Microcantilever based disposable viscosity sensor for serum and blood plasma measurements.

This 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 µl and can be reduced significantly with optimized cartridge design. Both the actuation and sensing are carried out remotely, which allows for disposable sensor cartridges.

Deterministic assembly of channeling cracks as a tool for nanofabrication.

To address the necessity for a predictive computational tool for layout design in crack lithography, a tool for nanowire fabrication, a computational study is carried out using finite element analysis, where crack-free edge and crack-crack interactions are studied for various material combinations. While the first scenario addresses the ability to induce a controlled curvature in a nanowire, the latter provides an estimation of the minimum distance which can be kept between two straight nanowires. The computational study is accompanied by an experimental demonstration on Si/SiO2 multilayers. Finite element results are found to be well aligned with experimental observations and theoretical predictions. Stronger interaction is evident with a curved crack front modeling as well as with increasing first and decreasing second Dundurs' parameters. Therefore cracks can be packed closer with decreasing film stiffness.