Showing papers by "University of Almería published in 2009"

Au@pNIPAM Colloids as Molecular Traps for Surface‐Enhanced, Spectroscopic, Ultra‐Sensitive Analysis

Abstract: Surface-enhanced Raman scattering (SERS) is a powerful analytical technique that allows ultra-sensitive chemical or biochemical analysis. Since the first reported SERS on silver and gold colloids in 1979, they have become one of the most commonly used nanostructures for SERS, both as a testing ground for the most thorough theoretical modeling, and for the achievement of single-molecule detection (SMD). Analytical applications based on average SERS are mature, and current work is focused on specific tuning of the experimental conditions for each particular analyte. For example, the enhancement factors (EF) reported for organic acids and alcohols are several orders of magnitude lower than those achieved for thiols and amines. The main reason for this situation is the different affinity of the functional groups in the analyte toward colloidal gold or silver surfaces, and it is the affinity which determines the analytes retention. To circumvent this problem, various approaches have been proposed, including the functionalization of silver nanoparticles with different surface functional groups (e.g. calixarenes, viologen derivatives), so as to increase their compatibility with polycyclic aromatic compounds. A problem inherent to this alternative is that usually the assembled molecules provide strong SERS signals that overlap and screen those corresponding to the analyte. Another alternative relies on controlling the surface charge of the nanoparticles to promote the electrostatic attraction of the analyte onto the particle surface. This approach has been reported to consistently enhance the signal for acids and amines, but it hardly helps in the case of alcohols, ethers, and other oxygencontaining groups, as well as for non-functionalized molecules. Therefore, there is a clear need for development of colloidal systems containing a noble-metal component together with a material that can trap a wide variety of molecular analytes. Herein we present the application of a recently developed core–shell colloidal material comprising gold nanoparticles coated with a thermally responsive poly-(N-isopropylacrylamide) (pNIPAM) microgel, which we denote Au@pNIPAM. While the gold cores provide the necessary enhancing properties, the pNIPAM shells can swell or collapse as a function of temperature, this change is expected to serve as a means to trap molecules and get them sufficiently close to the metal core for providing the SERS signal. Although similar systems have been proposed for applications in catalysis, temperature and pH sensing, or light-responsive materials, we propose that our particular configuration, with sufficiently big metal cores, can function as a general sensor for detection of all types of analytes. Apart from the SERS enhancement, this system can also be used to modulate the fluorescence intensity of adsorbed chromophores as a function of temperature. It is important to note that, the porous, protective pNIPAM shell not only enhances the long-term colloidal stability of the system in aqueous solutions, but additionally prevents electromagnetic coupling between metal particles, thus providing highly reproducible SERS signal and intensity, which is crucial for quantitative applications. Through a rational choice of model analytes, we demonstrate the application of these thermoresponsive hybrid materials for surface-enhanced Raman scattering, fluorescence, and resonance Raman scattering (SERS, SEF, and SERRS, respectively). This demonstration includes the first report of the SERS spectrum of 1-naphthol, which had remained elusive to SERS ultra-sensitive analysis until now. 1-Naphthol is a relevant biomarker for quantifying the exposure to polycyclic aromatic hydrocarbons in urine, as well as the presence of carbaryl pesticides in the environment and in fruits. Additionally, chronic exposure of humans to 1-naphthol has been reported to result in genotoxicity. The synthesis of the core–shell Au@pNIPAM colloids has been described in detail elsewhere and involves initial growth of a thin polystyrene (PS) shell on cetyl trimethyl ammonium bromide (CTAB) coated, 67 nm gold nanoparticles, followed by polymerization of N-isopropylacrylamide (NIPAM) and a cross-linker (N,N-methylenebisacrylamide; see Experimental Section for details). NIPAM monomers are polymerized in situ on the Au@PS surfaces using 2,2’azobis(2-methylpropionamidine) dihydrochloride (AAPH) as an initiator (Scheme 1a and Figure 1a). Particles with larger metal cores (116 nm) were prepared by seeded growth of the coated gold cores through addition of HAuCl4 and ascorbic acid (Figure 1 b). The SERS spectrum of Au@PS [*] Dr. R. A. lvarez-Puebla, Dr. I. Pastoriza-Santos, Dr. J. P rez-Juste, Prof. L. M. Liz-Marz n Departamento de Qu mica-F sica and Unidad Asociada CSICUniversidade de Vigo, 36310 Vigo (Spain) http://webs.uvigo.es/coloides/nano E-mail: ramon.alvarez@uvigo.es lmarzan@uvigo.es

