Characterization and Preliminary Demonstration of Microcantilever Array Integrated Sensors

Characterization and Preliminary Demonstration of Microcantilever Array Integrated Sensors Ryan R. Anderson Department of Electrical and Computer Engineering, BYU Doctor of Philosophy I characterize the behavior of microcantilever arrays which utilize the in-plane photonic transduction that I’ve previously developed and evaluate the performance of the microcantilever arrays in simple sensing scenarios with integrated microfluidics. First the thermal responses of microcantilevers with a variety of patterns of deposited gold films are compared. Using a scanning electron microscope, I observe the deflection thermal sensitivities of 300 μm long microcantilevers to be -170.82 nm/K for a full gold coating and -1.93 nm/K for no gold coating. Using the photonic transduction method I measure a thermal sensitivity of -1.46 nm/K for a microcantilever array with no gold. A microcantilever array integrated with microfluidics is exposed to a solution of bovine serum albumin (BSA) followed by solutions of various pH’s. In all cases I observe a previously unreported transient deflection response. We find that the transient response is due to temporary nonuniform concentration distributions. In response to nonspecific binding of BSA, I observe a transient surface stress of -0.23 mN/m that agrees well with the -0.225 mN/m predicted by simulations. We hypothesize that the deflection response to pH changes is due to stress generated by conformational changes of bound BSA. The deflection response of an integrated microcantilever array to different types of flow and different flow rates is observed. Simulations of the deflection response match well with experimental results but disagree at higher flow rates. For flow rates greater than 200 μL/min, the limitation of the differential signal’s dynamic range becomes apparent. We then investigate flow driven by an on-chip reciprocating reservoir pump. We demonstrate that it is possible to use the reciprocating pump to achieve high flow rates while making deflection measurements in-between reservoir actuations. Investigations of the microcantilever array noise show that flicker noise dominates below 10 Hz, while above 10 Hz, readout noise dominates. A minimum deflection noise density of 15 pW/ √ Hz is achieved. To improve the signal-to-noise ratio I develop algorithms for a digital lock-in amplifier with a digital phase-lock loop. In simulation the lock-in amplifier is able to improve the SNR by up to a factor of 6000, and self-lock to a noisy carrier signal without an external reference signal.