The metering function in centrifugal microfluidic systems: From comparative analysis to design guidelines

Metering (also known as aliquoting) is a critical function in centrifugal microfluidic systems, enabling the division of a larger inlet volume into smaller, well-defined downstream volumes. However, existing metering techniques often face challenges related to accuracy, reproducibility, and adaptability to varying fluid volumes, geometric layouts, and operational conditions. In this study, we systematically investigate the metering process by characterizing its performance with respect to key parameters: inlet volume, rotational speed, chamber geometry, and the formation of liquid plugs. Extensive experiments were conducted using two distinct microfluidic configurations, each designed to evaluate metering performance across nano- and microliter scales. Comparative analysis of the designs revealed critical dependencies between metering accuracy and structural features, such as circuit architecture and surface wettability. Liquid plugs within geometries connected to the metering chamber were analyzed both experimentally and theoretically. A critical threshold in plug length and centrifugal acceleration was identified, above which plugs were consistently displaced. Additionally, we examined the influence of in-plane circuit layout by comparing chips patterned in either Cartesian or cylindrical coordinates. Systematic differences in metering precision and reproducibility were observed, arising purely from geometric alignment relative to the centrifugal force. This work establishes a comprehensive framework for optimizing the metering functionality in centrifugal microfluidics. It offers practical design guidelines for the development of robust Lab-on-a-Disk systems.