Physics Commons^™

Modulation Of Voltage-Gating And Hysteresis Of Lysenin Channels By Cu2+ Ions, Andrew Bogard, Pangaea W. Finn, Aviana R. Smith, Ilinca M. Flacau, Rose Whiting, Daniel Fologea

Physics Faculty Publications and Presentations

The intricate voltage regulation presented by lysenin channels reconstituted in artificial lipid membranes leads to a strong hysteresis in conductance, bistability, and memory. Prior investigations on lysenin channels indicate that the hysteresis is modulated by multivalent cations which are also capable of eliciting single-step conformational changes and transitions to stable closed or sub-conducting states. However, the influence on voltage regulation of Cu²⁺ ions, capable of completely closing the lysenin channels in a two-step process, was not sufficiently addressed. In this respect, we employed electrophysiology approaches to investigate the response of lysenin channels to variable voltage stimuli in the presence …

Hypo-Osmotic Stress And Pore-Forming Toxins Adjust The Lipid Order In Sheep Red Blood Cell Membranes, Rose Whiting, Sevio Stanton, Maryna Kucheriava, Aviana R. Smith, Matt Pitts, Daniel Robertson, Jacob Kammer, Zhiyu Li, Daniel Fologea

Physics Faculty Publications and Presentations

Lipid ordering in cell membranes has been increasingly recognized as an important factor in establishing and regulating a large variety of biological functions. Multiple investigations into lipid organization focused on assessing ordering from temperature-induced phase transitions, which are often well outside the physiological range. However, particular stresses elicited by environmental factors, such as hypo-osmotic stress or protein insertion into membranes, with respect to changes in lipid status and ordering at constant temperature are insufficiently described. To fill these gaps in our knowledge, we exploited the well-established ability of environmentally sensitive membrane probes to detect intramembrane changes at the molecular level. …

Lysenin Channels As Sensors For Ions And Molecules, Andrew Bogard, Gamid Abatchev, Zoe Hutchinson, Jason Ward, Pangaea W. Finn, Fulton Mckinney, Daniel Fologea

Physics Faculty Publications and Presentations

Lysenin is a pore-forming protein extracted from the earthworm Eisenia fetida, which inserts large conductance pores in artificial and natural lipid membranes containing sphingomyelin. Its cytolytic and hemolytic activity is rather indicative of a pore-forming toxin; however, lysenin channels present intricate regulatory features manifested as a reduction in conductance upon exposure to multivalent ions. Lysenin pores also present a large unobstructed channel, which enables the translocation of analytes, such as short DNA and peptide molecules, driven by electrochemical gradients. These important features of lysenin channels provide opportunities for using them as sensors for a large variety of applications. In …

Kinetic Exclusion Assay Of Biomolecules By Aptamer Capture, Mark H. Smith, Daniel Fologea

Physics Faculty Publications and Presentations

DNA aptamers are short nucleotide oligomers selected to bind a target ligand with affinity and specificity rivaling that of antibodies. These remarkable features recommend aptamers as candidates for analytical and therapeutic applications that traditionally use antibodies as biorecognition elements. Numerous traditional and emerging analytical techniques have been proposed and successfully implemented to utilize aptamers for sensing purposes. In this work, we exploited the analytical capabilities offered by the kinetic exclusion assay technology to measure the affinity of fluorescent aptamers for their thrombin target and quantify the concentration of analyte in solution. Standard binding curves constructed by using equilibrated mixtures of …

Temporary Membrane Permeabilization Via The Pore-Forming Toxin Lysenin, Nisha Shrestha, Christopher A. Thomas, Devon Richtsmeier, Andrew Bogard, Rebecca Hermann, Malyk Walker, Gamid Abatchev, Raquel J. Brown, Daniel Fologea

Physics Faculty Publications and Presentations

Pore-forming toxins are alluring tools for delivering biologically-active, impermeable cargoes to intracellular environments by introducing large conductance pathways into cell membranes. However, the lack of regulation often leads to the dissipation of electrical and chemical gradients, which might significantly affect the viability of cells under scrutiny. To mitigate these problems, we explored the use of lysenin channels to reversibly control the barrier function of natural and artificial lipid membrane systems by controlling the lysenin’s transport properties. We employed artificial membranes and electrophysiology measurements in order to identify the influence of labels and media on the lysenin channel’s conductance. Two cell …

