CAT and neoplasm: Furthermore, the continual release of oxygen means it can be used as a durable contrast enhancer for ultrasound imaging of tumor cells.63 The combination of catalase and a polymeric nanocarrier for O2-mediated PDT was developed by Phua et al.64 In their research, catalase was conjugated with β-cyclodextrin-functionalized hyaluronic acid (HA) loaded with photosensitizer chlorin e6 (Ce6) to form HA–CAT@aCe6 NPs.