Aggregate stability in range sandy loam soils Relationships with runoff and erosion

Abstract: The spatial variability of soil aggregate stability and its relationship to runoff and soil erosion were examined in a catena of soils and vegetation in a semiarid environment at the Rambla Honda field site (Tabernas, Almeria, SE Spain) to evaluate the validity of structural stability as a soil erosion indicator in sandy loam range soils. The influence of soil properties and topography on the variability of aggregate stability was also examined. Methods include: 1) aggregate stability assessment at 12 sites (3 repetitions per site) on the hillslope by two methods: a) aggregate size distribution by dry sieving b) water drop test; 2) soil organic carbon content; 3) particle size distribution determination; 4) terrain attributes derived from a digital elevation model (1-m resolution); 5) monitoring runoff and erosion for nearly 3 years in eight (10 × 2 m) plots distributed over the hillslope. Results: 41% of the average soil mass is formed by > 2-mm aggregates. However, wet aggregate stability is poor, with a mean (of a total of 1440 aggregates) of only 26 drop impacts necessary to break up a wet aggregate (pF = 1). Significant relationships were found in the number of water drops required for aggregate breakdown and runoff and erosion rates. However, no significant relationships between the mean weight diameter of aggregates under dry conditions and runoff or erosion rates were observed. The relationships of aggregates with other soil properties, hillslope position and proximity to plants are also analysed. The most significant correlation found was between the number of drop impacts and soil organic matter content. The stability of topsoil aggregates seems to be a valuable indicator of field-assessed runoff and inter-rill erosion of sandy loam range soils under semiarid conditions.

Accurate-Mass Databases for Comprehensive Screening of Pesticide Residues in Food by Fast Liquid Chromatography Time-of-Flight Mass Spectrometry

Abstract: Because of the international trade of fruits and vegetables and the lack of harmonized regulations on the use of pesticides worldwide, the development of comprehensive screening methods for analyzing hundreds of pesticides and other banned chemicals is very convenient. This work reports the development and evaluation of a rapid automated screening method for determining pesticide residues in food using liquid chromatography electrospray time-of-flight mass spectrometry (LC-TOFMS) based on the use of an accurate-mass database. The database created includes data not only on the accurate masses of the target ions but also the characteristic in-source fragment ions (over 400 fragments included) and retention time data. This customized database was associated to commercially available software which extracted all the potential compounds of interest from the LC-TOFMS raw data of each sample and matched them against the database to search for targeted compounds in the sample. This automatic screening method requires a careful optimization of the accurate-mass window and retention time tolerances, which play a determinant role on the selectivity, accuracy, and throughput of the whole procedure. Values of 10 mDa for preliminary screening and 1 mDa/5 ppm for confirmation along with a +/-0.15 min retention time window were found to be optimum for the compounds and samples tested. The optimized methods enable the automated screening of ca. 300 compounds in less than 20 min including the LC-MS run and data processing. The proposed method was applied to 60 real samples, and the results of the positive findings compared well with those obtained using a liquid chromatography tandem mass spectrometry (LC-MS/MS) method (triple quadrupole). The rates obtained on the identification of compounds in spiked and real samples in an automated fashion at different concentration levels were over 95% of the compounds, thus revealing as a convenient tool for the large-scale screening of pesticides in foodstuffs.

