Magnetic properties of biofunctionalized iron oxide nanoparticles as magnetic resonance imaging contrast agents

• Natalia E. Gervits,
• Andrey A. Gippius,
• Alexey V. Tkachev,
• Evgeniy I. Demikhov,
• Sergey S. Starchikov,
• Igor S. Lyubutin,
• Alexander L. Vasiliev,
• Vladimir P. Chekhonin,
• Maxim A. Abakumov,
• Alevtina S. Semkina and
• Alexander G. Mazhuga

Beilstein J. Nanotechnol. 2019, 10, 1964–1972, doi:10.3762/bjnano.10.193

• . The contrast between the tissues in MRI images depends on their properties such as fat and water content as well as on the sequence of the procedure parameters. There are three main characteristics that determine the contrast of the image: 1) proton density; 2) the spin–lattice relaxation time T1; and

• 3) the spin–spin relaxation time T2. Generally, these natural differences in tissue properties provide the necessary contrast, but in some cases, the pathological focus cannot be visualized in the images, for instance, due to size effects or the difficulty in delineating boundaries to determine

• containing paramagnetic gadolinium, reduce the spin–lattice relaxation time (T1), which makes the pathological focus brighter. Negative contrast agents typically contain MNPs with Fe2+ and Fe3+ ions. They reduce the T2 relaxation time and therefore weaken the signal from the tissues that absorbed the agent

Engineered superparamagnetic iron oxide nanoparticles (SPIONs) for dual-modality imaging of intracranial glioblastoma via EGFRvIII targeting

• Xianping Liu,
• Chengjuan Du,
• Haichun Li,
• Ting Jiang,
• Zimiao Luo,
• Zhiqing Pang,
• Daoying Geng and
• Jun Zhang

Beilstein J. Nanotechnol. 2019, 10, 1860–1872, doi:10.3762/bjnano.10.181

• , gadolinium (Gd)-based agents (often Gd-diethylenetriaminepentaacetic acid (DTPA)) and superparamagnetic iron oxide nanoparticles (SPIONs) are the paramagnetic materials generally used as contrast agents to impact the relaxation time T1 or T2, thus generating bright or dark images via MR imaging. Gd-DTPA, as

Toxicity and safety study of silver and gold nanoparticles functionalized with cysteine and glutathione

• Barbara Pem,
• Igor M. Pongrac,
• Lea Ulm,
• Ivan Pavičić,
• Valerije Vrček,
• Darija Domazet Jurašin,
• Marija Ljubojević,
• Adela Krivohlavek and
• Ivana Vinković Vrček

Beilstein J. Nanotechnol. 2019, 10, 1802–1817, doi:10.3762/bjnano.10.175

• ). The chemical shifts were expressed in parts per million (ppm) and are referenced to the residual water signal. All spectra were recorded at 25 °C. For all experiments, a recycle delay of 5 s was used, which was sufficiently greater than the relaxation time T1. To suppress the solvent signal, the WET

On the relaxation time of interacting superparamagnetic nanoparticles and implications for magnetic fluid hyperthermia

• Andrei Kuncser,
• Nicusor Iacob and
• Victor E. Kuncser

Beilstein J. Nanotechnol. 2019, 10, 1280–1289, doi:10.3762/bjnano.10.127

• Andrei Kuncser Nicusor Iacob Victor E. Kuncser National Institute of Materials Physics, P.O. Box MG 7, 077125, Magurele, Romania 10.3762/bjnano.10.127 Abstract A critical discussion on the presently available models for the relaxation time of magnetic nanoparticles approaching the

• performed on ferrofluids of different volume fractions. The theoretical support for the specific evolution of the relaxation time constant and the anisotropy energy barrier versus the interparticle interactions in a perturbation approach of the simple Néel expression for the relaxation time is provided via

• static and time-dependent micromagnetic simulations. Keywords: magnetic hyperthermia; magnetic nanoparticles; magnetic relaxation time; micromagnetic simulation; Introduction Magnetic relaxation phenomena in nanoparticulate systems are under intensive investigation today, especially due to their

Co-doped MnFe₂O₄ nanoparticles: magnetic anisotropy and interparticle interactions

• Bagher Aslibeiki,
• Parviz Kameli,
• Hadi Salamati,
• Giorgio Concas,
• Maria Salvador Fernandez,
• Alessandro Talone,
• Giuseppe Muscas and
• Davide Peddis

