Microcantilevers that are properly functionalized with chemo- or bioselective coatings have been shown to be extremely sensitive to chemical and biological analytes in both vapor and liquid media. Microcantilevers therefore exhibit great promise as molecular and atomic recognition sensors for an extremely diverse set of applications including environmental monitoring, industrial process control, biological research, and homeland defense. Microcantilever operation is characterized by chemical reaction or adsorption of molecular species at the microcantilever surface which results in a change in the microcantelever's deflection and in properties such as its resonance frequency. While these induced changes can be very small (sub-nanometer cantilever deflection, for example), they are readily measurable with a laser beam reflection technique developed for atomic force microscope (AFM) cantilever measurements.
To realize the full promise of microcantilever sensor technology, arrays of individually functionalized microcantilevers are required to enable the simultaneous detection of multiple target molecules while rejecting interference from other chemical species in the environment as well as stochastic noise such as thermal fluctuations. A critical problem is that current cantilever measurement methods do not lend themselves to practical implementation for large numbers of cantilevers that are suitable for high sensitivity operation in both vapor and liquid ambients. This proposal focuses on a solution to this problem based on waveguide cantilevers combined with a receiver waveguide splitter structure that enables differential detection of cantilever deflection. Combining these elements with recently invented compact waveguide components and with grating couplers to enable fiber coupling to off-chip detectors and an off-chip optical source permits the realization of a small microcantilever-based sensor with interchangeable or disposable microcantilever array chips. Compatibility of the waveguide structures with batch microfabrication techniques suggests that such arrays can be produced very inexpensively. Initial analysis indicates that the proposed waveguide cantilever array sensor appears to offer an attractive path for the realization of practical, highly functional sensors.
Intellectual Merit of Proposed Activity
The proposed work concentrates on the development of a general photonic microcantilever array-based sensor platform that relies on a compact integrated optical readout mechanism to realize scalable, small area microcantilever arrays. A successful research and development effort will lay the foundation for microcantilever arrays to become a common and easy to use high sensitivity sensor for many application areas. The elements of waveguide microcantilever sensors to be explored in the proposed work build directly on the experience and expertise of the four senior personnel, which includes photonic device design and fabrication, chemistry and materials science, biology, and industry experience in cantilever process development.
Broader Impacts
As evidenced by its status as an EPSCoR state, Alabama has been historically viewed as less than a full participant in the national science and engineering enterprise. The proposed work will help North Alabama become a center of microcantilever sensor research and development. Moreover, the proposal contains funding to support two undergraduate students from underrepresented groups to come to UAH and work during each summer in UAH's recently expanded 8,000 square foot Nano/Microfabrication Facility (NMF). As described in the proposal, outreach to students in predominantly minority local high schools is also planned, as well as activities for elementary school students to stimulate their interest in science and engineering. These activities are intended to foster interaction with local elementary and high school programs. Graduate student mentoring will also be a key aspect of the proposed work. In addition, as described in the proposal, partnership with Oak Ridge National Laboratory will be significantly expanded.
