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Abstract
The aim of this project is to explore the feasibility of developing plasmonic ELISAs and LFIAs with an enhanced sensitivity by incorporating static plasmonic and dynamic plasmonic properties of AgNPs. The primary objectives of the study were: (1) to optimise the photchemical synthesis conditions for shape and size stable AgNPs and AuNPs; (2) to develop H2O2-mediated competitive plasmonic ELISAs incorporating prismatic and disk AgNPs with dynamic plasmonic properties for the detection of EE2; and (3) to study the feasibility of developing LFIAs using AuNPs and AgNPs as the biomolecule labels with a colorimetric toggling system for a rapid measurement of EE2.
The photochemical synthesis of the disk and prismatic AgNPs was successfully optimised to produce shape-stable AgNPs. Our study found that the initial synthesis conditions and chemical species formed as precursors for the subsequent AgNPs synthesis played an important role in their post-synthesis shape and size stability. The optimised synthesis condition thus involved the addition of the co-stabiliser bis(p-sulfonatophenyl)phenylphosphine dihydrate dipotassium salt (BSPP) prior to the reduction of silver salts produced prismatic AgNPs structures that had resistance to shape transformation.
Two competitive plasmonic ELISAs involving two different approaches of incorporating the dynamic plasmonic properties of AgNPs, i.e., the oxidation of prismatic AgNPs and the growth of disk-shaped AgNPs, were developed for EE2 detection. The prismatic AgNPs oxidation-based plasmonic ELISA exhibited an IC50 of 4.5 ng/mL and a LOD of 1.0 ng/mL. The Dakin reaction-mediated plasmonic ELISA exhibited an IC50 of 33.0 ng/mL and a LOD of 2.1 ng/mL.
The performance of prismatic and disk-shaped AgNPs in LFIAs was investigated and compared to the traditional AuNP-based LFIAs for EE2 detection. The instrumental LOD for the AuNP-based LFIAs was 0.91 ng/mL, whereas for the disk and prismatic AgNPs, the instrumental LODs were 0.74 and 0.58 ng/mL. The study showed that the incorporation of anisotropic AgNPs as antibody labels in LFIA was feasible and could result in a better sensitivity compared to the conventional AuNP-based LFIAs. The toggling of the test and control lines intensities in the AuNP-based LFIA was also successfully demonstrated with polyclonal antibody as a quantitative assay.