Chemical evaluation of contaminants in wastewater effluents and the environmental risk of reusing effluents in agriculture

Abstract: Due to increasing interest in reusing wastewater in water-deficient regions, we suggest environmental risk assessment (ERA) as a suitable tool to evaluate potential risks from trace pollutants in irrigation water. We propose a simple method for screening environmental risks associated with reusing wastewater, which can predict potential risks in terrestrial ecosystems based on the concentration of pollutants in the effluent to be reused. This method was tested in a case study including 27 priority and emerging pollutants found in effluents from two Spanish wastewater-treatment plants (WWTPs). The results showed that secondary effluents from these Spanish WWTPs were likely to cause adverse effects, due particularly to the presence of some pharmaceuticals and heavy metals. A need for effective tertiary treatment prior to reuse of wastewater effluents in agriculture is highlighted.

Au@pNIPAM Thermosensitive Nanostructures: Control over Shell Cross‐linking, Overall Dimensions, and Core Growth

Abstract: Thermoresponsive nanocomposites comprising a gold nanoparticle core and a poly(N-isopropylacrylamide) (pNIPAM) shell are synthesized by grafting the gold nanoparticle surface with polystyrene, which allows the coating of an inorganic core with an organic shell. Through careful control of the experimental conditions, the pNIPAM shell cross-linking density can be varied, and in turn its porosity and stiffness, as well as shell thickness from a few to a few hundred nanometers is tuned. The characterization of these core–shell systems is carried out by photon-correlation spectroscopy, transmission electron microscopy, and atomic force microscopy. Additionally, the porous pNIPAM shells are found to modulate the catalytic activity, which is demonstrated through the seeded growth of gold cores, either retaining the initial spherical shape or developing a branched morphology. The nanocomposites also present thermally modulated optical properties because of temperature-induced local changes of the refractive index surrounding the gold cores.

Preliminary validation in Spanish of a scale designed to measure motivation in physical education classes: the Perceived Locus of Causality (PLOC) Scale.

Abstract: The purpose of this paper was to validate the Spanish version of the Perceived Locus of Causality Scale (PLOC; Goudas, Biddle, & Fox, 1994). To achieve this, two studies with samples of 1535 and 400 physical education students, of ages 12 to 17 years, were carried out. The psychometric properties of the PLOC were examined through the following analyses: confirmatory factor analysis, factor invariance, correlation among factors, reliability (Cronbach’s alpha), temporal stability (test-retest), and criterion validity. The results partially supported the fivefactor structure. This structure was invariant across the two study samples. Correlations among the subscales indicated a simplex pattern, supporting construct validity of the scale. Alpha values over .70 (except for introjected regulation) and high temporal stability (intra-class correlation coefficient = .83 to .90) over a four-week period were obtained. The mastery-approach goal positively predicted self-determined motivation, whereas the performanceavoidance goal predicted it negatively. Future studies should continue to analyze the psychometric properties of the PLOC, as the validation of an instrument should be an ongoing process.

Effect of dietary administration of probiotics on growth and intestine functionality of juvenile Senegalese sole (Solea senegalensis, Kaup 1858)

Abstract: The effects of the dietary administration of two bacterial probiotic strains (Ppd11 and Pdp13) from the Alteromonadaceae family for 60 days, were assessed by measuring growth and feed efficiency, activities of leucine aminopeptidase and alkaline phosphatase and structural changes in the intestine of juvenile Senegalese sole. In addition, the profile of intestinal microbiota was studied by Denaturing Gradient Gel Electrophoresis. Growth and nutrient utilization were significantly higher in fish receiving probiotics than in those fed the control diet. No differences were observed in proximal composition between treatments, though higher lipid muscle content was measured in fish receiving Pdp13. Those fish also exhibited higher activities of AP when compared to Ppd11 and control groups. The profile of intestinal microbiota clearly separated those fish receiving probiotics from those of the control group. Microscopical examination revealed accumulation of lipid droplets in the enterocytes of fish receiving the control diet, but not in those fed on probiotics. Interactions between those structural changes and growth performance are discussed

Simulation of greenhouse climate monitoring and control with wireless sensor network and event-based control.

