Optimizing Gold Nanoparticle Size and Aggregation Strategies for Enhanced Sers: A Comprehensive Review

Abstract: Surface-enhanced Raman scattering (SERS) is an ultrasensitive spectroscopy technique that leverages localized surface plasmon resonance (LSPR) in nanostructured metallic substrates. Its ability to detect and analyze molecules at very low concentrations is certain; however, the effectiveness is highly dependent on the size and aggregation state of the nanoparticles used as a substrate. This study analyzes the correlation between key sensitivity parameters consisting of enhancement factor (EF) and limit of detection (LOD) in relation to the enhanced SERS. The effects of sensitivity associated with suitably sized nanoparticles focusing on gold nanoparticles (AuNPs) and their implementation of SERS are comprehensively analyzed. The method for controlling nanoparticle aggregation is also reviewed as a complementary strategy to enhance SERS performance alongside the optimal size. The findings indicate that the AuNPs with sizes below 55 nm provide higher EF and lower LOD due to the increased strength of the electromagnetic field, although they may suffer from aggregation instability compared to the larger nanoparticles. To manage this concern, the integrated strategies involving chemical, physical, and self-assembly techniques of controlled aggregation of AuNPs have a significant impact on forming SERS hot spots and amplifying signals. Therefore, an adaptation of the approaches to obtain the optimal size and well-distributed aggregation of AuNPs to achieve a reliable SERS substrate in various applications serves as a decisive factor. This study identifies the current gaps to address the diversity of accessible sizes of AuNPs, aggregation control, and challenges in evaluating AuNPs and introduces a future path for achieving a reliable SERS substrate in diverse applications.