High Ionic Strength Solutions Research Articles

Surfactant-free nanoparticle-DNA complexes with ultrahigh stability against salt for environmental and biological sensing.

We report the development of surfactant free-gold nanoparticle (AuNP)-DNA complexes that remained stable in solutions with extremely high ionic strength, using seawater as a model solution. Although the stability of AuNPs can be increased to a certain degree by functionalizing negatively charged DNA strands on their surfaces, they still have limited stability in highly concentrated salt solutions. However, we found that AuNPs functionalized with poly-T bases have exceptional stability in high ionic strength solutions. For example, AuNPs functionalized with a 5T spacer remained highly stable in seawater, with no color change and no red-shift in absorbance spectra for up to 9 days. Using this surprising property of poly-T spacers, we prepared highly stable AuNP-DNA complexes containing random sequences by introducing 5T spacers on the random sequenced DNA strand. The random sequenced AuNP-DNA complexes remained stable in seawater, several molar concentrations of monovalent metal ion solutions (6.1 M Na(+) or 4.8 M K(+)), and millimolar concentrations of diverse divalent metal ions. In addition, the highly stable AuNP-DNA complex maintained biological activity in seawater, which was demonstrated by complementary reaction and aptamer based biosensing. These results provide important insight into NP use for various applications under harsh biological and environmental conditions.

Laboratory Batch Experiments and Geochemical Modelling of Water-rock-super Critical CO2 Reactions in Gulf of Mexico Miocene Rocks: Implications for Future CCS Projects

Abstract Storage of CO 2 in deep saline formations in a super critical liquid state has been proposed as a way to mitigate the effects of increased atmospheric CO 2 levels. The ultimate fate of the CO 2 after injection requires an understanding of mineral dissolution/precipitation reactions occurring between the target formation minerals and the existing formation brines at formation temperatures and pressures in the presence of supercritical CO2. In this experiment core material taken from a Miocene age Gulf of Mexico core from a depth of 2806 m was reacted with synthetic brine at varied but high temperatures and pressures in the presence of super critical CO2. XRD and SEM analyses were conducted before and after reaction to identify dissolution of existing minerals and precipitation of authigenic mineral phases. Periodic geochemical analysis of the reaction fluid was used to quantify changes in the elemental composition of the reaction fluid which helps identify potential mineral dissolution/precipitation reactions. Reaction brine (140 ml) was loaded into a high pressure reaction vessel with 8 g of core sample. Experimental temperature was set to 70, 100 or 130 °C; pressure was set to 200 or 300 bar, and solution chemistry was changed from de-ionized (DI) water to a 1.88 M NaCl solution. After the introduction of CO 2 the Ca and alkalinity concentrations showed the largest increases, Ca concentrations increased ∼1000 ppm, suggesting carbonate dissolution was the dominant geochemical reaction. Final equilibrium Ca concentrations increased with decreasing reaction temperature because of greater CO 2 solubility. In addition, the reactions with the NaCl brine produced higher equilibrium Ca concentrations than the DI water experiment, likely due to the decrease in ion activity with higher ionic strength solutions. Pressure change from 200 to 300 bar did not significantly alter reaction rates. Unlike Ca, silicate dissolution reactions appear to be positively correlated with reaction temperature. Silicate dissolution rates are 2 orders of magnitude slower than carbonate dissolution rates. In this study, PHREEQC was used to simulate brine-rock-CO 2 interactions in batch experiments under high pressure and high temperature. Generally, the geochemical models reproduced concentration of Ca, Mg, K and Si seen in the water rock experiments suggesting that carbonate and K-feldspar dissolution are the dominant geochemical reactions. In addition, geochemical models show that dawsonite precipitates in higher salinity (higher Na+ concentration) experiments.

Prevention of bacterial adhesion on polyamide reverse osmosis membranes via electrostatic interactions using a cationic phosphorylcholine polymer coating

A simple and easy anti-adhesive coating method against bacteria via electrostatic interaction was developed for polyamide reverse osmosis (RO) membranes using a cationic phosphorylcholine polymer. A commercial polyamide RO membrane was immersed into an aqueous solution of phosphorylcholine polymer containing cationic amino groups, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-2-aminoethylmethacrylate (AEMA)] (p(MPC-co-AEMA)). From the results of contact angle and surface potential measurements, the surface of the coated RO membrane became more hydrophilic than that of raw membranes and had a neutral charge. Conversely, the surface of an RO membrane immersed in an aqueous solution of MPC homopolymer without AEMA groups was not coated by the polymer. Therefore, p(MPC-co-AEMA) was adsorbed via electrostatic interaction between the cationic amino groups of AEMA and anionic carboxylic groups on the polyamide RO membrane. X-ray photoelectron spectroscopy showed the existence of phosphorylcholine groups from p(MPC-co-AEMA) on the coated membranes. The result of quartz crystal microbalance with dissipation monitoring measurements showed that adsorbed p(MPC-co-AEMA) was hardly desorbed from the polyamide surface in a high ionic strength solution at least for one day. The coated RO membrane had high resistance to bacterial adhesion and retained its original rejection performance.

