DNA origami-engineered gold nanoparticle multimers for ultrasensitive, label-free SERS detection of small molecules...

Surface-Enhanced Raman Spectroscopy (SERS) is a powerful vibrational spectroscopy technique capable of single-molecule sensitivity, yet its performance is critically dependent on the precise engineering of plasmonic hotspots. Conventional dimer-based substrates offer limited enhancement due to their restricted hotspot volume and intensity. Here, we overcome this limitation by leveraging the programmable addressability of DNA origami to construct a plasmonic nanofork antenna (DONA) that directs the assembly of 80 nm gold nanoparticles into well-defined multimers (trimers, tetramers, and pentamers). By systematically increasing the number of thiolated staple strands and refining the post-assembly conjugation workflow, we achieve reproducible sub-2 nm interparticle gaps, enabling dense and intense electromagnetic hotspots. This multimeric platform enables label-free SERS detection of Rhodamine 6G (R6G) down to an ultralow concentration of 10^-14 M, with characteristic Raman peaks at 613 cm^-1 and 1512 cm^-1 clearly resolved. Furthermore, we demonstrate the versatility of this platform by detecting proteins (streptavidin, thioredoxin) at sub-picomolar levels. Our work establishes DNA-origami-engineered multimers as a robust and generalizable strategy for ultrasensitive, label-free biochemical sensing.