Conditional siphon priming for multi-step assays on centrifugal microfluidic platforms

Centrifugal microfluidics has proven to be successful in biomedical diagnostics, biological analysis and environmental monitoring. However, the automation of multi-step sample processing, reaction and detection remains a great challenge. In this study, a conditional siphon priming technique is introduced for multi-step liquid addition or selective routing. Since the siphon channel is locally modified or venting is blocked by liquid in another chamber, siphon priming can be triggered by liquid addition or venting at low frequency. Using this technique, sequential release of liquids and selective routing in multiple manners were successfully achieved. As a proof of concept, a centrifugal microfluidic platform was designed for on-site ammonium analysis in water samples. The linear range of ammonium concentrations is extended by integration of a dilution process. This novel valving technique provides new solutions for integration of complex liquid handling processes on centrifugal platforms.