Detection of Cordycepin Using Indicator Displacement Assay of Cucurbit [7] Uril and Environmentally Sensitive Fluorescent Dyes

Abstract

Ophiocordyceps and Cordyceps spp. are some of the most popular Chinese herbs because of their bioactive compounds, for example cordycepin that has many pharmacological functions such as anti-tumor, anti-microbes, anti-inflammatory, and immunomodulator. The abundant supply of products in the market has different variations in purity and quality, so the rapid and simple quantitative analysis method to access the quality of Ophiocordyceps and Cordyceps products is urgently required. Indicator displacement assay (IDA) using environmentally sensitive fluorescence (FL) dye can be used for quantitative analysis of the target compound. The concept of this assay is replacing the FL dye in the receptor-dye inclusion complex by the analyte. In this study, screening of host series, such as cucurbits[n]uril (CB[n]) and cyclodextrins as well as the finding of the suitable environmental sensitive FL dyes i.e. esculetin, cascade yellow, nonyl acridine orange (NAO), berberine, and 2-p-toluidinyl naphthalene-6-sulphonate (2,6-TNS) were performed. The FL emission of esculetin, cascade yellow, and NAO either decreased or increased slightly upon addition of all hosts mentioned above. Among FL dyes tested, berberine and 2,6-TNS participated in the inclusion complex with CB7 as suggested by the approximately 500-fold and 4-fold FL increment observed when CB7 was added respectively. Cordycepin showed the highest displacement ability when it was titrated with an inclusion complex of berberine/CB7 and 2,6-TNS/CB7 in pH 4.0. Moreover, in the selectivity assay, cordycepin performed the distinguished displacement ability among the other compounds, suggesting about the high potential for using IDA method as a rapid and simple quality assessment of commercial Ophiocordyceps and Cordyceps product.