Cubic Prussian Blue Nanoparticles as Colorimetric and Nanozyme Labels and Their Application in Lateral Flow Immunoassay

Abstract The distinctive properties of Prussian blue nanoparticles (PB NPs) have led to their use in biomedical and bioanalytical applications. PB NPs are employed as colorimetric labels in bioanalytical systems, such as lateral flow immunoassay (LFIA), with potential of signal enhancement due to their enzyme‐mimicking catalytic properties. However, PB NPs’ limited mobility on LFIA membranes and stability issues prevent their broader use. In this study, we outline the assay conditions that support mobility and stability of cubic PB NPs in model LFIA, as well as substantial improvement of the analytical signal. In order to determine chicken IgY, three types of colorimetric and catalytic labels were used: 1) PB NPs; 2) complex of PB NPs and horseradish peroxidase (HRP); 3) complex of gold nanoparticles (GNPs) and HRP. The limit of visual detection was decreased by an order of magnitude using the chemical signal amplification (up to 5–8 times). The color intensity of PB NPs enhanced with 3,3',5,5'‐tetramethylbenzidine (TMB) substrate solution was similar to that of the complex of GNPs with an enzyme. Our findings show that PB NPs support HRP stability as carrier nanoparticles, as opposed to HRP with GNP, allowing the enzyme to retain a significant amount of its initial activity.