Metallic Nanoparticles for Expanding the Point-of-Care Applications of Paper-Based Diagnostic Devices

As early diagnosis is essential for improving patient outcomes when treating both communicable and noncommunicable diseases, it is necessary to develop diagnostic tests that are accessible at the point of care. Thus, there is a need for rapid, robust, and inexpensive diagnostic tests, especially in resource-limited areas where access to healthcare is reduced. One such test is the lateral-flow immunoassay (LFA), which has seen a drastic rise in use during the COVID-19 pandemic. However, the conventional LFA suffers from a couple limitations, which this thesis aims to address. First, we address the limited sensitivity of the LFA by incorporating nanozyme signal enhancement to improve detection of the SARS-CoV-2 nucleocapsid protein in serum. By developing dehydrated signal enhancement reagents and an innovative 3D printed casing to store and deliver reagents at the push of a button, we were able to improve the limit of detection of the LFA by at least 10-fold without introducing additional complexity for the user. Next, we shifted our focus to introducing semi-quantitative results to the LFA through the multicolor etching of gold nanorods (GNRs). We demonstrated the first integration of the LFA with GNRs to produce a multicolor readout for the quantification of digoxin levels in serum. We then expanded upon this work by developing a fully paper-based assay to incorporate both the LFA detection and GNR etching steps together, which involved the design of novel color-changing GNR pads. The color hues generated by GNR etching are easily distinguishable by the naked eye, thus allowing for quantification of target biomarker concentrations at the point of care.