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The Application of Mn-Doped Nanocrystal Signal Transducers Towards Sensitive Point-of-Care Bioassays
AdvisorZhu, Xiaoshan XZ
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In this work, Mn-doped semiconductor nanomaterials and their use in time-resolved luminescence biosensing/imaging were reviewed. While multiple types of luminescent particles were discussed, Mn-doped binary and multinary nanocrystals were highlighted due to their excellent optical properties, such as high brightness, small sizes, excellent luminescence lifetimes, good stability, and are excitable by visible light. By fine-tuning these properties, it is possible to achieve Mn-doped nanocrystals that are ideal for time-resolved luminescence measurement in a variety of applications, especially aiming for use in field or for point of care testing. Using previously developed Mn-doped I(II)-III-VI NCs, techniques to enhance bioassay sensitivity were hypothesized and investigated. A hypothesis that surface treatment and time-resolved reading can improve bioassay sensitivity was then drafted. To investigate the hypothesis, poly(styrene-co-maleic anhydride)-encapsulated Mn-doped AgZnInS/ZnS nanocrystal probes for the immunoassay of CPS, a biomarker for Burkholderia pseudomallei were developed. Using the synergistic effects of Mn-doped NC surface treatment and the use of a previously developed instrument that captures time-resolved measurements, the hypothesis that immunoassays adopting surface-treated NC-probes conjugated with anti-CPS antibodies alongside time-resolved reading achieved greater sensitivity than the ones adopting non-surface-treated NC-probes or non-time-resolved reading was validated. The developed NC-probes demonstrated a comparable limit of detection compared to typical immunoassays for CPS, which primarily utilize enzymes such as horseradish peroxidase and therefore required greater care in handling, transport, and use than the nanocrystal probes. The surface-treated nanocrystal probes were then applied to lateral flow assays, to investigate the feasibility of using the nanocrystal probes for in field or point of care testing. Through the use of a developed compact time-resolved imaging instrument, lateral flow assays for CPS were made possible using the NC-probes conjugated with anti-CPS antibodies. By only using the compact imaging instrument and a smartphone, it was possible to visually detect the test and control lines. Furthermore, comparisons of the same strip under continuous or time-resolved excitation were made. Strips under continuous excitation did not possess visually identifiable test or control lines, but would exhibit a test and control line under time-resolved reading using the same conditions.