Date of Award
Doctor of Philosophy in Chemistry
The present study explores the development and practical utilization of a new electroanalytical methodology, nanoemulsion-integrated single-entity electrochemistry (NI-SEE) to fundamentally elucidate the intriguing nanoemulsion (NE) system and sense/quantify biomedical or environmental toxicants at ultra-trace level. SEE is a modern electrochemical technique, where one can measure the change in the current or the potential upon the individual collision of a nano object on to the nano or the micro sized electrode at a time. We performed in situ and real-time study by uniquely employing SEE to investigate a physicochemical property, e.g., a partition coefficient (P) at intact individual NEs, which is demanded for the accurate dosage control of drugs in NEs as a drug delivery system. Unlike average and ex situ analytical techniques, direct and in situ measurements at single NEs by SEE enabled us to determine a P of a model molecule, 2-aminobiphenyl (2-ABP) as ~1.9 × 1010, c.a. 7 orders of magnitude higher than bulk phase. Molecular dynamics simulation revealed that the hidden intermolecular interactions via non-covalent bonding e.g., lone pair electron-anti π* bonding, hydrogen bonding and van der Waals interaction contributed to stabilizing the extracted 2-ABP inside a NE, thereby unexpectedly enhancing the P compared to the bulk phase. We further present promising capabilities of NI-SEE in biomedical and environmental analysis. NEs were employed as a versatile nanoprobe with SEE owing to the unprecedentedly high P. For ultra-trace level analysis of Pb+2 in blood samples, polyaromatic hydrocarbons (PAHs) as aromatic toxicants in water, and multi-metal ion contaminants in water, we electrochemically or thermodynamically modulated the selectivity of NEs to target analytes by incorporating a Pb2+-ion selective ionophore or a chelator i.e., dithizone, thereby efficiently separating analytes from a sample, extracting and preconcentrating them into NEs. The concurrent combination of SEE enabled the simultaneous and real time sensing of analytes extracted to NEs with a preconcentration factor up to 6~7 orders of magnitude, thus resulting in an unprecedentedly high sensitivity. Moreover, we could additionally adjust the sensitivity of NI-SEE by varying NE amounts dispersed in the bulk solution and achieve a sub ppb level of limit of detection (LOD), comparable to the sensitivity of inductively coupled plasma-mass spectrometry. Notably, charge density plots as a function of analyte concentration in bulk solutions were constructed from discretely integrated current spikes in SEE measurements, and distinctly utilized as calibration curves for quantification, thereby validating an analytical utility of the demonstrated methodology as well. This work is not only the first practical application of NI-SEE in the quantitative electroanalysis, but also is suggesting a new avenue of the biomedical and environmental analysis with the highly accessible, versatile electrochemical method with unprecedentedly high sensitivity.
Madawala, Hiranya Malshani, "DEVELOPMENT AND APPLICATIONS OF AN ELECTROCHEMICAL METHOD, NANOEMULSION-INTEGRATED SINGLE-ENTITY ELECTROCHEMISTRY" (2023). Open Access Dissertations. Paper 1618.
Available for download on Sunday, January 19, 2025