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

Abstract

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-block-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 BF-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 pK 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.

Downscaling screening cultures in a multifunctional bioreactor array‐on‐a‐chip for speeding up optimization of yeast‐based lactic acid bioproduction

“…The synthesis of the oxygen‐sensitive particles as well as their characterization and calibration were described in previous works (Ehgartner, J., Strobl, et al, 2016; Ehgartner, Sulzer, et al, 2016). Oxygen monitoring was carried out at a sampling frequency of 1 Hz using a FireStingO2 optical oxygen meter (Pyroscience, Germany) connected to optical fibers (length 1 m, outer diameter 2.2 mm, fiber diameter 1 mm; Sticker et al, 2019).…”

Technology Advancements in Blood Coagulation Measurements for Point-of-Care Diagnostic Testing

“…Electrochemical biosensors embedded inside microfluidic chips facilitate multiplexed sensing of different parameters such as pH, oxygen, glucose, lactate, and chloride (Ehgartner et al, 2016). In addition, microfluidic centrifugal technology has enabled miniaturization of typical laboratory processes such as blood plasma separation (Haeberle et al, 2006) and enzymelinked immunosorbent assay (Lai et al, 2004).…”

Integration and application of optical chemical sensors in microbioreactors

“…Even multiple parameters in one sensor are now possible. 7 The quantification of key variables of biotechnological processes is thus feasible with optical sensors alone. Furthermore, not only have new analytes been added, there is now also a range of novel dyes and sensor matrices, and with it a host of sensor preparation and integration methods.…”

“…Ehgartner et al (2016) 7 showed that it is possible to simultaneously monitor oxygen and pH using core-shell nanosensors in a microfluidic flow system. For this purpose lipophilic oxygen and pH nanoparticles were embedded into polyIJstyrene-block-vinylpyrrolidone) nanoparticles.…”