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Many biological surfaces have hairs, known as trichomes in plants. Here, the wettability and macro- and micro-scale features of olive leaves are analyzed. The upper leaf side has few trichomes, while the lower side has a high trichome density. By combining different techniques including electron and atomic force microscopy, trichome surfaces are found to be chemically (hydrophilic-hydrophobic) heterogeneous at the nano-scale. Both olive leaf surfaces are wettable by water, having a high water contact angle hysteresis and great drop adhesion. The ultra-structural pattern observed for epidermal pavement cells differs from the reticulate cuticle structure of trichomes which shows that leaf surface areas may be substantially different despite being located nearby. Our study provides evidence for the nano-scale chemical heterogeneity of a trichome which may influence the functional properties of biological surfaces, such as water and solute permeability or water capture as discussed here for plants.

We studied the effect of gold nanoparticles (Au NPs) deposited on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy (PA-KPFM), to study the process at the single Au NP level. We found that the photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light intensity due to the combined contribution of electron¿hole pair generation in the space charge region in the TiO2¿air interface and in the metal¿semiconductor junction. Our measurements on single particles provide direct evidence for electron trapping that hinders electron¿hole recombination, a key factor in the enhancement of photo(electro)catalytic performance [1].

We present a study of the effect of gold nanoparticles (Au NPs) on TiO2 on charge generation and trapping during illumination with photons of energy larger than the substrate band gap. We used a novel characterization technique, photoassisted Kelvin probe force microscopy, to study the process at the single Au NP level. We found that the photoinduced electron transfer from TiO2 to the Au NP increases logarithmically with light intensity due to the combined contribution of electron-hole pair generation in the space charge region in the TiO2-air interface and in the metal-semiconductor junction. Our measurements on single particles provide direct evidence for electron trapping that hinders electron-hole recombination, a key factor in the enhancement of photo(electro)catalytic activity.

Graphene oxide (GO) is a chemically modified form of graphene containing many different types of oxygen functional groups on its basal plane and edges. Their presence imparts hydrophilicity and allows for ease of processing from water dispersions. We recently have shown that sheets of graphene oxide critically affect the aggregate structure of water dispersible nanoparticles P3HTNPs and thus the performance of optoelectronic thin film devices. In this work we elucidate the photogenerated charge tranfer dynamics of (P3HTNPs-GO) ensembles with defined aggregate structure across their interface by Kelvin Probe Force microscopy (KPFM).

In eukaryotes, the formation of a 5'-cap and 3'-poly(A) dependent protein-protein bridge is required for translation of its mRNAs. In contrast, several plant virus RNA genomes lack both of these mRNA features, but instead have a 3'-CITE (for cap-independent translation enhancer), a RNA element present in their 3'-untranslated region that recruits translation initiation factors and is able to control its cap-independent translation. For several 3'-CITEs, direct RNA-RNA long-distance interactions based on sequence complementarity between the 5'- and 3'-ends are required for efficient translation, as they bring the translation initiation factors bound to the 3'-CITE to the 5'-end. For the carmovirus melon necrotic spot virus (MNSV), a 3'-CITE has been identified, and the presence of its 5'-end in cis has been shown to be required for its activity. Here, we analyze the secondary structure of the 5'-end of the MNSV RNA genome and identify two highly conserved nucleotide sequence stretches that are complementary to the apical loop of its 3'-CITE. In in vivo cap-independent translation assays with mutant constructs, by disrupting and restoring sequence complementarity, we show that the interaction between the 3'-CITE and at least one complementary sequence in the 5'-end is essential for virus RNA translation, although efficient virus translation and multiplication requires both connections. The complementary sequence stretches are invariant in all MNSV isolates, suggesting that the dual 5'-3' RNA: RNA interactions are required for optimal MNSV cap-independent translation and multiplication.

