Available at: https://digitalcommons.calpoly.edu/theses/3430
Date of Award
8-2026
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Engineering
Advisor
Amro El Badawy
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
Rapid, reliable detection of viral pathogens remains a significant challenge across water-treatment and environmental monitoring systems, including drinking-water, wastewater, water reuse, and environmental surveillance applications. Waterborne viral contamination can pose substantial public-health risks, making early detection essential for protecting water quality and responding quickly to treatment failures or contamination events. Direct potable reuse (DPR) is one particularly demanding example because it requires continuous verification of treatment performance and the broader need for rapid virus monitoring extends across many water-treatment and environmental surveillance applications. Norovirus is a priority target because of its widespread occurrence in wastewater, environmental persistence, and exceptionally low infectious dose.
Nanotechnology-based optical biosensors offer a fundamentally different detection paradigm, enabling rapid, sensitive pathogen detection closer to the point of treatment or monitoring than conventional laboratory methods. The synthesized carbon quantum dots (CQDs) and gold nanoparticles (AuNPs) are intended to serve as the fluorescent and plasmonic components of a future aptamer-based optical biosensor for norovirus detection. In the proposed sensing strategy, aptamer-functionalized CQDs and AuNPs would be brought into close proximity upon norovirus binding, producing a target-dependent fluorescence response through CQD–AuNP interactions.
This study addresses one of the practical barriers to developing nanomaterial-based optical biosensors by optimizing rapid, microwave-assisted synthesis of CQDs and a simplified citrate reduction (Turkevich-Frens) synthesis of AuNPs. Specifically, CQD synthesis time was reduced to 40-42 seconds using a household microwave, with a comparable protocol developed for the MARS 6 reactor, while AuNP synthesis was simplified by omitting the reflux condenser and using an intermediate citrate-to-gold molar ratio (~11:1) relative to published protocols. This work instead develops simplified aqueous synthesis routes using only consumer- or standard-laboratory-grade equipment while substantially reducing reaction time and cost compared to current published protocols.
CQDs were synthesized from citric acid and urea using a household microwave and a CEM MARS 6 microwave reaction system. Four household microwave batches and three MARS batches were produced. The household-microwave products reproducibly exhibited green-to-cyan fluorescence, whereas the MARS products reproducibly exhibited blue fluorescence after 0.22 µm filtration. Representative samples were further separated using 3,000 Da molecular-weight-cutoff (MWCO) centrifugal filters; one batch was processed with a 10,000 Da MWCO filter because 3,000 Da filters were not available at the time, providing an incidental comparison across cutoffs rather than a planned variable. Nanomaterial products were characterized by UV-visible absorbance, fluorescence spectroscopy, dynamic light scattering (DLS), X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). Fluorescence was retained in both centrifugal-filter retentate and permeate fractions, indicating a heterogeneous emissive population. ATR-FTIR supported formation of oxygen- and nitrogen-containing products distinct from the citric acid and urea precursors, while XRD indicated poorly ordered or largely amorphous dried material. SEM/EDS confirmed carbon-, nitrogen-, and oxygen-containing dried products but did not resolve individual CQDs. DLS outputs varied substantially among fractions and were frequently flagged as unreliable because of weak scattering, sub-nanometer modeled sizes, and sensitivity to trace aggregates; reported values were therefore treated as apparent hydrodynamic distributions rather than confirmed primary particle diameters.
Citrate-reduced AuNPs exhibited a localized surface plasmon resonance maximum near 525 nm (n = 3), a Z-average hydrodynamic diameter of 28.37 ± 0.20 nm, and a strongly negative zeta potential of −54.42 ± 0.18 mV, consistent with a stable, citrate-capped colloid.
These simplified synthesis routes provide a practical foundation for future optical biosensor development across a range of water-quality monitoring applications, including drinking-water treatment, wastewater surveillance, environmental monitoring, water reuse, and direct potable reuse. However, direct nanoscale imaging and stronger separation of nanoparticle and molecular-fluorophore products are still required before the fluorescent carbonaceous material can be conclusively identified and advanced to aptamer conjugation and norovirus-detection studies.
Included in
Condensed Matter Physics Commons, Engineering Physics Commons, Environmental Chemistry Commons, Environmental Engineering Commons, Materials Chemistry Commons, Optics Commons, Other Materials Science and Engineering Commons, Water Resource Management Commons, Water Resources Engineering Commons