Comparison of Measurement Protocols for Internal Channels of Transparent Microfluidic Devices

The microfluidic industry faces a significant challenge due to the lack of sensitive and standardized methods. One critical need is the measurement of internal channel dimensions in fully assembled chips. This study presents and compares several protocols for measuring these dimensions, including optical profilometry, optical microscopy, and tiled digital imagery. Standardized chips made from two materials commonly used in microfluidics (borosilicate glass and Cyclic Olefin Copolymer) were evaluated using each protocol. A consistency analysis using normalized error statistics identified optical profilometry as the most reliable method, offering the lowest uncertainty and the highest consistency with nominal geometry values. However, all protocols encountered difficulties with vertical depth measurements of internal structures. Future research should focus on addressing these limitations, including investigating the influence of multiple refractive surfaces on optical profilometry and exploring confocal microscopy. In conclusion, this work provides a comprehensive comparison of measurement protocols for internal microfluidic structures and offers a practical solution for applications in the microfluidic industry, while also identifying important directions for future research.