An Effective Electric Dipole Model For Voltage-Induced Gating Mechanism Of Lysenin, Eric Krueger, Daniel Fologea

Physics Faculty Publications and Presentations

Lysenin is a pore-forming toxin, which self-inserts open channels into sphingomyelin containing membranes and is known to be voltage regulated. The mechanistic details of its voltage gating mechanism, however, remains elusive despite much recent efforts. Here, we have employed a novel combination of experimental and computational techniques to examine a model for voltage gating, that is based on the existence of an “effective electric dipole” inspired by recent reported structures of lysenin. We support this mechanism by the observations that (i) the charge-reversal and neutralization substitutions in lysenin result in changing its electrical gating properties by modifying the strength of …

Single-Molecule Imaging Reveals The Interplay Between Transcription Factors, Nucleosomes, And Transcriptional Bursting, Matthew L. Ferguson

Physics Faculty Publications and Presentations

Transcription factors show rapid and reversible binding to chromatin in living cells, and transcription occurs in sporadic bursts, but how these phenomena are related is unknown. Using a combination of in vitro and in vivo single-molecule imaging approaches, we directly correlated binding of the Gal4 transcription factor with the transcriptional bursting kinetics of the Gal4 target genes GAL3 and GAL10 in living yeast cells. We find that Gal4 dwell time sets the transcriptional burst size. Gal4 dwell time depends on the affinity of the binding site and is reduced by orders of magnitude by nucleosomes. Using a novel imaging platform …

Insights Into The Voltage Regulation Mechanism Of The Pore-Forming Toxin Lysenin, Sheenah Lynn Bryant, Tyler Clark, Christopher Alex Thomas, Kaitlyn Summer Ware, Andrew Bogard, Colleen Calzacorta, Daniel Prather, Daniel Fologea

Physics Faculty Publications and Presentations

Lysenin, a pore forming toxin (PFT) extracted from Eisenia fetida, inserts voltage-regulated channels into artificial lipid membranes containing sphingomyelin. The voltage-induced gating leads to a strong static hysteresis in conductance, which endows lysenin with molecular memory capabilities. To explain this history-dependent behavior, we hypothesized a gating mechanism that implies the movement of a voltage domain sensor from an aqueous environment into the hydrophobic core of the membrane under the influence of an external electric field. In this work, we employed electrophysiology approaches to investigate the effects of ionic screening elicited by metal cations on the voltage-induced gating and hysteresis …

Zno Nanoparticles Modulate The Ionic Transport And Voltage Regulation Of Lysenin Nanochannels, Sheenah L. Bryant, Josh E. Eixenberger, Steven Rossland, Holly Apsley, Connor Hoffman, Nisha Shrestha, Michael Mchugh, Alex Punnoose, Daniel Fologea

Physics Faculty Publications and Presentations

Background: The insufficient understanding of unintended biological impacts from nanomaterials (NMs) represents a serious impediment to their use for scientific, technological, and medical applications. While previous studies have focused on understanding nanotoxicity effects mostly resulting from cellular internalization, recent work indicates that NMs may interfere with transmembrane transport mechanisms, hence enabling contributions to nanotoxicity by affecting key biological activities dependent on transmembrane transport. In this line of inquiry, we investigated the effects of charged nanoparticles (NPs) on the transport properties of lysenin, a pore-forming toxin that shares fundamental features with ion channels such as regulation and high transport rate.

Results: …

Identifying The Sources Of Ferromagnetism In Sol-Gel Synthesized Zn1-XCoXO (0 ≤ X ≤ 0.10) Nanoparticles, J. J. Beltrán, C. A. Barrero, A. Punnoose

Physics Faculty Publications and Presentations

We have carefully investigated the structural, optical and electronic properties and related them with the magnetism of sol-gel synthesized Zn_1-xCo_xO (0 ≤ x ≤ 0.10) nanoparticles. Samples with x ≤ 0.05 were pure and free of spurious phases, whereas ZnCo₂O₄ was identified as the impurity phase for samples with x ≥ 0.08. Samples with x < 0.05 were found to be true solid solutions with only high spin Co²⁺ ions into ZnO structure, whereas sample with x = 0.05, exhibited the presence of high spin Co²⁺ and low spin Co³⁺. For the impurity-free samples we found that as Co concentration increases, a and …