Interactions between Rotavirus and Natural Organic Matter Isolates with Different Physicochemical Characteristics

Interaction forces between rotavirus and Suwanee River natural organic matter (SRNOM) or Colorado River NOM (CRNOM) were studied by atomic force microscopy (AFM) in NaCl solutions and at unadjusted pH (5.7-5.9). Compared to CRNOM, SRNOM has more aromatic carbon and phenolic/carboxylic functional groups. CRNOM is characterized with aliphatic structure and considerable presence of polysaccharide moieties rich in hydroxyl functional groups. Strong repulsive forces were observed between rotavirus and silica or mica or SRNOM. The interaction decay length derived from the approaching curves for these systems involving rotavirus in high ionic strength solution was significantly higher than the theoretical Debye length. While no adhesion was observed for rotavirus and SRNOM, attraction was observed between CRNOM and rotavirus during approach and adhesion during retraction. Moreover, these adhesion forces decreased with increasing ionic strength. Interactions due to ionic hydrogen bonding between deprotonated carboxyl groups on rotavirus and hydroxyl functional groups on CRNOM were suggested as the dominant interaction mechanisms between rotavirus and CRNOM.

Swelling and Mechanical Properties of Alginate Hydrogels with Respect to Promotion of Neural Growth

Soft alginate hydrogels support robust neurite outgrowth, but their rapid disintegration in solutions of high ionic strength restricts them from long-term in vivo applications. Aiming to enhance the mechanical stability of soft alginate hydrogels, we investigated how changes in pH and ionic strength during gelation influence the swelling, stiffness, and disintegration of a three-dimensional (3D) alginate matrix and its ability to support neurite outgrowth. Hydrogels were generated from dry alginate layers through ionic crosslinks with Ca(2+) (≤ 10 mM) in solutions of low or high ionic strength and at pH 5.5 or 7.4. High- and low-viscosity alginates with different molecular compositions demonstrated pH and ionic strength-independent increases in hydrogel volume with decreases in Ca(2+) concentrations from 10 to 2 mM. Only soft hydrogels that were synthesized in the presence of 150 mM of NaCl (Ca-alginate NaCl) displayed long-term volume stability in buffered physiological saline, whereas analogous hydrogels generated in NaCl-free conditions (Ca-alginate) collapsed. The stiffnesses of Ca-alginate NaCl hydrogels elevated from 0.01 to 19 kPa as the Ca(2+)-concentration was raised from 2 to 10 mM; however, only Ca-alginate NaCl hydrogels with an elastic modulus ≤ 1.5 kPa that were generated with ≤ 4 mM of Ca(2+) supported robust neurite outgrowth in primary neuronal cultures. In conclusion, soft Ca-alginate NaCl hydrogels combine mechanical stability in solutions of high ionic strength with the ability to support neural growth and could be useful as 3D implants for neural regeneration in vivo.

Ionic strength and pH dependent multi-site sorption of Cs onto a micaceous aquifer sediment

Caesium-137 (t1/2=30years) is a common contaminant at nuclear legacy sites. Often the mobility of 137Cs in the environment is governed by its sorption to charged sites within the sediment. To this end it is important to understand the sorption behaviour of caesium across a wide range of environmental conditions. This work investigates the effect of varying solution composition (pH and competing ions) on the sorption of caesium to micaceous aquifer sediment across a large concentration range (1.0×10−11 – 1.0×10−1molL−1 Cs+). Experimental results show that Cs+ exhibits three distinct sorption behaviours at three different concentration ranges. At very low concentrations<1.0×10−6molL−1 Cs+ sorption was unaffected by competition with Na+ or H+ but significantly reduced in high ionic strength K+ solution. Secondly between 1×10−6 and 1.0×10−3molL−1 Cs+ is strongly sorbed in a neutral pH, low ionic strength background but sorption is significantly reduced in solutions with either a high concentration of Na+ or K+ ions or low pH. At high concentrations>1.0×10−3molL−1 Cs+ sorption is reduced in all systems due to saturation of the sediment’s sorption capacity. A multi-site cation exchange model was used to interpret the sorption behaviour. From this it was determined that at low concentrations Cs+ sorbs to the illite frayed edge sites only in competition with K+ ions. However, once the frayed edge sites are saturated the Cs+ sorbs to the Type II and Planar sites in competition with K+, Na+ and H+ ions. Therefore sorption of Cs+ at concentrations>1.0×10−6molL−1 is significantly reduced in both high ionic strength and low pH solutions. This is a significant result with regard to predicting the migration of 137Cs+ in acidic or high ionic strength groundwaters.

