Improving Detection Limits of Large-Area Monolayer Films of Au Nanoparticles in Quantitative SERS Analysis

In this work, large-area monolayer films of hexagonally close-packed gold nanoparticles (LAMF-HCP-Au NPs) were fabricated by optimizing commonly prepared large-area monolayer films of ordered arrays of Au NPs (LAMF-OA-Au NPs) via the interfacial self-assembly of Au NPs. The relative standard deviation (RSD) value of the as-prepared LAMF-HCP-Au NP substrate for detecting CV probe molecules was reduced to below 5%, owing to the improved overall degree of order in the arrangement among Au NPs. Moreover, thanks to the reduction in the interparticle spacing among Au NPs in the as-prepared LAMF-HCP-Au NP substrate, its limit of detection (LOD) for both commercial CV probe molecules and MG molecules was lowered to 10–11 M, compared with 10–10 M for the commonly prepared LAMF-OA-Au NP substrates. Additionally, the as-prepared LAMF-HCP-Au NP substrates enable quantitative detection over the range of 10–11 to 10–6 M for CV and MG molecules. Furthermore, the LOD of the LAMF-HCP-Au NP substrate for detecting commercial CV probe molecules can be further improved to 5 × 10–12 M via protonation treatment, and even to 10–12 M by increasing both the solution volume of target analytes and the laser power.