1,721,043 research outputs found
Polymeric hollow micro and nanospheres for biotechnological applications: A focused review
No full textThe rapid advancement of nanotechnology in the last ten years opened in medicine a real perspective of a significant breakthrough in the ability of therapeutics and imaging contrast agents to reach exactly the desired targets, with marginal or no collateral damages. Nanotechnologies based on the self-assembly of molecules resulting in nano-sized complexes play a key role in this advancement. In fact, molecular assemblies promise a tremendous potential for developing new diagnostic and therapeutic tools, as genuine 'nano-devices', able to interact with biological systems at molecular levels and with a high degree of specificity. However, the strong expectations raised by this approach, despite the great effort in terms of research and investments, have been since now frustrated by the rather low efficiency of the existing vectors. Nevertheless, taking into account the difficulty of the challenge, results are encouraging, and considering the importance of the stake, research in this field continues to be intensive. In this review we focus on a particular class of "micro/nano-devices", i.e. hollow spheres, that appear to be particularly useful as "carriers" of active substances in biotechnological applications. © 2013 Elsevier B.V.The rapidadvancementofnanotechnologyinthelasttenyearsopenedinmedicinearealperspectiveof
a significant breakthroughintheabilityoftherapeuticsandimagingcontrastagentstoreachexactlythe
desired targets,withmarginalornocollateraldamages.Nanotechnologiesbasedontheself-assemblyof
molecules resultinginnano-sizedcomplexesplayakeyroleinthisadvancement.Infact,molecular
assemblies promiseatremendouspotentialfordevelopingnewdiagnosticandtherapeutictools,as
genuine ‘nano-devices’, abletointeractwithbiologicalsystemsatmolecularlevelsandwithahigh
degree ofspecificity.However,thestrongexpectationsraisedbythisapproach,despitethegreateffortin
terms ofresearchandinvestments,havebeensincenowfrustratedbytheratherlowefficiency ofthe
existingvectors.Nevertheless,takingintoaccountthedifficulty ofthechallenge,resultsareencouraging,
and consideringtheimportanceofthestake,researchinthis field continuestobeintensive.Inthis
reviewwefocusonaparticularclassof “micro/nano-devices”, i.e.hollowspheres,thatappeartobe
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Hydrogen bond network relaxation in aqueous polyelectrolyte solutions: the effect of temperature
No full textDielectric spectroscopy data over the range 100 MHz–40 GHz allow for a reliable analysis of two of the major relaxation phenomena for polyelectrolytes (PE) in water. Within this range, the dielectric relaxation of pure water is dominated by a near-Debye process at D 18:5 GHz corresponding to a relaxation time of D 8:4 ps at 25 C. This mode is commonly attributed to the cooperative relaxation specific to liquids forming a hydrogen bond network (HBN) and arising from long range H-bond-mediated dipole–dipole interactions. The presence of charged polymers in water partially modifies the dielectric characteristics of the orientational water molecule relaxation due to a change of the dielectric constant of water surrounding the charges on the polyion chain. We report experimental results on the effect of the presence of a standard flexible polyelectrolyte (sodium polyacrylate) on the HBN relaxation in water for different temperatures, showing that the HBN relaxation time does not change by increasing the polyelectrolyte density in water, even if relatively high concentrations are reached (0:02 monomol C 0:4 monomol ). We also find that the effect of PE addition on the HBN relaxation is not even a broadening of its distribution, rather a decrease of the spectral weight that goes beyond the pure volume fraction effect. This extra decrease is larger at low T and less evident at high T, supporting the idea that the correlation length of the water is less affected by the presence of charged flexible chains at high temperatures
Experimental determination of the fluctuational dissipation in YBCO films in tilted magnetic fields
No full textIn-plane and out of plane resistivities in BiSrCaCuO(2212) single crystals at different doping level.
No full textUsing an eight terminal geometry in standard current/voltage contact configurations we have determined both the out-of-plane and the in-plane d.c. resistivity in BSCCO(2212) samples at different doping level. Comparison of the temperature behaviors for these transport quantities highlights that use of these configurations results in incorrect determinations for the in-plane components. Exploiting the possibility of crossed comparisons when using a multi-terminal technique we are able to ascribe this effect at presence on the sample of surface layer with oxygen contents different from the bulk
Resistivity tensor in the normal state of BSCCO single crystals as a function of doping
No full textWe present measurements of the resistivity tensor of Bi2Sr2CaCu2O8+δ single crystals with different oxygen concentrations. Sample doping varies from underdoped to slightly overdoped. Measurements are performed through multiterminal technique, which allows for a simultaneous determination of both in-plane and out-of-plane components of the resistivity tensor. Data are analyzed in terms of a model that assumes two different mechanisms for the out-of-plane conduction, markedly thermal activation and incoherent tunneling. Within this model we are able to describe data of normal state resistivity for all samples with different doping levels. We also analyze data from the literature. In all cases, the proposed model describes very well the data in the normal state
Dielectric properties of polyelectrolytes and lipid vesicles
No full textThe study of dielectric properties of biological systems and their components is important not only for fundamental scientific knowledge but also for its applications in medicine biology and biotechnology. This text covers the theoretical basis and practical aspects of the study of dielectric properties of biological systems
Fluctuation-induced resistivity in YBCO across Tc from angular measurements in magnetic field
No full textExcess conductivity of overdoped Bi2Sr2CaCu2O8+x crystals well above Tc.
No full textWe have used a multiterminal technique in order to measure the (a,b) plane excess conductivity Δσ in several Bi2Sr2CaCu2O8+x single crystals. We find that the experimental Δσ does not follow a simple power law Δσ∼ε-α, with ε=ln(T/Tc), and that it drops faster than the two-dimensional Aslamazov-Larkin law, α=1, with increasing temperature. In addition, data for samples with different doping do not scale on a universal curve. We discuss our data in terms of microscopic and Ginzburg-Landau theories, where high-momentum fluctuations are either not excited, or phenomenologically cut off. The experimental Δσ drops even faster than the prediction of the extended microscopic theory. However, we can accurately describe all our data up to T≈1.3 Tc with the GL theory, assuming a sample-dependent cutoff value. We relate the cutoff parameter to the doping level of our samples
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