| Microfluidic "Total Analysis Systems" for high-efficiency and high-throughput integrated biochemical analysis represent a powerful technological advance in the biological sciences and in medical diagnostics. The construction of such replicate low-cost processing units involves the development and optimization of different fluidic, reaction, separation and sensing components and their successful integration into a complete self-contained "lab-on-a-chip" system for widespread dissemination.; We have developed a self-calibrating, self-contained and fully automated nanoliter capillary viscometer that measures the viscosity of Newtonian and no-Newtonian power law liquids with possible applications in chemical, biological and medical laboratories as well as in personal health care. The viscometer can generate a wide range of shear rates during a single experimental run enabling analysis of non-Newtonian liquids. The measurement of viscosity is based on capillary pressure driven flow inside microfluidic channels (depth∼30mum and width∼300mum). The silicon-glass device (18mm by 15mm) contains on-chip components that measure the driving capillary pressure difference and relevant geometrical parameters; these components make the nanoliter viscometer completely self-calibrating, robust and easy to use.; Blood plasma samples collected from patients with the symptoms of hyperviscosity syndrome were tested on the nanoliter capillary viscometer to an accuracy of 3%. The device has further been tested with dilute as well as semi-dilute solutions of flexible elastic polymers including Polyethylene Oxide (PEO) and hydrolyzed Polyacrylamide (PAM) to an aqueous solution of a stiff rod-like polymer molecule of Xanthan Gum, a popular emulsifier and food thickener, with ink-jet printing inks and a complex suspension of whole bovine blood.; Finally, we have developed three droplet sensing techniques: a digital electrode, an analog electrode, and a thermal method that may then be used to automate the functioning of a microfluidic analysis system and thus enabling its use at the point of care. We have used the digital electrode method, which utilizes an array of electrodes located at preset distances, to automate the operation of the viscometer. The nanoliter viscometer is completely controlled by a laptop, and the total time for operation from setting up the device, on-chip calibration, adding the liquid sample and obtaining an electronically displayed viscosity value is 4 minutes. |
