A switchable magnetic resonance imaging nanoplatform for microRNA imaging

Aberrant microRNA (miRNA) expression is associated with various types of carcinogenesis, making miRNA a promising candidate for diagnostic and therapeutic biomarkers. However, in situ miRNA diagnostics remains a significant challenge owing to the various biological barriers. Herein, we report a novel miRNA imaging probe consisting of PEG-polylysine-PNIPAM polymer matrix-modified small Fe 3 O 4 (PAA-Fe 3 O 4 -DNA@PPP) nanoparticles with an improved circulatory half-life, efficient tissue permeability, and enhanced tumor accumulation, for in situ miRNA magnetic resonance imaging (MRI). In this strategy, we employed large size PAA-Fe 3 O 4 -DNA@PPP to improve circulatory time and utilized PEG-polylysine-PNIPAM as a GSH-responsive moiety to dissociate PAA-Fe 3 O 4 -DNA@PPP and release small size PAA-Fe 3 O 4 -DNA for enhanced tumor permeability. Specifically, the target miRNA acts as a cross-linker for PAA-Fe 3 O 4 -DNA, forming larger assemblies that not only amplify the MRI signal for detection but also enhance retention for prolonged observation. Both the in vitro and in vivo results validate that the imaging probe exhibits an enhanced MRI signal with 3.69-fold amplification for tumor interior miRNA detection, allowing the dynamic changes in miRNA to be monitored by the probe. Given its long circulation, efficient penetration, and enhanced tumor accumulation, the PAA-Fe 3 O 4 -DNA@PPP probe holds great promise for in situ miRNA imaging and spatial genomics analysis in situ . A "large-small-large" size-switchable PAA-Fe 3 O 4 -DNA@PPP nanoplatform maintains a large size in the circulation system and discomposites into small-size in the TME condition and finally assembles into larger-size by miRNA.