Fig. 4: In vivo brightness of Ag₂S superdots: a comparison with their competitors.

a NIR-II fluorescence decay curves of PEG-coated Ag₂S dots (provided by Sinano Corp., China) and Ag₂S superdots, both dispersed in PBS. b NIR-II fluorescence images of a group of four mice subcutaneously injected with colloidal aqueous dispersions containing Ag₂S superdots, commercial Ag₂S dots, SWNTs, and LaF₃:Nd NPs. The same NP volume (100 µL) and concentration (1.5 mg mL⁻¹) were injected in all cases. The different images for same optical probe correspond to different 808 nm illumination power densities. c Signal-to-noise ratio (SNR) as a function of power density quantified from the analysis of images in b for the four NIR-II nanoprobes evaluated. d Fluorescence images of Ag₂S superdots accumulated in the liver obtained at three different 808 nm excitation power densities. e Power density dependence of SNR calculated from in vivo NIR-II fluorescence images at different excitation power densities. f NIR-II fluorescence images of the left hind limbs of two mice immediately before (top) and 15 s after (bottom) of an intravenous injection of Ag₂S dots (left) or superdots (right). g Net intensity images obtained from subtracting the background images (top row in f) from the signal images (bottom row in f). h Signal-to-background images obtained by dividing the signal intensity images (bottom row in f) by the background images (top row in f). Scale bars in f, g, and h are 2 mm. i Net intensity and j signal-to-background ratio obtained along a line profile across the saphenous artery (indicated as dashed white lines in g and h).