Hollow Au/Ag nanostars displaying broad plasmonic resonance and high surface-enhanced Raman sensitivity

9 pas.; 7 figs.; 2 tabs.This journal is © The Royal Society of Chemistry. Bimetallic Au/Ag hollow nanostar (HNS) nanoparticles with different morphologies were prepared in this work. These nanoplatforms were obtained by changing the experimental conditions (concentration of silver and chemical reductors, hydroxylamine and citrate) and by using Ag nanostars as template nanoparticles (NPs) through galvanic replacement. The goal of this research was to create bimetallic Au/Ag star-shaped nanoparticles with advanced properties displaying a broader plasmonic resonance, a cleaner exposed surface, and a high concentration of electromagnetic hot spots on the surface provided by the special morphology of nanostars. The size, shape, and composition of Ag as well as their optical properties were studied by extinction spectroscopy, hyperspectral dark field microscopy, transmission and scanning electron microscopy (TEM and SEM), and energy dispersive X-ray spectroscopy (EDX). Finally, the surface-enhanced Raman scattering (SERS) activity of these HNS was investigated by using thioflavin T, a biomarker of the β-amyloid fibril formation, responsible for Alzheimer's disease. Lucigenin, a molecule displaying different SERS activities on Au and Ag, was also used to explore the presence of these metals on the NP surface. Thus, a relationship between the morphology, plasmon resonance and SERS activity of these new NPs was made.This work has been supported by the Spanish Ministerio de Economía y Competitividad (MINECO, grant FIS2014-52212- R). A. G.-L. acknowledges CSIC and FSE 2007–2013 for a JAE-CSIC predoctoral grant.Peer Reviewe

Femtosecond laser-controlled self-assembly of amorphous-crystalline nanogratings in silicon

8 págs.; 5 figs.; 1 tab.Self-assembly (SA) of molecular units to form regular, periodic extended structures is a powerful bottom-up technique for nanopatterning, inspired by nature. SA can be triggered in all classes of solid materials, for instance, by femtosecond laser pulses leading to the formation of laser-induced periodic surface structures (LIPSS) with a period slightly shorter than the laser wavelength. This approach, though, typically involves considerable material ablation, which leads to an unwanted increase of the surface roughness. We present a new strategy to fabricate high-precision nanograting structures in silicon, consisting of alternating amorphous and crystalline lines, with almost no material removal. The strategy can be applied to static irradiation experiments and can be extended into one and two dimensions by scanning the laser beam over the sample surface. We demonstrate that lines and areas with parallel nanofringe patterns can be written by an adequate choice of spot size, repetition rate and scan velocity, keeping a constant effective pulse number (N ) per area for a given laser wavelength. A deviation from this pulse number leads either to inhomogeneous or ablative structures. Furthermore, we demonstrate that this approach can be used with different laser systems having widely different wavelengths (1030 nm, 800 nm, 400 nm), pulse durations (370 fs, 100 fs) and repetition rates (500 kHz, 100 Hz, single pulse) and that the grating period can also be tuned by changing the angle of laser beam incidence. The grating structures can be erased by irradiation with a single nanosecond laser pulse, triggering recrystallization of the amorphous stripes. Given the large differences in electrical conductivity between the two phases, our structures could find new applications in nanoelectronics.This work has been supported by the LiNaBioFluid project of the H2020 program of the European Commission (FETOPEN- 665337) as well as by the Spanish TEC2014-52642-C2- 1-R. MG-L and JH-R acknowledge the grants respectively awarded by the Spanish Ministry of Education and the Spanish Ministry of Economy and Competiveness.Peer Reviewe

Development and validation of a Spanish translation of the Yale activity questionnaire

