Plasmon-catalysed decarboxylation of dicarboxybipyridine ligands in Ru(II) complexes chemisorbed on Ag nanoparticles: conditions, proposed mechanism and role of Ag(0) adsorption sites.

Plasmon-catalyzed decarboxylation reactions of Ru(II) bis(2,2'-bipyridine)(4,4'-dicarboxy-bipyridine) denoted as Ru(bpy)2(dcbpy) and Ru(II) tris(4,4'-dicarboxy-bipyridine) denoted as Ru(dcbpy)3 complexes in hydrosol systems with Ag nanoparticles (NPs) conditioned by the presence of Ag(0) adsorption sites on Ag NP surfaces have been revealed by surface-enhanced (resonance) Raman scattering (SERRS and/or SERS) spectral probing and monitoring further supported by factor analysis. Interpretation of the experimental results was based on an identification of specific marker bands of the Ru-dcbpy and of the Ru-bpy units. Furthermore, by a series of specifically targeted SERRS and/or SERS experiments complemented by UV/vis spectral measurements and TEM imaging of deposited Ag NPs, plasmon catalysis by charge carriers, namely hot electrons (e-) and hot holes (h+), has been established as the most probable mechanism of decarboxylation reactions undergone by the carboxylate-chemisorbed Ru-dcbpy units of the complexes. The presence of Ag(0) adsorption sites on Ag NP surfaces as the necessary condition of the reaction progress is in full accord with the charge carrier mechanism of plasmon catalysis. In particular, the neutral Ag(0) sites create the interface required for the transport of hot e- to H+ co-reactants complementing thus the C-C bond breaking and CO2 formation caused by hot h+.

Controlled Tuning of the Size of Ag-Hydrosol Nanoparticles by Nonstabilized THF and Detection of Peroxides in THF.

Surface plasmon extinction (SPE) spectra of plasmonic nanoparticles (NPs) are sensitive indicators of their composition, size, shape, interparticle interactions, and of the dielectric constant of their ambient. In this study, rapid changes in SPE spectra of Ag NPs suggesting variations in NP size and concentration were detected after addition of aged tetrahydrofuran (THF). Using time-dependent UV/vis spectroscopy combined with factor analysis, transmission electron microscopy imaging, selected-area electron diffraction, and energy-dispersive X-ray analysis, we observed that an over-limit amount of aged THF fully dissolved Ag NPs with no plasmon recovery. By contrast, an under-limit amount led to incomplete dissolution of Ag NPs and, after reaching the turnover point, to spontaneous recrystallization on residual Ag nuclei, as demonstrated by the SPE band intensity recovery to the original or even higher values. The newly formed Ag NPs were isometric, and their diameter was dependent on the added amount of THF. Furthermore, both Ag NP dissolution and recrystallization were caused by THF peroxides and their reduction products. Therefore, the dissolution of Ag NPs and the resulting hydrosol bleaching may be used as an indicator of the presence of peroxides in THF. Moreover, the reaction of aged THF with Ag NPs can be employed as a tool for tuning the size of Ag NPs in hydrosols.

Effect of Ethanethiolate Spacer on Morphology and Optical Responses of Ag Nanoparticle Array-Single Layer Graphene Hybrid Systems.

Single layer graphene (SLG) and two-dimensional (2-D) plasmonic Ag nanoparticle arrays assembled by chemisorption of ethanethiol (ET) molecules (AgNPs-ET) were employed as components of two types of hybrid systems designed for surface-enhanced Raman scattering (SERS) spectral probing of SLG localized in the vicinity of plasmonic NPs. Both hybrids were characterized by optical microscopy, transmission electron microscopy (TEM), surface plasmon extinction (SPE), and SERS microRaman spectral measurements at four excitation wavelengths spanning the 445-780 nm range. SERS spectral probing of the glass/SLG/AgNPs-ET hybrid prepared by overdeposition of SLG on glass by the array of ET-modified Ag NPs has shown that the chemisorbed ET acts as an efficient molecular spacer between SLG and Ag NPs surface which, in turn, enabled to obtain SERS spectra of SLG unperturbed by doping or strain. TEM imaging and SERS spectral probing of the second hybrid prepared by overdeposition of AgNPs-ET array on glass by SLG revealed removal of the adsorbed ET molecules and annealing of Ag NPs during the SLG deposition. The characteristics of the resulting glass/AgNPs/SLG hybrid system, namely (i) broad distribution of the annealed Ag NPs sizes and shapes, (ii) SPE curve covering the overall visible spectral region, (iii) absence of the ET spectral bands in SERS spectra, and (iv) fairly uniform SERS enhancement of the G and 2D mode of SLG in the 532-780 nm range in the straight sample geometry indicate that this hybrid can provide a suitable platform for investigation of the excitation wavelength dependence of combined SERS/GERS (graphene-enhanced Raman scattering) enhancement experienced by various molecular species brought into contact with SLG in this hybrid. Finally, weak optical effects attributed to increased reflectivity of SLG in the near field of Ag NPs arrays have been observed in the excitation wavelength dependence of the SERS spectra of both types of hybrid systems.