Evaluation of naphthenic acidity number and temperature on the corrosion behavior of stainless steels by using Electrochemical Noise technique

The processing of heavy oils in Brazilian refineries has exposed the equipment to more severe corrosive processes, mainly due to the presence of contaminants. The naphthenic acids can be quoted as an example of these contaminants, which are made of organic acids saturated rings and one or more carboxylic groups. Consequently, refiners are adjusting their metallurgy facilities and investing in real time instrumentation for monitoring the corrosion rates, thus enabling the optimization of the consumption of opportunity crude oils and dosing of anti-corrosive products. As an alternative to commonly used techniques for corrosion monitoring, such as weight loss coupons and electrical resistance probes, studies are being conducted to evaluate and validate the use of the Electrochemical Noise technique in oily media. This method has proven to be the most appropriate for high ionic strength solutions, as the case of oil, corrosive and it is proven to be sensitive for corrosion processes caused by naphthenic acids. This study aims to evaluate the influence of temperature – 25°C, 65°C and 120°C – and the total acidity number (TAN) – 0.5, 1.5 and 2.5mgKOH/g – in the naphthenic acid corrosion in austenitic stainless steel type 316. An electrochemical reactor consisting of three identical electrodes of 316 stainless steels roads, with an area of 8.95cm2 for each electrode, was used to evaluate the corrosive process, along with electrolytes consisting of pure mineral oil and mineral oil with naphthenic acids. The Electrochemical Noise technique was applied in the first 5h of contact between the electrodes and the electrolyte, with a frequency of 10Hz acquisition. As a result, it was observed that when the temperature or the TAN increase, both the susceptibility of the 316 steel to general corrosion and the incidence of localized corrosion also increase. Meanwhile, the temperature effect was more significant in the studied conditions. Besides, the Electrochemical Noise technique demonstrated sensitivity to identify corrosive process variations even in conditions considered to be of very low severity.

Cloning, expression and characterization of a new enantioselective esterase from a marine bacterium Pelagibacterium halotolerans B2T

• An esterase was cloned from a marine bacterium and overexpressed in Escherichia coli . • The enzyme was alkalitolerance and halotolerance. • The enzyme preferred short chain p -nitrophenyl esters, and was not a metalloenzyme. • The enzyme was useful in the synthesis of methyl ( R )-3-(4-fluorophenyl)glutarate. • ( R )-3-MFG was obtained in 71.6% ee and 73.2% yield after 36 h reaction. An esterase, designated as PE8 (219 aa, 23.19 kDa), was cloned from a marine bacterium Pelagibacterium halotolerans B2 T and overexpressed in Escherichia coli Rosetta, resulting an active, soluble protein which constituted 23.1% of the total cell protein content. Phylogenetic analysis of the protein showed it was a new member of family VI lipolytic enzymes. Biochemical characterization analysis showed that PE8 preferred short chain p -nitrophenyl esters (C2–C6), exhibited maximum activity toward p -nitrophenyl acetate, and was not a metalloenzyme. PE8 was an alkaline esterase with an optimal pH of 9.5 and an optimal temperature of 45 °C toward p -nitrophenyl acetate. Furthermore, it was found that PE8 exhibited activity and enantioselectivity in the synthesis of methyl ( R )-3-(4-fluorophenyl)glutarate (( R )-3-MFG) from the prochiral dimethyl 3-(4-fluorophenyl)glutarate (3-DFG). ( R )-3-MFG was obtained in 71.6% ee and 73.2% yield after 36 h reaction under optimized conditions (0.6 M phosphate buffer (pH 8.0) containing 17.5% 1,4-dioxane under 30 °C). In addition, PE8 was tolerant to extremely strong basic and high ionic strength solutions as it exhibited high activity even at pH 11.0 in 1 M phosphate buffer. Given its highly soluble expression, alkalitolerance, halotolerance and enantioselectivity, PE8 could be a promising candidate for the production of ( R )-3-MFG in industry. The results also demonstrate the potential of the marine environment as a source of useful biocatalysts.

