Parmar Avanish S, Muschol Martin
Department of Physics, University of South Florida, Tampa, FL 33620, USA.
J Colloid Interface Sci. 2009 Nov 1;339(1):243-8. doi: 10.1016/j.jcis.2009.07.031. Epub 2009 Jul 18.
Measuring tracer diffusion provides a convenient approach for monitoring local changes in solution viscosity or for determining viscosity changes in response to multiple solution parameters including pH, temperature, salt concentrations or salt types. One common limitation of tracer diffusion in biologically relevant saline solutions is the loss of colloidal stability and aggregation of the tracer particles with increasing ionic strength. Using dynamic light scattering to measure tracer diffusion, we compared the performance of two different types of tracer particles, polystyrene nanobeads vs. the small protein lysozyme, for viscosity measurements of saline solutions. Polystyrene beads provide reliable values for water viscosity, but begin flocculating at ionic strengths exceeding about 100mM. Using lysozyme, in contrast, we could map out viscosity changes of saline solutions for a variety of different salts, for salt concentrations up to 1M, over a wide range of pH values, and over the temperature range most relevant for biological systems (5-40 degrees C). Due to its inherently high structural and colloidal stability, lysozyme provides a convenient and reliable tracer particle for all these measurements, and its use can be readily extended to other optical approaches towards localized measurements of tracer diffusion such as fluorescence correlation spectroscopy.
测量示踪剂扩散为监测溶液粘度的局部变化或确定响应多种溶液参数（包括pH值、温度、盐浓度或盐类型）的粘度变化提供了一种便捷的方法。在生物相关盐溶液中，示踪剂扩散的一个常见限制是随着离子强度的增加，示踪剂颗粒的胶体稳定性丧失和聚集。我们使用动态光散射来测量示踪剂扩散，比较了两种不同类型的示踪剂颗粒（聚苯乙烯纳米珠与小蛋白溶菌酶）在盐溶液粘度测量中的性能。聚苯乙烯珠能提供可靠的水粘度值，但在离子强度超过约100mM时开始絮凝。相比之下，使用溶菌酶，我们可以绘制出各种不同盐、盐浓度高达1M、在很宽的pH值范围内以及在与生物系统最相关的温度范围（5-40摄氏度）内盐溶液的粘度变化。由于其固有的高结构和胶体稳定性，溶菌酶为所有这些测量提供了一种便捷且可靠的示踪剂颗粒，并且其应用可以很容易地扩展到其他用于局部测量示踪剂扩散的光学方法，如荧光相关光谱法。
