Optically driven fluid flow along arbitrary microscale patterns using thermoviscous expansion
Optically driven fluid flow along arbitrary microscale patterns using thermoviscous expansion
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DOI：
10.1063/1.3026526
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发表时间：
2008-11-15
影响因子：
3.2
通讯作者：
Braun, Dieter
中科院分区：
文献类型：
--
作者：
Weinert, Franz M.;Braun, Dieter
我们展示了如何通过激光扫描显微镜移动流体。流体膜的选定部分沿着由红外激光焦点的重复运动产生的移动热点的路径被泵浦。通过这项技术，我们可以远程驱动分辨率为 2 μm 的任意二维流体流动模式。在水中达到 150 μm/s 的泵速，局部点的最大温度增加为 10 K。各种实验证实流体运动是由粘度梯度中的动态热膨胀引起的。现场的粘度因温度升高而降低。这导致光斑前部和尾部的热膨胀和热收缩之间的对称性被破坏。结果，由于光斑前部的不对称热膨胀和其尾迹的不对称热收缩，流体沿与光斑方向相反的方向移动。我们从纳维-斯托克斯方程推导出流体速度的解析表达式。其预测在许多不同条件下无需拟合参数即可通过实验得到证实。在水中，这种非线性导致光斑每次通过的流体步长< 100 nm。由于点运动可以在千赫兹范围内重复，因此流体速度可以超过 100 μm/s。使用这种技术，我们将纳米颗粒泵入凝胶中超过毫米。对于夹在未经处理和非结构化的一次性显微镜盖玻片之间的液体，演示了通过等分和混合来全光学创建 DNA 和生物分子稀释系列。所示的流体流动光学远程控制将微流体范式扩展到以前无法达到的微小体积、封闭流路、流动模式之间的快速切换以及极端流体条件下的远程流体控制。
We show how fluid can be moved by a laser scanning microscope. Selected parts of a fluid film are pumped along the path of a moving warm spot which is generated by the repetitive motion of an infrared laser focus. With this technique, we remotely drive arbitrary two-dimensional fluid flow patterns with a resolution of 2 mu m. Pump speeds of 150 mu m/s are reached in water with a maximal temperature increase in the local spot of 10 K. Various experiments confirm that the fluid motion results from the dynamic thermal expansion in a gradient of viscosity. The viscosity in the spot is reduced by its enhanced temperature. This leads to a broken symmetry between thermal expansion and thermal contraction in the front and the wake of the spot. As result the fluid moves opposite to the spot direction due to both the asymmetric thermal expansion in the spot front and the asymmetric thermal contraction in its wake. We derive an analytical expression for the fluid speed from the Navier-Stokes equations. Its predictions are experimentally confirmed without fitting parameters under a number of different conditions. In water, this nonlinearity leads to a fluid step of < 100 nm for each passage of the spot. Since the spot movement can be repeated in the kilohertz regime, fluid speeds can exceed 100 mu m/s. Using this technique, we pump nanoparticles over millimeters through a gel. An all-optical creation of a dilution series of DNA and biomolecules by aliquotation and mixing is demonstrated for fluids sandwiched between untreated and unstructured, disposable microscope cover slips. The shown optical remote control of fluid flow expands the microfluidic paradigm into previously inaccessible regimes of tiny volumes, closed flow paths, fast switching between flow patterns, and remote fluid control under extreme fluid conditions.