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Scheme 1. All-in-one immunoassay capable of sensing positive and negative samples with naked eyes.
All-in-One immunoassays can be applied to observe positive or negative results with the naked eye. For example, the color of Zonyl FSN-100 functionalized gold nanoparticles (FSN-AuNPs) is changed changes from red to purple in the presence of cysteamine formed from the reaction of ALP-labeled antibody linked to antigen and cysteamine S-phosphate. The strength of purple shown with the aggregation of FSN-AuNPs is enhanced with the increase of the antigen concentration in a sample because cysteamine supports the aggregation of FSN-AuNPs. Thus, it is possible to develop an all-in-one immunoassay capable of sensing positive and negative samples with the naked eye based on the mechanism shown in Scheme 1.