Beilstein J. Nanotechnol. 2019, 10, 856–865, doi:10.3762/bjnano.10.86

• is the anisotropy energy of the single particle, kB the Boltzmann constant and τ0 the characteristic relaxation time. The fit to the Arrhenius law led to unphysical values of the characteristic relaxation time and anisotropy constant. Since this model describes a non-interacting system, the results

Enhancement in thermoelectric properties due to Ag nanoparticles incorporated in Bi₂Te₃ matrix

• Srashti Gupta,
• Dinesh Chandra Agarwal,
• Bathula Sivaiah,
• Sankarakumar Amrithpandian,
• Kandasami Asokan,
• Ajay Dhar,
• Binaya Kumar Panigrahi,
• Devesh Kumar Avasthi and
• Vinay Gupta

Beilstein J. Nanotechnol. 2019, 10, 634–643, doi:10.3762/bjnano.10.63

• electrons is caused by the existence of an electrostatic potential at the interface. The Seebeck coefficient depends on the energy derivative of the relaxation time at the Fermi energy. Thus the electron-energy filtering, in which high-energy electrons remain unaffected, strongly enhances Seebeck

Review of time-resolved non-contact electrostatic force microscopy techniques with applications to ionic transport measurements

• Aaron Mascaro,
• Yoichi Miyahara,
• Tyler Enright,
• Omur E. Dagdeviren and
• Peter Grütter

Beilstein J. Nanotechnol. 2019, 10, 617–633, doi:10.3762/bjnano.10.62

• operating (scanning) parameters (bandwidth of ca. 100 Hz) the PLL response will not affect the extracted values obtained from directly fitting the data. However, as the relaxation time approaches the response time of the PLL, the output signal will become a convolution of the PLL response function and the

• extract the relaxation time constant; the initial jump only leads to a higher statistical uncertainty, which is due to the slow initial response of the PLL relative to the fast jump from 0 to 2.5 V. This becomes especially apparent for τ* ≈ τPLL. The stretching factor displays exactly the same behaviour

• currently commercially available have frequencies of f0≈ 5 MHz, thus the realistic minimum measurable relaxation time of this technique is ca. 2 μs. Voltage-pulse averaging EFM Motivation Improving the time resolution beyond the limitations of direct time-domain measurements is possible in several ways

Intuitive human interface to a scanning tunnelling microscope: observation of parity oscillations for a single atomic chain

• Sumit Tewari,
• Jacob Bakermans,
• Christian Wagner,
• Federica Galli and
• Jan M. van Ruitenbeek

Beilstein J. Nanotechnol. 2019, 10, 337–348, doi:10.3762/bjnano.10.33

• temperature difference with the reference temperature T0 with an adjustable coupling to a heat bath: where τB is the temperature relaxation time, related to the strength of the coupling. The velocities of all atoms are rescaled at every timestep (Δt) with the same factor: A typical value for τB in condensed

Size-selected Fe₃O₄–Au hybrid nanoparticles for improved magnetism-based theranostics

• Maria V. Efremova,
• Yulia A. Nalench,
• Eirini Myrovali,
• Anastasiia S. Garanina,
• Ivan S. Grebennikov,
• Polina K. Gifer,
• Maxim A. Abakumov,
• Marina Spasova,
• Makis Angelakeris,
• Alexander G. Savchenko,
• Michael Farle,
• Natalia L. Klyachko,
• Alexander G. Majouga and
• Ulf Wiedwald

Beilstein J. Nanotechnol. 2018, 9, 2684–2699, doi:10.3762/bjnano.9.251

• × 448 pixel, field of view 120 × 82.5 mm2. The signal intensities were determined using ImageJ software, and the T2-relaxation time was calculated by exponential fitting as a function of echo time. The r2-relaxivity values were calculated from linear fitting of T2−1 relaxation times as a function of Fe

• of Fe3O4–Au hybrid NPs. ZFC/FC curves at B = 5 mT (A). TV indicates the Verwey transition temperature for samples MNP-25 and MNP-44. Hysteresis loops at T = 5 K and T = 300 K (B). Inverse of the MRI proton T2-relaxation time as a function of iron concentration for MNP-6, MNP-15, MNP-25 and MNP-44 in

Metal-free catalysis based on nitrogen-doped carbon nanomaterials: a photoelectron spectroscopy point of view

• Mattia Scardamaglia and
• Carla Bittencourt

Beilstein J. Nanotechnol. 2018, 9, 2015–2031, doi:10.3762/bjnano.9.191

• structure of bulk and nanoscale objects, illustrating the so-called “phonon bottleneck” phenomenon. The excitation relaxation time is enhanced when the spacing between the size-quantized energy levels ΔE is larger than the vibrational energy ħω. This mechanism is discussed for illustration purposes only

