Electronic Supporting Information Highly Porous PVA Dried Gel with Gold Nanoparticles Embedded in the Network as a Stable and Ultrasensitive SERS Substrate

Transmission electron microscopy (TEM) observations were conducted on a CM 120 transmission electron microscope (Philips, Netherlands) at an acceleration voltage of 80 kV. Scanning electron microscopy (SEM) images were obtained on a TS-5136MM scanning electron microscope (Tescan, Czech) at an accelerating voltage of 20 kV. Ultraviolet-visible (UV-Vis) absorption spectra were measured on a UV-2550 spectrometer (Shimadz, Japan) with ISR240A Integrating Sphere Attachment. For the UV-Vis measurement of gold colloidal solution, deionized water was used as the reference, while for the UV-Vis measurement of wet Gel I (Gel I without being freeze-dried), the reference is the wet PVA gel prepared under the same conditions as the wet Gel I but in the absence of GNPs and pore-forming agent. In the experiments of determining the concentration of the remaining CV (crystal violet) methanol solution after 24 h immersion of Gel I or Gel II, methanol was used as the reference for the UV-Vis measurement. Surface-enhanced Raman spectra were collected using a LabRam-1B micro-Raman spectrometer (Jobin Yvon, France) with incident wavelength of 632.8 nm. The measurement was conducted with 10s exposure time and 1mW laser power. The focused laser spot was 0.7 μm.