Assembly-based titration for the determination of monodisperse plasmonic nanoparticle concentrations using DNA

We present a stoichiometric titration method to determine the concentration of nanoparticles of various materials, sizes, and shapes. We have discovered that the optical response associated with the assembly formation is maximized when two types of nanoparticles attractively interact at a specific ratio, regardless of the particle type. Based on the reversible hybridization properties of two cDNA sequences used to assemble the particles, the assembly-based titration of various nanoparticles of unknown concentrations is visually demonstrated with high accuracy and reliability, which is analogous to the classic molecular titration method.