Nanocomposites comprised of homogeneously dispersed magnetic iron-oxide nanoparticles and poly(methyl methacrylate)

• Sašo Gyergyek,
• David Pahovnik,
• Ema Žagar,
• Alenka Mertelj,
• Rok Kostanjšek,
• Miloš Beković,
• Marko Jagodič,
• Heinrich Hofmann and
• Darko Makovec

Beilstein J. Nanotechnol. 2018, 9, 1613–1622, doi:10.3762/bjnano.9.153

• field corresponds closely to the relaxation time of the nanoparticles. More specifically, in our case, this corresponds to the Néel relaxation time because the particles are fixed in the polymer and therefore Brownian relaxation is not possible. The important point is that even at low frequency and AC

• , clearly lower than the calculated ones. The reasons for this are the magnetic dipolar interactions at this high particle concentration and the applied field strengths, which lead to a longer relaxation time, and therefore, to a lower SLP value at the given frequency [38][39]. Conclusion We have

Formation and development of nanometer-sized cybotactic clusters in bent-core nematic liquid crystalline compounds

• Yuri P. Panarin,
• Sithara P. Sreenilayam,
• Jagdish K. Vij,
• Anne Lehmann and
• Carsten Tschierske

Beilstein J. Nanotechnol. 2018, 9, 1288–1296, doi:10.3762/bjnano.9.121

• Kirkwood correlation factor [56]. In that study [48] they used the reasoning that the relaxation time and the dielectric strength of the short-range polar correlations are proportional to the correlation length or the cluster size. The molecular mode corresponded to the dynamics of individual molecules

• the high frequency dielectric permittivity that depends on the electronic and atomic polarizability of the material, ω = 2πf is the angular frequency of the probe field, ε0 is the permittivity of free space, σDC is DC conductivity, τj is the relaxation time of the jth process, Δεj is the dielectric

Field-controlled ultrafast magnetization dynamics in two-dimensional nanoscale ferromagnetic antidot arrays

• Anulekha De,
• Sucheta Mondal,
• Sourav Sahoo,
• Saswati Barman,
• Yoshichika Otani,
• Rajib Kumar Mitra and
• Anjan Barman

Beilstein J. Nanotechnol. 2018, 9, 1123–1134, doi:10.3762/bjnano.9.104

• contains two exponentials with time constants tm and te representing the demagnetization and the fast relaxation time, respectively. H(t) and δ(t) represent the Heaviside step function and the Dirac delta function, respectively. A1, A2, and A3 are constants. From the fit we have obtained the ultrafast

• (symbols) and fit with a three-temperature model (solid line) for extraction of the ultrafast demagnetization and fast relaxation time. The zero delay is shown by the vertical dotted line. (d) Background-subtracted time-resolved Kerr rotation data showing the precessional oscillation of magnetization. (a–f

Non-equilibrium electron transport induced by terahertz radiation in the topological and trivial phases of Hg_1−xCd_xTe

• Alexandra V. Galeeva,
• Alexey I. Artamkin,
• Alexey S. Kazakov,
• Sergey N. Danilov,
• Sergey A. Dvoretskiy,
• Nikolay N. Mikhailov,
• Ludmila I. Ryabova and
• Dmitry R. Khokhlov

Beilstein J. Nanotechnol. 2018, 9, 1035–1039, doi:10.3762/bjnano.9.96

• processes characterized by different relaxation time parameters. We will address here only to relatively fast processes with the characteristic times of 100–200 ns. The long-term photoconductivity observed at longer times after the laser pulse end may be due to photoinduced transitions to or from the local

Dynamic behavior of nematic liquid crystal mixtures with quantum dots in electric fields

• Emil Petrescu,
• Cristina Cirtoaje and
• Octavian Danila

Beilstein J. Nanotechnol. 2018, 9, 399–406, doi:10.3762/bjnano.9.39

• on a sample containing 0.89% (mass fraction) of CdSe/ZnS quantum dots revealed a decrease of the relaxation time compared to pure 5CB. Keywords: Fréedericksz transition; nematic liquid crystals; quantum dots; Introduction The expansion of liquid crystal (LC)-based devices in common life domains as

• quantum dot surface. Dynamic experiments performed in alternating electric fields proved that by adding a small amount of CdSe/ZnS quantum dots in thermotropic nematic liquid crystal with positive dielectric anisotropy, we obtain a decrease of the relaxation time. When an external electric field higher

