in a gas media range from 0.5% up to 20%, and in liquid media from 0.5 mg/L up to 3.3 mg/L at 1 atm, 25 °C. As a result, we propose a simple and cost-effective system based on a LED membrane photodiode system to detect low oxygen concentrations for in situ applications.
Highlights
The need for oxygen analysis led to the inevitable search for more efficient, robust and low-cost technologies to detect O2 in a variety of media and applications
We present an optical sensor for dissolved oxygen, based on a LED membrane
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Summary
The need for oxygen analysis led to the inevitable search for more efficient, robust and low-cost technologies to detect O2 in a variety of media and applications. This work focuses on in situ ocean applications, for low oxygen zones. This technology uses standard PDMS fabrication processes and could be potentially useful to analyze oxygen in microfluidic channels, for medical devices, biology and chemistry applications, marine research and other lab-on-a-chip devices. The most available oxygen sensors are based on electrochemical or optical detection methods The former, despite providing low-cost and label-free-based sensors, need periodic calibration adjustments and regular maintenance whenever external conditions change. They consume oxygen in their reading process, invalidating the results, which require a constant flow of fluid so that oxygen is not completely consumed
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