Fig. 1. Illustration of SD hydrogel-based exosome detection method (images are not to scale). (a) Preparation of SERS nanoprobes; (b) preparation of SD hydrogels; (c) principles of SD hydrogels for detection of tumor-derived exosomes

Fig. 2. Characteristics of SERS probes. (a) Zeta potential of Au, SiO₂, SiO₂-Au@DTNB, Janus AD, and Janus ADD measured by dynamic light scattering (DLS); TEM images of (b) SiO₂-Au and (c) Janus AD

Fig. 3. Optical properties of SERS probes. (a) Extinction spectra of Au, SiO₂-Au@DTNB, Janus AD, and Janus ADD; (b) SERS spectra of SiO₂-Au@DTNB, Janus AD, and Janus ADD

Fig. 4. Characteristics of SD hydrogels. (a) SEM image of SD hydrogels; photographs of (b) pure hydrogels and (c) SD hydrogels

Fig. 5. Performance of SD hydrogels. (a) SERS spectra of SD hydrogels with or without Ag NPs; (b) SERS spectra of 1323 points collected from three areas of 480 μm×480 μm on SD hydrogels (the background noise has been removed); (c) SERS spectra collected from three batches of SD hydrogels, for each SD hydrogel, SERS spectra of 32 points were measured; (d) concentration-dependent SERS spectra for the detection of targeted DNA ranging from 10 pmol/L to 100 nmol/L and a blank control

Fig. 6. Detection results of exosomes. (a) Averaged concentration versus size for NTA experiments of SKBR3 exosomes (inset: TEM image of SKBR3 exosomes); (b) intensity profiles of exosomes in SD hydrogels labeled with DID along the solid line (inset: super-resolution images of SKBR3-derived exosomes in SD hydrogels); (c) concentration-dependent SERS spectra for the detection of SKBR3-derived exosomes ranging from 22 to 22000 μL^-1 and a blank control; (d) concentration-dependent signal change for target exosomes, the error bars represent the standard deviation for 8 individual measurements, and the dotted line is linear fitting of concentration-dependent signal change