• sample. The time period after which a constant intensity is obtained, which means that an equilibrium state is reached, is characterized by the relaxation time and can be experimentally evaluated from plotting the intensity as a function of the time. A theoretical analysis of the LC + QDs system based on

Periodic structures on liquid-phase smectic A, nematic and isotropic free surfaces

• Anna N. Bagdinova,
• Evgeny I. Demikhov,
• Nataliya G. Borisenko,
• Sergei M. Tolokonnikov,
• Gennadii V. Mishakov and
• Andrei V. Sharkov

Beilstein J. Nanotechnol. 2018, 9, 342–352, doi:10.3762/bjnano.9.34

• by similar equations. This mechanism explains why several minutes are needed to form the stripes. This time corresponds to charge diffusion to the stable position in the striped structure. This mechanism explains the striped appearance in the nematic phase and isotropic liquid. After some relaxation

• time in the SmA phase, the stripes become smoother and the periodicity larger. Because of the layered structure of the SmA phase, the energy barrier exits for the surface reconstruction, therefore the stripes are more pronounced in the SmA phase. The observation of stripes in the nematic phase and

Dynamic behavior of a nematic liquid crystal with added carbon nanotubes in an electric field

• Emil Petrescu and
• Cristina Cirtoaje

Beilstein J. Nanotechnol. 2018, 9, 233–241, doi:10.3762/bjnano.9.25

• theoretical model based on elastic continuum theory was developed and the relaxation times of nematic liquid crystals with CNTs were evaluated. Experiments made with single-walled carbon nanotubes dispersed in nematic 4-cyano-4’-pentylbiphenyl (5CB) indicated a significant difference of the relaxation time

• when compared to pure liquid crystal. We also noticed that the relaxation time when the field is switched off depends on how long the field was applied. It is shorter when the field is switched off immediately after application and longer when the field was applied for at least one hour. Keywords

• movement is characterized by the relaxation time. Experimentally it can be determined by measuring the intensity of a light beam traversing the sample as a function of the time. A theoretical model based on elastic continuum theory, in which the interaction between carbon nanotubes and LC molecules is

Dielectric properties of a bisimidazolium salt with dodecyl sulfate anion doped with carbon nanotubes

• Doina Manaila Maximean,
• Viorel Cîrcu and
• Constantin Paul Ganea

Beilstein J. Nanotechnol. 2018, 9, 164–174, doi:10.3762/bjnano.9.19

• low frequencies confirm the presence of EP. Keywords: activation energy; carbon nanotubes; dielectric spectroscopy; ionic liquid crystal; relaxation time; Introduction Ionic liquid crystals (ILCs) represent a very appealing class of materials that has found various recent applications in dye

• the high-frequency (HF) limit and τmax is the characteristic relaxation time of the dielectric relaxation process. The dependency τmax = f(1/T) can be modeled using the Vogel–Fulcher–Tammann (VFT) law, as follows: where A is a material constant, kB is Boltzmann’s constant, T is the temperature, TV is

• the Vogel temperature and τ∞ is a pre-exponential factor. Figure 7 presents the characteristic relaxation time as a function of the inverse temperature for the pure ILC and the CNT-doped ILC. For the pure ILC and for the lower CNT doping concentrations, there are two slopes, attributed to the

Electrical properties of a liquid crystal dispersed in an electrospun cellulose acetate network

• Doina Manaila Maximean,
• Octavian Danila,
• Pedro L. Almeida and
• Constantin Paul Ganea

Beilstein J. Nanotechnol. 2018, 9, 155–163, doi:10.3762/bjnano.9.18

• techniques, such as polarized optical microscopy, dielectric spectroscopy and impedance measurements. Dielectric constant and electric energy loss were studied as a function of frequency and temperature. The activation energy was evaluated and the relaxation time was obtained by fitting the spectra of the

• and ε″(ω) is the dielectric loss, εLF is the low frequency permittivity, ε∞ is the permittivity in the HF limit, and τmax is the characteristic relaxation time of the medium. Figure 6 presents the characteristic relaxation time as a function of the inverse of temperature for the cellulose acetate

• the activation energy were determined, and found to be in good agreement with previously obtained data. The relaxation time was obtained by fitting the spectra of the dielectric loss with the Havriliak–Negami function. Impedance measurements were evaluated using Cole–Cole diagrams and the three

Study of the vertically aligned in-plane switching liquid crystal mode in microscale periodic electric fields

