Engineering the Hot-Spots in Au–Ag Alloy Nanoparticles through Meniscus-Confined 3D Printing for Microplastic Detection

The escalating concern surrounding microplastic (MP) pollution necessitates urgent attention and the development of rapid techniques for quantifying extremely low concentrations. Surface-enhanced Raman spectroscopy (SERS) has emerged as a promising method due to its simplicity, high sensitivity, and rapid quantification capabilities. Herein, the efficacy of gold-silver alloy nanoparticles (3DPAu-Ag) substrates for detecting poly(methyl methacrylate) (PMMA) and polystyrene (PS) MPs is investigated. The 3DPAu-Ag SERS substrates are fabricated using the meniscus-confined electrochemical 3D printing (MC-E3DP) process, employing a nozzle of 0.8 mm size with 2.5 V potential at a printing speed of 0.4 mm s^-1. The proposed SERS substrates exhibit exceptional sensitivity and are capable of detecting PMMA concentrations as low as 0.2 μg mL^-1 and PS concentrations of 1.2 μg mL^-1 within the ranges of 1-10³ μg mL^-1 and 10-10⁴ μg mL^-1, respectively. Remarkable enhancement factors (EFs) of up to 3.2 × 10⁴ for PMMA and 9.3 × 10³ for PS are achieved, underscoring the substrates' effectiveness. Furthermore, the investigation demonstrates outstanding uniformity and reproducibility of the 3DPAu-Ag substrates, with relative standard deviation (RSD) values of only 4.1 and 6.4%, respectively, across 31 and 5 measurements. Additionally, a minimal 17% decrease in the initial SERS signal value after 5 weeks highlights the substrates' high stability. This not only highlights the superior quality of the substrates but also positions them ahead of previously reported works in the literature. Moreover, this study also comes up with a plausible mechanism for MPs SERS detection facilitated by the 3DPAu-Ag substrates, offering insights into the underlying processes. Overall, 3DPAu-Ag substrates show promise for sensitive, stable MP detection, which is crucial for environmental monitoring.