Laboratory for MEMS Applications, IMTEK - Department of Microsystems Engineering, University of Freiburg, Georges-Koehler-Allee 103, 79110 Freiburg, Germany.
Lab Chip. 2018 Jan 16;18(2):362-370. doi: 10.1039/c7lc01249g.
In centrifugal microfluidics, dead volumes in valves downstream of mixing chambers can hardly be avoided. These dead volumes are excluded from mixing processes and hence cause a concentration gradient. Here we present a new bubble mixing concept which avoids such dead volumes. The mixing concept employs heating to create a temperature change rate (TCR) induced overpressure in the air volume downstream of mixing chambers. The main feature is an air vent with a high fluidic resistance, representing a low pass filter with respect to pressure changes. Fast temperature increase causes rapid pressure increase in downstream structures pushing the liquid from downstream channels into the mixing chamber. As air further penetrates into the mixing chamber, bubbles form, ascend due to buoyancy and mix the liquid. Slow temperature/pressure changes equilibrate through the high fluidic resistance air vent enabling sequential heating/cooling cycles to repeat the mixing process. After mixing, a complete transfer of the reaction volume into the downstream fluidic structure is possible by a rapid cooling step triggering TCR actuated valving. The new mixing concept is applied to rehydrate reagents for loop-mediated isothermal amplification (LAMP). After mixing, the reaction mix is aliquoted into several reaction chambers for geometric multiplexing. As a measure for mixing efficiency, the mean coefficient of variation (C[combining macron]V[combining macron], n = 4 LabDisks) of the time to positivity (t) of the LAMP reactions (n = 11 replicates per LabDisk) is taken. The C[combining macron]V[combining macron] of the t is reduced from 18.5% (when using standard shake mode mixing) to 3.3% (when applying TCR actuated bubble mixing). The bubble mixer has been implemented in a monolithic fashion without the need for any additional actuation besides rotation and temperature control, which are needed anyhow for the assay workflow.
在离心微流控中，混合腔室下游的阀中的死体积几乎无法避免。这些死体积被排除在混合过程之外，因此会导致浓度梯度。在这里，我们提出了一种新的气泡混合概念，该概念可避免此类死体积。该混合概念采用加热的方式，在混合腔室下游的空气体积中产生温度变化率（TCR）引起的过压。主要特点是具有高流体阻力的空气出口，相对于压力变化而言，它是一个低通滤波器。快速的温度升高会导致下游结构中的压力迅速增加，从而将液体从下游通道推入混合腔室。随着空气进一步进入混合腔室，气泡形成，由于浮力而上升并混合液体。缓慢的温度/压力变化通过高流体阻力的空气出口平衡，从而实现顺序加热/冷却循环以重复混合过程。混合后，通过快速冷却步骤触发 TCR 驱动的阀，将反应体积完全转移到下游流体结构中。新的混合概念应用于重新水合环介导等温扩增（LAMP）的试剂。混合后，将反应混合物分装入几个反应室中，以实现几何多路复用。作为混合效率的度量，将时间到阳性（t）的 LAMP 反应（每个 LabDisk 重复 11 次）的变异系数（C[combining macron]V[combining macron]，n = 4 个 LabDisks）的平均值。当使用标准摇动混合模式时，t 的 C[combining macron]V[combining macron]从 18.5%（n = 4 个 LabDisks）降低到 3.3%（当应用 TCR 驱动的气泡混合时）。气泡混合器已以单片方式实现，无需任何额外的致动，除了旋转和温度控制之外，这是无论如何都需要进行测定工作流程的。
