An enzyme-linked immunosorbent assay (ELISA) using monoclonal antibody (MAb), Fab antibody, and single-chain variable fragment (scFv) antibody has become one of the most promising analytical methods owing to its rapidity, sensitivity, and reliability. Recently, a chimera of green fluorescent protein (GFP) with a scFv antibody, named fluobody, was proposed as a probe for an alternative immunosorbent assay; i.e., fluorescence-linked immunosorbent assay (FLISA). In this FLISA, an even more sensitive, simple, and rapid immunoassay can be performed by detecting the highly sensitive fluorophore of GFP that is genetically and directly fused to the scFv antibody. In addition, the time- and cost-consuming secondary antibody reaction and the following enzyme-substrate reaction, necessary for conventional ELISA, can be avoided, making it possible to complete the assay more rapidly. Focusing on naturally occurring bioactive products, fluobody recognizing 1,4-naphthoquinone, plumbagin and triterpenoid saponin, ginsenosides were successfully expressed in Escherichia coli (E. coli) and applied to FLISA. The construction, the expression, and the potential use of fluobody in quantitative/qualitative analysis of bioactive natural products are reviewed in this article.