**2.1 Materials synthesis**

Poly-GC and Poly-AT were synthesized by Invitrogen (Shanghai, China) with a length of 20 bases. Cationic gelatin was synthesized by using Ethylenediamine-modification according to the reported methods (Matsumoto et al., 2006). The conversion rate of carboxyl groups to amino groups was measured by the TNBS method to characterize the product (Eklund, 1976). PEG-His-modified alginate was synthesized according the following methods: A total of 500 mg of alginate (Sigma) was dissolved in 20 ml of 10 mM N,N,N',N' tetramethylethylenediamine (TEMED) / HCl buffer solution (pH 4.7). A total of 1.0 g of EDC was added to this solution and stirred at 40 ◦C for 24 h. Then, different1.5 g histidine were added and stirred for another 24 h at 40 ◦C. The resulting His-alginate were dialyzed for 4 days against Milli Q water and lyophilized. The resulted His-alginate was examined for its pKa value. The following Pegylation was achieved by conjugating a 2000 Da mPEG-NH2 to the His-alginate using a Pegylation kit (YARE Chem, Shanghai, China). Rhodamine-labled PEG-His-alginate and FITC-labled cationic gelatine was synthesized by using fluorescencelabel kits (DAZHI Biotech, Nanjing, China) injected into liver tumor bearing mice.
