Single-step multimodal fluorescence immunosensor based on gated nanosystem for morphine detection

To ensure public health and safety, it is crucial to develop highly sensitive, rapid, and visually interpretable platforms for detecting prohibited drugs and psychoactive substances. This study presents an innovative multimodal fluorescence immunosensor (MSN-MAb-AuNCs) based on a gated nanostructure, using morphine as a model antigen for trace detection. The platform employs mesoporous silica nanoparticles (MSN) for internal loading and external coupling of signaling molecules. A competitive immunoassay mechanism precisely activates the gated system, while fluorescence resonance energy transfer (FRET) ensures efficient signal transduction. A key innovation is the use of polyethyleneimine (PEI) as a "pseudo-hapten", which enhances the fluorescence of gold nanoclusters (AuNCs) and prevents premature FRET through its long-chain structure. This design enables accurate gating responses and seamless integration of multimodal detection. The immunosensor achieves an ultralow detection limit of 0.086 ng/mL for morphine and supports a one-step protocol for both visual semiquantification and precise quantification. Additionally, the versatility of the gated system allows adaptation to diverse analytes and detection modes, providing a robust strategy for rapid and visual trace substance detection. By overcoming limitations of conventional methods, this study makes a significant contribution to advancing biosensing and analytical chemistry.