Ultrabright fluorescent label improves assay speed and sensitivity

A new ultrabright fluorescent label might make bioassays faster and more sensitive. Srikanth Singamaneni and coworkers at Washington University in St. Louis make their “plasmonic-fluor” labels of a bovine serum albumin scaffold attached to approximately 210 copies of a near-infrared-active fluorophore, a biotin biorecognition group, and a polymer-coated gold nanorod (Nat. Biomed. Eng. 2020, DOI: 10.1038/s41551-020-0547-4). The nanorod boosts fluorescence intensity, resulting in a label that is about 6,700 times as bright as an individual fluorophore. The biotin recognition element enables binding to streptavidin, which is commonly used in various types of bioassays. In this way, the plasmonic-fluor can be incorporated as a final step in otherwise normal assay protocols. The researchers used the new label in a variety of bioassays, including immunomicroarrays, flow cytometry, and immunocytochemistry. By using the label, the researchers detected analytes in fluorescence-linked immunosorbent assays (FLISA) at about 20 fg/mL, compared with 95 pg/mL for conventional FLISA. In addition, they were able to use smaller samples and shorten the analysis time from 280 min for enzyme-linked immunosorbent assays to 20 min for the plasmonic FLISA.