Effect of pH on The Self Assembly of Janus Particles

The use of pH-adjusted self-assembly in Janus particles is a promising approach for controlling Raman scattering. These Janus particles, known for their asymmetry in composition and properties, provide distinct benefits for crafting precise nanostructures in surface-enhanced Raman scattering (SERS) applications. The study investigates using pH-controlled self-assembly of Janus particles to observe the changes in their Surface-Enhanced Raman Scattering (SERS) and Raman signals. Characterization methods such as scanning electron microscopy (SEM) and focused ion beam (FIB) technology were implemented for detailed information regarding the shape, size variation, and inner structure of Janus particles. Various analytical techniques, including TEM, EDAX, and elemental mapping, were employed to assess the assembled Janus particles by examining their elemental composition and how it is distributed. By adjusting the pH of the solution, electrostatic interactions between the Janus particles were manipulated, leading to controlled aggregation and spatial arrangement. As the pH value rises, the gap between the particles widens. At specific pH levels, self-assembly of Janus particles occurs, forming ordered nanostructures that concentrate analyte molecules. This spatial confinement caused significant changes in electromagnetic field intensity and Raman signals. Optimal pH selection enables control over interparticle spacing, plasmonic coupling, and electromagnetic field distribution, leading to remarkable modulation of Raman signals. This research also focused on analyzing electromagnetic fields, uncovering how electric and magnetic fields are distributed between Janus particles when exposed to excitation light. A decrease in Raman Intensity with the increasing number of Janus particles were observed at the Raman wavenumber. Using Finite-Domain-Time-Difference (FDTD) simulations, a decrease in electromagnetic field intensity with the number of particles were also observed, which validates our experimental finding. Analyzing the structure and optical and electromagnetic properties of Janus particles will further help us understand their behavior and potential applications. pH-tuned Janus particle self-assembly shows promise in creating sensitive and selective Raman sensing platforms. This research advances our understanding of Janus particle assembly for SERS-based sensing, with broad applications in areas like chemical analysis, bioassays, and environmental monitoring.