We present a pressure sensor based on the piezoresistive effect of graphene. The sensor is a 100 nm thick, 280 lm wide square silicon nitride membrane with graphene meander patterns located on the maximum strain area. The multilayer, polycrystalline graphene was obtained by chemical vapor deposition. Strain in graphene was generated by applying differential pressure across the membrane. Finite element simulation was used to analyze the strain distribution. By performing electromechanical measurements, we obtained a gauge factor of $1.6 for graphene and a dynamic range from 0 mbar to 700 mbar for the pressure sensor. V C 2013 AIP Publishing LLC [http://dx

Membrane proteins are central to many biological processes, and the interactions between transmembrane protein receptors and their ligands are of fundamental importance in medical research. However, measuring and characterizing these interactions is challenging. Here we report that sensors based on arrays of resonating microcantilevers can measure such interactions under physiological conditions. A protein receptor--the FhuA receptor of Escherichia coli--is crystallized in liposomes, and the proteoliposomes then immobilized on the chemically activated gold-coated surface of the sensor by ink-jet spotting in a humid environment, thus keeping the receptors functional. Quantitative mass-binding measurements of the bacterial virus T5 at subpicomolar concentrations are performed. These experiments demonstrate the potential of resonating microcantilevers for the specific, label-free and time-resolved detection of membrane protein-ligand interactions in a micro-array format.

Micromechanical cantilever arrays are used to measure time-resolved adsorption of tiny masses based on protein-ligand interactions. Here, streptavidin-biotin interactions are investigated in a physiological environment. A measurement method is introduced using higher flexural modes of a silicon cantilever in order to enhance the sensitivity of mass detection. Modeling the cantilever vibration in liquid allows the measurement of absolute mass changes. We show time-resolved mass adsorption of final 7+/-0.7 ng biotinylated latex beads. The sensitivity obtained is about 2.5 pg/Hz measuring at a center frequency of 750 kHz.

We evaluated the potential and limitations of resonating nanomechanical microcantilevers for the detection of mass adsorption. As a test system we used mass addition of gold layers of varying thickness. Our main findings are: (1) A linear increase in mass sensitivity with the square of the mode number-a sensitivity increase of two orders of magnitude is obtained from mode 1 to mode 7 with a minimum sensitivity of 8.6 ag Hz −1 μm −2 and mass resolution of 0.43 pg at mode 7 for a 1 μm thick cantilever. (2) The quality factor increases with the mode number, thus helping to achieve a higher sensitivity. (3) The effective spring constant of the cantilever remains constant for deposition of gold layers up to at least 4% of the cantilever thickness.

A study of nanomechanical cantilevers vibrating at various resonating modes in liquid is presented. Resonant frequency spectrum with 16 well resolved flexural modes is obtained. The quality factor increased from 1 at mode 1 to 30 at mode 16. The theoretical estimate of eigenfrequency using the Elmer-Dreier model ͓F.-J. Elmer and M. Dreier, J. Appl. Phys. 81, 12 ͑1997͔͒ and Sader's extended viscous model ͓C. A. Van Eysden and J. E. Sader, J. Appl. Phys. 101, 044908 ͑2007͔͒ matched well with the experimental data. The apparent mass of the liquid comoved by the oscillating cantilevers decreased asymptotically with mode number.