This invention is a novel nanoparticle that can deliver therapeutics, RNA, and imaging molecules to the intraperitoneal space. The nanoparticles are composed of block copolymers with a hydrophobic core and a hydrophilic corona. Drug and imaging molecules are covalently linked to the hydrophobic core of the nanoparticles, and the hydrophilic arms of the nanoparticle can carry an RNA cargo. As a proof of principle, the inventors used an in vivo mouse transplant model of ovarian cancer to demonstrate effective tumor targeting and dosing. When nanoparticles carrying NIR-II imaging molecules are injected into the IP cavity of tumor-bearing mice the nanoparticles target very specifically to the tumor and facilitate NIR imaging with a high signal to noise ratio. Additionally, the inventors loaded the nanoparticles with platinum-based chemotherapeutic agents and siRNA or CRISPR/Cas9 RNAs against the gene BCL-2, which has a known role in ovarian cancer recurrence. Mice treated with oxaliplatin-BCL-2 conjugated nanoparticles demonstrate striking reductions in tumor size and increased lifespan, even in mice with platinum-resistant tumors. In conclusion, this nanoparticle technology has tremendous potential as both an imaging tool and a drug delivery method for treating IP cancers.