Construction of a bio-mimetic outer membrane layer via autodisplay of scFv on E. coli for SPR-based amyloid-β...

The development of highly sensitive biointerfaces is essential for the early diagnosis of Alzheimer's disease, characterized by the accumulation of amyloid-β(Aβ). In this study, a functionalized outer membrane layer using an scFv autodisplay system was constructed to enhance the performance of Surface Plasmon Resonance (SPR) biosensors. The single-chain variable fragment (scFv) against Aβ was genetically fused to an autotransporter and successfully expressed on the Escherichia coli outer membrane (OM). The biological activity and orientation of the autodisplayed scFv were validated via flow cytometry and fluorescence microscopy, showing a 35-fold higher binding affinity to Aβ compared to non-engineered controls. For the construction of the biointerface, isolated OM fractions were immobilized onto a gold substrate, forming a stable OM layer as confirmed by FT-IR spectroscopy. SPR analysis demonstrated that the scFv autodisplaying OM layer exhibited superior sensitivity with a limit of detection below 0.1 μg/mL and highly specific, concentration-dependent binding to Aβ. Crucially, the inherent physicochemical properties of the OM layer effectively minimized non-specific interactions, eliminating the need for additional blocking agents and ensuring structural stability even after washing steps. These findings establish the scFv autodisplay on an OM layer as a robust, scalable, and orientation-controlled platform for the label-free detection of biomarkers in complex biointerfaces.