Do low surfactants concentrations change lysozyme colloid properties?

Multi-component aqueous/octane systems, which contain low-molecular-weight ionic surfactants (sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB)) and lysozyme, were investigated using the scintillation phase method and the pendant drop technique. Experiments were carried out in the solutions of high ionic strength. Interfacial tension measurements reveal the appearance of local extremums for the SDS–lysozyme mixture that were attributed to changes in the nature of the SDS–lysozyme complex, which was confirmed by a radiochemical approach (determination of the distribution ratios and values of the surface excess of each component on the background of the other component). The formation of lysozyme–ionic surfactant complexes was observed for both cationic and anionic surfactants. Low surfactant concentrations of both SDS and DTAB result in the same changes of the colloidal behavior of protein. We proposed two possible mechanisms of interaction of lysozyme with cationic and anionic surfactants at low concentrations. The interactive process associated with the formation of lysozyme–ionic surfactant complexes by means of protein binding sites following by co-adsorption with SDS and by step-by-step hydrophilization and displacement from the adsorption layer by DTAB. The increase in the detergent concentration results in the usual substitution of protein from the adsorption layer that was observed by interfacial tension measurements and the radiochemical method.

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) make them good candidates for high sensitivity biosensors. When a charged molecule binds to such a sensor surface, it alters the carrier density in the sensor, resulting in changes in its DC conductance. However, in an ionic solution a charged surface also attracts counter-ions from the solution, forming an electrical double layer (EDL). This EDL effectively screens off the charge, and in physiologically relevant conditions ~100 millimolar (mM), the characteristic charge screening length (Debye length) is less than a nanometer (nm). Thus, in high ionic strength solutions, charge based (DC) detection is fundamentally impeded. We overcome charge screening effects by detecting molecular dipoles rather than charges at high frequency, by operating carbon nanotube field effect transistors as high frequency mixers. At high frequencies, the AC drive force can no longer overcome the solution drag and the ions in solution do not have sufficient time to form the EDL. Further, frequency mixing technique allows us to operate at frequencies high enough to overcome ionic screening, and yet detect the sensing signals at lower frequencies. Also, the high transconductance of SWNT transistors provides an internal gain for the sensing signal, which obviates the need for external signal amplifier. Here, we describe the protocol to (a) fabricate SWNT transistors, (b) functionalize biomolecules to the nanotube, (c) design and stamp a poly-dimethylsiloxane (PDMS) micro-fluidic chamber onto the device, and (d) carry out high frequency sensing in different ionic strength solutions.

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

Influence of acidic and alkaline waste solution properties on uranium migration in subsurface sediments

This study shows that acidic and alkaline wastes co-disposed with uranium into subsurface sediments have significant impact on changes in uranium retardation, concentration, and mass during downward migration. For uranium co-disposal with acidic wastes, significant rapid (i.e., hours) carbonate and slow (i.e., 100 s of hours) clay dissolution resulted, releasing significant sediment-associated uranium, but the extent of uranium release and mobility change was controlled by the acid mass added relative to the sediment proton adsorption capacity. Mineral dissolution in acidic solutions (pH2) resulted in a rapid (<10 h) increase in aqueous carbonate (with Ca(2+), Mg(2+)) and phosphate and a slow (100 s of hours) increase in silica, Al(3+), and K(+), likely from 2:1 clay dissolution. Infiltration of uranium with a strong acid resulted in significant shallow uranium mineral dissolution and deeper uranium precipitation (likely as phosphates and carbonates) with downward uranium migration of three times greater mass at a faster velocity relative to uranium infiltration in pH neutral groundwater. In contrast, mineral dissolution in an alkaline environment (pH13) resulted in a rapid (<10h) increase in carbonate, followed by a slow (10 s to 100 s of hours) increase in silica concentration, likely from montmorillonite, muscovite, and kaolinite dissolution. Infiltration of uranium with a strong base resulted in not only uranium-silicate precipitation (presumed Na-boltwoodite) but also desorption of natural uranium on the sediment due to the high ionic strength solution, or 60% greater mass with greater retardation compared with groundwater. Overall, these results show that acidic or alkaline co-contaminant disposal with uranium can result in complex depth- and time-dependent changes in uranium dissolution/precipitation reactions and uranium sorption, which alter the uranium migration mass, concentration, and velocity.

