Breast cancer remains a leading cause of mortality among women globally, underscoring the critical need for effective theranostic strategies. MicroRNA-21 (miR-21) imaging-guided photodynamic therapy (PDT) has attracted significant attention in recent years due to its selectivity and sensitivity toward breast cancer. However, key challenges remain, particularly regarding the low abundance of miR-21 caused by low-quality imaging at the tumor site and the low efficiency of PDT. To address these issues, we developed theranostic Ce6-DNAzyme@ZIF-8@PEG nanoparticles (CDZP NPs) for breast cancer, which integrates dual-cycling signal amplification for miR-21 detection and enhanced PDT through GPX4-DNAzyme-mediated gene editing to inhibit reactive oxygen species (ROS) scavenging. The CDZP NPs are based on a dodecahedral metal-organic framework (MOF) ZIF-8, encapsulating a dual-cycling miR-21 imaging system and Ce6-DNAzyme therapeutic system one-pot synthesis. CDZP NPs exhibit excellent biocompatibility, acid-responsive release behavior, and a high loading capacity. These properties enable the control release of Zn, Ce6, and dual-cycling signal magnification system for miR-21 detection and enhanced PDT. studies with tumor-bearing mice demonstrated that intravenous injection of CDZP NPs could effectively target tumors. The dual-cycling signal amplification system, comprising three hairpin probes (H, H, and H), achieved a detection limit for miR-21 as low as 3.4 pM. Moreover, Zn-activated GPX4-DNAzyme significantly inhibited GPX4 protein expression, reducing ROS scavenging and further enhancing PDT efficiency with a high tumor inhibition rate of 72.3%. This proposed theranostic strategy holds promise for advancing precision theranostics in breast cancer treatment.