Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel , Mattenstrasse 26, CH-4058 Basel, Switzerland.
Anal Chem. 2013 Sep 17;85(18):8676-83. doi: 10.1021/ac4014918. Epub 2013 Aug 23.
A microcantilever based method for fluid viscosity and mass density measurements with high temporal resolution and microliter sample consumption is presented. Nanomechanical cantilever vibration is driven by photothermal excitation and detected by an optical beam deflection system using two laser beams of different wavelengths. The theoretical framework relating cantilever response to the viscosity and mass density of the surrounding fluid was extended to consider higher flexural modes vibrating at high Reynolds numbers. The performance of the developed sensor and extended theory was validated over a viscosity range of 1-20 mPa·s and a corresponding mass density range of 998-1176 kg/m(3) using reference fluids. Separating sample plugs from the carrier fluid by a two-phase configuration in combination with a microfluidic flow cell, allowed samples of 5 μL to be sequentially measured under continuous flow, opening the method to fast and reliable screening applications. To demonstrate the study of dynamic processes, the viscosity and mass density changes occurring during the free radical polymerization of acrylamide were monitored and compared to published data. Shear-thinning was observed in the viscosity data at higher flexural modes, which vibrate at elevated frequencies. Rheokinetic models allowed the monomer-to-polymer conversion to be tracked in spite of the shear-thinning behavior, and could be applied to study the kinetics of unknown processes.
提出了一种基于微悬臂梁的方法，用于以高时间分辨率和微升样品消耗测量流体的粘度和质量密度。纳米机械悬臂梁振动由光热激励驱动，并通过使用两个不同波长的激光束的光学光束偏转系统检测。将与周围流体的粘度和质量密度相关的悬臂梁响应的理论框架扩展到考虑在高雷诺数下振动的更高挠曲模式。使用参考流体验证了所开发的传感器和扩展理论的性能，在 1-20 mPa·s 的粘度范围和相应的 998-1176 kg/m(3)的质量密度范围内。通过两相配置将样品塞与载体流体分离，并结合微流控流动池，允许在连续流动下顺序测量 5 μL 的样品，从而使该方法适用于快速可靠的筛选应用。为了演示动态过程的研究，监测了丙烯酰胺自由基聚合过程中发生的粘度和质量密度变化，并与已发表的数据进行了比较。在更高的挠曲模式下观察到粘度数据中的剪切稀化，这些模式以升高的频率振动。流变动力学模型允许在存在剪切稀化行为的情况下跟踪单体到聚合物的转化率，并且可以应用于研究未知过程的动力学。
