Portable Monitoring System for Assessing Therapeutic Efficacy in HER2‐Overexpressing Breast Cancer: One‐Step Simultaneous Detection of Cancer‐Derived Exosomal Proteins and mRNA in Urine

Abstract Point‐of‐care (POC) monitoring of patient condition is crucial for effective cancer treatment and prognosis. This can be achieved non‐invasively by analyzing exosomes in body fluids. However, the heterogeneity of exosomes and non‐standardized quantification methods may interfere with clearly determining the patient's condition. Therefore, there is a need for technology that can precisely analyze both tumor‐derived exosomes and normal exosomes. Herein, this study presents the exosome multiple‐separation for simultaneous detection (EXO‐MUSSID) platform, which simultaneously isolates different exosomes based on their magnetization properties and monitors therapeutic efficacy of drugs. Using immunoaffinity magnetophoresis technology, HER2‐overexpressing and normal exosomes are collected separately, enabling real‐time monitoring of HER2 (also known as ERBB2) expression by analyzing the mRNA of each exosome based on a catalytic hairpin assembly (CHA) reaction. A portable fluorescence reader customized for the EXO‐MUSSID platform is developed for POC monitoring of HER2‐overexpressing breast cancer (HER2 + BC). The performance of the EXO‐MUSSID platform is validated using urine samples from HER2 + BC mouse models, confirming the progression of HER2 + BC and the changes in HER2 expression due to trastuzumab treatment. It is expected to serve as a valuable tool for exosome‐based liquid biopsy in disease monitoring.