ABSTRACT

To interact and function in today's environment, the human nervous system has developed specific sensory systems or organs, one or in some cases several dedicated to each sense. The five familiar senses are sight, taste, hearing, smell, and touch. Our senses create joy and pleasure, but also pain and sorrow. In some cases they warn us from imminent danger, in other cases they do not or only when it is already too late. This project focuses on liquid crystal-nanoparticle sensors for the qualitative and quantitative detection of toxic gases and vapors. These integrative sensors systems can display an unmistakable warning in the form of text or an image in the presence of toxic gases and vapors without any electrical power, and provide parts-per-million level sensitivity. The active component of these sensors is based on reactive, ink-jet printed nanoparticle alignment layers for nematic liquid crystals. In analogy to omnipresent liquid crystal displays, an image (or readable pattern) emerges due to the presence of specific hazardous toxic gases and vapors that could affect the lives and health of firefighters, military personnel in conflict zones, first responders, and workers in chemical manufacturing among others. Sensors for volatile compounds exhaled by humans can also be used to monitor disease states and disease progression such as in diabetes, liver disease, or cancer.

The focus of the proposed activities is to advance recent findings that nanoparticles and particularly their surface functionalization induce and alter the orientation of nematic liquid crystal molecules in direct contact with them. By applying this concept, gold nanoparticles in the size regime between 1 and 10 nm with reactive surface ligands are synthesized and patterned via ink-jet printing to devise sensors for multiple hazardous (chlorine, phosgene, cyanide, amines, dialkyl chalcogenides) or less hazardous gases and vapors (ketones). The combination of nanoparticle ink-jet printing and established concepts of optical and electro-optical responses of nematic liquid crystals in contact with nanoparticles and other surfaces enables the creation of highly sensitive and selective sensors, where the sensing event produces a direct visual readout or warning without the use of electrical power. The proposed research in collaboration with an industrial partner offers new prospects for sensing harmful environments and monitoring disease progression, both quantitative and qualitative, wearable and remote, and with multiple detection modes. In conjunction with simulations, measurements of light transmission and birefringence in the presence and absence of applied electric fields provide unparalleled datasets for the development of liquid crystal sensors for the simultaneous quantitative and qualitative detection of multiple toxic and non-toxic gases and vapors. Overall, these activities create knowledge for advanced sensor materials and foster strong advanced material science education.

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.

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