Comparison of different zinc precursors for the construction of zeolitic imidazolate framework-8 artificial shells on living cells

The robust cell-in-shell structure is highly desirable for endowing living cells with an artificial exoskeleton to defend them from many environmental factors such as osmotic pressure, shear force, heat, UV radiation, and enzymes. Cell encapsulation has shown potential applications in many fields and attracted increasing interest. However, the influences of the precursors on the cell viability during the shell formation process are not clear and seldom investigated. Here, zinc nitrite, zinc acetate and zinc sulfate were applied individually to synthesize zeolitic imidazolate framework-8 (ZIF-8) shells on living cells. All the zinc salt precursors could convert to a ZIF-8 layer on the living cell surface. The zinc salts and organic ligand did not exhibit obvious toxicity to yeast cells when applied individually. However, dead cells were observed during the living cell encapsulation process using different zinc precursors. Compared with zinc nitrate and zinc acetate, ZIF-8 formed by zinc sulfate led to a higher percentage of cell death, especially under high concentrations of zinc sulfate. Cell division was suppressed by the ZIF-8 shell but restored fully upon shell removal by EDTA solution or pH 4.0 buffer. Escherichia coli (E. coli) cells showed a lower percentage of cell death, indicating excellent tolerance to the ZIF-8 encapsulation process. This work illustrates the cell toxicity during the formation of ZIF-8 cell shells by different zinc salts and engineering of the cell growth by MOF coating, which could provide a foundation for further quantitative analysis and potential applications in biomedicine and bioengineering.