Arrays of Ag and Au Nanoparticles with Terpyridine- and Thiophene-Based Ligands: Morphology and Optical Responses.

The assembly of Ag and Au nanoparticles (NPs) into nanoparticulate arrays mediated by terpyridine (tpy), 4'-(2-thienyl)terpyridine (T-tpy), and short α,ω-bis(tpy)oligothiophene ligands has been accomplished at the interface between the Ag or Au NP hydrosol and a solution of the molecular species in dichloromethane. The relationship between the morphology and the optical responses of the arrays has been investigated by advanced methods of TEM (transmission electron microscopy) image analysis and surface plasmon extinction (SPE) spectra. It has been established that the size of islands of closely spaced NPs rather than the average interparticle distance affects the extent of delocalization of the surface plasmon excitations and thus also the SPE spectra. Furthermore, the structure of surface-adsorbate complexes formed in these arrays has been investigated by SERS spectral measurements carried out as a function of the excitation wavelength. Photoinduced charge transfer (CT) transitions from the neutral Ags0 and Aus0 adsorption sites on metal NPs to antibonding orbitals of the adsorbates have been identified for Ag/tpy, Ag/T-tpy, Au/tpy, and Au/T-tpy nanoparticulate arrays. Although the surface-adsorbate complexes displaying a photoinduced CT are known for Ag NPs, the Aus0 surface complexes with this CT are newly reported. Bis(tpy)oligothiophenes were found to be attached to both Ag and Au NPs via the tpy group(s). The match between the interparticle distances within the NP islands and the lengths of the oligomers molecules indicates that the molecules act as interparticle linkers. In this case, unequivocal spectral marker band evidence of the Ags0 as well as Aus0 surface complex formation has not been obtained.

Can Clinical Assessment of Postural Control Explain Locomotive Body Function, Mobility, Self-Care and Participation in Children with Cerebral Palsy?

Trunk control may influence self-care, mobility, and participation, as well as how children living with cerebral palsy (CP) move around. Mobility and Gross Motor performance are described over environmental factors, while locomotion can be understood as the intrinsic ontogenetic automatic postural function of the central nervous system, and could be the underlying element explaining the relationship between these factors. Our goal is to study the correlation among Trunk Control Measurement Scale (TCMS) and Pediatric Evaluation of Disability Inventory (PEDI) domains, as well as Locomotor Stages (LS). METHODS: A feasibility observational analysis was designed including 25 children with CP who were assessed with these scales. RESULTS: The strong correlation confirms higher levels of trunk control in children with better self-care, mobility and participation capacities. Strong correlations indicate also that higher LS show better levels of PEDI and TCMS domains. CONCLUSIONS: Our results suggest that more mature LS require higher levels of trunk control, benefitting self-care, mobility and social functions.

Resonance Raman Excitation Profiles of Fe(II)-Terpyridine Complexes: Electronic Effects of Ligand Modifications.

Metal 2,2':6',2″-terpyridine (tpy) complexes are readily used as building blocks in metallo-supramolecular polymers that stand out for their photophysical properties in solar energy assemblies. Furthermore, Resonance Raman (RR) excitation profiles are sensitive indicators of the electronic properties of chromophores. Previously, using RR spectroscopy, we studied the [Fe(tpy)2]2+ complex and metallo-supramolecular polymers formed by tpy derivatives and Fe(II) ions. Here, we compare RR spectra of iron (Fe(II)) complexes with 4'-substituted tpy ligands─[Fe(4'-R-tpy)2]2+, with R = H (1a), Cl (2a), 4-chlorophenyl (3a), and 2-thienyl (4a) to describe changes in their electronic structure after functionalization. By combining theoretical calculations, RR, and UV/vis spectra, we elucidated differences in the RR excitation profiles of 1a, 2a, and 4a complexes. In all Raman modes, complexes 1a and 2a showed maximal enhancement only at 532 nm excitation, whereas complex 4a exhibited maximal enhancement selectively at either 532 or 633 nm excitations. Based on our calculations, the mixed metal/ligand character of the highest occupied molecular orbital (HOMO) of 4a complex manifests itself through selective enhancement of vibration modes, mainly localized on the 2-thienyl unit at 633 nm excitation, which may explain the unique behavior of this complex. Therefore, complex 4a is a prospective candidate for further detailed photophysical explorations toward developing sensitizers for solar cells.