Background: Valid measures of physical activity are critical research tools. The objective of this study was to develop a Spanish translation of the Yale Physical Activity Survey, and to provide preliminary evidence of its validity in a population of Dominican patients with lower extremity arthritis. Methods: A Dominican bilingual health care professional translated the Yale Physical Activity Survey (YPAS) from English to Spanish. Several Dominican adults reviewed the translation to ensure it was linguistically and culturally appropriate. The questionnaire was back-translated to English by a North American researcher who is fluent in Spanish. Discrepancies between the original and back-translated versions were resolved by the translator and back-translator. The Spanish translation was administered to 108 Dominican subjects with advanced hip or knee arthritis prior to (N = 44) or one to four years following (N = 64) total joint replacement. We assessed construct validity by examining the association of YPAS scores and measures of functional status and pain (WOMAC), quality of life (EQ-5D) and the number of painful lower extremity joints. Results: A higher YPAS Part II Activity Dimensions Summary Index score had weak to modest correlations with worse function and quality of life as measured with the WOMAC function scale (r = 0.21, p = 0.03), SF-36 Physical Activity Scale (r = 0.29, p = 0.004) and EQ-5D (r = 0.34, p = 0.0007). Total minutes of vigorous activity and walking had weak to modest correlation with these measures (WOMAC Function Scale (r = 0.15, p = 0.15), SF-36 Physical Activity Scale (r = 0.21, p = 0.04) and EQ-5D utility (r = 0.24, p = 0.02)). Correlations between the YPAS Part I energy expenditure score and these measures were lower (WOMAC Function Scale (r = 0.07, p = 0.49), SF-36 Physical Activity Scale (r = 0.03, p = 0.74) and EQ-5D utility (r = 0.18, p = 0.07)). Conclusions: We have developed a new Spanish translation of the Yale Physical Activity Survey and provided evidence of convergent validity in a sample of Dominican patients prior to or 1–4 years following total joint replacement

Label-Free Detection and Self-Aggregation of Amyloid β-Peptides Based on Plasmonic Effects Induced by Ag Nanoparticles: Implications in Alzheimer's Disease Diagnosis

11 pags., 7 figs.Plasmon-assisted effects were used in this work to study the dynamical behavior of amyloid β peptides (Aβ), in particular Aβ(25-35), on silver nanoparticles. Amyloid peptides derive from the proteolytic cleavage of the glycoprotein named amyloid precursor protein (APP). Aβ(25-35) represents the sequence that concentrates the biological active region of all of the amyloid peptide family, being the shortest fragment of Aβ that retains the toxicity of the full length. The plasmon effects employed in this work were the localized surface plasmon resonance (LSPR), the plasmon hybridization resulting from plasmonic NPs aggregation, and the enhancement of electric field leading to the so-called surface-enhanced Raman scattering (SERS) spectroscopy on nanostructures. While LSPR and plasmon hybridization of nanoparticles are highly sensitive to adsorption and dynamical processes undergone by these peptides on the metal surface, direct nonlabeled SERS spectra provided valuable information regarding the secondary structure of peptides. Specifically, SERS revealed the interaction mechanism of peptides with the metal and the structural rearrangement processes involved in the self-aggregation leading to fibrillation. These effects were also followed at different peptide concentrations. Plasmon resonance and SERS results were obtained with transmission electron microscopy (TEM) images that also corroborated the self-aggregation processes undergone by these peptides leading to the formation of supramolecular aggregates at different concentrations. Nanospheres and protofibrils formed in the first stages of the amyloid assembly were identified by TEM. The physicochemical information provided by this work will be of great importance to design plasmon-based nanoplatforms for simultaneous amyloid detection and structural characterization. Furthermore, these platforms have promising applications in the detection of Alzheimer's disease and its treatment based on the bioaccumulation of these toxic peptides on NPs, where they can be trapped and removed from biological systems, thus reducing their neurotoxicity.This work was supported by the Spanish Ministerio de Economía y Competitividad and FEDER funds (FIS2017- 84318-R)

Synthesis of magnetic nanoparticles with plasmonic properties. Applications in surface-enhanced Raman scattering

XXII Reunión Nacional de Espectroscopía. VI Congreso Iberico de Espectroscopía, Porto 8th to 10th September 2010Peer Reviewe

Morphological tuning of plasmonic silver nanostars by controlling the nanoparticle growth mechanism: Application in the SERS detection of the amyloid marker Congo Red

