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The properties of nanoparticle superstructuresdepend on many factors,including the structural metrics of the nanoparticle superstructure(particle diameter, interparticle distances, etc.). Here, we introducea family of gold-binding peptide conjugate molecules that can directnanoparticle assembly, and we describe how these molecules can besystematically modified to adjust the structural metrics of lineardouble-helical nanoparticle superstructures. Twelve new peptide conjugatesare prepared via linking a gold-binding peptide, AYSSGAPPMPPF(PEPAu), to a hydrophobic aliphatic tail. The peptide conjugateshave 1, 2, or 3 PEPAuheadgroups and a C12,C14, C16, or C18aliphatic tail.The soft assembly of these peptide conjugates was studied using transmissionelectron microscopy (TEM), atomic force microscopy (AFM), and infrared(IR) spectroscopy. Several peptide conjugates assemble into 1-D twistedfibers having measurable structural parameters such as fiber width,thickness, and pitch that can be systematically varied by adjustingthe aliphatic tail length and number of peptide headgroups. The linearsoft assemblies serve as structural scaffolds for arranging gold nanoparticlesinto double-helical superstructures, which are examined via TEM. Thepitch and interparticle distances of the gold nanoparticle doublehelices correspond to the underlying metrics of the peptide conjugatesoft assemblies, illustrating that designed peptide conjugate moleculescan be used to not only direct the assembly of gold nanoparticlesbut also control the metrics of the assembled structure. [ABSTRACT FROM AUTHOR]

Bottom-up assemblies of plasmonic nanoparticles exhibit unique optical effects such as tunable reflection, optical cavity modes, and tunable photonic resonances. Here, we compare detailed simulations with experiment to explore the effect of structural inhomogeneity on the optical response in DNA-gold nanoparticle superlattices. In particular, we explore the effect of background environment, nanoparticle polydispersity (>10%), and variation in nanoparticle placement (~5%). At volume fractions less than 20% Au, the optical response is insensitive to particle size, defects, and inhomogeneity in the superlattice. At elevated volume fractions (20% and 25%), structures incorporating different sized nanoparticles (10-, 20-, and 40-nm diameter) each exhibit distinct far-field extinction and near-field properties. These optical properties are most pronounced in lattices with larger particles, which at fixed volume fraction have greater plasmonic coupling than those with smaller particles. Moreover, the incorporation of experimentally informed inhomogeneity leads to variation in far-field extinction and inconsistent electric-field intensities throughout the lattice, demonstrating that volume fraction is not sufficient to describe the optical properties of such structures. These data have important implications for understanding the role of particle and lattice inhomogeneity in determining the properties of plasmonic nanoparticle lattices with deliberately designed optical properties. [ABSTRACT FROM AUTHOR]

This paper demonstrates the direct sensing of glucose at physiologically relevant concentrations with surface-enhanced Raman spectroscopy (SERS) on gold film-over-nanosphere (AuFON) substrates functionalized with bisboronic acid receptors. The combination of selectivity in the bisboronic acid receptor and spectral resolution in the SERS data allow the sensors to resolve glucose in high backgrounds of fructose and, in combination with multivariate statistical analysis, detect glucose accurately in the 1–10 mM range. Computational modeling supports assignments of the normal modes and vibrational frequencies for the monoboronic acid base of our bisboronic acids, glucose and fructose. These results are promising for the use of bisboronic acids as receptors in SERS-based in vivo glucose monitoring sensors. [ABSTRACT FROM AUTHOR]