Reflex zone stimulation reduces ventilation inhomogeneity in cystic fibrosis: A randomised controlled cross-over study.

BACKGROUND: The reflex zone stimulation technique (RST) activates complex motor responses and has a positive impact on the locomotor system. This technique may also indirectly affect breathing; however, the use of this technique as adjunct of the treatment of cystic fibrosis (CF) has not yet been characterised. METHODS: We performed a randomised controlled single-centre interventional trial to evaluate the short-term effects of RST on lung function in 21 paediatric CF patients with normal baseline spirometry. The effect of 30 min of RST was compared to that of sham therapy in a crossover design. The interventions were performed in random order and planned 6 months apart. The primary outcome was a change in global ventilation inhomogeneity after intervention, assessed by lung clearance index (LCI2.5 ) derived from a nitrogen multiple breath washout test. Secondary outcomes included changes in regional ventilation inhomogeneity (indices of acinar [Sacin*Vt] and conductive airway [Scond*Vt] inhomogeneity) and spirometry parameters (inspiratory capacity, forced vital capacity, and forced expiratory volume in 1 s). Trunk deformity was assessed by physiotherapists at study entry. RESULTS: After the RST intervention, the LCI2.5 (p = .004) and Scond*Vt (p = .009) decreased significantly, while inspiratory capacity increased (p = .012). In the sham-therapy group, none of the parameters changed significantly. Trunk deformity was seen in 76.5% of all patients, and 92.9% of those with trunk deformity showed a decrease in LCI2.5 after RST. CONCLUSION: RST has multiple positive short-term effects on lung function, especially in CF patients with trunk deformities.

Adsorbate-induced silver nanoparticle aggregation kinetics.

Metal sols are often stabilized in solution by the presence of a charged double layer surrounding each colloidal nanoparticle that produces a coulomb barrier to aggregation. The nanoparticles can be induced to aggregate by replacing the charged surface species by uncharged adsorbate. We present a simple analysis that produces an expression for the initial rate constant describing the aggregation process, which is shown to depend nontrivially on the adsorbate concentration. The expression is tested experimentally by following and analyzing the time rate of decrease of the surface plasmon resonance absorption of isolated Ag nanoparticles in aqueous solution. The experimental result accords well with theory, producing a rough estimate of the (adsorbate-concentration dependent) barrier to aggregation that in the absence of added adsorbate is approximately equal to 0.08 eV.

Steady-state and time-resolved luminescence of Ru(II) polypyridine complexes attached to Ag nanoparticles: Effect of chemisorption in comparison with electrostatic bonding.

Steady state and nanosecond time resolved luminescence (namely, (3)MLCT phosphorescence) of [Ru(bpy)3](2+) and of [Ru(bpy)2(dcbpy)](2+)/bpy=2,2'-bipyridine; dcbpy=2,2'-bipyridyl-4,4'-dicarboxylic acid/attached to Ag NPs (the former by the electrostatic bonding, the latter by chemisorption) in non-aggregated Ag NP hydrosol systems has been investigated, and compared to the luminescence characteristics of the complexes in aqueous solutions. The intensity decrease of the 452 nm (and/or 455 nm, respectively) main band and elimination of the short wavelength shoulders in the excitation spectra and the intensity decrease of the emission spectra observed for both complexes upon their attachment to Ag NPs is attributed to the overlap of the excitation spectra with the surface plasmon extinction (SPE) of Ag NPs. The overlap leads to a loss of excitation energy by SPE as well as to a decrease of the (1)MLCT to (3)MLCT intersystem crossing efficiency. The time-resolved luminescence study shows that the (3)MLCT phosphorescence lifetimes of both complexes are markedly (by 3 and 4 orders of magnitude, respectively) shortened upon their attachment to Ag NPs. Nevertheless, the (3)MLCT lifetime of the chemisorbed [Ru(bpy)2(dcbpy)](2+) is by at least one order of magnitude shorter than that of the electrostatically bonded [Ru(bpy)3](2+), which indicates, that the phosphorescence lifetimes of these luminophores are strongly affected by the type of Ag NP surface-luminophore bonding.

