A micro-volume viscosity measurement technique based on μPIV diffusometry

Liquid viscosity is a vital metric in numerous biochemical applications. A precise bio-assay often needs to determine viscosity prior to processing. This article presents a simple viscosity measurement technique based on the μPIV diffusometry. Assessing Brownian motion of neutrally buoyant particles in a micro-sized chamber provides a fast link to the liquid viscosity. The ensemble cross-correlation algorithm was used to extract the viscosity information out of a series of particle images. The width of a correlation peak decreased with the increased viscosity. For an accurate measurement, the study also evaluated deviations resulting from hindered diffusion. A correction factor was obtained by comparing the measured viscosity of glycerol solutions with the reference data. A calibration curve was made to fix the shifted measurements. The advantages of this technique are as follows: small volume (<1 μL), noninvasiveness, ease of use, and low cost. The good agreement between the data measured from the μPIV system and a commercial vis-cometer validated the approach. To prove the effectiveness, the technique was used to study the viscosity change of dextran solutions and its effect on the kinematics of the micro-swimmer, Caenorhabditis ele-gans. A broad range of viscosity measurements (> 10₃ mPa s) were achieved. The demonstration confirms the possible use of the technique in other biological applications that requires broad-range and small-volume measurement capabilities for viscosity.