Purple of Cassius is a coloured pigment (enamel) formed through the simultaneous redox reaction of nanostructures of gold and tin chlorides. Inspired by the same Sn/Au chemistry, we have developed tin oxide-gold (SnO₂@Au) core-shell nanostructures using di-block copolymer (PolyStyrene-b-Poly2VinylPyridine) reverse micelle templating. Tin oxide (SnO₂) is a versatile semiconductor widely used in various applications, and coupled with gold (Au), it has high potential for sensing and optoelectronic applications. However, the synthesis of small nanoscale particles with high uniformity remains a considerable challenge. To address this, we employed a di-block copolymer based reverse micelle deposition (RMD) method. This method helps in the production of monodispersed, uniformly ordered, close-packed, hexagonal arrays of SnO₂@Au nanoparticles [1], [2]. It is also a highly efficient strategy for producing nanoparticles tailored to specific applications. Depending on the structure and molecular weight of its components (PS - polystyrene and P2VP - polyvinyl pyridine blocks), these micelles can be classified as lower molecular weight "crew-cut" or higher molecular weight "dense core," each supporting the synthesis of nanoparticles with unique shapes, sizes, and dispersions [3]. In this study, we synthesized SnO₂@Au nanoparticles using four distinct types of micelles: Low molecular weight, high PS ratio (LMW-PS) (54,000-b-26,000), Low molecular weight, high P2VP ratio (LMW-P2VP) (57,000-b-71,000), High molecular weight, high P2VP ratio (HMW-P2VP) (28,000-b-36,000) and High molecular weight, high PS ratio (HMW-PS) (75,000-66,500). Polymer and salt concentrations were varied to achieve closely packed nanoparticle arrays optimized for enhanced conductivity. The arrangement and topography of the formed micelles were evaluated using atomic force microscopy (AFM). Raman and UV-Vis spectroscopy were used to confirm the formation of SnO2 and Au nanoparticles. Additionally, the stability and performance of the particles were also evaluated using simple gas sensing measurements. It was found that the dense-core micelles were able to produce small, stable and uniformly dispersed nanoparticles whereas the crew-cut micelles produced larger and less stable nanoparticles. This work provides valuable insights into nanoparticle synthesis using reverse micelle templating and their optimization for building ideal heterostructures. In addition, the stability and longevity of the nanoparticles plays a crucial role in assessing the efficiency of sensors based on their usage. Hence, these findings pave the way for the development of advanced chemiresistive gas sensors and other future applications. References [1] Lewis, K.; Arbi, R.; Ibrahim, A.; Smith, E.; Olivera, P.; Garza, F.; Turak, A. Gold-Coated Tin Oxide Nanoparticles as Potential Optical Isolator Materials: Simulation of Absorption and Faraday Rotation and Comparison with Micelle Templated Core-Shell Nanoparticles. J Mater Sci: Mater Electron 2023, 34 (8), 750. https://doi.org/10.1007/s10854-023-10134-1. [2] Garza, F. J.; Arbi, R.; Munir, M.; Lim, J.-H.; Turak, A. Quantification of the Shell Thickness of Tin Oxide/Gold Core–Shell Nanoparticles by X-Ray Photoelectron Spectroscopy. J. Phys. Chem. C 2023, 127 (9), 4594–4600. https://doi.org/10.1021/acs.jpcc.2c07832. [3] Arbi, R.; Ibrahim, A.; Goldring-Vandergeest, L.; Liang, K.; Hanta, G.; Hui, L. S.; Turak, A. Role of Hydration and Micellar Shielding in Tuning the Structure of Single Crystalline Iron Oxide Nanoparticles for Designer Applications. Nano Select 2021, 2 (12), 2419–2431. https://doi.org/10.1002/nano.202100085