Hahn-Schickard, Georges-Koehler-Allee 103, 79110 Freiburg, Germany.
Lab Chip. 2017 Feb 28;17(5):864-875. doi: 10.1039/c6lc01536k.
We present new unit operations for valving and switching in centrifugal microfluidics that are actuated by a temperature change rate (TCR) and controlled by the rotational frequency. Implementation is realized simply by introducing a comparatively large fluidic resistance to an air vent of a fluidic structure downstream of a siphon channel. During temperature decrease at a given TCR, the air pressure inside the downstream structure decreases and the fluidic resistance of the air vent slows down air pressure compensation allowing a thermally induced underpressure to build up temporarily. Thereby the rate of temperature change determines the time course of the underpressure for a given geometry. The thermally induced underpressure pulls the liquid against a centrifugal counterpressure above a siphon crest, which triggers the valve or switch. The centrifugal counterpressure (adjusted by rotation) serves as an independent control parameter to allow or prevent valving or switching at any TCR. The unit operations are thus compatible with any temperature or centrifugation protocol prior to valving or switching. In contrast to existing methods, this compatibility is achieved at no additional costs: neither additional fabrication steps nor additional disk space or external means are required besides global temperature control, which is needed for the assay. For the layout, an analytical model is provided and verified. The TCR actuated unit operations are demonstrated, first, by a stand-alone switch that routes the liquid to either one of the two collection chambers (n = 6) and, second, by studying the robustness of TCR actuated valving within a microfluidic cartridge for highly integrated nucleic acid testing. Valving could safely be prevented during PCR by compensating the thermally induced underpressure of 3.52 kPa with a centrifugal counterpressure at a rotational frequency of 30 Hz with a minimum safety range to valving of 2.03 kPa. Subsequently, a thermally induced underpressure of 2.55 kPa was utilized for robust siphon valving at 3 Hz with a minimum safety range of 2.32 kPa.
我们提出了新的离心微流控阀和开关单元操作，其由温度变化率（TCR）驱动，并由旋转频率控制。通过在虹吸管下游的流道的空气出口处引入相对较大的流体阻力，就可以简单地实现这种操作。在给定 TCR 下温度降低时，下游结构内的空气压力降低，空气出口的流体阻力减缓空气压力补偿，从而允许热诱导的负压暂时建立。因此，温度变化率决定了给定几何形状下负压的时间过程。热诱导的负压将液体拉向虹吸管顶部上方的离心反压，从而触发阀或开关。离心反压（通过旋转调节）用作独立的控制参数，以允许或防止在任何 TCR 下进行阀或开关操作。因此，这些单元操作与阀或开关之前的任何温度或离心协议兼容。与现有方法相比，这种兼容性无需额外成本即可实现：除了用于检测的全局温度控制之外，不需要额外的制造步骤、磁盘空间或外部手段。对于布局，提供了一个分析模型，并对其进行了验证。首先通过一个独立的开关演示了 TCR 驱动的单元操作，该开关将液体路由到两个收集室之一（n = 6），其次通过研究高度集成的核酸测试微流控芯片中 TCR 驱动的阀的稳健性来研究。通过在 30 Hz 的旋转频率下用离心反压补偿 3.52 kPa 的热诱导负压，可以安全地防止 PCR 期间的阀动作，阀动作的最小安全范围为 2.03 kPa。随后，利用 2.55 kPa 的热诱导负压在 3 Hz 下进行稳健的虹吸管阀动作，最小安全范围为 2.32 kPa。
