Engineering the Hot-Spots\nin Au–Ag Alloy Nanoparticles\nthrough Meniscus-Confined 3D Printing for Microplastic Detection

The escalating concern surrounding microplastic (MP)\npollution\nnecessitates urgent attention and the development of rapid techniques\nfor quantifying extremely low concentrations. Surface-enhanced Raman\nspectroscopy (SERS) has emerged as a promising method due to its simplicity,\nhigh sensitivity, and rapid quantification capabilities. Herein, the\nefficacy of gold–silver alloy nanoparticles (3DPAu-Ag) substrates\nfor detecting poly(methyl methacrylate) (PMMA) and polystyrene (PS)\nMPs is investigated. The 3DPAu-Ag SERS substrates are fabricated using\nthe meniscus-confined electrochemical 3D printing (MC-E3DP) process,\nemploying a nozzle of 0.8 mm size with 2.5 V potential at a printing\nspeed of 0.4 mm s<sup>–1</sup>. The proposed SERS substrates\nexhibit exceptional sensitivity and are capable of detecting PMMA\nconcentrations as low as 0.2 μg mL<sup>–1</sup> and PS\nconcentrations of 1.2 μg mL<sup>–1</sup> within the ranges\nof 1–10<sup>3</sup> μg mL<sup>–1</sup> and 10–10<sup>4</sup> μg mL<sup>–1</sup>, respectively. Remarkable\nenhancement factors (EFs) of up to 3.2 × 10<sup>4</sup> for PMMA\nand 9.3 × 10<sup>3</sup> for PS are achieved, underscoring the\nsubstrates’ effectiveness. Furthermore, the investigation demonstrates\noutstanding uniformity and reproducibility of the 3DPAu-Ag substrates,\nwith relative standard deviation (RSD) values of only 4.1 and 6.4%,\nrespectively, across 31 and 5 measurements. Additionally, a minimal\n17% decrease in the initial SERS signal value after 5 weeks highlights\nthe substrates’ high stability. This not only highlights the\nsuperior quality of the substrates but also positions them ahead of\npreviously reported works in the literature. Moreover, this study\nalso comes up with a plausible mechanism for MPs SERS detection facilitated\nby the 3DPAu-Ag substrates, offering insights into the underlying\nprocesses. Overall, 3DPAu-Ag substrates show promise for sensitive,\nstable MP detection, which is crucial for environmental monitoring.