Creating Chirality by Magnetic Assembly of Plasmonic Nanostructures

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With support from the Macromolecular, Supramolecular and Nanochemistry (MSN) Program in the Division of Chemistry, Professor Yadong Yin of the University of California – Riverside is exploring how magnetic fields can drive nanoparticles to assemble into larger structures that have an inherent “handedness,” analogous to the left-right mirror symmetry seen in many living organisms. Since structures with different handedness interact with light differently, this property is very useful for decoding the fine structures of many important biomolecules such as nucleic acids and proteins. However, practical applications in sensing and detection based on this property face significant challenges due to subtle differences in light-molecule interactions. Professor Yin and his students are developing hybrid nanoparticles that contain magnetic oxides and noble metals. The magnetic component allows the hybrid nanoparticles to be assembled into larger structures with the desired handedness under a magnetic field. The resulting handedness can be transferred to noble metal components, exhibiting substantial handedness-dependent optical responses. Their discoveries could lead to the development of more effective mechanical and chemical sensors and novel anti-counterfeiting devices. The team is also working on promoting research-based learning approaches for K-12 and undergraduate students at UCR, local schools, community colleges, and beyond.Based on a theoretical understanding of the inherent chirality of gradient magnetic fields, Professor Yin and his co-workers are developing magnetic assembly strategies to create novel plasmonic chiral superstructures. Magnetic/plasmonic hybrid nanostructures are assembled in magnetic field gradients into superstructures with substantial and wavelength-controllable chiroptical responses. Hybrid nanospheres and nanorods will be used as the model building blocks to explore their interactions with magnetic field gradients, the formation of chiral superstructures, and the field-responsive chiroptical properties of the resulting assemblies. In parallel, the team is also exploring the creation of chirality in uniform magnetic fields by taking advantage of the unique assembly behaviors of colloidal hybrid nanostructures with specially designed shape anisotropy. Systematic studies will be carried out to understand how nanoparticle shape can determine assembly behavior in uniform magnetic fields. An in-depth understanding of these two systems would allow for further exploration of nanostructure assembly with specific shape anisotropy in magnetic field gradients. The ultimate goal is to generate hierarchical superstructures featuring primary and secondary chirality of different length scales. By taking advantage of the field-responsive chiroptical properties of these novel chiral materials, the team is designing systems that have the potential for application as highly sensitive mechanical sensors, color-switching materials, and even anti-counterfeiting devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.