• Artur R. Geivandov,
• Mikhail I. Barnik,
• Irina V. Kasyanova and
• Serguei P. Palto

Beilstein J. Nanotechnol. 2018, 9, 11–19, doi:10.3762/bjnano.9.2

• of the bulk LC. The speed of the fast (surface) mode is defined by half of a period of the electrode grating, while the relaxation time of the bulk depends on the LC layer thickness and the length of the driving electric pulses. Thus, the use of the surface mode and the reduction of the electrode

• results for the three geometries are presented in Figure 4. The increase of the electrode period causes an increase of the relaxation time. Also the switching-ON time is increased, especially at lower voltages. For all the samples the thickness of the LC layer was the same within our technological

• inaccuracy. Thus, the smaller electrodes period is desirable for shortening the response time. At an electrode grating period of 3 μm the relaxation time (τoff) is below 1 ms for ZLI-1957/5 LC. Note that for the typical modes used in practice (such as for example the twisted nematic mode) the relaxation time

A robust AFM-based method for locally measuring the elasticity of samples

• Alexandre Bubendorf,
• Stefan Walheim,
• Thomas Schimmel and
• Ernst Meyer

Beilstein J. Nanotechnol. 2018, 9, 1–10, doi:10.3762/bjnano.9.1

• inverse of typical material relaxation time, we can assume that the measured storage modulus is independent on the frequency. The measurements yielded values in the range of the Young’s moduli of bulk LLDPE, PP and PS as seen in Table 3. The investigation also evidenced regions of different elastic moduli

Electro-optical characteristics of a liquid crystal cell with graphene electrodes

• Nune H. Hakobyan,
• Hakob L. Margaryan,
• Valeri K. Abrahamyan,
• Vladimir M. Aroutiounian,
• Arpi S. Dilanchian Gharghani,
• Amalya B. Kostanyan,
• Timothy D. Wilkinson and
• Nelson Tabirian

Beilstein J. Nanotechnol. 2017, 8, 2802–2806, doi:10.3762/bjnano.8.279

• (high voltage, V >> Vth) and slow switching (the voltage is close to the threshold, V < 5Vth). In the fast switching mode (Figure 7), under the influence of a strong electric field, the bulk and boundary layers of the LC are involved in the reorientation process. This reduces the relaxation time due to

Thermo- and electro-optical properties of photonic liquid crystal fibers doped with gold nanoparticles

• Agata Siarkowska,
• Miłosz Chychłowski,
• Daniel Budaszewski,
• Bartłomiej Jankiewicz,
• Bartosz Bartosewicz and
• Tomasz R. Woliński

Beilstein J. Nanotechnol. 2017, 8, 2790–2801, doi:10.3762/bjnano.8.278

• about 8.0 V/µm and higher, the relaxation time could exceed even the times for an undoped LC. This effect could be connected with the electric constant of metallic dopants. High concentrations of Au NPs give good response times (25–30% shorter than for the undoped LC), but the relaxation times reduce

Dynamic behavior of a nematic liquid crystal mixed with CoFe₂O₄ ferromagnetic nanoparticles in a magnetic field

• Emil Petrescu,
• Cristina Cirtoaje and
• Cristina Stan

Beilstein J. Nanotechnol. 2017, 8, 2467–2473, doi:10.3762/bjnano.8.246

• relaxation times for this mixture were calculated using experimental results and the theoretical model described above. They are presented in Table 1 where τon is the relaxation time after the field is switched on, and τoff is the relaxation time after the field is switched off. In pure nematic substances

• , the relaxation time τoff does not depend on the applied field as long as it is higher than the Fréedericksz transition threshold. As it can be observed from Table 1, when ferro-particles are added, the relaxation time decreases with increase of the applied field. Conclusion A new alignment was

• sample and improves the stability, proving to provide important benefits for magneto-optic devices. We obtained a stable structure with controllable phase modulation without backflow effect, and fast response. An important step was made to reduce the relaxation time, a major problem in magnetic devices

Material property analytical relations for the case of an AFM probe tapping a viscoelastic surface containing multiple characteristic times

• Enrique A. López-Guerra and
• Santiago D. Solares

Beilstein J. Nanotechnol. 2017, 8, 2230–2244, doi:10.3762/bjnano.8.223

• , which is its high scanning speed. At the same time, knowing that the observation of viscoelasticity demands agreement between the material timescale (e.g., relaxation time) and the experimental timescale (ca. 1/ω), we expect that in tapping mode AFM the observables are mainly governed by the elements of