Date of Award

12-2024

Document Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Environmental Engineering and Earth Science

Committee Chair/Advisor

Diana Vanegas Gamboa

Committee Member

Eric S McLamore

Committee Member

Tzuen-Rong Jeremy Tzeng

Abstract

The Food and Drug Administration (FDA) established standards during the growing, harvesting, packing, and holding of produce for human consumption as part of implementing the Food Safety Modernization Act (FSMA). One of the main requirements for farmers is to detect environmental pathogens such as Salmonella enterica species in water and sprout samples. S. enterica is a bacterium of significant concern due to its pathogenicity and ability to survive and persist in diverse environmental conditions. S. enterica has been associated with recalls in ready-to-eat foods. Traditional detection methods include Enzyme-Linked Immunosorbent Assay (ELISA), Polymerase Chain Reaction (PCR), and plate counting, which generally take 24 to 72 hours to complete and require advanced laboratory facilities and skilled personnel. Thus, there is a need for user-friendly detection technology such as biochips for agricultural applications. An electrochemical aptamer-based chip was developed to detect intact S. enterica serovar Enteritidis on hydroponic green onion roots (Allium Fistulosum L.). A laser-induced graphene (LIG) 1.0 prototype system with a USB plug-and-play was designed by graphitization of a polyimide film using a CO2 laser. The working electrode was decorated with platinum nanoparticles (nPt) via Frequency Modulated Electrodeposition (FMED) to increase performance and conductivity. Electrochemical characterization was carried out via cyclic voltammetry (CV), and calculations of electroactive surface area (ESA), the area between the curve (ABC), and the heterogeneous electron transfer (HET) were made. Scanning Electron microscopy (SEM) and energy-dispersive X-ray Spectroscopy (EDS) were performed in a scanning electron microscope SU5000 for material characterization of LIG and LIG-nPt working electrode. Also, a quality control step was performed to reduce LIG batch-to-batch variation via CV measurements for further biofunctionalization. LIG Chips were biofunctionalized with a thiol-tagged Se1 aptamer. A loading study of Se1 aptamer against bacteria concentration was conducted via Electrochemical Impedance Spectroscopy (EIS) in sodium chloride/sodium bicarbonate solution supplemented with 1 mM of magnesium chloride. The biochip was tested using seven concentrations of Se1 aptamer from 0 to 2.7 µg/mL. Then, three concentrations (0.3, 0.6, and 1.1 µg/mL) of Se1 aptamer were selected to test against S. enterica from 3 to 300,000 CFU/mL. The synthesized fractal structures of nPt onto the LIG working electrode increased the conductive behavior of the LIG-nPt chip. It also displayed a quasi-reversible redox behavior where the current is limited by the charge transfer kinetics and mass transport. LIG-nPt chip with ABC between and and between and was chosen. EIS data outputs were used to select total capacitance as the response variable and 0.03 to 0.05 Hz as the multivariate cutoff frequency. Capacitance decreased in response to increased Se1 aptamer concentration. Regarding bacteria detection, the best in this study was at 0.3 µg/mL aptamer concentration. The accuracy reached 80%, and the Youden index was 0.5. Moreover, the total response time was 32 min., and the operating rate was between 3 to 300 CFU/mL. After 300 CFU/mL of bacteria, a hook effect was observed.

Author ORCID Identifier

https://orcid.org/0000-0002-1703-988X

Download

Available for download on Wednesday, December 31, 2025

Share

COinS