Microfluidic fluorescence biosensor for quantitative detection of HER2 in serum using an antibody-aptamer sandwich...

Early detection of cancer biomarkers requires analytical platforms capable of sensitive quantification in complex biological matrices. Here we report a microfluidic fluorescence biosensor for the quantification of the breast cancer biomarker Human epidermal growth factor receptor 2 in human serum. The system integrates a hybrid bead-based antibody-aptamer sandwich assay with thin-film hydrogenated amorphous silicon (a-Si:H) photodiodes and a dielectric interference filter, enabling compact on-chip fluorescence detection within a fully integrated microfluidic architecture. Protein G-functionalized microbeads enabled oriented immobilization of capture antibodies, while a fluorophore-labeled HER2 aptamer served as the detection probe, forming a hybrid antibody-aptamer recognition scheme that minimized non-specific interactions in serum matrices. The microfluidic architecture and washing direction were optimized to suppress residual unbound aptamer, significantly improving the signal-to-background ratio. Under optimized conditions, the biosensor exhibited a near-linear fluorescence response for HER2 concentrations in 90% human serum across clinically relevant levels, achieving a limit of detection of 7-8 ng mL^-1, below the clinical threshold of 15 ng mL^-1. Photodiode measurements were consistent with fluorescence microscopy, confirming reliable on-chip signal acquisition. These results demonstrate a scalable strategy that combines hybrid molecular recognition, microfluidic background suppression, and integrated thin-film photodetection within a compact fluorescence biosensing platform for quantitative biomarker analysis.