Department of Biomedical Engineering, National Cheng Kung University, Tainan 701, Taiwan.
Institute of Chemistry, Vietnam Academy of Science and Technology, Hanoi 1000, Vietnam.
Sensors (Basel). 2019 Mar 10;19(5):1217. doi: 10.3390/s19051217.
Viscosity is an important property of liquids. A viscosity change of aqueous substances that deviates from their normal levels usually implies a compromise in quality due to degradation or microorganism proliferation. Monitoring of macro-scale viscosity can be simply realized by various conventional tools, such as rotational viscometers, capillary tubes, falling bodies, and so forth. Nevertheless, today, micro-volume viscosity measurement remains a challenging endeavor, resulting in rare, expensive, or difficult-to-obtain samples not very well studied. For this reason, a novel technique for micro-viscosity based on rotational Brownian motion is presented in this paper. Janus microbeads were made by coating fluorescent polystyrene beads with gold film. Taking advantage of the bead configuration of half gold/half fluorescence, the rotational Brownian signal was expressed in terms of blinking fluorescent intensity. The characteristic correlation time was derived from the blinking intensity of trace amounts of a selected medium over a certain time period, and results were correlated with viscosity. Given a volume of only 2 μL for each measurement, calibration of a series of glycerol⁻water mixtures (100%⁻1% (/) water content) yielded good agreement with the expected viscosity predictions over the range of 0.8⁻574.8 cP. Five common oil products, including lubricant oil, baby oil, food oil, olive oil, and motor oil, were further investigated to demonstrate the feasibility and practicability of the proposed technique. Data measured by the rotational Brownian motion-based diffusometer were comparable with those measured by a commercial rotational viscometer. The method also explicitly showed viscosity degradation after the oils were heated at a high temperature of over 100 °C for 10 min. Evaluation proved the proposed Janus microbead-enabled rotational diffusometric technique to be a promising approach for rapid and micro-scale viscosity measurement.
粘度是液体的一个重要性质。水相物质的粘度变化偏离正常水平通常意味着由于降解或微生物增殖而导致质量下降。各种常规工具，如旋转粘度计、毛细管、落体等，可以简单地实现宏观粘度的监测。然而，目前，微体积粘度测量仍然是一项具有挑战性的工作，导致很少、昂贵或难以获得的样本研究不足。为此，本文提出了一种基于旋转布朗运动的微粘度新方法。通过在荧光聚苯乙烯珠上涂覆金膜来制备 Janus 微珠。利用金和荧光的一半一半的珠状结构，旋转布朗信号可以用闪烁荧光强度来表示。从选定介质在一定时间内的微量旋转布朗信号的闪烁强度中得出特征相关时间，并将结果与粘度相关联。每次测量仅需要 2 μL 的体积，一系列甘油-水混合物（100%-1%水含量）的校准结果与预期粘度预测值在 0.8-574.8 cP 的范围内非常吻合。进一步研究了五种常见的油产品，包括润滑油、婴儿油、食用油、橄榄油和机油，以证明所提出技术的可行性和实用性。基于旋转布朗运动的扩散计测量的数据与商用旋转粘度计测量的数据相当。该方法还明确显示了在将油加热至 100°C 以上 10 分钟后，油的粘度下降。评估证明了所提出的基于 Janus 微珠的旋转扩散测量技术是一种快速、微尺度粘度测量的有前途的方法。