Heterojunction Metal-Oxide-Metal Au-Fe3O4-Au Single Nanowire Device For Spintronics, K. M. Reddy, Nitin P. Padture, Alex Punnoose, Charles Hanna

Physics Faculty Publications and Presentations

In this report, we present the synthesis of heterojunction magnetite nanowires in alumina template and describe magnetic and electrical properties from a single nanowire device for spintronics applications. Heterojunction Au-Fe-Au nanowire arrays were electrodeposited in porous aluminum oxide templates, and an extensive and controlled heat treatment process converted Fe segment to nanocrystalline cubic magnetite phase with well-defined Au-Fe₃O₄ interfaces as confirmed by the transmission electron microscopy. Magnetic measurements revealed Verwey transition shoulder around 120 K and a room temperature coercive field of 90 Oe. Current–voltage (I-V) characteristics of a single Au-Fe₃O₄-Au nanowire have …

Magnetoresistance Characteristics In Individual Fe3O4 Single Crystal Nanowire, K. M. Reddy, Nitin P. Padture, Alex Punnoose, Charles Hanna

Physics Faculty Publications and Presentations

We report on the magnetoresistance (MR) and electron transport measurements observed on asingle crystal magnetite nanowire prepared using a hydrothermal synthesis method. High-resolution electron microscopy revealed the single crystal magnetite nanowires with 80–120 nm thickness and up to 8 μm in length. Magnetic measurements showed the typical Verwey transition around 120 K with a 100 Oe room temperature coercivity and 45 emu/g saturationmagnetization, which are comparable to bulk magnetite. Electrical resistance measurements in 5-300 K temperature range were performed by scanning gate voltage and varying appliedmagnetic field. Electrical resistivity of the nanowire was found to be around 5 × …

Cytotoxicity Of Zno Nanoparticles Can Be Tailored By Modifying Their Surface Structure: A Green Chemistry Approach For Safer Nanomaterials, Alex Punnoose, Kelsey Dodge, John W. Rasmussen, Jordan Chess, Denise Wingett, Catherine Anders

Physics Faculty Publications and Presentations

ZnO nanoparticles (NP) are extensively used in numerous nanotechnology applications; however, they also happen to be one of the most toxic nanomaterials. This raises significant environmental and health concerns and calls for the need to develop new synthetic approaches to produce safer ZnO NP, while preserving their attractive optical, electronic, and structural properties. In this work, we demonstrate that the cytotoxicity of ZnO NP can be tailored by modifying their surface-bound chemical groups, while maintaining the core ZnO structure and related properties. Two equally sized (9.26 ± 0.11 nm) ZnO NP samples were synthesized from the same zinc acetate precursor …

Reproducible Nanostructure Fabrication Using Atomic Force Microscopy Indentation With Minimal Tip Damage, Seunghee Jeon, Bongwoo Ryu, Wonho Jhe, Zheong G. Khim, Byung I. Kim

Physics Faculty Publications and Presentations

A uniform pattern of quantum dots and nanowires were reproducibly fabricated by creating holes in a two-layer structure using atomic force microscopy (AFM) indentation, dry-etching of polymer resists, and metal deposition through the indentation holes. The two-layer structure was created by depositing a thin gold layer onto a polymethyl methacrylate (PMMA) layer on a silicon substrate. The indentation depth was set so that the AFM tip penetrated the thin gold layer without the tip contacting the silicon substrate. This two-layer indentation was used to create a pattern of holes in the thin gold layer. Then, the PMMA was exposed to …

Force-Feedback High-Speed Atomic Force Microscope, Byung I. Kim, Ryan D. Boehm

Physics Faculty Publications and Presentations

High-speed atomic force microscopy (HSAFM) has enabled researchers to view the nanometer-scale dynamic behavior of individual biological and bio-relevant molecules at a molecular-level resolution under physiologically relevant time scales, which is the realization of a dream in life sciences. These high-speed imaging applications now extend to the cellular/bacterial systems with the use of a smaller cantilever. By reducing the sizes of the HSAFM cantilevers by a factor of ten, systems have demonstrated image speeds up to 0.1 frames per second for larger biological systems such as bacteria. However, this imaging speed is insufficient to understand many rapid large-scale biological phenomena. …

