Enzyme-free and label-free detection of HER2 in human serum based on Ag+-released hybridization chain reaction signal amplification

The overexpression of human epidermal growth factor receptor 2 (HER2) has been linked to aggressive breast cancer and worse clinical outcomes. However, accurately measuring HER2 remains challenging, due to its low serum content. Herein, we developed a novel method for HER2 detection in serum by the combination of aptamer with C-Ag+-C structure, Ag+-released hybridization chain reaction (Ag+-HCR) and coprecipitation of Ag+ and gold nanoparticles (AuNPs) in the solution including Eosin Y (EY) and AgI colloids. Following the aptamer bound to HER2, signal amplification occurred through the release of numerous Ag+ by Ag+-HCR. This process subsequently induced AuNPs aggregation on the surface of AgI colloids, resulting in reduced fluorescence intensity of EY in the supernatant. The reduced value of EY fluorescence intensity in the supernatant was proportional to the level of HER2. Under optimized reaction conditions, a wide detection range was obtained between 0.09 to 9000 pg/mL with a limit of detection of 11.7 fg/mL in diluted human serum, and 96 serum samples in a 96-well plate could be measured simultaneously by a microtiter plate reader within 2 h. Moreover, the quantitative results of HER2 were consistent with those obtained using the enzyme-linked immunosorbent assay kit (r = 0.9995). Therefore, leveraging the delicate design of Ag+-HCR signal amplification, this enzyme-free, label-free, and effective method has demonstrated to be capable of detecting HER2 in serum due to its high sensitivity. Remarkably, this method may be extended to detect other cancer-related proteins and genes by replacing the corresponding target sequences.