Kelvin probe force microscopy in darkness and under illumination is reported to provide nanoscale-resolved surface photovoltage maps of hybrid materials. In particular, nanoscale charge injection and charge recombination mechanisms occurring in ZnO polycrystalline surfaces functionalized with Protoporphyrin IX (H2PPIX) are analyzed. Local surface potential and surface photovoltage maps not only reveal that upon molecular adsorption the bare ZnO work function increases, but also they allow study of its local dependence. Nanometer-sized regions not correlated with apparent topographic features were identified, presenting values significantly different from the average work function. Depending on the region, the response to the light excitation is different, distinguishing two relaxation processes, one faster than the other. This behavior can be explained in terms of electrons trapped closed to the molecule–semiconductor interface or electrons pushed into the ZnO bulk, respectively. Moreover, the origin of these differences is correlated with the H2PPIX–ZnO bonding and molecules configuration and aggregation. The chenodeoxycholic acid (CDCA) coadsorption leads to a more homogeneous surface potential distribution, confirming the antiaggregate effect of this additive, while the surface photovoltage is mostly dominated by the slow relaxation component. This work reveals the complexity of real device architectures with ill-defined surfaces even in a relatively simple system with only one type of dye molecule and hightlights the importance of nanoscale characterization with appropriate tools.

The surface potential of conducting polymers has been studied with scanning Kelvin probe microscopy. The results show that this technique can become an excellent tool to really 'see' interesting surface charge interaction effects at the nanoscale. The electron glass model, which assumes that charges are localized by the disorder and that interactions between them are relevant, is employed to understand the complex behavior of conducting polymers. At equilibrium, we find surface potential domains with a typical lateral size of 50 nm, basically uncorrelated with the topography and strongly fluctuating in time. These fluctuations are about three times larger than thermal energy. The charge dynamics is characterized by an exponentially broad time distribution. When the conducting polymers are excited with light the surface potential relaxes logarithmically with time, as usually observed in electron glasses. In addition, the relaxation for different illumination times can be scaled within the full aging model.

En los últimos años la Nanociencia se ha convertido en uno de los campos más desarrollados en la ciencia. Es ésta un área multidisciplinar que engloba la investigación aplicada como fundamental, de diversas áreas, teniendo únicamente en común el hecho de que las investigaciones se realizan a escala nanométrica. En particular, la biofísica es el campo que estudia la forma y las funciones biológicas para comprender el funcionamiento de los mecanismos en los sistemas biológicos utilizando principalmente los principios de la física y la química que gobiernan dichos procesos. La membrana biológica es un complejo supramolecular de lípidos, carbohidratos y proteínas, formado como resultado de interacciones no covalentes. Su base estructural es una bicapa lipídica, que posee una región hidrofóbica central separada de la fase acuosa por dos regiones polares [Boal02]. La estructura, dinámica y propiedades mecánicas de las biomembranas vienen determinadas principalmente por las propiedades físico-químicas de los lípidos. Éstos imponen un orden líquidocristalino que se extiende también a las proteínas o péptidos insertados en la bicapa [Esteban-Martin07a], pudiendo verse afectados en su estructura, orientación, dinámica y estado de agregación [Nyholm07; Kandasamy06; Esteban-Martin07b].

Scanning force microscopy and near-edge X-ray absorption spectroscopy are used to study the attachment of Protoporphyrin IX dye molecules to the low-index single-crystal faces of ZnO, namely, the polar (0001̄) face and the nonpolar (101̄0) face. We found that surface etching depends on the crystal face for various dye immobilization procedures: whereas the polar (0001̄) surface remains nearly unaltered, the nonpolar (101̄0) surface is strongly etched by acidic solutions; these results demonstrate the selective attachment of dye molecules to ZnO surfaces, showing that the dye attachment is extremely sensitive to both the exposed facet and the immobilization protocol. This could be a factor in the surprisingly poor efficiency observed for ZnO-based dye-sensitized solar cells, especially those using ZnO nanorod arrays. © 2013 American Chemical Society.