Date of Award

12-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Committee Chair/Advisor

Apparao M. Rao

Committee Member

Jeffrey N. Anker

Committee Member

Sumanta Tewari

Committee Member

Sriparna Bhattacharya

Abstract

We present Soret effect-driven electrochemical devices that generate >1 V with a mere 10 K temperature difference with the cold end at room temperature, i.e., a thermopower of > 100 mV K−1 – almost four to five times the record to date [Adv. Energy Mater., 2019, 9, 1901085]. We show that the thermopower depends not only on the electrolyte composition but also on the electrode porosity and microstructure, which has remained an understudied area of research. Interestingly, our devices show novel voltage oscillations (unlike electrochemical oscillations observed previously, which were a result of either (a) stochastic single molecule electrochemistry or (b) redox reactions) arising from an interplay between ionic diffusion and ionic migration within the electric double-layer, highlighting the potential for novel applications. Notably, the real-world use of TRECO is demonstrated by (a) facile continuous operation, (b) harvesting body heat (∼825 mV obtained for a temperature difference of 6 K), and (c) powering a pocket calculator using a single large-format TRECO cell to harvest waste heat from warm continuously operating lab equipment.

While the first part of my thesis focuses on waste heat harvesting, in the second part, I have investigated methods to use light for chemically imaging the local environment surrounding implants, which may require electrical energy to power the LEDs. While we anticipate that TRECO may supply this electrical energy through body heat harvesting, this thesis does not explore these links in detail. In the second part of this thesis, I have just focused on developing the tools for using light to image the local environment around implants chemically.

Bacteria can form biofilms on the surface of implanted medical devices, and these biofilms tolerate antibiotics and can cause systemic infection. Sensors must be placed at the device surface to measure and understand the local chemical concentrations during infection and enable the development of biofilm-targeting therapeutics and diagnostics. Herein, we leverage a commercial mechanically flexible organic light-emitting diode (OLED) display as an implantable local light source along with a pH-indicating film covering the display for bioimaging and chemical sensing through tissue. Raster-scanning the light from the display enabled us to image targets and detect changes in pH indicator films through porcine tissues up to at least 24 mm thick. The light that passed through the tissues and optical reference targets was captured either using a consumer DLSR camera or a photomultiplier tube (PMT). Reconstructed images of the targets showed submillimeter resolution, limited by the OLED pixel size, and much less than the point spread function of light from any one pixel emitted from the tissue (~27 mm through 1 cm of tissue). The system also measured pH-dependent absorption changes in bromothymol blue encapsulated hydrogel films compared to nearby reference regions. These findings highlight the potential use of OLED-based imaging systems for non-invasive, effective imaging of implant-associated infections.

Author ORCID Identifier

https://orcid.org/0000-0003-1294-1011

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