Abstract

Point-of-use sensors are essential for environmental monitoring, food quality assessment, and disease diagnostics, particularly in remote and in-field settings. However, sensitivity, user-friendliness, and portability challenges limit their commercial availability, highlighting the need for improved sensing platforms. Gold nanoparticles (AuNPs) are promising for assay development due to their rapid synthesis, functionalization, and naked-eye colorimetric response, making them ideal for point-of-use applications. The central objective of this research is to develop a novel sensing platform called "lab-on-a-tablet" device as a potential point-of-use detection system.
This thesis introduces a low-cost, portable, and user-friendly detection platform using dextran-gold nanoparticles (dAuNPs), selected for their enhanced stability and simple synthesis. The dAuNPs-based tablet platform was developed using a pipette-out technique, ensuring solid, stable tablet formation (dAuNPs-Tablet). The pH-responsive behaviour of the tablet was assessed in various ionic solutions; the concentration of dextran was optimized; and different solid supports (e.g., composite, powder) were tested for optimal performance. The tablet-based approach offers superior portability, storage, and transportation compared to solution-phase dAuNPs (dAuNPs-Solution), quick production, easy handling, long-term stability (over four years), and low-cost (~1.22 CAD/100 tablets). Spectroscopic and microscopic analyses confirmed that dAuNPs retain their morphology during tablet formation, making dAuNPs-Tablet a robust and user-friendly alternative. A plasmonic tablet sensor was developed using dAuNPs-Solution, prepared under reflux conditions with post-synthetic dextran addition to facilitate tablet formation. This sensor detected reactive small species like hypochlorite and hydrogen peroxide. Hypochlorite was tested in swimming pool water, while hydrogen peroxide as an oxidative stress biomarker, was analyzed in urine sample using Fenton chemistry. Additionally, the antioxidant effect of green tea in reducing oxidative stress was explored.
Next, the tablet platform was advanced by developing a dual-functional system. We directly transformed dAuNPs-Solution into a tablet form, eliminating reflux conditions and post-synthetic dextran addition, resulting in the formation of a "direct tablet". This dual-functional tablet detected uric acid via its plasmonic response and glucose through its nanozyme activity, producing colorimetric signals within biologically relevant range. Thus, this thesis presents a transformative tablet-based detection platform with multiplexed capabilities, advancing point-of-use assays. The biocompatibility of dextran in dAuNPs-Tablets further highlights their potential for biomedical applications.