Abstract: Monitoring and control of the greenhouse environment play a decisive role in greenhouse production processes. Assurance of optimal climate conditions has a direct influence on crop growth performance, but it usually increases the required equipment cost. Traditionally, greenhouse installations have required a great effort to connect and distribute all the sensors and data acquisition systems. These installations need many data and power wires to be distributed along the greenhouses, making the system complex and expensive. For this reason, and others such as unavailability of distributed actuators, only individual sensors are usually located in a fixed point that is selected as representative of the overall greenhouse dynamics. On the other hand, the actuation system in greenhouses is usually composed by mechanical devices controlled by relays, being desirable to reduce the number of commutations of the control signals from security and economical point of views. Therefore, and in order to face these drawbacks, this paper describes how the greenhouse climate control can be represented as an event-based system in combination with wireless sensor networks, where low-frequency dynamics variables have to be controlled and control actions are mainly calculated against events produced by external disturbances. The proposed control system allows saving costs related with wear minimization and prolonging the actuator life, but keeping promising performance results. Analysis and conclusions are given by means of simulation results.

Automated monitoring of coastal aquifers with electrical resistivity tomography

Abstract: An Automated time-Lapse Electrical Resistivity Tomography (ALERT) system has been developed for the long-term monitoring of coastal aquifers. This ALERT system has been permanently installed in the River Andarax, Almeria, Spain to monitor and manage the impact of climatic change and land-use practice on the underlying Quaternary aquifer. An electrode array, nearly 1.6 km long, has been buried below the normally dry riverbed with electrode take-outs at regular intervals of 10 m. The maximum depth of investigation is about 160 m below ground level. An unmanned, permanent control station, in a secure location, allows the aquifer to be interrogated remotely from the BGS office in the UK. Volumetric geoelectric images of the subsurface can be obtained ‘on demand’ or at regular intervals; thereby eliminating the need for expensive repeat surveys. The entire process from data capture to image on the office PC is fully automated and seamless. The ALERT technology can provide early warning of potential threats to vulnerable water systems such as over-exploitation, rising sea levels, anthropogenic pollutants and seawater intrusion. The electrical images obtained (in space and time) are interpreted in terms of the hydrogeologic features including the seawater-freshwater interface. The timely detection and imaging of groundwater changes can help to regulate pumping and irrigation schemes.

Characterization of seawater intrusion using 2D electrical imaging

Abstract: We have investigated the potential of 2D electrical imaging for the characterization of seawater intrusion using field data from a site in Almeria, SE Spain. Numerical simulations have been run for several scenarios, with a hydrogeological model reflecting the local site conditions. The simulations showed that only the lower salt concentrations of the seawater-freshwater transition zone could be recovered, due to the loss of resolution with depth. We quantified this capability in terms of the cumulative sensitivity associated with the measurement setup and showed that the mismatch between the targeted and imaged parameter values occurs from a certain sensitivity threshold. Similarly, heterogeneity may only be determined accurately if located in an adequately sensitive area. At the field site, we identified seawater intrusion at the scale of a few kilometres down to a hundred metres. Borehole logs show a remarkable correlation with the image obtained from surface data but indicate that the electrically derived mass fraction of pure seawater could not be recovered due to the discrepancy between the in-situ and laboratory-derived petrophysical relationships. Surface-to-hole inversion results suggest that the laterally varying resolution pattern associated with such a setup dominates the image characteristics compared to the laterally more homogeneous resolution pattern of surface only inversion results and hence, surface-to-hole images are not easily interpretable in terms of larger-scale features. Our results indicate that electrical imaging can be used to constrain seawater intrusion models if image appraisal tools are appropriately used to quantify the spatial variation of sensitivity and resolution. The most crucial limitation is probably the apparent non-stationarity of the petrophysical relationship during the imaging process.

Acceptance and commitment therapy for smoking cessation: a preliminary study of its effectiveness in comparison with cognitive behavioral therapy.

