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Various types of valving techniques, especially passive valves, have been demonstrated on centrifugal microfluidic devices, which are simple to fabricate and easy to implement. In this study, a novel interruptible siphon valving technique is proposed to enhance the flexibility for the flow control on passive centrifugal microfluidic platforms. Differs from traditional siphon valves, the main feature of the interruptible valve is having an additional air vent at the crest of the siphon channel. Using this design, a primed siphon can discharge liquids in a proper range of spin speed, or be cut off by further increasing the rotation frequency. An analytical model of the interruptible siphon valving is proposed and verified to estimate the cut-off spin speed, which can be a guidance for the device design. To demonstrate the potential of this valve for flow control, five typical applications based on interruptible siphon valving were proposed and evaluated, including band-pass siphon valving, repeated washing, inward pumping, programmable flow control and flow sequencing. Our methods are well balanced in simplicity and flexibility, and have significant potential to be applied in multistep biochemical analysis, immunoassays and nucleic acid tests.

To prevent the propagation of pathogens and minimize the damage to humans, an ultrasensitive and colorimetric dual detection method for pathogens was developed and validated based on the Multiplex Super Polymerase Chain Reaction (MS-PCR) and Asymmetric Tailing Hybridization Chain Reaction (AT-HCR). In the 5-min MS-PCR, dual pathogens were recognized and amplified simultaneously, generating plenty of dsDNA products with protruding ssDNA toeholds. Since a blocker of oxyethyleneglycol bridge was exquisitely inserted into two-set forward primers, which hindered the polymerase extension. Then, two-set ssDNA toeholds initiated two-set AT-HCR in 20-min and 60-min visual analysis depending on G-quadruplex DNAzyme was induced by Terminal deoxynucleotidyl Transferase (TdT) at the tails of AT-HCR at 3′-OH. During the process, the first magnetic separation was conducted after MS-PCR based on our home-made XP beads, to remove primer-dimers and other impurities in 30-min. The second magnetic separation was performed before TdT catalysis based on dynabeads, to eliminate unreacted AT-HCR hairpins in 15-min. To challenge the practical application capability of this strategy, the detection of analyte in fat-free milk was also tested and demonstrated similar detection capability to visualize single cell. Therefore, the proposed sensor exhibited a high selectivity and sensitivity and is thus applicable for visual single cell detection of dual-pathogens of Salmonella spp. and Staphylococcus aureus simultaneously in 130-min. Generally, it provides a visual, ultrasensitive, rapid and universal detective method for dual-target analysis.

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.

Bacterial contamination has become an important issue for food safety in recent years. Culture-based methods, though a gold standard for bacterial detection, usually take a long time for detection. Microfluidic-based molecular diagnosis can help to achieve rapid and accurate detection of bacteria; however, existing microfluidic systems have limited portability because bulky and complicated instruments are needed. In this study, a portable analyzer was developed to rapidly and simultaneously detect five types of foodborne bacteria (Staphylococcus aureus, Salmonella, Shigella, enterotoxigenic Escherichia coli, and Pseudomonas aeruginosa) on a centrifugal chip. Integration of the processes, including bacteria lysis, visible loop-mediated amplification (LAMP) and detection, was accomplished within 70 min. The analyzer has a compact size (151 × 134 × 110 mm) and two motors positioned on both sides of the centrifugal chip. The upper motor was used to generate a rotating magnetic field for lysing bacteria by bead-beating, whereas the lower motor rotated the chip on demand to execute the following processes: sedimentation of bacteria lysate, mixing of the LAMP buffer and bacteria lysate, and distribution of the mixture to the designated reaction chambers. The LAMP results were detected by a color sensor in the analyzer. Using this portable analyzer, similar detection sensitivities for the five bacteria were achieved compared to that of conventional LAMP in Eppendorf tubes. Considering the portability of the system and its simplicity of operation, the analyzer developed in this study may be of potential use in point-of-care applications.

The burden of chronic diseases is unquestionably a predominant challenge to global health. Chronic diseases are the long-term diseases and their intervention requires frequent monitoring of disease development, which makes the self-checkup of blood biochemistry at home highly desired. However, there is few devices that can be used at home for simultaneous test of multiple finger-prick blood biochemicals. In this study, a fully integrated microfluidic analyzer which can perform multiple blood biochemical analysis is proposed. The finger-prick blood can be directly aspirated into the chip containing diluent and lyophilized reagents, and the following processes, including serum/plasma separation and metering, diluent release and metering, quantified serum/plasma and diluent mixing, the diluted serum/plasma distribution to the reaction chambers, and the biochemical reaction and results measurement, were sequentially and automatically performed on the self-contained microfluidic chip. Using this one key operated portable analyzer, users can easily accomplish their own biochemical detection without medical training, making self-served health monitoring for chronic diseases at biochemical level possible. In the current report, fully automated detection for three blood biochemical indexes, including blood glucose, total cholesterol and triglycerides, were achieved in 15 min. The finger-prick blood samples from volunteers were measured by this microfluidic analyzer, and the results were comparable to those obtained from a commercial biochemical analyzer used in hospital.