Characterization and surface-enhanced Raman spectral probing of silver hydrosols prepared by two-wavelength laser ablation and fragmentation.

A four step Ag foil laser ablation-Ag nanoparticle fragmentation procedure in ultrapure water was carried out both under argon and in air. Pulses of a high power Nd/YAG laser were used for laser ablation (1064 nm) and for the three step Ag hydrosol treatment in the absence of Ag foil in the sequence 1064-532-1064 nm. Transmission electron microscopy (TEM) and surface plasmon (SP) extinction spectra provide evidence of Ag nanoparticle fragmentation in the second and third step of the procedure carried out under argon. While polydispersity of Ag hydrosol increases in the second step, both the polydispersity and the mean size of the nanoparticles are reduced in the third step. Qualitative and quantitative surface-enhanced Raman scattering (SERS)/surface-enhanced resonance Raman scattering (SERRS) spectral probing of systems with Ag hydrosols and the selected adsorbates at 514.5 nm excitation shows that Ag hydrosols obtained in the second step of the preparation procedure carried out in air are the most suitable substrates for SERS/SERRS experiments performed at this excitation wavelength.

Morphology and optical responses of SERS active pi-conjugated poly(N-ethyl-2-ethynylpyridinium iodide)/Ag nanocomposite systems.

The influence of the poly(N-ethyl-2-ethynylpyridinium iodide) (PEEP-I) concentration on the morphology and optical properties of nanocomposite systems prepared by mixing the polymer solution with a hydrosol of ca. 9 nm Ag nanoparticles (NPs) was investigated by a combination of surface plasmon extinction (SPE) measurements, transmission electron microscope (TEM) imaging and surface-enhanced Raman spectroscopy (SERS). The PEEP-I concentration was found to have a strong impact on the assembly of Ag NPs and, consequently, on the optical responses of the composite systems. At low polymer concentrations in the composite (corresponding to ca. 50-1800 monomer units/NP), the formation of fractal aggregates was observed. In particular, the average fractal dimension D = 1.9 +/- 0.1 was determined for aggregates in the system with 5 x 10(-6) M polymer concentration. By contrast, in systems with polymer concentrations higher than about 1 x 10(-5) M, relatively small aggregates of Ag NPs with large interparticle distances were formed. The differences in the morphology of the composite systems with various polymer concentrations manifested themselves clearly in their SPE spectra. Furthermore, upon optical excitation with appropriate wavelengths (488.0 and 514.5 nm), the fractal aggregates acted as carriers of "hot spots", i.e. strong, localized, nanoscale optical fields, from which intense and well resolved SERS spectra of the polymer were obtained.

SERS-activating effect of chlorides on borate-stabilized silver nanoparticles: formation of new reduced adsorption sites and induced nanoparticle fusion.

Changes in morphology, surface reactivity and surface-enhancement of Raman scattering induced by modification of borate-stabilized Ag nanoparticles by adsorbed chlorides have been explored using TEM, EDX analysis and SERS spectra of probing adsorbate 2,2'-bipyridine (bpy) excited at 514.5 nm and evaluated by factor analysis. At fractional coverages of the parent Ag nanoparticles by adsorbed chlorides <0.6, the Ag colloid/Cl(-)/bpy systems were found to be constituted by fractal aggregates of Ag nanoparticles fairly uniform in size (10 +/- 2 nm) and SERS spectra of Ag(+)-bpy surface species were detected. The latter result was interpreted in terms of the presence of oxidized Ag(+) and/or Ag(n)(+) adsorption sites, which have been encountered also in systems with the chemically untreated Ag nanoparticles. At chloride coverages >0.6, a fusion of fractal aggregates into the compact aggregates of touching and/or interpenetrating Ag nanoparticles has been observed and found to be accompanied by the formation of another surface species, Ag-bpy, as well as by the increase of the overall SERS enhancement of bpy by factor of 40. The same Ag-bpy surface species has been detected under the strongly reducing conditions of reduction of silver nitrate by sodium borohydride in the presence of bpy. The formation of Ag-bpy is thus interpreted in terms of the stabilization of reduced Ag(0) adsorption sites by adsorbed bpy. The formation of reduced adsorption sites on Ag nanoparticle surfaces at chloride coverages >0.6 is discussed in terms of local changes in the work function of Ag. Finally, the SERS spectral detection of Ag-bpy species is proposed as a tool for probing the presence of reduced Ag(0) adsorption sites in systems with chemically modified Ag nanoparticles.

