Abstract
The influence of Au@Pt nanoparticles' composition, morphology, and peroxidase-mimicking activity on the limit of detection (LOD) of lateral flow immunoassay (LFIA) has been investigated. Fourteen types of nanoparticles were synthesized by varying the concentration of Pt4+ (20-2000μM), using gold nanoparticles (GNP, diameter 20.0 ± 2.6nm) as the seeds and ascorbic acid as a reducing agent. Au@Pt nanoparticles and GNPs were conjugated with antibodies specific to the target analyte, a widespread and dangerous phytopathogenic bacteria species (Clavibacter michiganensis). We found that the 100-fold growth of the Pt4+ concentration was accompanied by an increase of the Au@Pt nanoparticle diameter (24-55nm) and surface area with the formation of urchin-shaped morphology. These changes led to a 70-fold increase in peroxidase-mimicking activity in the solution (specific activity 0.06-4.4Umg-1) and a 30-fold decrease in LOD using the catalytic activity of Au@Pt. The Au@Pt nanoparticles synthesized at 1000-2000μM of Pt4+ demonstrated statistically indistinguishable catalytic activity. The highest sensitivity of LFIA was reached for Au@Pt nanoparticles synthesized at Pt4+ concentration equal to1000μM. Au@Pt nanoparticles saved most of their peroxidase-mimicking activity, whereas endogenous plant peroxidases were completely inhibited by sodium azide. The LOD of LFIA with Au@Pt nanoparticles synthesized at 1200μM of Pt4+ was 300colony-forming units (CFU) per mL of buffer and 500CFU per mL of potato tuber extract, which provides 330- and 200-fold improvement compared tothe conventional LFIA with GNPs. The assay consists of three rapid 5-min stages, namely, extraction, lateral flow, and color enhancement (oxidation of diaminobenzidine by Au@Pt nanoparticles). LFIA with the urchin Au@Pt nanoparticles allows the detection of latent bacterial infections rapidly without equipment or special skills. Graphical abstract.
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