Fluctuant Magnetism In Metal Oxide Nanocrystals Capped With Surfactants, Aaron Thurber, Michael S. Jones, Dmitri Tenne, Charles B. Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

We demonstrate experimentally that magnetism in ZnO, TiO₂, CeO₂, andSnO₂ nanocrystals (NCs) has a fluctuant nature that varies with capping surfactant type and concentration. By developing a forced hydrolysis approach with additional postprocessing for the synthesis and surfactant capping of these NCs, we effectively avoid the influence of size, shape, and magnetic impurities on the magnetic behavior of NCs, thus revealing the systematic influence of the capping surfactants on the NC magnetism. The x-ray photoelectron spectroscopy results and theoretical calculations clearly show that the magnetism fluctuation with surfactant concentration can be attributed to the periodic …

Optimization Of Force Sensitivity In Q-Controlled Amplitude-Modulation Atomic Force Microscopy, Jongwoo Kim, Baekman Sung, Byung I. Kim, Wonho Jhe

Physics Faculty Publications and Presentations

We present control of force sensitivity in Q-controlled amplitude-modulation atomic force microscopy (AM-AFM) that is based on the high-Q quartz tuning-fork. It is found that the phase noise is identical to the amplitude noise divided by oscillation amplitude in AM-AFM. In particular, we observe that while Q-control does not compromise the signal-to-noise ratio, it enhances the detection sensitivity because the minimum detectable force gradient is inversely proportional to the effective quality factor for large bandwidths, which is due to reduction of frequency noise. This work demonstrates Q-control in AM-AFM is a useful technique for enhancement of …

Direct Observation Of Self-Assembled Chain-Like Water Structures In A Nanoscopic Water Meniscus, Byung I. Kim, Ryan D. Boehm, Jeremy R. Bonander

Physics Faculty Publications and Presentations

Sawtooth-like oscillatory forces generated by water molecules confined between two oxidized silicon surfaces were observed using a cantilever-based optical interfacial force microscope when the two surfaces approached each other in ambient environments. The humidity-dependent oscillatory amplitude and periodicity were 3-12 nN and 3-4 water diameters, respectively. Half of each period was matched with a freely jointed chain model, possibly suggesting that the confined water behaved like a bundle of water chains. The analysis also indicated that water molecules self-assembled to form chain-like structures in a nanoscopic meniscus between two hydrophilic surfaces in air. From the friction force data measured simultaneously, …

Magnetic Properties Of Fe Doped, Co Doped, And Fe+Co Co-Doped Zno, J. J. Beltrán, J. A. Osorio, C. A. Barrero, Charles B. Hanna, A. Punnoose

Physics Faculty Publications and Presentations

The structural, electronic, and magnetic properties of Zn_0.95Co_0.05O, Zn_0.95Fe_0.05O, and Zn_0.90Fe_0.05Co_0.05O nanoparticles prepared by a sol-gel method are presented and discussed. X-ray diffraction and optical analysis indicated that high spin Co²⁺ ions substitute for the Zn²⁺ ions in tetrahedral sites. ⁵⁷Fe Mössbauer spectroscopy showed the presence of isolated paramagnetic Fe³⁺ ions in both Fe doped and Fe+Co co-doped ZnO, however, no evidence of ferromagnetically ordered Fe³⁺ ions is observed. In the Zn_0.95Fe_0.05O sample, weak presence of ZnFe …

Cantilever-Based Optical Interfacial Force Microscope In Liquid Using An Optical-Fiber Tip, Byung I. Kim, Luke Smith, Thanh Tran, Steven Rossland, Erik Parkinson

Physics Faculty Publications and Presentations

We developed a novel cantilever-based optical interfacial force microscope (COIFM) to study molecular interaction in liquid environments. The force sensor was created by attaching a chemically etched optical-fiber tip to the force sensor with UV epoxy, and characterized by imaging on a calibration grid. The performance of the COIFM was then demonstrated by measuring the force between two oxidized silicon surfaces in 1 mM KCl as a function of distance. The result was consistent with previously reported electrical double layer forces, suggesting that a COIFM using an optical-fiber tip is capable of measuring force in a liquid environment.

