*4.1. Synthesis of Glutathione Responsive* β*-cyclodextrin-Based Nanosponges*

Glutathione-responsiveβ-cyclodextrin-based nanosponges (GSH-NSs) were synthetized according to the method developed by Trotta et al. [35].

Briefly, GSH-NSs were obtained using a one-step synthetic route by reacting β-cyclodextrin and pyromellitic dianhydride, in the presence of 2-hydroxyethyl disulfide to insert disulfide bridges in the NS nanostructure [35]. Varying amounts of 2-hydroxyethyl disulfide were used to obtain a series of GSH-NS with different disulfide bridge percentages in the polymer matrix. In particular, 2-hydroxyethyl disulfide/β-cyclodextrin molar ratios of 1:20 and 1:5 were used for the synthesis of GSH-NS with low (GSH-NS B) and high disulfide-bridge content (GSH-NS D), respectively. The reaction was estimated at room temperature under stirring for 24 h. The nanosponges were then purified by Soxhlet extraction with acetone for a few hours. The percentage of sulfur in the two types of GSH-NS was measured by elemental analysis and was 0.62 and 1.90 for GSH-NS B and GSH-NS D, respectively.
