Using Particle Lithography to Tailor the Architecture of Au Nanoparticle Plasmonic Nanoring Arrays.

The facile assembly of metal nanostructured arrays is a fundamental step in the design of plasmon enhanced chemical sensing and solar cell architectures. Here we have investigated methods of creating controlled formations of two-dimensional periodic arrays comprised of 20 nm Au nanoparticles (NPs) on a hydrophilic polymer surface using particle lithography. To direct the assembly process, capillary force and NP concentration both play critical roles on the resulting nanostructured arrays. As such, tuning these experimental parameters can directly be used to modify the nature of the nanostructures formed. To explore this, two different concentrations of Au NP solutions (∼7 × 1011 or 4 × 1012 NPs/mL) were used in conjunction with a fixed concentration of polystyrene microspheres (PS MS, ∼6 × 109 PS MS/mL). Assembly at a relative humidity (RH) of 45% with the higher concentration resulted in the formation of well-defined Au nanorings of ca. 23 nm in height and 881 nm in diameter with a pitch of 2.5 µm. Assembly at 65% RH with the lower concentration of NPs resulted in Au nanodonut arrays comprised of isolated single Au NPs. To explore the extent of coupling in the well-defined structures, dark field scattering spectra were collected and showed a broad localized surface plasmon resonance (LSPR) peak with a shoulder, which full-wave electrodynamics modeling (finite-difference time domain (FDTD) method) attributed to be a result of pronounced particle-particle coupling along the circumference of the nanoring array.

Suppression of quenching in plasmon-enhanced luminescence via rapid intraparticle energy transfer in doped quantum dots.

We show the suppression of luminescence quenching by metal nanoparticles (MNPs) in the plasmon enhancement of luminescence via fast sensitized energy transfer in Mn-doped quantum dots (QDs). The rapid intraparticle energy transfer between exciton and Mn, occurring on a few picoseconds time scale, separates the absorber (exciton) from the emitter (Mn), whose emission is detuned far from the plasmon of the MNP. The rapid temporal separation of the absorber and emitter combined with the reduced spectral overlap between Mn and plasmonic MNP suppresses the quenching of the luminescence while taking advantage of the plasmon-enhanced excitation. We compared the plasmon enhancement of exciton and Mn luminescence intensities in undoped and doped QDs simultaneously as a function of the distance between MNP and QD layers in a multilayer structure to examine the expected advantage of the reduced quenching in the sensitized luminescence. At the optimum MNP-QD layer distance, Mn luminescence exhibits stronger net enhancement than that of the exciton, which can be explained with a model incorporating fast sensitization along with reduced emitter-MNP spectral overlap. This study demonstrates that materials exhibiting fast sensitized luminescence that is sufficiently red-shifted from that of the sensitizer can be superior to usual luminophores in harvesting plasmon enhancement of luminescence by suppressing quenching.

Cutin deficiency in the tomato fruit cuticle consistently affects resistance to microbial infection and biomechanical properties, but not transpirational water loss.

Plant cuticles are broadly composed of two major components: polymeric cutin and a mixture of waxes, which infiltrate the cutin matrix and also accumulate on the surface, forming an epicuticular layer. Although cuticles are thought to play a number of important physiological roles, with the most important being to restrict water loss from aerial plant organs, the relative contributions of cutin and waxes to cuticle function are still not well understood. Tomato (Solanum lycopersicum) fruits provide an attractive experimental system to address this question as, unlike other model plants such as Arabidopsis, they have a relatively thick astomatous cuticle, providing a poreless uniform material that is easy to isolate and handle. We identified three tomato mutants, cutin deficient 1 (cd1), cd2 and cd3, the fruit cuticles of which have a dramatic (95-98%) reduction in cutin content and substantially altered, but distinctly different, architectures. This cutin deficiency resulted in an increase in cuticle surface stiffness, and in the proportions of both hydrophilic and multiply bonded polymeric constituents. Furthermore, our data suggested that there is no correlation between the amount of cutin and the permeability of the cuticle to water, but that cutin plays an important role in protecting tissues from microbial infection. The three cd mutations were mapped to different loci, and the cloning of CD2 revealed it to encode a homeodomain protein, which we propose acts as a key regulator of cutin biosynthesis in tomato fruit.