Ultrasensitive lateral-flow assays via plasmonically active antibody-conjugated fluorescent nanoparticles

Lateral-flow assays (LFAs) are rapid and inexpensive, yet they are nearly 1,000-fold less sensitive than laboratory-based tests. Here we show that plasmonically active antibody-conjugated fluorescent gold nanorods can make conventional LFAs ultrasensitive. With sample-to-answer times within 20 min, plasmonically enhanced LFAs read out via a standard benchtop fluorescence scanner attained about 30-fold improvements in dynamic range and in detection limits over 4-h-long gold-standard enzyme-linked immunosorbent assays, and achieved 95% clinical sensitivity and 100% specificity for antibodies in plasma and for antigens in nasopharyngeal swabs from individuals with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Comparable improvements in the assay's performance can also be achieved via an inexpensive portable scanner, as we show for the detection of interleukin-6 in human serum samples and of the nucleocapsid protein of SARS-CoV-2 in nasopharyngeal samples. Plasmonically enhanced LFAs outperform standard laboratory tests in sensitivity, speed, dynamic range, ease of use and cost, and may provide advantages in point-of-care diagnostics. The sensitivity of conventional lateral-flow assays can be improved by orders of magnitude by using plasmonically active fluorescent gold nanorods as antibody-conjugated labels.

Automated summary

By conjugating fluorescent gold nanorods with antibodies, conventional lateral-flow assays can achieve ultrahigh sensitivity, with a 1,000-fold improvement compared to laboratory-based tests. Plasmonically enhanced LFAs, read out using a standard fluorescence scanner, demonstrated 30-fold improvements in dynamic range and detection limits over gold-standard enzyme-linked immunosorbent assays and showed high clinical sensitivity and specificity for SARS-CoV-2 antibodies and antigens. This enhanced performance can also be achieved using an inexpensive portable scanner for the detection of IL-6 and SARS-CoV-2 nucleocapsid protein. The use of plasmonically enhanced LFAs offers significant advantages in sensitivity, speed, dynamic range, ease of use, and cost, making them promising for point-of-care diagnostics.