In this contribution, the effect of silica particle size (28 and 210 nm) and surface chemistry (i.e., hydroxyl, methyl, or amino groups) on peptide binding response is studied with a specific emphasis on the effect of the extent of functionalization on binding. Exhaustive characterization of the silica surfaces was crucial for knowledge of the chemistry and topography of the solid surface under study and, thus, to understand their impact on adsorption and the conformational ensemble of the peptides. The extent of surface functionalization was shown to be particle-size dependent, a higher level of 3-aminopropyl functionality being obtained for smaller particles, whereas a higher degree of methyl group functionality was found for the larger particles. We demonstrated that peptide interactions at the aqueous interface were not only influenced by the surface chemistry but also by the extent of functionalization where a "switch" of peptide adsorption behavior was observed, whereas the changes in the conformational ensemble revealed by circular dichroism were independent of the extent of functionalization. In addition to electrostatic interactions and hydrogen bonding driving interaction at the silica-peptide interface, the data obtained suggested that stronger interactions such as hydrophobic and/or covalent interactions may moderate the interaction. The insights gained from this peptide-mineral study give a more comprehensive view of mechanisms concerning mineral-peptide interactions which may allow for the design and synthesis of novel (nano)materials with properties tailored for specific applications.

ARTICLE This journal isPolypeptide based biosilica composites show promise as next generation multi-functional nano-platforms for diagnostics and bio-catalytic applications. Following identification of a strong silica binder (LDHSLHS) by phage display, we conduct structural analysis of the polypeptide at the interface with amorphous silica nanoparticles in an aqueous environment. Our approach relies on modelling of Infrared and Raman spectral responses using predictions of molecular dynamics simulations and quantum studies of the normal modes for several potential structures. By simultaneously fitting both Infrared and Raman responses in the Amide spectral region, we show that the main structural conformer has a beta-like central region and helix-twisted terminals. Classical simulations, as conducted previously (Chem. Mater., 2014, 26, 5725), predict that association of the main structure with the interface is stimulated by electrostatic interactions though surface binding also requires spatially distributed sodium ions to compensate negatively charged acidic silanol groups. Accordingly, diffusion of sodium ions would contribute to a stochastic character of the peptides association with the surface. Consistent with the described dynamics at the interface, results from isothermal titration calorimetry (ITC) confirm significant enhancement of polypeptide binding to silica under higher concentrations of Na + . The results of this study suggest that the tertiary structure of a phage capsid protein plays a significant role in regulating the conformation of peptide LDHSLHS, increasing its binding to silica during the phage display process. The results presented here support design-led engineering of polypeptide-silica nanocomposites for bio-technological applications. . †Electronic supplementary information (ESI) available. It provides details on: a) details on MD simulations and extracted structural properties along trajectories b) details of DFT studies on the normal modes of imidazole ring of methyl terminated histidine under different protonation conditions; c) the details on the normal modes of the structural cases including relative contributions of carbonyls and carboxyl groups into the described normal modes; d) results of isothermal titration calorimetry.

A fundamental problem in thermodynamics is the recovery of macroscopic equilibrated interaction energies from experimentally measured single-molecular interactions. The Jarzynski equality forms a theoretical basis in recovering the free energy difference between two states from exponentially averaged work performed to switch the states. In practice, the exponentially averaged work value is estimated as the mean of finite samples. Numerical simulations have shown that samples having thousands of measurements are not large enough for the mean to converge when the fluctuation of external work is above 4 kBT, which is easily observable in biomolecular interactions. We report the first example of a statistical gamma work distribution applied to single molecule pulling experiments. The Gibbs free energy of surface adsorption can be accurately evaluated even for a small sample size. The values obtained are comparable to those derived from multi-parametric surface plasmon resonance measurements and molecular dynamics simulations.

Preparation and characterization of polariton Bose–Einstein condensates in micro-cavities of high quality are at the frontier of contemporary solid state physics. Here, we report on three-dimensional polariton condensation and confinement in pseudo-spherical ZnO microcrystals. The boundary of micro-spherical ZnO resembles a stable cavity that enables sufficient coupling of radiation with material response. Exciting under tight focusing at the low frequency side of the bandgap, we detect efficiency and spectral nonlinear dependencies, as well as signatures of spatial delocalization of the excited states which are characteristics of dynamics in polariton droplets. Expansion of the photon component of the condensate boosts the leaky field beyond the boundary of the ZnO microcrystals. Using this, we observe surface polariton field enhanced Raman responses at the interface of ZnO microspheres. The results demonstrate how readily available spherical semiconductor microstructures facilitate engineering of polariton based electronic states and sensing elements for diagnostics at interfaces.

Protein-mediated doping of ZnO with plasmonic nanoparticles offers control over surfaces, electronic states, carrier dynamics, and spectral fingerprints. Here, we report on ZnO-nano-Au bioinorganic heterostructures prepared using a chimeric polypeptide that combines most of the ZnO-binding sequence GLHVMHKVAPPR and the gold-binding AYSSGAPPMPPF sequence. The one-pot peptide-mediated synthesis was performed in the presence and absence of HAuCl4 to determine the impact of the peptide and metallic component on the structural and electronic properties of the ZnO assembly. Electron microscopy confirms that the chimera polypeptide promotes the synthesis of both spherical and nonspherical gold nanoparticles, which are properly embedded in ZnO. The optical absorption spectra describe a complex palette of plasmon modes, while the luminescence spectra show a dominant subset of near-infrared spectral fingerprints that suggest an increasing role of surfaces in carrier relaxation. Simulations using finite difference time-domain theory describe collective plasmon phenomena specific to gold nanoparticles embedded in ZnO. Furthermore, to confirm experimental data, theory suggests an interinclusion nanogold spacing of 10 nm or less. Flexibility of the primary sequence of the chimera in the synthesis of ZnO-nano-Au composites opens up possibilities for plasmon-modulated ZnO junctions with Ohmic contacts as sought in sensor technologies and for security applications.

A new approach to analyze band‐gap and defect states within semiconductors is reported. Solid state excitation‐emission matrices are used to deconvolve spectral signatures that will be superimposed in 1D spectral space; for example, the 570 nm emission peak in ZnO whose emissive state is of a different physical nature depending on the excitation wavelength used. The broad applicability of the technique is shown for a library of widely studied inorganic semiconductors CdS, CdSe, ZnS, ZnSe, ZnO (analytical standard and nanorods), and TiO2. Anthracene is included as a representative example of an organic semiconductor. The developed approach can identify spectral features from the band gap, defects, and trace impurities and provide information on the relative contributions of the different emission pathways. The technique, based on using a plate‐reader conventionally used for the study of biological samples in solution has applicability in both academic and industrial settings for semiconductor studies and quality control applications.