A Multifunctional Peptide Nucleic Acid/Peptide Copolymer-Based Dual-Mode Biosensor with Macrophage-Hitchhiking for Enhanced Tumor Imaging and Urinalysis

Biosensors are capable of diagnosing tumors through imaging <i>in vivo</i>or liquid biopsy, but they face the challenges of inefficient delivery into tumor sites and the lack of reliable tumor-associated biomarkers. Herein, we constructed a dual-mode biosensor based on a multifunctional peptide nucleic acid (PNA)/peptide copolymer and DNA tetrahedron for tumor imaging and urinalysis. The biosensor could enter the cancer cells to initiate a microRNA-21-specific catalytic hairpin assembly reaction after cleavage by matrix-metalloprotease (MMP) in the tumor microenvironment, and the MMP cleavage product was released into the bloodstream and then was filtered out by the kidney. As PNA was a synthetic DNA analogue that could not be degraded by nucleases and proteases, it could serve as a reliable synthetic biomarker and be easily detected by high-performance liquid chromatography in urine. Importantly, the biosensor was hitchhiked on the macrophage membrane to realize efficient delivery in the depth of tumor utilizing the macrophage ability of actively homing to the tumor site and infiltrating into the tumor. The results indicated that the signal output of the biosensor was improved remarkably and mice with a tumor volume as little as 30-40 mm³ could be reliably discriminated through urine assay. This innovative macrophage-hitchhiking dual-mode biosensor holds a great potential as a non-invasive and convenient tool for tumor diagnosis and tumor progression evaluation.