Fig. 5

SPN surface monofunctionalisation. a Schematic of the modification of the surface of SPN-N₃ with active dye, enabling FRET between dye and nanoparticle. b Normalised absorbance (solid lines) and emission (black lines) spectra of the dye (red lines) and the nanoparticles (black lines). c PL spectra of SPN-N₃ with increasing equivalents of active dye, x = 423 dye molecules per nanoparticle (concentration of nanoparticle calculated with NTA) excited at 450 nm, all at the same nanoparticle concentration. d Schematic of the EDC coupling on the surface of SPN–COOH with a biotin functionalised amine. e Illustration of the components of a poly-streptavidin test strip with image of the test line run with particles functionalised with and without EDC present at increasing concentrations of biotin-NH₂: (i) 1 μg mL⁻¹, (ii) 10 μg mL^−1, (iii) 100 μg mL⁻¹ and (iv) 200 μg mL⁻¹ in water