Surface plasmon resonance as a tool for investigation of non-covalent nanoparticle interactions in heterogeneous self-assembly & disassembly systems.

Biomolecule-driven assembly of nanoparticles is a powerful and convenient approach for development of advanced nanosensors and theranostic agents with diverse "on-demand" composition and functionality. While a lot of research is being devoted to fabrication of such agents, the development of non-invasive analytical tools to monitor self-assembly/disassembly processes in real-time substantially lags behind. Here, we demonstrate the capabilities of localized surface plasmon resonance (SPR) phenomenon to study non-covalent interactions not just between plasmonic particles, but between gold nanoparticles (AuNP) and non-plasmonic ones. We show its potential to investigate assembly and performance of a novel type of advanced smart materials, namely, biocomputing agents. These agents, self-assembled from nanoparticles via biomolecular interfaces such as proteins, DNA, etc., can analyze presence of biomolecular inputs according to Boolean logic and undergo the input-induced disassembly in order to implement the proper output action. Using UV-Vis spectroscopy to monitor the assembly/disassembly processes of the basic YES-gate structure that consists of a polymer core particle with a multitude of associated gold nanoparticles, we found that the structure transformations are well-characterized by pronounced difference in SPR spectral band position (shifting up to 50nm). This SPR shift correlates remarkably well with biochemical estimation of the assembly/disassembly extent, and can provide valuable real-time kinetic analysis. We believe that the obtained data can be easily extended to other non-plasmonic nanoparticle systems having similar chemical and colloidal properties. SPR method can become a valuable addition to analytical toolbox for characterization of self-assembled smart nanosystems used in biosensing, imaging, controlled release and other applications.