The Research on Adsorption Behaviors and Mechanisms of Geopolymers on Sr&lt;sup&gt;2+&lt;/sup&gt;, Co&lt;sup&gt;2+&lt;/sup&gt; and Cs&lt;sup&gt;+&lt;/sup&gt;

The adsorption behaviors and mechanism of geopolymers based on metakaolin-fly ash for Sr2+, Co2+ and Cs+ were investigated in static method. The results showed that the geopolymer has a strong adsorbability for Sr2+, Co2+ and Cs+ and the adsorbances are mainly affected by ion concentration and pH value of the solution. The adsorption dynamic model of the material for Sr2+, Co2+ and Cs+ is confirmed to be the first-order reaction and the adsorption isotherm curves showed that the adsorption behaviors belong to monolayer adsorption which is simulated by the Langmuir model very well. Desorption of Sr2+, Co2+ and Cs+could be carried on by immersing the adsorbents in the solutions with low pH or high ionic strength solution. Desorption experiments and XRD analysis indicate that the adsorption behaviors of geopolymer for the three kinds of ions are mainly chemical adsorption, according to the ion-exchange mechanism.

The rate of oxygen isotope exchange between nitrate and water

The oxygen isotope exchange rate between nitrate and water was measured at a temperature of 50–80°C and pH −0.6 to 1.1. Oxygen isotope exchange is a first-order reaction, with the exchange rate being strongly affected by both reaction temperature and pH, with increased rates of isotope exchange at higher temperatures and lower pH values. The rate of oxygen isotope exchange under natural conditions is extremely slow, with an estimated half-life for isotope exchange of 5.5×109years at 25°C and pH 7. The extremely slow rate of oxygen isotope exchange between nitrate and water under typical environmental conditions illustrates that nitrate-δ18O signatures (and also nitrate δ17O and Δ17O signatures) associated with various nitrate sources, as well as isotope compositions produced by biogeochemical processes, will be preserved. Hence, it is valid to use the value of nitrate-δ18O to investigate the sources and biogeochemical behavior of nitrate, in a similar manner to the use of sulfate-δ18O signatures to study the sources and biogeochemical behavior of sulfate.Equilibrium oxygen isotope fractionation factors have been determined, although quantification of the nitrate–water equilibrium fractionation factor is not possible due to the presence of nitrate as both protonated (i.e. HNO3) and unprotonated forms (i.e. NO3-) under the experimental conditions, and the difficulty in accurately calculating nitrate speciation in low pH, high ionic strength solutions.

A Functional Analysis of the Projection Domain of the Microtubule Associated Protein Tau Using Force Spectroscopy

The microtubule associated proteins (MAP) tau helps stabilize and organize microtubules and plays a role in several neurodegenerative diseases. This study focused specifically on the projection domain of the tau protein, which is a region of the protein that projects outward from the microtubule surface in the tau‐microtubule complex and controls spacing between microtubules in vivo. Our aim was to measure the long‐range repulsive interactions produced by the projection domains of three versions of tau, where this region has been modified, using atomic force microscopy and force spectroscopy. The tau is immobilized on mica surfaces, a model substrate that binds protein in a similar manner to microtubules. We found that as increasingly larger portions of tau's projection domain are removed, the long‐range repulsive interactions decrease. Systematic examination of the behavior of the protein under a range of experimental conditions indicated that a high ionic strength solution essentially removes the long‐range tau‐tau interactions and is consistent with interactions that are primarily electrostatic in nature. Furthermore, we have determined that buffer type does not influence force measurements of the protein, which is evidence that our measurements may be generalized to describe how tau behaves in vivo.

Electrolyte‐Gated Organic Field‐Effect Transistor Sensors Based on Supported Biotinylated Phospholipid Bilayer

Anchored, biotinylated phospholipids forming the capturing layers in an electrolyte-gated organic field-effect transistor (EGOFET) allow label-free electronic specific detection at a concentration level of 10 nM in a high ionic strength solution. The sensing mechanism is based on a clear capacitive effect across the PL layers involving the charges of the target molecules.

