*2.2. Synthesis of the POSS–EGCG Conjugate*

The POSS–EGCG conjugate was synthesized as follows. API-POSS (174.9 mg, 0.2 mmol) and EGCG (137.5 mg, 0.3 mmol) were first dissolved in 30 mL of a mixed solvent of THF/IPA/deionized water (DW) at a ratio of 2:1:1 before adding a solution of HRP (5 mg, 750 units) dissolved in 3 mL of Dulbecco's phosphate-buffered saline (DPBS, pH 7.4). To this resultant solution, 5 mL of 5 wt% H2O2 was added five times every 10 min. After 4 h, the resultant POSS–EGCG conjugate was dialyzed in DW for 48 h. Then, the precipitated conjugate was isolated by centrifugation and washing with DW in four replicates, followed by drying in vacuo. The amount of EGCG conjugated to API-POSS was determined by elemental analysis using a Flash 2000 elemental analyzer (Thermo Fisher Scientific, USA). The structures of EGCG, API-POSS, and the POSS–EGCG conjugate were determined by 1H NMR spectroscopy (AVANCE III 400, Bruker BioSpin, USA).

1H NMR of EGCG (400 MHz, D2O), δ (ppm) = 6.91 (CH of D-ring), 6.52 (CH of B-ring), 6.10, 6.07 (CH of A-ring), 5.48, 4.97 (CH of C-ring), 2.88 (CH2 of C-ring).

1H NMR of API-POSS (400 MHz, CDCl3), δ (ppm) = 2.83 (CH2NH), 1.84 (CHCH3), 1.58 (CH2CH2CH2), 0.95 (CHCH3), 0.56 (SiCH2).

1H NMR of POSS–EGCG (400 MHz, DMSO-d6), δ (ppm) = 6.81 (CH of D-ring), 6.41 (CH of B-ring), 5.95, 5.84 (CH of A-ring), 5.36, 4.98 (CH of C-ring), 2.77 (CH2 of C-ring) for EGCG, 2.69 (CH2NH), 1.82 (CHCH3), 1.58 (CH2CH2CH2), 0.95 (CHCH3), 0.54 (SiCH2) for API-POSS.