Probing strong optical fields in compact aggregates of silver nanoparticles by SERRS of protoporphyrin IX.

TEM images and measurements of SERRS (surface-enhanced resonance Raman scattering) spectra as a function of the porphyrin concentrations in systems with unmodified and chloride-modified Ag nanoparticles and protoporphyrin IX (PPIX) are reported. TEM images have shown formation of compact aggregates in systems with chloride modified Ag nanoparticles, as opposed to systems with the unmodified particles constituted by isolated particles. SERRS spectra of PPIX as a function of PPIX concentration were measured and subjected to factor analysis. Two spectral components were identified and tentatively attributed to unperturbed PPIX and to Ag+ -PPIX surface species. Concentration value of the SERRS spectral detection limit of the latter species was determined to be nearly three orders of magnitude lower in the system with the compact aggregates than in the system with separated nanoparticles and achieves the value of 1 x 10(-10) M in a macrosampling Raman experiment. TEM images and SERRS-micro-Raman spectra of single compact aggregates of chloride-modified Ag nanoparticles incorporating PPIX molecules were acquired from a sample prepared by attachment of the aggregates to amine groups of derivatized, SiOx/formvar coated copper grids for TEM. The SERRS signal has shown large temporal fluctuations as well as variations from one aggregate to another. Within the signal fluctuations, a SERRS spectrum showing the characteristic bands of both SERRS spectral forms of PPIX and originating most probably from a few PPIX molecules located in hot spots in the interstices between the Ag nanoparticles, was obtained.

Probing of porphyrin surface chemistry in systems with laser-ablated Ag nanoparticle hydrosol: role of thiosulfate anions.

The influence of sodium thiosulfate (THS) concentration in Ag colloid/THS/H(2)TMPyP and Ag colloid/H2TMPyP/THS systems (H2TMPyP = 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin) was investigated by a combination of surface-enhanced resonance Raman scattering (SERRS) spectroscopy, surface plasmon extinction (SPE) measurements, and transmission electron microscopy (TEM). THS was found to have a strong impact on Ag nanoparticle surface structure and aggregation state and on interaction with H2TMPyP probe molecules, as evidenced by variations of the SERRS spectrum. In the Ag colloid/THS/H2TMPyP system, when laser-ablated Ag colloid was THS pretreated prior to the porphyrin addition, a critical threshold THS concentration (4 x 10(-5) M) was discovered. At concentrations below the threshold, THS mainly reduces the number of Ag+ adsorption sites. This leads to increased Ag nanoparticle aggregation prior to the porphyrin addition and significant weakening of the overall SERRS signal. Dominant contributions in the SERRS spectrum correspond to free base H2TMPyP and Ag+ containing the AgTMPyP form. At concentrations above the threshold, THS mediates also the formation and stabilization of new adsorption sites, probably Ag(0) sites. This induces a turn in the aggregation state of the pretreated Ag-c/THS system, an increase of the overall SERRS signal, and the appearance of a new spectral form of Ag metalated porphyrin.

Bimetallic (Ag)Au nanoparticles prepared by the seed growth method: two-dimensional assembling, characterization by energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, and surface enhanced raman spectroscopy, and proposed mechanism of growth.

Layered core-shell bimetallic silver-gold nanoparticles were prepared by overdeposition of Au over Ag seeds by the seed-growth method using tetrachloroauric acid, with hydroxylamine hydrochloride as the reductant. The effects of pH, reduction rate, and seeding conditions on the morphology and surface plasmon extinction of the bimetallic nanoparticles were investigated. Nanoparticles prepared by a rapid reduction in the neutral ambient and assembled into two-dimensional nanoparticulate films by adsorption of 2,2'-bipyridine were characterized by energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, surface-enhanced Raman scattering spectroscopy, and transmission electron microscopy. The results are consistent with Ag core and Ag/Au-alloyed shell composition of the nanoparticles. Evidence of the presence of Ag on the surface of the nanoparticles, of enrichment of the Ag/Au alloy shell by Ag toward or at the nanoparticle surface, and of modification of the nanoparticle surface by adsorbed chlorides is also provided. Reduction of the size of the Ag seeds, alloying of Ag and Au in the shell of the nanoparticles, and modification of their surfaces by adsorbed chlorides are tentatively attributed to positive charging of the nanoparticles during the electrocatalytic overdeposition of Au over Ag seeds.