Rodriguez, Brian J.
Rodriguez, Brian J.
Rodriguez, Brian J.
Now showing 1 - 10 of 105
- PublicationSelf-Assembly of Amyloid-Beta and Its Piezoelectric PropertiesInvestigating amyloid nanofibril self-assembly, with an emphasis on the electromechanical property of amyloid peptides, namely, piezoelectricity, may have several important implications: 1) the self-assembly process can hinder the biological stability and give rise to the formation of amyloid structures associated with neurodegenerative diseases; 2) investigations in this field may lead to an improved understanding of high-performance, functional biological nanomaterials, 3) new technologies could be established based on peptide self-assembly and the resultant functional properties, e.g., in the creation of a piezoelectric device formed with vertical diphenylalanine peptide tubes as a piezoelectric biosensor, and 4) new knowledge can be generated about neurodegenerative disorders, potentially yielding new therapies. Therefore, in this review, we will present the current investigations associated with self-assembly of amyloid-beta, the mechanisms that generate new structures, as well as theoretical calculations exploring the functionality of the structures under physiological pressure and electric field.
- PublicationThermal and aqueous stability improvement of graphene oxide enhanced diphenylalanine nanocompositesNanocomposites of diphenylalanine (FF) and carbon based materials provide an opportunity to overcome drawbacks associated with using FF micro- and nanostructures in nanobiotechnology applications, in particular, their poor structural stability in liquid solutions. In this study, FF/graphene oxide (GO) composites were found to self-assemble into layered micro- and nanostructures, which exhibited improved thermal and aqueous stability. Dependent on the FF/GO ratio, the solubility of these structures was reduced to 35.65% after 30 min as compared to 92.4% for pure FF samples. Such functional nanocomposites may extend the use of FF structures to, e.g., biosensing, electrochemical, electromechanical or electronic applications.
- PublicationKelvin Probe Force Microscopy in liquid using Electrochemical Force MicroscopyConventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid-gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid-liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe-sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q water and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does notrequire a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid-liquid interface.
390Scopus© Citations 33
- PublicationInvestigation of the mechanism of polarization switching in ferroelectric capacitors by three- dimensional piezoresponse force microscopyA mechanism for the switching behavior of (111)-oriented Pb(Zr,Ti)O3-based 1×1.5 μm2 capacitors has been investigated using three-dimensional piezoresponse force microscopy (3D-PFM). A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM) has been used to map the out-of-plane and the in-plane components of the polarization. The three-dimensional polarization distribution was reconstructed by quantitative analysis of the PFM amplitude images of poled PZT capacitors while taking into account contrast variations in the PFM phase images. The switching behavior of the capacitors was determined by comparison of the static domain patterns in the same capacitors after both positive and negative poling. While 180° degree switching was observed, surprisingly, the switching process was dominated by 90° polarization vector rotation. Furthermore, central regions of the capacitors were characterized by the presence of charged domain boundaries, which could lead to imprint (preference of one polarization state over another.
263Scopus© Citations 28
- PublicationMacromolecularly crowded in vitro microenvironments accelerate the production of extracellular matrix-rich supramolecular assembliesTherapeutic strategies based on the principles of tissue engineering by self-assembly put forward the notion that functional regeneration can be achieved by utilising the inherent capacity of cells to create highly sophisticated supramolecular assemblies. However, in dilute ex vivo microenvironments, prolonged culture time is required to develop an extracellular matrix-rich implantable device. Herein, we assessed the influence of macromolecular crowding, a biophysical phenomenon that regulates intra- and extra-cellular activities in multicellular organisms, in human corneal fibroblast culture. In the presence of macromolecules, abundant extracellular matrix deposition was evidenced as fast as 48 h in culture, even at low serum concentration. Temperature responsive copolymers allowed the detachment of dense and cohesive supramolecularly assembled living substitutes within 6 days in culture. Morphological, histological, gene and protein analysis assays demonstrated maintenance of tissue-specific function. Macromolecular crowding opens new avenues for a more rational design in engineering of clinically relevant tissue modules in vitro
386Scopus© Citations 77
- PublicationDynamics of ferroelectric domain growth in the field of atomic force microscopeApplication of very high voltage to atomic force microscope tip leads to the growth of narrow, stringlike domains in some ferroelectrics, a phenomenon that was named ``ferroelectric domain breakdown.'' In this work the dynamics of domain breakdown have been studied experimentally and theoretically in stoichiometric lithium niobate (LN). The theory has been found to be in a good agreement with the measured domain radius temporal dependence. Dynamics of domain growth has also been studied in ultrathin LN crystals, where the domain breakdown phenomenon does not take place. It is also shown that domain formation processes occurring in bulk and ultrathin crystals are very different, and this is ascribed to the observed difference in depolarization energy dependence on the domain length. (c) 2006 American Institute of Physics.
