Fluorescence Method-Based Nonlinear Hybridization Chain Reaction for Highly Sensitive and Specific Detection of HER2

Human epidermal growth factor receptor 2 (HER2) is a critical biomarker for targeted therapy of gastric cancer. Tissue-based HER2 testing via immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) remains the clinical gold standard, while serum HER2 represents a potential complementary circulating biomarker for disease monitoring. However, conventional serum HER2 assays often suffer from limited sensitivity. Herein, we develop a highly sensitive fluorescence assay for serum HER2 detection using nonlinear hybridization chain reaction (NHCR) coupled with a HER2-specific aptamer (HB5). Unlike linear hybridization chain reaction (HCR), NHCR enables branching-mediated exponential amplification, in which each trigger initiates multiple independent HCR cascades, leading to nonlinear signal growth. The method exhibited a good linear relationship (R ² = 0.993) in the HER2 concentration range of 0.5-90 ng·mL^-1, with a detection limit as low as 38 pg·mL^-1. The sensor demonstrated excellent specificity for HER2, good reproducibility, and reliable stability. Clinical serum sample detection results indicated that the method was highly correlated with the clinically commonly used chemiluminescence immunoassay (CLIA), with spiked recoveries ranging from 95.4% to 109.6%. The NHCR-based fluorescent detection strategy established in this study provides a new tool for accurate and noninvasive detection of serum HER2, featuring simple operation and controllable cost.