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.