Abstract
The use of lateral flow immunoassays (LFIAs) for rapid on-site testing is restricted by their relatively high limit of detection (LoD). One possible way to decrease the LoD is to optimize nanoparticle properties that are used as labels. We compare two types of Au nanoparticles: usual quasispherical gold nanoparticles (C-GNPs), obtained by the Turkevich–Frens method, and superspherical gold nanoparticles (S-GNPs), obtained by a progressive overgrowth technique. Average diameters were 18.6–47.5 nm for C-GNPs and 20.2–90.4 nm for S-GNPs. Cardiomarker troponin I was considered as the target analyte. Adsorption and covalent conjugation with antibodies were tested for both GNP types. For C-GNPs, the minimal LoD was obtained with 33.7 nm nanoparticles, reaching 12.7 ng/mL for covalent immobilization and 9.9 ng/mL for adsorption. The average diameter of S-GNPs varied from 20.2 to 64.5 nm, which resulted in a decrease in LoD for an LFIA of troponin I from 3.4 to 1.2 ng/mL for covalent immobilization and from 2.9 to 2.0 ng/mL for adsorption. Thus, we obtained an 8-fold decrease in LoD (9.9 to 1.2 ng/mL) by using S-GNPs. This effect can be related to more effective antibody immobilization and improved S-GNP optical properties. The obtained results can improve LFIAs for various practically significant analytes.
Highlights
Lateral flow immunoassay (LFIA)— known as immunochromatography—has been suggested as an effective analytical method for point-of-care diagnostics [1,2]
C-gold nanoparticles (GNPs) and superspherical gold nanoparticles (S-GNPs) series were synthesized with varied ratios of reactants to reach different average nanoparticle diameters
For C-GNP, the position of the maximum extinction spectra depends on the amount of sodium citrate added during synthesis
Summary
Lateral flow immunoassay (LFIA)— known as immunochromatography—has been suggested as an effective analytical method for point-of-care diagnostics [1,2]. The fast reaction kinetics and absence of the additional signal amplification step lead to the relatively low sensitivity of LFIA compared to other types of immunoassay. Various approaches have been considered for increasing LFIA sensitivity, including multistep analysis and specific detection techniques [5,6,7]. Such improvements result in the loss of the main advantage of LFIA as a simple point-of-care test.
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