Hellman Amy N, Rau Kaustubh R, Yoon Helen H, Bae Stephanie, Palmer James F, Phillips K Scott, Allbritton Nancy L, Venugopalan Vasan
Department of Chemical Engineering and Materials Science, University of California, Irvine, California 92697, USA.
Anal Chem. 2007 Jun 15;79(12):4484-92. doi: 10.1021/ac070081i. Epub 2007 May 18.
We demonstrate a novel strategy for mixing solutions and initiating chemical reactions in microfluidic systems. This method utilizes highly focused nanosecond laser pulses from a Q-switched Nd:YAG laser at lambda = 532 nm to generate cavitation bubbles within 100- and 200-microm-wide microfluidic channels containing the parallel laminar flow of two fluids. The bubble expansion and subsequent collapse within the channel disrupts the laminar flow of the parallel fluid streams and produces a localized region of mixed fluid. We use time-resolved imaging and fluorescence detection methods to visualize the mixing process and to estimate both the volume of mixed fluid and the time scale for the re-establishment of laminar flow. The results show that mixing is initiated by liquid jets that form upon cavitation bubble collapse and occurs approximately 20 micros following the delivery of the laser pulse. The images also reveal that mixing occurs on the millisecond time scale and that laminar flow is re-established on a 50-ms time scale. This process results in a locally mixed fluid volume in the range of 0.5-1.5 nL that is convected downstream with the main flow in the microchannel. We demonstrate the use of this mixing technique by initiating the horseradish peroxidase-catalyzed reaction between hydrogen peroxide and nonfluorescent N-acetyl-3,7-dihydroxyphenoxazine (Amplex Red) to yield fluorescent resorufin. This approach to generate the mixing of adjacent fluids may prove advantageous in many microfluidic applications as it requires neither tailored channel geometries nor the fabrication of specialized on-chip instrumentation.
我们展示了一种在微流控系统中混合溶液并引发化学反应的新策略。该方法利用调Q Nd:YAG激光器产生的高度聚焦的纳秒激光脉冲(波长λ = 532 nm),在包含两种流体平行层流的100微米和200微米宽的微流控通道内产生空化气泡。通道内气泡的膨胀和随后的坍塌会扰乱平行流体流的层流,并产生混合流体的局部区域。我们使用时间分辨成像和荧光检测方法来可视化混合过程,并估计混合流体的体积以及层流重新建立的时间尺度。结果表明,混合是由空化气泡坍塌时形成的液体射流引发的,并且在激光脉冲发射后约20微秒发生。图像还显示,混合发生在毫秒时间尺度上,层流在50毫秒时间尺度上重新建立。这个过程会产生0.5 - 1.5纳升范围内的局部混合流体体积,该体积会随着微通道中的主流向下游对流。我们通过引发辣根过氧化物酶催化的过氧化氢与非荧光的N - 乙酰 - 3,7 - 二羟基吩恶嗪(Amplex Red)之间的反应以产生荧光试卤灵,展示了这种混合技术的用途。这种使相邻流体混合的方法在许多微流控应用中可能具有优势,因为它既不需要定制的通道几何形状,也不需要制造专门的片上仪器。