Sensing Single Mixed-Monolayer Protected Gold Nanoparticles by the alpha-Hemolysin Nanopore

Gold nanoparticles are widely used in various applications in fields including chemistry, engineering, biology, medicine, and electronics. These materials can be synthesized and modified with ligands containing different functional groups. Among nanoparticles' characteristics, chemical surface composition is likely to be a crucial feature, demanding robust analytical methodologies for its assessment. Single molecule analysis using the biological nanopores alpha-hemolysin and its E111A mutant is presented here as a promising methodology to stochastically sense organic monolayer protected gold-nanoparticles with different ligand shell compositions. By monitoring the ionic current across a single protein nanopore, differences in the physical and chemical characteristics (e.g., size, ligand shell composition, and arrangement) of individual nanoparticles can be distinguished based on the differences in the current blockade events that they cause. Such differences are observed in the spread of both the amplitude and duration of current blockades. These values cannot be correlated with a single physical characteristic. Instead the spread represents a measure of heterogeneity within the nanoparticle population. While our results compare favorably with the more traditional analytical methodologies, further work will be required to improve the accuracy of identification of the NPs and understand the spread of values within a nanoparticle preparation as well as the overlap between similar preparations.