263Scopus© Citations 87
- PublicationReal space mapping of polarization dynamics and hysteresis loop formation in relaxor-ferroelectric PbMg1/3Nb2/3O3-PbTiO3 solid solutionsPolarization switching in ergodic relaxor and ferroelectric phases in the PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT) system is studied using piezoresponse force microscopy, single point electromechanical relaxation measurements, and voltage spectroscopy mapping. The dependence of relaxation behavior on voltage pulse amplitude and time is found to follow a universal logarithmic behavior with a nearly constant slope. This behavior is indicative of the progressive population of slow relaxation states, as opposed to a linear relaxation in the presence of a broad relaxation time distribution. The role of relaxation behavior, ferroelectric nonlinearity, and the spatial inhomogeneity of the tip field on hysteresis loop behavior is analyzed in detail. The hysteresis loops for ergodic PMN-10\%PT are shown to be kinetically limited, while in PMN with larger PT content, true ferroelectric hysteresis loops with low nucleation biases are observed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3474961]
463Scopus© Citations 42
- PublicationPlasmon Enhanced Raman From Ag Nanopatterns Made Using Periodically Poled Lithium Niobate and Periodically Proton Exchanged Template MethodsWe study Ag nanopattern arrays formed using ferroelectric lithography based on two separate approaches, i.e., periodically poled lithium niobate (PPLN) and periodically proton exchanged (PPE) template methods. We demonstrate that such nanoarrays are plasmon active. Raman spectroscopy was applied to study molecular probe 4-aminothiophenol (4-ABT) absorbed onto a silver nanostructured array. The observed Raman spectra show peaks arising from b2 modes, which occur for plasmon enhanced Raman from 4-ABT in place of a1 modes, which occur in normal Raman scattering. We demonstrate that the PPLN and PPE substrates possess different plasmonic properties with PPE creating a stronger SERS signal relative to PPLN substrates.
537Scopus© Citations 47
- PublicationElectromechanical properties of dried tendon and iso-electrically focused collagen hydrogelsAssembling artificial collagenous tissues with structural, functional, and mechanical properties which mimic natural tissues is of vital importance for many tissue engineering applications. While the electro-mechanical properties of collagen are thought to play a role in, for example, bone formation and remodeling, this functional property has not been adequately addressed in engineered tissues. Here the electro-mechanical properties of rat tail tendon are compared with those of dried isoelectrically focused collagen hydrogels using piezoresponse force microscopy under ambient conditions. In both the natural tissue and the engineered hydrogel D-periodic type I collagen fibrils are observed, which exhibit shear piezoelectricity. While both tissues also exhibit fibrils with parallel orientations, Fourier transform analysis has revealed that the degree of parallel alignment of the fibrils in the tendon is three times that of the dried hydrogel. The results obtained demonstrate that isoelectrically focused collagen has similar structural and electro-mechanical properties to that of tendon, which is relevant for tissue engineering applications.
977Scopus© Citations 37
- PublicationBubble polarization domain patterns in periodically ordered epitaxial ferroelectric nanodot arraysIn this work, bubble polarization domains in periodically ordered ferroelectric Pb(Zr(0.4)Ti(0.6))O(3) nanodot arrays and their formation mechanisms have been investigated by piezoresponse force microscopy (PFM) and Monte-Carlo simulations. The PFM observations reveal the coexistence of single domain and apparent bubble domain patterns within the same nanodot array, which also exhibit dissimilar polarization reversal processes. The formation of various polarization configurations can be accounted for by the interplay of various factors, such as polarization anisotropy and depolarization field. Using Monte-Carlo simulation, we are able to reproduce bubble and single domains and further predict that these patterns can be tailored by varying the nanodot parameters, including dot height, aspect ratio, etc. (C) 2011 American Institute of Physics.
280Scopus© Citations 10