Showing papers by "Brian J. Rodriguez published in 2019"

Giant negative electrostriction and dielectric tunability in a van der Waals layered ferroelectric

Abstract: The interest in ferroelectric van der Waals crystals arises from the potential to realize ultrathin ferroic systems owing to the reduced surface energy of these materials and the layered structure that allows for exfoliation. Here, we quantitatively unravel giant negative electrostriction of van der Waals layered copper indium thiophosphate (CIPS), which exhibits an electrostrictive coefficient ${Q}_{33}$ as high as $\ensuremath{-}3.2\phantom{\rule{0.16em}{0ex}}{\mathrm{m}}^{4}/{\mathrm{C}}^{2}$ and a resulting bulk piezoelectric coefficient ${d}_{33}$ up to \ensuremath{-}85 pm/V. As a result, the electromechanical response of CIPS is comparable in magnitude to established perovskite ferroelectrics despite possessing a much smaller spontaneous polarization of only a few $\ensuremath{\mu}\mathrm{C}/\mathrm{c}{\mathrm{m}}^{2}$. In the paraelectric state, readily accessible owing to low transition temperatures, CIPS exhibits large dielectric tunability, similar to widely used barium strontium titanate, and as a result both giant and continuously tunable electromechanical response. The persistence of electrostrictive and tunable responses in the paraelectric state indicates that even few-layer films or nanoparticles will sustain significant electromechanical functionality, offsetting the inevitable suppression of ferroelectric properties in the nanoscale limit. These findings can likely be extended to other ferroelectric transition metal thiophosphates and (quasi-) two-dimensional materials, and might facilitate the quest toward alternative ultrathin functional devices incorporating electromechanical response.

Electric Field-Induced Chemical Surface-Enhanced Raman Spectroscopy Enhancement from Aligned Peptide Nanotube–Graphene Oxide Templates for Universal Trace Detection of Biomolecules

Abstract: Semiconductor–graphene oxide-based surface-enhanced Raman spectroscopy substrates represent a new frontier in the field of surface-enhanced Raman spectroscopy (SERS) However, the application of graphene oxide has had limited success because of the poor Raman enhancement factors that are achievable in comparison to noble metals In this work, we report chemical SERS enhancement enabled by the application of an electric field (10–25 V/mm) to aligned semiconducting peptide nanotube–graphene oxide composite structures during Raman measurements The technique enables nanomolar detection sensitivity of glucose and nucleobases with up to 10-fold signal enhancement compared to metal-based substrates, which, to our knowledge, is higher than that previously reported for semiconductor-based SERS substrates The increased Raman scattering is assigned to enhanced charge-transfer resonance enabled by work function lowering of the peptide nanotubes These results provide insight into how semiconductor organic peptide n

Enhanced photocatalysis and biomolecular sensing with field-activated nanotube-nanoparticle templates

Abstract: The development of new catalysts for oxidation reactions is of central importance for many industrial processes. Plasmonic catalysis involves photoexcitation of templates/chips to drive and enhance oxidation of target molecules. Raman-based sensing of target molecules can also be enhanced by these templates. This provides motivation for the rational design, characterization, and experimental demonstration of effective template nanostructures. In this paper, we report on a template comprising silver nanoparticles on aligned peptide nanotubes, contacted with a microfabricated chip in a dry environment. Efficient plasmonic catalysis for oxidation of molecules such as p-aminothiophenol results from facile trans-template charge transfer, activated and controlled by application of an electric field. Raman detection of biomolecules such as glucose and nucleobases are also dramatically enhanced by the template. A reduced quantum mechanical model is formulated, comprising a minimum description of key components. Calculated nanotube-metal-molecule charge transfer is used to understand the catalytic mechanism and shows this system is well-optimized. Plasmonic nanomaterials offer new frontiers as photocatalysis and sensor materials, yet elucidating factors controlling each is a challenge. Here, authors examine the role of electric fields in photocatalysis and biomolecule sensing abilities of peptide-nanotubesupported silver nanoparticles.

Liquid-phase 3D bioprinting of gelatin alginate hydrogels: influence of printing parameters on hydrogel line width and layer height

Abstract: Extrusion-based 3D bioprinting is a direct deposition approach used to create three-dimensional (3D) tissue scaffolds typically comprising hydrogels. Hydrogels are hydrated polymer networks that are chemically or physically cross-linked. Often, 3D bioprinting is performed in air, despite the hydrated nature of hydrogels and the potential advantage of using a liquid phase to provide cross-linking and otherwise functionalize the hydrogel. In this work, we print gelatin alginate hydrogels directly into a cross-linking solution of calcium chloride and investigate the influence of nozzle diameter, distance between nozzle and surface, calcium chloride concentration, and extrusion rate on the dimensions of the printed hydrogel. The hydrogel layer height was generally found to increase with increasing extrusion rate and nozzle distance, according to the increased volume extruded and the available space, respectively. In addition, the hydrogel width was generally found to increase with decreasing nozzle distance and cross-linking concentration corresponding to confinement-induced spreading and low cross-linking regimes, respectively. Width/height ratios of ~ 1 were generally achieved when the nozzle diameter and distance were comparable above a certain cross-linking concentration. Using these relationships, biocompatible 3D multilayer structures were successfully printed directly into calcium chloride cross-linking solution.

