Bending dynamics of viscoelastic photopolymer nanowires

In this work, we demonstrate that the mechanical dynamics of polymer nanowires prepared by two-photon polymerization direct laser writing lithography is strongly influenced by their viscoelastic characteristics. Bending recovery measurements were carried out on cantilevered nanowires deflected by optical tweezers in a liquid environment. The assumption of purely elastic cantilever response (as defined by Young's modulus of the polymer material) fails to explain the observed overdamped oscillatory motion. A mechanical model is proposed to account for the nanowire viscoelastic behavior. The experimental data indicate that the origin of the nanowire viscous component is twofold. Both the partially cross-linked polymer structure and the solvent penetrating the polymer network contribute to frictional forces inside the nanowire. The present results provide guidance for the future design of nanosized polymer devices operated in a dynamic regime

Assessing the Viscoelasticity of Photopolymer Nanowires Using a Three-Parameter Solid Model for Bending Recovery Motion

Photopolymer nanowires prepared by two-photon polymerization direct laser writing (TPP-DLW) are the building blocks of many microstructure systems. These nanowires possess viscoelastic characteristics that define their deformations under applied forces when operated in a dynamic regime. A simple mechanical model was previously used to describe the bending recovery motion of deflected nanowire cantilevers in Newtonian liquids. The inverse problem is targeted in this work; the experimental observations are used to determine the nanowire physical characteristics. Most importantly, based on the linear three-parameter solid model, we derive explicit formulas to calculate the viscoelastic material parameters. It is shown that the effective elastic modulus of the studied nanowires is two orders of magnitude lower than measured for the bulk material. Additionally, we report on a notable effect of the surrounding aqueous glucose solution on the elasticity and the intrinsic viscosity of the studied nanowires made of Ormocomp

Power Spectral Density Analysis of Nanowire-Anchored Fluctuating Microbead Reveals a Double Lorentzian Distribution

In this work, we investigate the properties of a stochastic model, in which two coupled degrees of freedom are subordinated to viscous, elastic, and also additive random forces. Our model, which builds on previous progress in Brownian motion theory, is designed to describe water-immersed microparticles connected to a cantilever nanowire prepared by polymerization using two-photon direct laser writing (TPP-DLW). The model focuses on insights into nanowires exhibiting viscoelastic behavior, which defines the specific conditions of the microbead. The nanowire bending is described by a three-parameter linear model. The theoretical model is studied from the point of view of the power spectrum density of Brownian fluctuations. Our approach also focuses on the potential energy equipartition, which determines random forcing parametrization. Analytical calculations are provided that result in a double-Lorentzian power density spectrum with two corner frequencies. The proposed model explained our preliminary experimental findings as a result of the use of regression analysis. Furthermore, an a posteriori form of regression efficiency evaluation was designed and applied to three typical spectral regions. The agreement of respective moments obtained by integration of regressed dependences as well as by summing experimental data was confirmed

Molecular linkage of plasmonic nanoparticles in colloidal suspensions for enhanced pollutant sensing,

Meeting of Nanoscience and Nanotechnology (N&N) in Spain, Madrid, March 11-14 (2014) ; http://www.nanospainconf.org/2014/index.php?conf=14Spanish Ministerio de Economía y Competitividad (MINECO, Grant FIS2010-15405) and Comunidad de Madrid through the MICROSERES II network (Grant S2009/TIC-1476)Peer Reviewe

Gaps induced by molecular linkage of plasmonic nanoparticles in colloidal suspensions for SERS enhanced pesticide sensing