A thermodynamic model for silica and aluminum in alkaline solutions with high ionic strength at elevated temperatures up to 100 C: Applications to zeolites

In this study, a thermodynamic model for silica and aluminum in high ionic strength solutions at elevated temperatures up to 100 °C is constructed. Pitzer equations are utilized for the thermodynamic model construction. This model is valid up to ionic strengths of ~24 molal (m) in NaOH solutions with silicate concentrations up to ~1.5 m. The speciation of silica (including monomers and polymers) and aluminum at elevated temperatures is taken into account. Also, the equilibrium constants for silicic acid and its polymer species (H4SiO4, H5Si2O7- , H4Si2O72-, and H5Si3O73-) at elevated temperatures up to 100 °C, are obtained based on theoretical calculations. Using this thermodynamic model, thermodynamic properties, including equilibrium constants, and respective reaction enthalpies are obtained for sodium silicates, zeolite A, and the amorphous form of zeolite A, based on solubility experiments at elevated temperatures. The equilibrium constants for zeolite A and amorphous precursor of zeolite A regarding the following reactions up to 100 °C,

The effects of monovalent and divalent cations on the stability of silver nanoparticles formed from direct reduction of silver ions by Suwannee River humic acid/natural organic matter

The formation and characterization of AgNPs (silver nanoparticles) formed from the reduction of Ag+ by SRNOM (Suwannee River natural organic matter) is reported. The images of SRNOM-formed AgNPs and the selected area electron diffraction (SAED) were captured by high resolution transmission electron microscopy (HRTEM). The colloidal and chemical stability of SRNOM- and SRHA (Suwannee River humic acid)-formed AgNPs in different ionic strength solutions of NaCl, KCl, CaCl2 and MgCl2 was investigated in an effort to evaluate the key fate and transport processes of these nanoparticles in natural aqueous environments. The aggregation state, stability and sedimentation rate of the AgNPs were monitored by Dynamic Light Scattering (DLS), zeta potential, and UV–vis measurements. The results indicate that both types of AgNPs are very unstable in high ionic strength solutions. Interestingly, the nanoparticles appeared more unstable in divalent cation solutions than in monovalent cation solutions at similar concentrations. Furthermore, the presence of SRNOM and SRHA contributed to the nanoparticle instability at high ionic strength in divalent metallic cation solutions, most likely due to intermolecular bridging with the organic matter. The results clearly suggest that changes in solution chemistry greatly affect nanoparticle long term stability and transport in natural aqueous environments.

Gelatin–nanogold bioconjugates as effective plasmonic platforms for SERS detection and tagging

It is well known that standard citrate-reduced gold nanoparticles (AuNPs) are unstable at high ionic strength solution, which limits their applications in the biomedical field. In this work we present an environmentally friendly approach for the stabilization of citrate-reduced AuNPs in aqueous solution. Specifically, the stability of the AuNPs against salt-induced aggregation was greatly improved in the presence of gelatin biopolymer and stabilization of individual or small assemblies of nanoparticles can be controlled by the amount of gelatin. Furthermore, the gelatin–nanogold bioconjugates were demonstrated to be operational as highly sensitive surface-enhanced Raman scattering (SERS) active substrate for the detection of Rose Bengal fluorophore in solution at very low concentration. The results suggest that such bioconjugates can be successfully employed not only for detection of analytes, but more interestingly for building SERS-active tags in view of imaging purpose. The stabilization of bioconjugates was analyzed by localized surface plasmon resonance spectroscopy (LSPR), transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta-potential, and the chemical interaction of gelatin with AuNPs was inferred from Fourier transform infrared spectroscopy (FT-IR).

Structures formed by ultrasonic standing waves in active fluids and suspensions

The acoustic radiation force concentrates particulate materials at the nodes or antinodes of an ultrasonic standing wave (USW), in function of different physicochemical parameters: size, shape, density or elastic properties. Thus, frequencies from 0.5 to 10 MHz are adapted for manipulating micron-sized particles, cells, bacteria, vesicles, drops, bubbles and even colloidal species. The interaction of different species with the ultrasonic radiation field generates levitation, aggregation or coalescence. In this presentation, new behaviors will be presented in active fluids: bacteria bath and self-propelled metallic micro-cylinders. Leaving bacteria in culture medium undergoing the USW field show a dynamics inducing complex structures. USW propel, rotate, align and assemble metallic micro-rods (2 µm long and 330 nm diameter) in water as well as in solutions of high ionic strength, generating “self-acoustophoresis”. Finally, new possibilities for controlling aggregation forming 2D and 3D particle and cancer cells structures using pulsed ultrasound will be shown.