Abstract: This controlled preliminary trial determined the feasibility and initial effectiveness of a promising behavioral intervention for smoking: Acceptance and Commitment Therapy (ACT). In a quasi-experimental design, the ACT intervention condition used metaphors and experiential exercises focused on personal values to motivate quitting smoking and enhancing the willingness to experience internal cues to smoke (e.g., urges) and abstinence-related internal distress. The comparison condition was cognitive behavioral therapy (CBT)--the current standard in behavioral intervention for smoking cessation. Each treatment was delivered in seven weekly 90-min sessions in a group format to 81 (43 in ACT; 38 in CBT) adult smokers. Results show that the ACT treatment was as feasible as the CBT treatment. They also demonstrate promising evidence of ACT's effectiveness: 30.2% intent-to-treat biochemically-supported 30-day point prevalence at twelve month follow-up, compared with 13.2% in the CBT condition (odds ratio = 5.13; p = .02). Replication in a well-powered, randomized, controlled trial is now needed.

Active and Nonlinear Microrheology in Dense Colloidal Suspensions

Abstract: We present a first-principles theory for the active nonlinear microrheology of colloidal model system; for a constant external force on a spherical probe particle embedded in a dense host dispersion, neglecting hydrodynamic interactions, we derive an exact expression for the friction. Within mode-coupling theory, we discuss the threshold external force needed to delocalize the probe from a host glass, and its relation to strong nonlinear velocity-force curves in a host fluid. Experimental microrheology data and simulations, which we performed, are explained with a simplified model.

Solar photo-Fenton treatment of pesticides in water: Effect of iron concentration on degradation and assessment of ecotoxicity and biodegradability

Abstract: A combined solar photo-Fenton and biological treatment is proposed for the decontamination of a mixture of five commercial pesticides commonly used in intensive agriculture Vydate (10% Oxamyl), Metomur (20% Methomyl), Couraze (20% Imidacloprid), Ditimur-40 (40% Dimethoate) and Scala (40% Pyrimethanil). Photo-Fenton experiments were conducted in a solar pilot reactor consisting of four compound parabolic collectors in which the pesticide mixture was treated at an original dissolved organic carbon (DOC) concentration of 200 mg/L in the presence of Fe 2+ or Fe 3+ concentration of 5, 20 and 55 mg/L. Ferrous ions were marginally more active than ferric in terms of active ingredient degradation, which followed zero order kinetics, more so in the early reaction stages. Photo-Fenton was also far more effective (by at least two orders of magnitude) than the respective dark reaction under identical experimental conditions. Irradiation for 50–100 min (normalized at 30 W/m 2 light intensity) at 20 mg/L Fe 2+ was able to completely eliminate the active ingredients, and reduce DOC by about 15–50% and COD by 40–70%, respectively. At these conditions, ecotoxicity to the marine bacteria V. fischeri was substantially lessened, while aerobic biodegradability in tests with activated sludge was enhanced.

Production of astaxanthin by Haematococcus pluvialis: taking the one-step system outdoors.

Abstract: The feasibility of a one-step method for the continuous production of astaxanthin by the microalga Haematococcus pluvialis has been verified outdoors. To this end, influence of dilution rate, nitrate concentration in the feed medium, and irradiance on the performance of continuous cultures of H. pluvialis was firstly analyzed indoors in bubble column reactors under daylight cycles, and then outdoors, using a tubular photobioreactor. At the laboratory scale, the behavior of the cultures agreed with that previously recorded in continuous illumination experiences, and attested that the major factors determining biomass and astaxanthin productivity were average irradiance and specific nitrate supply. The rate of astaxanthin accumulation was proportional to the average irradiance inside the culture, provided that a nitrate limiting situation had been established. The accumulation of astaxanthin under daylight cycles was maximal for a specific nitrate input of 0.5 mmol/g day. The recorded performance has been modeled on the basis of previously developed equations, and the validity of the model checked under outdoor conditions. Productivity values for biomass and astaxanthin of 0.7 g/L day and 8.0 mg/L day respectively, were obtained in a pilot scale tubular photobioreactor operating under continuous conditions outdoors. The magnitude of the experimental values, which matched those simulated from the obtained model, demonstrate that astaxanthin can be efficiently produced outdoors in continuous mode through a precise dosage of the specific nitrate input, taking also into consideration the average irradiance inside the culture. Biotechnol. Bioeng. 2009;102: 651–657. © 2008 Wiley Periodicals, Inc.