Actively Driven Light-Addressable Sensor/Actuator System for Automated pH Control for the Integration in Lab-On-A-Chip (LoC) Platforms

ACS Sensors, vol. 9, pp. 1533–1544

Abstract

The miniaturization of microfluidic systems usually comes at the cost of more difficult integration of sensors and actuators inside the channel. As an alternative, this work demonstrates the embedding of semiconductor-based sensor and actuator technologies that can be spatially and temporally controlled from outside the channel using light. The first element is a light-addressable potentiometric sensor, consisting of an Al/Si/SiO 2 /Si 3 N 4 structure, that can measure pH changes at the Si 3 N 4 /electrolyte interface. The pH value is a crucial factor in biological and chemical systems, and besides measuring, it is often important to bring the system out of equilibrium or to adjust and control precisely the surrounding medium. This can be done photoelectrocatalytically by utilizing light-addressable electrodes. These consist of a glass/SnO 2:F/TiO 2 structure, whereby direct charge transfer between the TiO 2 and the electrolyte leads to a pH change upon irradiation. To complement the advantages of both, we integrated a light-addressable sensor with a pH sensitivity of 41.5 mV·pH –1 and a light-addressable electrode into a microfluidic setup. Here, we demonstrated a simultaneous operation with the ability to generate and record pH gradients inside a channel under static and dynamic flow conditions. The results show that dependent on the light-addressable electrode (LAE)-illumination conditions, pH changes up to ΔpH of 2.75 and of 3.52 under static and dynamic conditions, respectively, were spatially monitored by the light-addressable potentiometric sensor. After flushing with fresh buffer solution, the pH returned to its initial value. Depending on the LAE illumination, pH gradients with a maximum pH change of ΔpH of 1.42 were tailored perpendicular to the flow direction. In a final experiment, synchronous LAE illumination led to a stepwise increase in the pH inside the channel.

Authors 6

1. Rene Welden Aachen Institute of Nano- and Biotechnologies (INB)

   KU Leuven · FH Aachen

   Affiliation as printed

   Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Heinrich-Mußmann-Str. 1, Jülich 52428, Germany

   Laboratory for Soft Matter and Biophysics, KU Leuven, Celestijnenlaan 200D, Leuven 3001, Belgium

2. Anirban Das

   Queen Mary University of London

   Affiliation as printed

   School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, U.K

3. Steffi Krause

   Queen Mary University of London

   Affiliation as printed

   School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, U.K

4. Michael Josef Schöning Aachen Institute of Nano- and Biotechnologies (INB)

   Forschungszentrum Jülich · FH Aachen

   Affiliation as printed

   Institute of Biological Information Processing (IBI-3), Forschungszentrum Jülich GmbH, Jülich 52428, Germany

   Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Heinrich-Mußmann-Str. 1, Jülich 52428, Germany

5. Patrick Hermann Wagner Aachen Institute of Nano- and Biotechnologies (INB)

   KU Leuven · FH Aachen

   Affiliation as printed

   Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Heinrich-Mußmann-Str. 1, Jülich 52428, Germany

   Laboratory for Soft Matter and Biophysics, KU Leuven, Celestijnenlaan 200D, Leuven 3001, Belgium

6. Torsten Wagner corresponding Aachen Institute of Nano- and Biotechnologies (INB)

   Forschungszentrum Jülich · FH Aachen

   Affiliation as printed

   Institute of Biological Information Processing (IBI-3), Forschungszentrum Jülich GmbH, Jülich 52428, Germany

   Institute of Nano- and Biotechnologies (INB), Aachen University of Applied Sciences, Heinrich-Mußmann-Str. 1, Jülich 52428, Germany