Imaging Stability In Force-Feedback High-Speed Atomic Force Microscopy, Byung I. Kim, Ryan Boehm

Physics Faculty Publications and Presentations

We studied the stability of force-feedback high-speed atomic force microscopy (HSAFM) by imaging soft, hard, and biological sample surfaces at various applied forces. The HSAFM images showed sudden topographic variations of streaky fringes with a negative applied force when collected on a soft hydrocarbon film grown on a grating sample, whereas they showed stable topographic features with positive applied forces. The instability of HSAFM images with the negative applied force was explained by the transition between contact and noncontact regimes in the force-distance curve. When the grating surface was cleaned, and thus hydrophilic by removing the hydrocarbon film, enhanced imaging …

Force-Feedback High-Speed Atomic Force Microscope For Studying Large Biological Systems, Byung I. Kim, Ryan Boehm

Physics Faculty Publications and Presentations

We designed and developed a high-speed atomic force microscope (HSAFM) utilizing a force-feedback scheme for imaging large biological samples. The system collects three simultaneous images: a deflection image, a topographic image, and a force image. We demonstrated that this force-feedback HSAFM is capable of acquiring large topographic images of Escherichia coli biofilms at approximately one frame per second in air. We discuss how the self-actuating cantilever and the piezo tube follow those larger biological topographic features during the HSAFM imaging process.

Influence Of Solvent On The Chiral Resolution Of Organic Molecules On Au(111): Ec-Stm Study Of Biphenyl Dicarboxylic Acid On Au(111) In An Aqueous Environment, Byung I. Kim, Joey Hanson, Matthew Turner, Lauren Reeder

Physics Faculty Publications and Presentations

Adsorption-induced chiral resolution of organic molecules is important due to its potential applications in stereo-selective catalysis. We studied the adsorption-induced chiral resolution using a model achiral molecule of 4,4′ biphenyl dicarboxylic acid (BPDA) on Au(111) in 0.1 M perchloric acid (HClO₄) by electrochemical scanning tunneling microscopy (EC-STM). Our experimental data showed that the BPDA molecules formed island structures with distinctive preferred orientations at the length scale of the molecular size. The molecules did not show any orientational ordering above the length scale, indicating that chiral resolution was absent in the aqueous environment. Previously, the molecules were found to …

Effects Of Long-Range Tip-Sample Interaction On Magnetic Force Imaging: A Comparative Study Between Bimorph Driven System And Electrostatic Force Modulation, Byung I. Kim

Physics Faculty Publications and Presentations

Magnetic force microscopy (MFM) using electrostatic force modulation has been designed and developed to avoid the drawbacks of the bimorph driven system. The bimorph driven system has poor frequency response and overlap of the topographic features on magnetic structures of the MFM images. In the electrostatic force modulation system, the amplitude increases in the noncontact regime as the tip approaches due to the capacitive coupling between tip and sample. MFM using electrostatic force modulation has been applied to observe maze-like stripe domain structures on a CoCr film. The contrast mechanism and imaging stability of MFM using electrostatic force modulation are …

Unusual Crystallite Growth And Modification Of Ferromagnetism Due To Aging In Pure And Doped Zno Nanoparticles, Aaron Thurber, Gordon A. Alanko, Geoffrey L. Beausoleil Ii, Kelsey Dodge, Charles Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

We report the unusual growth of pure and Fe-doped ZnO nanoparticles prepared by forced hydrolysis and the weakening of ferromagnetism due to aging in ambient conditions. More than four dozen nanoparticle samples in the size range of 4–20 nm were studied over 1 to 4 years. The as-prepared samples had significant changes in their crystallite sizes and magnetization as they aged in ambient conditions. Detailed studies using x ray diffraction and transmission electron microscopy (TEM) demonstrated that the crystallite size increased by as much as 1.4 times. Lattice parameters and strain also showed interesting changes. Magnetometry studies of Zn_{1−x …}

