Fig. 1. Preparation process of parahydrophobic nanostructures
(a): PI substrate; (b): Single-layer nanofibers after plasma treating; (c): Double-layer nanofibers after silicon etching; (d): Double-layer nanofibers after HMDS decoriting

Fig. 2. UV-VIS-NIR absorption spectrum (a) and SEM image (b) of the Ag nanoparticles

Fig. 3. SEM image (a) and infrared spectra (b) of the parahydrophobic substrate

Fig. 4. States of a droplet on the parahydrophobic substrate
(a): With a contact angle of 152° when on the front surface; (b): Hanging beneath the substrate when it is turned over

Fig. 5. Droplets on (a) a hydrophilic substrate and (b) a parahydrophobic substrate; Coffee rings formed on (c) a hydrophilic substrate and (d) a parahydrophobic substrate

Fig. 6. SEM images of a coffee ring formed on a parahydrophobic substrate

Fig. 7. SERS spectra of MG with different concentrations obtained from coffee rings on a hydrophilic substrate and a parahydrophobic substrate