A Multifunctional Peptide\nNucleic Acid/Peptide Copolymer-Based\nDual-Mode Biosensor with Macrophage-Hitchhiking for Enhanced Tumor\nImaging and Urinalysis

Biosensors are capable of diagnosing tumors through imaging <i>in vivo</i>or liquid biopsy, but they face the challenges of\ninefficient delivery into tumor sites and the lack of reliable tumor-associated\nbiomarkers. Herein, we constructed a dual-mode biosensor based on\na multifunctional peptide nucleic acid (PNA)/peptide copolymer and\nDNA tetrahedron for tumor imaging and urinalysis. The biosensor could\nenter the cancer cells to initiate a microRNA-21-specific catalytic\nhairpin assembly reaction after cleavage by matrix-metalloprotease\n(MMP) in the tumor microenvironment, and the MMP cleavage product\nwas released into the bloodstream and then was filtered out by the\nkidney. As PNA was a synthetic DNA analogue that could not be degraded\nby nucleases and proteases, it could serve as a reliable synthetic\nbiomarker and be easily detected by high-performance liquid chromatography\nin urine. Importantly, the biosensor was hitchhiked on the macrophage\nmembrane to realize efficient delivery in the depth of tumor utilizing\nthe macrophage ability of actively homing to the tumor site and infiltrating\ninto the tumor. The results indicated that the signal output of the\nbiosensor was improved remarkably and mice with a tumor volume as\nlittle as 30–40 mm<sup>3</sup> could be reliably discriminated\nthrough urine assay. This innovative macrophage-hitchhiking dual-mode\nbiosensor holds a great potential as a non-invasive and convenient\ntool for tumor diagnosis and tumor progression evaluation.