Ag Nanostars in Capillary-Enabled Digital SERS Quantification of Trace Hg²⁺

Mercury (Hg), as a highly toxic heavy metal pollutant, poses severe threats to ecological systems and human health even at trace concentrations of ppt levels. Current detection technologies face challenges including insufficient sensitivity, poor anti-interference capability, and complex operational procedures. This study proposes a capillary quartz tube-based silver nanostar (Ag NS) digital surface-enhanced Raman scattering (SERS) method for highly sensitive detection of trace Hg 2+ . The approach amplifies Raman scattering signals through localized surface plasmon resonance (LSPR) and tip-enhanced effects of Ag NSs, integrated with a digital signal recognition strategy via digital SERS (dSERS), and the intensity-fluctuating SERS signals were converted into digital signals “1” and “0” via predetermined threshold optimized analysis. Ag NSs with tunable tip structures were synthesized via a seed-mediated growth method. Electromagnetic simulations demonstrated significant SERS enhancement originating from the tip architecture. Specific coordination between diethylenetriaminepentaacetic acid (DTPA) ligands and Hg 2+ induced a carboxyl vibrational peak shift, enabling sensitive Hg 2+ detection. Experimental results revealed that the digital quantification model based on statistical analysis of SERS-active signals exhibited excellent linear response ( R 2 = 0.99) from 100 ppb to 10 ppt, achieving a detection limit of 10 ppt. The spike recovery error in real water sample analysis was maintained below 10%. This study provides an innovative solution for trace heavy metal detection in complex environments, demonstrating simultaneous ultrahigh sensitivity and anti-interference capability.