CAREER: Multi-chrome metasurfaces for dynamic structural color and naked eye diagnostics

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High sensitivity, fast, and accurate sensors and medical diagnostics offer positive impacts on societal well-being, national health, and aid decision making with economic consequences. However, modern scientific instrumentation and sensing technologies are often bulky, expensive, slow, and/or cumbersome to operate; and may be unavailable in disadvantaged, remote, or under-developed communities where access to laboratory grade diagnostics is sparse. Colorimetric sensors on the other hand offer a promising solution to these problems, as they can be analyzed with high resolution by digital cameras or the naked eye. However, the performance of colorimetric sensors is so far typically inferior to the bulky/expensive alternatives as it can be difficult to convert small sensor variations into a large color response. This research introduces and investigates a means to address and overcome this problem through optimization of the sensor design, coordinated with the design of the light source. This research opens the door to new types of high-performance colorimetric sensors, which may be competitive with and/or offer greater functionality than the bulky/expensive alternatives.Structural coloration faces fundamental limits which presently prevent the realization of strong dynamic color responses arising from small variations in spectral properties. As such, dynamic coloration and colorimetric sensing devices currently rely heavily on niche physical/chemical effects which must amplify spectral changes to yield their colorimetric response. Colorimetric sensors built on such approaches are not generalizable and ultimately fail to rival the performance of laboratory grade benchtop equipment which is often bulky, slow, and costly/complex to operate. The proposed research presents a transformative and general technique for color transduction and sensing which can overcome these challenges. The ultimate goal of this research is to break the present performance limits of dynamic structural color devices and to investigate a new class of structural color based diagnostics, readable by the naked eye, which can rival or even exceed the performance of benchtop alternatives. Objectives of this project include: (1) Establish the theoretical framework for our high-level approach, ‘hyperchromatic structural color’ (HSC), while mapping out and investigating the limits of dynamic color transduction and how to maximize perceived color variations in response to targeted stimuli; (2) Study the design of metasurfaces optimized for multi-chrome laser illuminants and tailored colorimetric trajectories; and fabricate, characterize, and analyze their performance while addressing integration and nanomanufacturing challenges; (3) Experimentally characterize the colorimetric sensing performance of the newly developed multi-chrome metasurfaces and advance the field of naked eye diagnostics; and (4) Implement an educational plan aimed at addressing an observed educational gap in high-school and undergraduate level optics and photonics in an effort to: (a) increase STEM exposure to local high-schoolers, (b) promote both STEM and graduate level education opportunities to underrepresented groups and minorities, and (c) bridge the gap between undergraduate education and industrial opportunities in optics and opto-electronic industries. The investigation of dynamic structural color using multi-chrome laser illuminants is compelling because it fundamentally offers access to the highest colorimetric sensitivities, and hence no alternative approach (i.e. broadband or monochromatic illumination) can principally produce stronger color variations in response to a given spectral perturbation. Our focus on studying multi-chrome metasurfaces and the integration of responsive nanomaterials will advance our understanding of: multi-resonant and moiré photonic systems, the design and optimization of moderate to low index metasurfaces and biosensors, how to nano-manufacture scalably chip-scale optics derived from unconventional media, and how to tailor spectral properties from arrays and pixelated structures.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.