Fig. 2: Quantitative p-LFA of human IL-6.

a, Schematic illustration of IL-6 LFA strips comprising an IL-6 capture antibody test spot and a sheep IgG control spot. b,c, Schematic illustration of AuNP-based IL-6 LFA (b) and dose-dependent mean grey values (c), corresponding to different IL-6 concentrations, acquired from these AuNP-based LFAs. d,e Schematic illustration of IL-6 p-LFA (d) and dose-dependent fluorescence intensities of IL-6 p-LFA (e). f,g, Eight-bit, ImageJ-processed images of AuNP-based IL-6 LFAs (f) and IL-6 p-LFAs (g), depicting the visual read-out mode. h, Fluorescence images of the IL-6 p-LFA strips depicting the fluorescence read-out mode. i, RMC curves for ELISA, p-FLISA and p-LFA (see Supplementary Information for calculations). The dashed lines indicate RMC cut-offs at µ = 2 and µ = 5; intersections of dashed lines and RMC curves indicate the range of concentrations over which a specific quantitative performance of the assay is achieved. For IL-6 p-LFA, µ < 2 over a concentration range of 0.13–86.0 pg ml⁻¹, suggesting that IL-6 p-LFA can distinguish signals corresponding to any two concentrations within that range that differ by at least 100% with at least 99% confidence. The relevant RMC parameters are listed in Supplementary Table 1. j, Stability of IL-6 p-LFA over 7 months, as evidenced by the error in concentration estimates of IL-6 concentration deduced using four different standard curves obtained over a span of 7 months. Schematics were created with BioRender.com.