Interfacially programmable triblock DNA probes enable highly specific PDGF-BB detection via proximity...

Selective detection of multimeric protein biomarkers is important for biomarker-related research and complex sample analysis; however, the performance of current sensing systems is often limited by insufficient control over the spatial organization of recognition probes at solid-phase interfaces. Herein, using platelet-derived growth factor-BB (PDGF-BB) as a homodimeric model target, we developed a fluorescence sensing strategy based on triblock polyadenine (polyA) DNA probes, in which the interfacial programmability is achieved through polyA length-mediated control of the spacing between recognition sites and proximity hybridization-induced competitive DNA strand displacement. The triblock probe integrates two terminal capture domains through a central polyA segment, which simultaneously serves as a high-affinity anchoring motif for gold nanoparticles, a covalent linker to maintain a defined stoichiometric arrangement of recognition modules, and a programmable spacer for regulating the interfacial distance between recognition sites. By optimizing the polyA length and the complementary region length of the competitive aptamer probe, the interprobe spacing, target-mediated dual-site recognition, competitive displacement efficiency, and background suppression were rationally balanced. Under optimized conditions, the sensor exhibited a linear response to PDGF-BB over 10-500 ng/mL, with a limit of detection of 7.5 ng/mL. Notably, the system produced only a weak response toward the structurally related PDGF-AB heterodimer, supporting the proposed homodimer-specific bridging mechanism. Spike-recovery experiments in a 10% human serum matrix yielded recoveries of 97.16%-108.55%, with relative standard deviations of 5.67%-7.84%. This work provides a general interface-programmable strategy for proximity-based sensing of multimeric and conformation-sensitive protein targets.