This ssDNA was successfully delivered into MCF-7 human breast cancer cells by nanocrystals of Ni-IRMOF-74-II (Fig. 4b and Supplementary Figure 99–101), in which it was released by pairing up with target mRNA (Supplementary Figure 101), thus inhibit the expression of EGR-1 gene with nearly 76% inhibition efficiency (Fig. 4d). This evidence concerns the gene EGR1 and breast cancer.