Espectroscopia, Universidad de la Rioja, Logroño, La Rioja, 9-11 de julio de 2014; http://www.unirioja.es/espectroscopia2014/Linear ¿,¿-dithiols with aliphatic nature have been used in this work as linkers to control the aggregation of silver nanoparticles and to induce the formation of interparticle gaps. The interest of these gaps resides in the well-known fact that when plasmonic surfaces are within a close distance, their plasmon modes couple. This event affects the electromagnetic field distribution in a manner that a drastic enhancement occurs in the gaps leading to the creation of hot spots. As a result, the optical response of substances situated inside the hot spots is strongly increased, which is highly valuable for their use in surface-enhanced spectroscopies. In this work we present a study of the formation and the characterization of the gaps formed by using dithiols of different lengths, where both thiol groups are connected by a linear aliphatic chain with 6, 8 and 10 CH2 groups. This characterization was done by using plasmon resonance and transmission electron microscopy (TEM). The Surface-Enhanced Raman Scattering (SERS) technique was employed in the investigation of the adsorption of these dithiols on the metal surface by analysing key structural spectral markers of the adsorption, metal coordination, orientation, ordering and interfacial packing of these molecules on surfaces of silver and gold NPs. The fingerprint character of SERS spectra, the propension rules of SERS and the high sensitivity of this technique make this study possible even at the very low concentration of dithiols sufficient to induce the NPs linking. Dithiol-linked nanoparticles were employed as sensors in the detection of the pesticides aldrin, dieldrin, endosulfan and linden at very low concentrations, taking advantage of the high affinity of these pollutants for aliphatic-like membranes. The sensing ability of these substrates was optimized by varying the surface coverage of dithiols.Peer Reviewe

Adsorption of linear aliphatic α,ω-dithiols on plasmonic metal nanoparticles: A structural study based on surface-enhanced Raman spectra

The adsorption mechanism of linear aliphatic α,ω-dithiols with chain lengths of 6, 8 and 10 carbon atoms on silver and gold nanoparticles has been studied by surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra provided the structural marker bands of these compounds and they were employed to obtain information about the adsorption and coordination mechanism, the orientation, conformational order, and packing of the aliphatic chains of dithiols on the metal nanoparticle surface. The effect of the type of metal (silver or gold) and the extent of surface coverage on all the above mentioned properties is discussed. It was found that the adsorption of dithiols on Au nanoparticles leads to a more disordered structure of the aliphatic chains of dithiols in comparison with the adsorption on Ag nanoparticles. The interaction through both thiol groups makes the adsorption of dithiols on metal surfaces substantially different from that of monothiols; in particular, the orientation of dithiols is perpendicular, while monothiols adopt a tilted orientation. Dithiols may act as linkers between metal nanoparticles and induce the formation of nanogaps with a controllable interparticle distance. The nanogaps thus formed are able to produce hot spots exhibiting a large intensification of electromagnetic field in these points which has been proved by the observation of intense SERS spectra of dithiols until a concentration of 10-8 M, corresponding to a large Raman enhancement factor of 5 × 106. © 2014 the Partner Organisations.This work has been supported by the Spanish Ministerio de Economía y Competitividad (MINECO, grant FIS2010-15405) and Comunidad de Madrid through the MICROSERES II network (grant S2009/TIC-1476), by the Agency of the Ministry of Education of Slovak Republic for the Structural Funds of the European Union, Operational program Education (Doctorand, ITMS code: 26110230013 and KVARK, ITMS code: 26110230084) and Operational program Research and Development (NanoBioSens (ITMS code: 26220220107) and CEVA II (ITMS code: 26220120040)), by the Slovak Research and Development Agency under the contract APVV-0242-11, and by the project CELIM (316310) funded by 7FP EU.Peer Reviewe

Oligonucleotide Delivery across the Caco-2 Monolayer: The Design and Evaluation of Self-Emulsifying Drug Delivery Systems (SEDDS)

