Certain chemotherapeutics can induce tumor cells’ immunogenic cell death (ICD), release tumor antigens, and thereby trigger personalized antitumor immune responses. Co-delivery of adjuvants using nanocarriers could amplify the ICD-induced tumor-specific immunity achieving a synergistic chemo-immunotherapeutic effect. However, complicated preparation, low drug loading efficiency, and potential carrier-associated toxicity are the major challenges that limited its clinical applications. Herein, a carrier-free core–shell nanoparticle (MPLA-CpG-sMMP9-DOX, MCMD NPs) was constructed by facile self-assembly of spherical nucleic acids (SNA) with two adjuvants of CpG ODN and monophosphoryl lipid A (MPLA) as a core and doxorubicin (DOX) radially around the dual-adjuvants SNA as a shell. The results demonstrated that MCMD NPs could enhance drugs accumulation in tumors, and release DOX upon enzymatic degradation of matrix metalloproteinase-9 (MMP-9) peptide in the tumor microenvironment (TME), which enhanced the direct-killing effect of DOX on tumor cells. The core of MPLA-CpG SNA efficiently boosted the ICD-induced antitumor immune response to further attack tumor cells. Thus, MCMD NPs achieved a synergistic therapeutic effect of chemo-immunotherapy with reduced off-target toxicity. This study provided an efficient strategy for the development of a carrier-free nano-delivery system for enhanced cancer chemo-immunotherapy.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12951-023-01916-0.