Super resolution imager sensing system using structured illuminated plasmonic spatial interferometers

Portable biomedical devices hold significant promises for various applications that have the potential to impact the fight against several global health problems. It was estimated that approximately two-thirds of global cell-phones are being used in the developing world (e.g. Africa, Asia). Therefore, sensitive biomedical devices integrated with smart-phones would yield a promising sensing system and introduce great impact on point-of-care diagnostics in developing countries and resource-limited areas. This proposal aims to develop a monochromatic structured illuminated plasmonic spatial interferometer suitable for highly sensitive sensing on digital cameras (e.g. on desktop microscopes and smart phones). The enhanced sensing performance is enabled by the super resolution strategy of structured illumination integrated with the plasmonic nanostructure developed in this project, which overcomes the resolution limit of the digital cameras. When successfully developed, such highly sensitive interferometers will allow a variety of biosensing applications at a much lower cost, with great societal impact on real time and in situ monitoring of global environmental (e.g. water) quality, liquid-food borne illnesses and personal health conditions. This research will be closely integrated with educational programs in the departments of Electrical Engineering and Biomedial Engineering at University at Buffalo. It will significantly impact the Electrical Engineering and Biomedial Engineering curriculum with its emphasis on experiential learning, and will provide an excellent educational opportunity for graduate and undergraduate student training of the next generation of researchers, educators and global leaders. The two PIs will provide excellent opportunities for undergraduate and graduate training in theoretical modeling, nanofabrication, miniaturized system design and optical super resolution image processing. The main goals of this educational and outreach program are to enhance the educational communication and collaboration, improve the participation of graduate and undergraduate students in cutting-edge researches, for outreach to K-12 students by organizing engineering summer campus, and provide opportunities for under-represented groups. While Surface Plasmon Resonance systems are currently used for label-free sensing, they remain inadequate for use in portable systems as the commercial instrumentation is expensive, complex, bulky and inconvenient for the integration with microfluidic platforms. Therefore, there is an urgent need to develop low-cost, compact, and high performance sensor systems for the ever-increasing sensing applications. Nanoplasmonic sensors are attractive miniaturized platforms to potentially meet these requirements. However, because nanoplasmonic sensors are mostly based on broadband wavelength shift interrogation which requires expensive spectrometers, high throughput sensing is still very challenging. This proposal will develop a plasmonic spatial interferometer structure to transfer the broadband wavelength peak/valley shift to the spatial interference pattern shift at a monochromatic wavelength such that the shift can be directly imaged by digital cameras on microscopes and smart-phones without the need of expensive spectrometers. To further enhance the sensing performance of the proposed system, the super resolution structured illumination strategy will be integrated into the sensor design by introducing a nanopatterned reference slit to generate Moire fringes with low spatial frequency information. This strategy enables a resolution much higher than the resolution limits of the optical imager system, thus allowing ultra-small spatial shift (sub-resolution-limit) to be observable even with portable cameras. The proposed system does not require spectrometer or angular tunable prism coupling system, leading to a significant reduction in device cost and instrumental complexity, especially when realized on smart-phone-based microscope systems. The potential of this sensing system will be demonstrated through the super-resolution-resolved peak/valley shift of 50 nm using inexpensive digital imagers, corresponding to an ultra-small sensing resolution approaching the performance of commercial bulky surface plasmon resonance imager systems. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.