The microfluidic chip is composed of a micro-nano-scale channel network. The microfluidic effect of biological, chemical, medical, and other samples is generated by the microchannel which carries the function of the "container" in the reaction. The dimensional accuracy such as the structure, shape, and size of the microchannel will directly impact the sample type, sample throughput, and sample injection rate in the microfluidic system. Therefore, it is of great significance to detect the three-dimensional topography of microfluidic chip channels. In recent years, scholars have continuously introduced new imaging detection methods for microfluidic chips, but most of the research focuses on the surface morphology of the reaction solution in the microchannel of the microfluidic chip or samples to be tested. There is little literature introduction on the measurement of microchannels. In this paper, digital holographic microscopic detection technology is combined with microfluidic technology. It provides a new imaging detection method for the microfluidic channel and has important application value for improving the quality of the chip.
This paper proposes a method for measuring the microchannels of microfluidic chips based on dual-wavelength image-plane digital holographic microscopy to meet the requirements of three-dimensional topography visualization of microfluidic chip channels. A reflective off-axis dual-wavelength image-plane digital holographic microscopic measurement system is built. Firstly, the lateral and vertical resolution and the magnification of the system are calibrated by the resolution target and standard sample. The results show that the dual-wavelength holographic microscope system has good accuracy and feasibility in the measurement of lateral and vertical depth. Then the straight channel of the polydimethylsiloxane (PDMS) microfluidic chip, the circular liquid phase chamber with vertical height transition, and the microchannel of the silicon-based microfluidic chip are measured. The phase distribution of the measurement surface is quantitatively recovered by combining the two-step phase division method and the
Firstly, a reflective off-axis dual-wavelength image-plane digital holographic microscopy experimental system is built (Fig. 1). To analyze and verify the accuracy and feasibility of the measurement system, this study adopts the 1951USAF resolution target, one-dimensional grid standard template, and segment difference standard film to calibrate the system respectively. The lateral resolution of this digital holographic microscope system can reach 2.2 μm (Fig. 4), and the actual magnification of the system is 13.5 times (Fig. 2). At the same time, the 20.79 μm segment difference standard film is measured, and the longitudinal depth is 19.9 μm with a relative error of 4.2% (Fig. 5). In addition, the three-dimensional morphology of the straight channel of the PDMS microfluidic chip, the circular liquid phase chamber with vertical height transition, and the microchannel of the silicon-based microfluidic chip are reproduced. Microchannels with different structures are obtained. The depth and the width of the straight channel and the circular chamber microchannel are 48.6 μm & 75.8 μm (Fig.9) and 48.5 μm & 76.6 μm (Fig. 10), respectively; the channel depth of silicon-based microfluidic chip is 61.6 μm (Fig. 11). Finally, the experimental results are well consistent with the white-light interferometry results (Table 1 & Table 2), which illustrates the reliability and accuracy of the dual-wavelength holographic microscope system, providing a new imaging detection method for the microchannel detection of microfluidic chips.
In this paper, a reflective off-axis dual-wavelength image-plane digital holographic microscopy measuring device is constructed based on digital holographic microscopy. The research on the three-dimensional topography measurement of microfluidic chip channels is carried out. The experimental results show that the lateral resolution of the system can reach 2.2 μm. The error range of the channel width and depth measurement is less than 4%, and the phase and plane distributions of the microchannel are accurately reproduced, indicating that the system has certain accuracy and feasibility. This research greatly expands the application field of digital holographic microscopic measurement, especially for closed microfluidic channels, meeting the needs of non-contact and label-free detection. In addition to the research on the structure of the chip channel itself, digital holographic microscopy can be extended to study the characteristics of the reaction solution, biological cells, and biological slice samples in the channel of the microfluidic chip. This study broadens the application scope of digital holographic microscopy and lays a foundation for the research on microfluidic-related technologies.
