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a b s t r a c tThis paper proposes a novel method for measuring blood plasma and serum viscosity with a microcantilever-based MEMS sensor. MEMS cantilevers are made of electroplated nickel and actuated remotely with magnetic field using an electro-coil. Real-time monitoring of cantilever resonant frequency is performed remotely using diffraction gratings fabricated at the tip of the dynamic cantilevers. Only few nanometer cantilever deflection is sufficient due to interferometric sensitivity of the readout. The resonant frequency of the cantilever is tracked with a phase lock loop (PLL) control circuit. The viscosities of liquid samples are obtained through the measurement of the cantilever's frequency change with respect to a reference measurement taken within a liquid of known viscosity. We performed measurements with glycerol solutions at different temperatures and validated the repeatability of the system by comparing with a reference commercial viscometer. Experimental results are compared with the theoretical predictions based on Sader's theory and agreed reasonably well. Afterwards viscosities of different Fetal Bovine Serum and Bovine Serum Albumin mixtures are measured both at 23°C and 37°C, body temperature. Finally the viscosities of human blood plasma samples taken from healthy donors are measured. The proposed method is capable of measuring viscosities from 0.86 cP to 3.02 cP, which covers human blood plasma viscosity range, with a resolution better than 0.04 cP. The sample volume requirement is less than 150 ll and can be reduced significantly with optimized cartridge design. Both the actuation and sensing are carried out remotely, which allows for disposable sensor cartridges.

ARTICLE This journal is © The Royal Society of Chemistry 2013Lab Chip, 2014, 00, 1-3 | 1 and Prothrombin Time (PT)). The system has a reader unit and a disposable cartridge. The reader has no electrical connections to the cartridge. This enables simple and low-cost cartridge designs and avoids reliability problems associated with the electrical connections. The cartridge consists of microfluidic channels and MEMS microcantilevers placed in each channel. Microcantilevers are made of electro-plated nickel. They are actuated remotely using an external electro-coil and the read-out is also conducted remotely by a laser. The phase difference between the cantilever oscillation and the coil drive is monitored in real-time. During coagulation, the viscosity of the blood plasma increases resulting in a change in phase read-out. The proposed assay was tested with human and control plasma samples for PT and aPTT measurements. PT and aPTT measurements with using control plasmas are comparable with manufacturer's data sheet and commercial reference device. The measurement system has an overall 7.28 % and 6.33 % CV for PT and aPTT, respectively. For further implementation, the microfluidic channels of the cartridge are functionalized for PT and aPTT tests by drying specific reagents in each channel. Since the simultaneous PT and aPTT measurements are needed in order to properly evaluate the coagulation system, one of the most prominent features of the proposed assay is the enabling parallel measurement of different coagulation parameters. Additionally, the design of the cartridge and the read out system, the obtained reproducible results with 10 µl plasma samples suggesting an opportunity of a possible Point-of -Care application.

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