Simultaneous Nucleation‐Nanowelding Generates Uniform Plasmonic Au–Au Nanojunctions in 3D‐Welded Gold Nanostructures

ABSTRACT A previously unexplored controllable one‐pot kinetically controlled growth‐coupled nanowelding strategy was introduced for engineering uniform plasmonic Au–Au nanojunctions in size‐matched 3D‐welded nanostructures, where nanojunctions are formed intrinsically during nanoparticle growth instead of traditional postwelding. The structural and physicochemical properties of the nanostructures were comprehensively characterized. Time‐dependent structural characterization and spectroscopic analyses supported the growth‐coupled nanowelding and revealed a relationship between nanojunctions and reproducible SERS performances of welded golds (intra‐month‐%RSD = 8.5%). The welded‐golds exhibited an SERS enhancement factor, EF, of 2.26 × 10 ^{+ 8} , improving EF by 2.4 × 10 ^{+ 4} ‐fold and 2.3 × 10 ^{+ 3} ‐fold relative to gold nanoparticles and gold aggregations, respectively, decreasing the pixel‐to‐pixel signal variations by 2.6‐fold, and improving the ensemble signal reproducibility by fourfold relative to aggregated golds. The nanojunction‐governed system was evaluated at three levels, including robust SERS‐sensing of malachite green isothiocyanate (LOD = 2.2 × 10 ⁻¹² m ), welded gold nanostructures (LOD = 6 × 10 ⁻¹³ m ), and gold nanoparticles (LOD = 4 × 10 ⁻¹³ m ). Besides, ultrasensitive immunosensing of cancer biomarker‐α‐fetoprotein‐through a nanojunction‐mediated SERS‐linked immunosorbent assay (Nanojunc‐SERS‐LISA) provided an LOD = 0.0022 ng mL ^{− 1} (86‐fold lower than that of conventional ELISA), a well‐to‐well‐%RSD = 4.8%, an area‐to‐area‐RSD% = 5.0%, and shortened the assay time by fourfold vs. ELISA. Overall, the nanojunction‐governed system opened a door toward improving the sensitivity and reproducibility of SERS through in situ nanowelding to form size‐matched welded golds containing equivalent nanojunctions.