Oligonucleotides (OND) represent a promising therapeutic approach. However, their instability and low intestinal permeability hamper oral bioavailability. Well-established for oral delivery, self-emulsifying drug delivery systems (SEDDS) can overcome the weakness of other delivery systems such as long-term instability of nanoparticles or complicated formulation processes. Therefore, the present study aims to prepare SEDDS for delivery of a nonspecific fluorescently labeled OND across the intestinal Caco-2 monolayer. The hydrophobic ion pairing of an OND and a cationic lipid served as an effective hydrophobization method using either dimethyldioctadecylammonium bromide (DDAB) or 1,2-dioleoyl-3-trimethylammonium propane (DOTAP). This strategy allowed a successful loading of OND-cationic lipid complexes into both negatively charged and neutral SEDDS. Subjecting both complex-loaded SEDDS to a nuclease, the negatively charged SEDDS protected about 16% of the complexed OND in contrast to 58% protected by its neutral counterpart. Furthermore, both SEDDS containing permeation-enhancing excipients facilitated delivery of OND across the intestinal Caco-2 cell monolayer. The negatively charged SEDDS showed a more stable permeability profile over 120 min, with a permeability of about 2 × 10−7 cm/s, unlike neutral SEDDS, which displayed an increasing permeability reaching up to 7 × 10−7 cm/s. In conclusion, these novel SEDDS-based formulations provide a promising tool for OND protection and delivery across the Caco-2 cell monolayer

Linking Ag nanoparticles by aliphatic α,ω-dithiols: A study of the aggregation and formation of interparticle hot spots

Linear α,ω-dithiols have been used as linkers to control the aggregation of silver nanoparticles. The characterization of the resulting nanoparticle clusters thus formed was carried out using plasmon resonance spectroscopy and transmission electron microscopy in both independent and correlated measurements. The obtained nanoparticle assemblies present morphologies that vary according to the dithiol length, displaying controllable-size interparticle gaps (plasmonic hot spots) with potential application in the detection of a large list of hydrophobic analytes. © 2013 American Chemical Society.ACKNOWLEDGMENTS This work has been supported by the Spanish Ministerio de Economía y Competitividad (grant FIS2010-15405), by the Comunidad de Madrid, through MICROSERES II network (grant S2009/TIC-1476). I.I.-L. also acknowledges CSIC and FSE 2007- 2013 for a JAE-CSIC predoctoral grant.Peer Reviewe

New Multilocus Sequence Typing Scheme for Enterococcus faecium Based on Whole Genome Sequencing Data

ABSTRACT The MLST scheme currently used for Enterococcus faecium typing was designed in 2002 and is based on putative gene functions and Enterococcus faecalis gene sequences available at that time. As a result, the original MLST scheme does not correspond to the real genetic relatedness of E. faecium strains and often clusters genetically distant strains to the same sequence types (ST). Nevertheless, typing has a significant impact on the subsequent epidemiological conclusions and introduction of appropriate epidemiological measures, thus it is crucial to use a more accurate MLST scheme. Based on the genome analysis of 1,843 E. faecium isolates, a new scheme, consisting of 8 highly discriminative loci, was created in this study. These strains were divided into 421 STs using the new MLST scheme, as opposed to 223 STs assigned by the original MLST scheme. The proposed MLST has a discriminatory power of D = 0.983 (CI95% 0.981 to 0.984), compared to the original scheme’s D = 0.919 (CI95% 0.911 to 0.927). Moreover, we identified new clonal complexes with our newly designed MLST scheme. The scheme proposed here is available within the PubMLST database. Although whole genome sequencing availability has increased rapidly, MLST remains an integral part of clinical epidemiology, mainly due to its high standardization and excellent robustness. In this study, we proposed and validated a new MLST scheme for E. faecium, which is based on genome-wide data and thus reflects the tested isolates’ more accurate genetic similarity. IMPORTANCE Enterococcus faecium is one of the most important pathogens causing health care associated infections. One of the main reasons for its clinical importance is a rapidly spreading resistance to vancomycin and linezolid, which significantly complicates antibiotic treatment of infections caused by such resistant strains. Monitoring the spread and relationships between resistant strains causing severe conditions represents an important tool for implementing appropriate preventive measures. Therefore, there is an urgent need to establish a robust method enabling strain monitoring and comparison at the local, national, and global level. Unfortunately, the current, extensively used MLST scheme does not reflect the real genetic relatedness between individual strains and thus does not provide sufficient discriminatory power. This can lead directly to incorrect epidemiological measures due to insufficient accuracy and biased results