Microcantilever arrays have been shown to be promising label-free nanomechanical sensing devices with high sensitivity. Two factors that affect the usefulness of microcantilevers in sensing scenarios are the sensitivity of the transduction method for measuring changes in microcantilever properties and the ability to create large compact arrays of microcantilevers. In this dissertation, we demonstrate that microcantilevers with an in-plane photonic transduction method are attractive because they maintain the sensitivity of the traditional laser beam reflection method while being scalable to simultaneous readout of large microcantilever arrays. First I demonstrate the integration of a compact waveguide splitter network with in-plane photonic microcantilevers which have amorphous silicon strip loading differential splitter and simultaneous microcantilever readout with an InGaAs line scan camera. A 16-microcantilever array is fabricated and measured. Use of a scaled differential signal yields reasonable correspondence of the signals from 7 surviving released microcantilevers in the array. The average sensitivity is 0.23 µm-1. To improve the sensitivity and consistency, and reduce fabrication difficulties, a new differential splitter design with 4 µm long double-step multimode rib waveguide is introduced. Furthermore, a modified fabrication process is employed to enhance the performance of the device. A new 16-microcanitiler array is designed and fabricated. The sensitivity of a measured 16-microcantilever array is improved to approximately 1 µm-1, which is comparable to the best reported for the laser reflection read out method. Moreover, most of the microcantilevers show excellent uniformity. To demonstrate large scale microcantilever arrays with simultaneous readout using the in-plane photonic transduction method, a 64-microcantilver array is designed, fabricated and measured. Measurement results show that excellent signal uniformiy is obtained for the scaled differential signal of 56 measured microcantilevers in a 64-array. The average sensitivity of the microcantilevers is 0.7 µm-1, and matches simulation results very well.

The microcantilever (MC) has become a common transducer for chemical and biological sensing in gas phase and liquid phase during recent years. MC sensors provide superior mass sensitivity by converting weak chemical and biological stimuli into high mechanical response. Moreover, other advantages such as small size, low cost and array format have made MCs more attractive than other comparable sensors. Selectivity in MC sensors can be enhanced by creating a differentially functionalized MC array (MCA) with responsive phases (RPs). A well-designed array should incorporate RPs exhibiting a variety of possible interactions with the analytes, and a specific analyte should induce a distinctive response pattern demonstrated by the array. The first major division of the dissertation research work focused on enhancing selectivity of MC sensor by creating a differentiating MCA. The MCs within the array were nanostructured in a previously developed manner. A self-designed capillary array was set up to chemically functionalize different ligands onto individual MCs in an array for metal ion sensing in liquid phase. Another array was prepared by selectively vapor depositing different organic RPs onto nanostructured MCs and applied to landfill siloxane sensing in gas phase. Both of the arrays demonstrated response diversity to the target analytes. The second major division of the dissertation research work focused on developing a new method to modify MC surfaces with a function nanostructure. Aluminium oxide nanoparticles (AONP) were uniformly dispersed onto MC and a roughened surface with high surface area was achieved as stable sensor platform. Alkoxysilyl compounds were then grafted onto this platform as RPs. For demonstration, a MCA functionalized with three different alkoxysilanes was prepared for volatile organic compound sensing in gas phase. Additionally, another MCA was functionalized with anti-human immunoglobulin G and anti-biotin for bio-sensing in liquid phase. Both of the arrays were prepared with the aforementioned capillary array setup. Selective responses of specific analytes, as well as good sensitivity, were obtained from each type of AONP MCA.

We have invented an in-plane all-photonic transduction method for photonic microcantilever arrays that is scalable to large arrays for sensing applications in both bio- and nanotechnology. Our photonic transduction method utilizes a microcantilever forming a single mode rib waveguide and a differential splitter consisting of an asymmetric multimode waveguide and a Y-branch waveguide splitter. The differential splitter's outputs are used to form a differential signal that has a monotonic response to microcantilever deflection. A differential splitter using an amorphous silicon strip-loaded multimode rib waveguide is designed and fabricated to demonstrate the feasibility of the in-plane photonic transduction method. Our initial implementation shows that the sensitivity of the device is 0.135×10^-3 nm^-1 which is comparable to that of other readout methods currently employed for static-deflection based sensors. Through further analysis of the optical characteristics of the differential splitter, a new asymmetric double-step multimode rib waveguide has been devised for the differential splitter. The new differential splitter not only improves sensitivity and reduces size, but also eliminates several fabrication issues. Furthermore, photonic microcantilever arrays are integrated with the differential splitters and a waveguide splitter network in order to demonstrate scalability. We have achieved a measured sensitivity of 0.32×10^-3 nm^-1, which is 2.4 times greater than our initial result while the waveguide length is 6 times shorter. Analytical examination of the relationship between sensitivity and structure of the asymmetric double-step rib waveguide shows a way to further improve performance of the photonic microcantilever sensor. We have demonstrated experimentally that greater sensitivity is achieved when increasing the step height of the double-step rib waveguide. Moreover, the improved sensitivity of the photonic microcantilever system, 0.77×10^-3 nm^-1, is close to the best reported sensitivities of other transduction methods (~10^-3 nm^-1).