(321b) Viscosity Measurement at the Point-of-Need: A Smartphone Capillary-Based Approach

Viscosity, an essential property of fluid behavior, plays an important role in many applications including quality control in chemical, food, and manufacturing industries, as an analytical tool in research and development settings, and in medical diagnosis, prognosis, and preventive medicine. Conventional viscometers typically require large sample volumes (several mL), use non-disposable sample holders, involve time-consuming protocols, require trained operators, lack portability, and are expensive. These limitations have hindered widespread use of viscosity measurements at the point-of-need, especially important for medical applications. Blood viscosity, for instance, has been shown to be a predictor of cardiovascular events in hypertensive men and it could be a risk factor for diabetes. Here we present a simple smartphone-enabled capillary-based approach for the measurement of a liquid’s viscosity using small sample volumes (~0.03 mL). A smartphone is employed to record short videos (at up to 240 frames per second) of capillary-driven flow in disposable glass capillaries of uniform circular cross-sections (100-800 micrometers in diameter) in a horizontal configuration. Videos of capillary filling, which typically lasts anywhere from 0.5 to 10 seconds, are then processed using automated video analysis to detect fluid displacement and retrieve the meniscus position as a function of time. Further analysis of the retrieved data provides rheological properties of the fluid while including the effects of a dynamic contact angle observed in capillaries with larger diameter. Results from our viscometer are in quantitative agreement with known fluids used as references, such as Newtonian water-glycerol solutions and shear-thinning water-xanthan gum solutions, while blood viscosity measurements illustrate its biosensing capabilities. The materials needed (capillaries and a smartphone camera) and the analysis performed (implemented as a user-friendly software) enable viscosity measurements to be performed rapidly and without requiring special knowledge or training. Thus, this approach is low cost and portable, overcomes important limitations of conventional viscometers, and facilitates measuring the rheology of various fluids in point-of-use and resource-limited settings.