3D-Printed Peptide-Hydrogel Nanoparticle Composites for Surface-Enhanced Raman Spectroscopy Sensing

Abstract: Precise control over the arrangement of plasmonic nanomaterials is critical for label-free single-molecule surface-enhanced Raman spectroscopy (SERS)-based sensing applications. SERS templates should provide high sensitivity and reproducibility and be cost-effective and easy to prepare. Additive manufacturing by extrusion-based three-dimensional (3D) printing is an emerging technique for the spatial arrangement of nanomaterials and is a method that may satisfy these SERS template requirements. In this work, we use 3D printing to produce sensitive and reproducible SERS templates using a fluorenylmethyloxycarbonyl diphenylalanine (Fmoc-FF) hydrogel loaded with silver or gold nanoparticles. The Fmoc-FF template allows the detection of low Raman cross-section molecules such as adenine at concentrations as low as 100 pM.

Bacteria-Resistant Single Chain Cyclized/Knotted Polymer Coatings.

Abstract: In addition to conventional linear, branched, crosslinked and dendritic polymers, single chain cyclized/knotted polymers (SCKPs) have emerged as a new class of polymer structure showing unique properties. Here, we report the development of bacterial resistant SCKPs and investigate how the single chain cyclized/knotted structure affects the performance of polymer materials in bacterial resistance. Four SCKPs were synthesized by reversible addition fragmentation chain transfer (RAFT) homopolymerization of multivinyl monomers (MVMs) and then crosslinked by ultraviolet (UV) light to form SCKP films. Regardless of MVM types, the four SCKP films always showed much higher bacterial resistance ability, and up to 75% of bacterial attachment and biofilm formation were reduced in comparison with the corresponding non‐SCKP films which are directly made from the polymerization of MVMs. These results highlight the critical role of the single chain cyclized/knotted structure in enhancing the bacterial resistance of polymeric materials. Further mechanistic studies revealed that the surface morphology and altered hydrophobicity induced by the single chain cyclized/knotted structure could account for the enhanced bacterial resistant performance of the SCKP films.

Nucleobase sensing using highly-sensitive surface-enhanced Raman spectroscopy templates comprising organic semiconductor peptide nanotubes and metal nanoparticles

Abstract: Templates formed from aligned diphenylalanine nanotubes with plasmon-active metal nanoparticles are a promising nanocomposite for large-scale, rapid, stable, and cost-effective surface-enhanced Raman spectroscopy (SERS) substrates. The high sensitivity of such templates arises from an arrangement of densely packed plasmon-active silver nanoparticles that enhance the localized electromagnetic field and allow the detection of the nucleobases adenine, cytosine, thymine, uracil, and guanine at concentrations in the range 10−5 to 10−9 M. Blinking of the SERS signal is observed, indicating sensitivity down to the single or few molecule limit. Such blinking could result from charge transfer processes. These results demonstrate the potential for using aligned diphenylalanine nanotube-metal nanoparticle templates for practical monitoring of biomolecules and are promising initial steps toward the use of peptide nanotube-based templates in diagnostic sensing applications.

Template-Assisted Synthesis of Luminescent Carbon Nanofibers from Beverage-Related Precursors by Microwave Heating.

Abstract: Luminescent carbon nanomaterials are important materials for sensing, imaging, and display technologies. This work describes the use of microwave heating for the template-assisted preparation of luminescent carbon nanofibers (CNFs) from the reaction of a range of beverage-related precursors with the nitrogen-rich polyethyleneimine. Highly luminescent robust carbon fibers that were 10 to 30 m in length and had a diameter of 200 nm were obtained under moderate conditions of temperature (250-260 °C) and a short reaction time (6 min). The high aspect ratio fibers showed wavelength-dependent emission that can be readily imaged using epifluorescence. The development of these multi-emissive one-dimensional (1D) carbon nanomaterials offers potential for a range of applications.

Self-assemble organic molecular micron-sized tubular structures for active and passive wave-guiding regimes

Abstract: Here we study self-assembled of 9-diethylamino-5-benzo[α]phenoxazinone 9 . AFM, SEM, Raman imaging, studies demonstrate that such materials form micron-sized tub-like structures with rectangular shape. These microstructures show both active and passive wave guiding modes. Applying wavelengths in resonance 532 nm, and in non-resonance (785nm) with the molecular electronic absorption bands was undertaken for active and passive wave guiding studies. PL spectra capping point, the body and emerging light points were investigated. Meanwhile, Raman scattered photons were also acquired which maintain the polarized light propagation direction(s) and its interaction with tube molecules. The hollow features and tubes defect were identified using Raman imaging. These studies showing that excellent wave guiding features are present using these self-assembled micron-tube structures.