Date of Award
Summer 9-1-2023
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Ultrasensitive, reliable, and rapid chemical vapor sensing is of paramount importance for a wide variety of applications including bio-diagnostics, homeland security and environmental monitoring. Despite decades of extensive efforts, the performance of artificial chemical sensing systems (‘e-noses’) still pales compared to the superior capabilities of their biological counterparts. On several important metrics such as sensitivity, stability, specificity, and tolerance to varying background conditions biological olfactory systems exhibit better performance. On the other hand, chemical sensing approaches that tap into biological capabilities present different sets of challenges, such as confounding behavioral response or sub-optimal neural response, that must be overcome to realize a viable bio-hybrid chemical sensing solution. These challenges constitute the motivation of this dissertation work. We aim to overcome several incessant bottlenecks in both artificial and bio-hybrid olfactory systems. Emerging functional nanomaterials, which exhibit unique optical, electrical, and chemical properties as well as offer abundant structure tuning capabilities, have taken a center stage in unveiling potential solutions for these challenges. First, we improved the sensitivity of surface enhanced Raman spectroscopy (SERS) based single-output chemical sensors. We demonstrate a novel “add-on” electromagnetic hotspot formation technique, which significantly improves the sensitivity of conventional SERS substrates comprised of individual plasmonic nanostructures. We also demonstrate that this technique can be effectively utilized for the vapor phase detection of explosives such as trinitrotoluene (TNT) using peptide recognition elements, otherwise undetectable by conventional substrates. While SERS is an attractive technology for the trace detection of small molecules, it is not ideal for detection of wide repertoire of gaseous molecules owing to the lack of target-specific recognition elements for odors of interest. To overcome this, we demonstrate a novel, facile and ubiquitously applicable strategy for fabricating a highly reliable and reproducible organothiol-functionalized gold nanoisland based chemiresistor. Upon exposure to a specific odor, the chemiresistor ensemble comprised of nine different chemical functionalities produced a unique and discernable odor fingerprint that is reproducible for at least up to 90 days, which was sufficient to enable successful identification of a diverse odor panel. Next, we set out to address the persisting challenge of sub-optimality in neural information read-out associated with bio-hybrid chemical sensing systems by harnessing the unique biophysicochemical properties of organic and inorganic nanoparticles. We first revealed that negative surface charge of the nanoparticles renders selective nano-neuro interaction with a strong correlation between the maturation stage of the individual neurons in the neural network and the density of the nanoparticles bound on the neurons, which is necessary for effective nano-neuromodulation. We then demonstrated the feasibility of employing a nano-enabled neuromodulation strategy to augment insect olfaction-based chemical sensors. By harnessing the photothermal properties of nanostructures and releasing a select neuromodulator on-demand, we show that the odor-evoked response from the interrogated regions of the insect olfactory system can not only be enhanced but can also improve odor identification. Taken together, these advances are expected to overcome the fundamental challenges associated with both artificial and bio-hybrid olfactory systems and open novel avenues in realizing ultrasensitive and selective chemical sensing strategies. Through this dissertation work we demonstrate the promise of nanotechnology in realizing next-generation chemical sensing tools that can outperform the current gold standard techniques in sensitivity, specificity, reliability, and speed.
Language
English (en)
Chair
Srikanth Singamaneni