12 pags., 8 figs., 2 tabs., app.Silver nanostars (AgNS) have promising applications in spectroscopic, theranostic and sensing applications. In this work we have tuned the morphology of AgNS by the modification of the experimental fabrication conditions. Silver nanostars were fabricated by following a two-step process that involves the use of two different chemical reducers: neutral hydroxylamine (HA), employed as primary chemical reducer, and citrate (CIT), in a second reduction step. The key experimental parameters which were modified in this work were the [HA]/[Ag] ratio (R), the [HA]/[CIT] ratio (R) and the time between reductions or elapsed time (T), which also determines a factor of the highest importance: the ratio between the Ag concentrations existing at the beginning of each reduction process (R). The growth mechanisms followed by Ag nanostars to reach their final size and shape determined different growth pathways which were identified in this work as well, as deduced by the analysis derived from the transmission electron micoroscopic (TEM) images and the extinction spectra from the resulting plasmons. The SERS effectiveness of the resulting substrates was analyzed by using thiophenol (TP) as molecular probe, and a correlation between morphology and SERS intensification factor was deduced. The experimental parameters leading to the highest SERS enhancement were identified. Finally, these Ag nanostars were probed in the sensitive detection of Congo Red, an amyloid marker dye usually employed in the detection of amyloid fibrils related to Alzheimer diseases.Ministerio de Economía y Competitividad (MINECO, grant FIS2014-52212-R).Peer Reviewe

BIMENS-Bimetallic nanostars (Ag@Au) with high surface enhanced raman scattering (SERS) performance: Detection of Beta-Amyloid and its marker thioflavin T

San Francisco, USA, December 01-03, 2014Peer Reviewe

Detection of Alzheimer¿s Disease Markers by High Performance Plasmonic Silver Nanostars

Peer Reviewe

Structural analysis of the neuropeptide substance P by using vibrational spectroscopy

12 pags., 8 figs., 1 tab.Substance P (SP) is one of the most studied peptide hormones and knowing the relationship between its structure and function may have important therapeutic applications in the treatment of a variety of stress-related illnesses. In order to obtain a deeper insight into its folding, the effects of different factors, such as pH changes, the presence of Ca ions, and the substitution of the Met-NH moiety in the SP structure, was studied by Raman and infrared spectroscopies. SP has a pH-dependent structure. Under acidic–neutral conditions, SP possesses a prevalent β-sheet structure although also other secondary structure elements are present. By increasing pH, a higher orderliness in the SP secondary structure is induced, as well as the formation of strongly bound intermolecular β-strands with a parallel alignment, which favour the self-assembly of SP in β-aggregates. The substitution of the Met-NH moiety with the acidic functional group in the SP sequence, giving rise to a not biologically active SP analogue, results in a more disordered folding, where the predominant contribution comes from a random coil. Conversely, the presence of Ca ions affects slightly but sensitively the folding of the polypeptide chain, by favouring the α-helical content and a different alignment of β-strands; these are structural elements, which may favour the SP biological activity. In addition, the capability of SERS spectroscopy to detect SP in its biologically active form was also tested by using different metal nanoparticles. Thanks to the use of silver NPs prepared by reduction of silver nitrate with hydroxylamine hydrochloride, SP can be detected at very low peptide concentration (~ 90 nM). However, the SERS spectra cannot be obtained under alkaline conditions since both the formation of SP aggregates and the lack of ion pairs do not allow a strong enough interaction of SP with silver NPs. [Figure not available: see fulltext.].This work was supported by the Scientific Grant Agency of the Ministry of the Education of Slovak Republic (APVV-15- 0485) and the Ministerio de Economía y Competitividad from Spain under the grant FIS2017-84314-R

Bimetallic Nanostars (Ag@Au) with High Surface Enhanced Raman Scattering (SERS) Performance: Detection of beta-Amyloid and Its Marker Thioflavin T

Conferencia invitada; Madrid, Spain, 15–18 June 2014Developing new synthesis methods to obtain metal nanoparticles (NPs) with three dimensional (3D) surface morphology is very important, due to their physical properties and versatility to diversify their applications[1]. Anisotropic metal NPs with a large variety of sizes and shapes have been recently fabricated displaying good Surface-enhanced Raman Scattering (SERS) properties. In this context, star-shaped NPs or metal nanostars (NS) have shown extraordinary properties in the intensification of the Electro Magnetic field, with promising applications in bioimaging and detection[2]. In this context, core@shell nanoparticles display advantageous properties to be used as SERS substrates. This work was aimed at the fabrication of Ag@Au NS by using AgNS as seeds by simple methods with high effectiveness in SERS and without the use of strong surfactants.Peer Reviewe