Size, Surface Structure, And Doping Effects On Ferromagnetism In Sno2, Gordon A. Alanko, Aaron Thurber, Charles Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

The effects of crystallite size, surface structure, and dopants on the magnetic properties of semiconducting oxides are highly controversial. In this work, Fe:SnO₂ nanoparticles were prepared by four wet-chemical methods, with Fe concentration varying from 0% to 20%. Analysis confirmed pure single-phase cassiterite with a crystallite size of 2.6 ± 0.1 nm that decreased with increasing. Fe% doped substitutionally as Fe³⁺. Pure SnO₂ showed highly reproducible weak magnetization that varied significantly with synthesis method. Interestingly, doping SnO₂ with Fe < 2.5% produced enhanced magnetic moments in all syntheses; the maximum of 1.6 × 10⁻⁴ µ_B/Fe ion at 0.1% Fe doping was much larger than the 2.6 × …

Concentration Dependence Of Magnetic Moment In Ce1-XFeXO2, Geoffrey L. Beausoleil Ii, Aaron Thurber, S. S. Rao, Gordon A. Alanko, Charles Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

In this study, we examined the impact of iron doping on the structural, chemical, and magnetic properties of ceria (Ce_1-xFe_xO₂). Samples were produced in triplicate through a coprecipitation approach in a forced hydrolysis synthesis that yielded consistently sized nanocrystals using three different cerium precursors: cerium chloride, cerium ammonium nitrate, and cerium nitrate. Particles were characterized by x ray diffraction (XRD), x ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, and vibrating sample magnetometry (VSM). XPS and EPR data shows iron to be in the Fe³⁺ state and confirms …

Cantilever-Based Optical Interfacial Force Microscopy, Byung I. Kim

Physics Faculty Publications and Presentations

Atomic force microscopy (AFM) is one of the most important tools that lead current nanoscience and nanotechnology in many diverse areas including physics, chemistry, material engineering, and nano-biology. The current AFM technique has been routinely applied to forced unbinding processes of biomolecular complexes such as antibody-antigen binding, ligand-receptor pairs, protein unfolding, DNA unbinding, and RNA unfolding studies (Butt et al., 2005; Fritz & Anselmetti, 1997; Schumakovitch et al., 2002). AFMs have also been applied to intermolecular friction studies (Carpick et al., 1997; Colchero et al., 1996; Fernandez-Torres et al., 2003; Goddenhenrich et al., 1994; Goertz et al., 2007; B.I. Kim …

A Large-Scale Synthesis And Characterization Of Quaternary CuinXGa1−XS2 Chalcopyrite Nanoparticles Via Microwave Batch Reactions, Chivin Sun, Richard D. Westover, Gary Long, Cyril Bajracharya, Jerry D. Harris, Alex Punnoose, Rene G. Rodriguez, Joshua J. Pak

Physics Faculty Publications and Presentations

Various quaternary CuIn_xGa_1−xS₂ (0 ≤ x ≤ 1) chalcopyrite nanoparticles have been prepared from molecular single-source precursors via microwave decomposition. We were able to control the nanoparticle size, phase, stoichiometry, and solubility. Depending on the choice of surface modifiers used, we were able to tune the solubility of the resulting nanoparticles. This method has been used to generate up to 5 g of nanoparticles and up to 150 g from multiple batch reactions with excellent reproducibility. Data from UV-Vis, photoluminescence, X-ray diffraction, TEM, DSC/TGA-MS, and ICP-OES analyses have shown high reproducibility in nanoparticle size, …

Simultaneous Measurement Of Normal And Friction Forces Using A Cantilever-Based Optical Interfacial Force Microscope, Byung I. Kim, Jeremy R. Bonander, Jared A. Rasmussen

Physics Faculty Publications and Presentations

We measured normal and friction forces simultaneously using a recently developed cantilever-based optical interfacial force microscope (COIFM) technique for studies of interfacial structures and mechanical properties of nanoscale materials. We derived how the forces can be incorporated into the detection signal using the classical Euler equation for beams. A lateral modulation with the amplitude of one nanometers was applied to create the friction forces between tip and sample. We demonstrated its capability by measuring normal and friction forces of interfacial water at the molecular scale over all distance ranges.