pH-tuned reversible self-assembly of Janus particles for enhanced Raman imaging and sensing.

The controlled self-assembly of Janus particles via pH modulation offers an effective strategy for optimizing surface-enhanced Raman scattering (SERS) and Raman signal amplification. These asymmetric microparticles enable precise spatial organization, influencing plasmonic coupling and electromagnetic field distribution critical for SERS enhancement. Here, we investigate the pH-mediated self-assembly of Janus particles and its impact on their optical sensing performance. By adjusting solution pH, we modulate electrostatic interactions that govern particle aggregation and structural formation, leading to tunable hotspots for Raman signal enhancement. Scanning electron microscopy (SEM) characterizes the resulting nanostructures, while Raman imaging and SERS measurements assess the enhancement capabilities across different pH conditions. Our findings demonstrate that pH-mediated self-assembly plays a pivotal role in optimizing interparticle spacing and plasmonic interactions, yielding significantly amplified Raman signals. This approach provides a versatile and reproducible method for engineering SERS-active substrates, advancing their application in bioanalytical sensing, molecular diagnostics, and environmental monitoring.