Whole blood diagnostics in standard gravity and microgravity by use of microfluidic structures (T-sensors)

In channels with dimensions much less than 1 mm, fluids with viscosities si milar to or higher than that of water and flowing at low velocities exhibit laminar behavior. This allows the adjacent flow of fluids and particles in a channel without mixing other than by diffusion. We demonstrate here the use of a 3-input microfluidic device known as a T-Sensor for the analysis o f blood. A sample solution (e.g. whole blood), a receptor solution (e.g. an indicator solution), and a reference solution (a known analyte standard) a re introduced into a common channel (T-Sensor), and flow side by side until they leave the structure. Smaller particles such as ions or small proteins diffuse rapidly across the fluid boundaries, whereas larger molecules diff use more slowly. Large particles (e.g. blood cells) show no significant dif fusion within the time the flow streams are in contact. Two interface zones are formed between the fluid layers. The ratio of a property (e.g. fluores cence intensity) of the outer portions of the two interface zones is a func tion of the concentration of the analyte, and is largely free of cross-sens itivities to other sample components and instrument parameters. This device allows, for example, one-time or continuous monitoring of the concentratio n of analytes in microliters of whole blood without the use of membranes or prior removal of blood cells. The principle is illustrated by the determin ation of pH and human albumin in whole blood and serum. Results are also pr esented for zero-gravity experiments performed with a T-Sensor on board a N ASA experimental plane. Due to its microfluidic flow characteristics, a T-S ensor functions independently of orientation and strength of the gravitatio nal field. This was demonstrated by exposing a T-Sensor to variations in gr avity from 0 to 1.8g in a NASA KC135A plane flying repetitive parabolic fli ght curves.