Fig. 1

Chemical synthesis and characterization of AgNIS for MEF. A Schematic illustration of the AuNP-catalyzed synthesis of AgNIS with broad spectral fluorescence enhancement. B UV–vis absorption spectra and C representative SEM images of AuNP-immobilized PS substrate at different seeding densities mediated by PLL concentrations. Shaded boundaries represent confidence intervals (CI) within ± 1 SD from three independent samples. D Photographs and E normalized absorption at 260 nm of the time-course Benedict’s assay for 50 mM reducing monosaccharides (n = 2). Solutions with no saccharides and the non-reducing disaccharide sucrose were introduced as controls. F Amperometric i-t curves of 10 mM saccharides in 0.1 M pH 7 PBS at a constant potential of + 1.5 V with a glassy carbon working electrode. G Heatmap showing fluorescence enhancement of fluorophore-labeled BSA probes on Ag structures. The Ag synthesis advanced at equivalent concentrations of reducing monosaccharides and varied in gradient concentrations of PLL and Tollens’ reagents that controlled seeding densities and growth availabilities. H 3D PCA biplot of Ag structures synthesized under different conditions. 83.82% of the total variance is explanatory by the first three components, with eigenvalues above the retention cut-off conforming to the Kaiser-Guttman rule (Additional file 1: Fig. S10). The loading vectors of PLL, Tollens’ reagent, and sugar reducing power diverge from those of EFs, which form small angles by themselves. I The energy-dispersive X-ray spectrum (EDS) of AgNIS. J Elemental mapping analysis on the nanostructural AgNIS. Nanoisland-like structures are primarily elemental silver, with low levels of oxygen intensities. Carbon originates from the PS substrate