Fig. 2.

Synthesis procedures and sample names for the LPEI group (2A). LPEI-1 has only the nanomachine modification, LPEI-2 has only the PEI surface coating, and LPEI-3 has both. Similar naming is used for the SPEIPEG group: SPEIPEG-1 has only the acid nanovalve, SPEIPEG-2 has only the PEI-PEG coating, and SPEIPEG-3 has both the nanovalves as well as the PEI-PEG co-polymer coating. In the SPEIPEG group, the overall synthesis steps are similar to that of the LPEI group, only that the polymer and nanovalves used are different. The detailed synthesis steps for the PEI-PEG co-polymer and the nanovalve stalk are shown in Figure 2B and Figure 2C respectively.