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.
ACS Sens. 2024 Mar 22;9(3):1533-1544. doi: 10.1021/acssensors.3c02712. Epub 2024 Mar 6.
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/SiN structure, that can measure pH changes at the SiN/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:F/TiO structure, whereby direct charge transfer between the TiO 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 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.
微流控系统的小型化通常会导致传感器和执行器更难以集成到通道内部。作为替代方案，这项工作展示了嵌入式半导体传感器和执行器技术，这些技术可以使用光从通道外部进行空间和时间控制。第一个元件是光寻址电位传感器，由 Al/Si/SiO/SiN 结构组成，可以测量 SiN/电解质界面处的 pH 值变化。pH 值是生物和化学系统中的关键因素，除了测量之外，通常还需要使系统脱离平衡状态，或者精确地调节和控制周围的介质。这可以通过光电催化利用光寻址电极来实现。这些电极由玻璃/SnO:F/TiO 结构组成，通过 TiO 和电解质之间的直接电荷转移，在照射时会导致 pH 值发生变化。为了补充两者的优势，我们将具有 41.5 mV·pH 光寻址传感器和光寻址电极集成到微流控装置中。在这里，我们演示了在静态和动态流动条件下，在通道内同时生成和记录 pH 梯度的能力。结果表明，取决于光寻址电极（LAE）的照明条件，在静态和动态条件下，通过光寻址电位传感器可以分别监测到高达 2.75ΔpH 和 3.52ΔpH 的 pH 值变化。用新鲜缓冲溶液冲洗后，pH 值恢复到初始值。根据 LAE 照明情况，可以沿垂直于流动方向定制具有最大 pH 值变化ΔpH 为 1.42 的 pH 梯度。在最后的实验中，同步的 LAE 照明导致通道内的 pH 值逐步增加。
