Preparation of Highly Concentrated Uniform-Sized Silver Nanoparticles via Use of Thermoresponsive Zwitterionic Surfactants.

Despite the popular use of citrate for the reduction of silver ions, this process suffers from slow crystal growth and broad size distribution. The rapid and effective synthesis of highly concentrated and stable spherical silver nanoparticles (AgNPs) confined in the surfactant-rich phase of thermoresponsive 3-(alkyldimethylammonio)-propyl sulfate surfactants obtained after reaction with citrate ions at high temperature is described. The present approach using the zwitterionic surfactant offers an alternative rapid approach for production of AgNPs and an in situ phase separation step that serves to "extract" and concentrate the AgNPs in the surfactant-rich phase. Almost all (synthetic yield 99.9%, extraction efficiency 98.6%) of the synthesized AgNPs with a diameter of 21.0 ± 2.5 nm were incorporated into the phase-separated surfactant-rich phase at pH 11, and the capacity (maximum concentration) was 3.4 × 1013 particles/mL. The AgNPs were stable upon long-term storage (at least 3 months).

Shape- and Size-Controlled Fabrication of Gold Nano-Urchins via Use of a Mixed Sodium Borohydride and Ascorbic Acid Reductant System.

Urchin-shaped gold nanoparticles (AuNUs) are anisotropic nanomaterials with unique chemical and physical properties of interest for a variety of applications. However, synthesizing AuNUs with controlled sizes and shapes remains challenging. We demonstrate that a combination of sodium borohydride (NaBH4) and ascorbic acid (AA) as reducing agents can produce an aqueous dispersion of AuNUs after just 9 min at room temperature (25 °C). The AuNUs were size- and shape-controlled using a molar ratio for NaBH4/AA/HAuCl4 = 1:1:1 at pH 3. The added aurate was almost entirely (98.8%) consumed in the formation of AuNUs. The resultant AuNU concentration was 1.1 × 1010 particles/mL. The diameters observed in transmission electron microscopy were 145.1 ± 37.4 nm. The AuNUs had an average of 12 spikes and an average volume of 3.7 × 105 nm3. The partition volume between the spikes and the core of particles was 3:2. The AuNUs had a pink color and exhibited an absorption wavelength maximum at 540 nm. It is assumed that the AuNUs originate from icosahedral seeds and urchin shapes emerge from connecting smaller-sized seeds and larger-sized core particles.

Rapid Micelle-Mediated Size-Controlled Fabrication of Calcium Sulfate Nanorods Using Silver Nanoparticles.

Calcium sulfate nanorods (CS-NRs) are valuable materials utilized in various applications, particularly in the medical field. In this work, the size-controlled synthesis of CS-NRs was carried out on the basis of the micelle-mediated phase separation phenomenon. A nonionic surfactant, Triton X-114, was employed for the thermoresponsive phase separation of a homogeneous solution to a surfactant-rich phase. Whereas each specific ion, Ca2+ and SO42-, was difficult to individually extract when present at concentrations less than their equilibrium concentration (solubility product constant, Ksp), the synthesized CS microrods (CS-µRs) were extracted into the surfactant-rich phase (enrichment factor = ca. 50). The presence of nitric acid increased the size of the materials up to 6707 ± 3488 nm on the long side and 87 ± 37 nm on the short side. The addition of silver nanoparticles (Ag-NPs) to the reaction mixture led to the formation of much smaller products, i.e., uniform CS-NRs whose sizes were in the range of 89 ± 15 nm (long side) and 25 ± 4 nm (short side). The size of the extracted Ag-NPs and CS-NRs decreased with an increase in added Ag-NP concentration until their microscopic observation became difficult. The factors (such as additive concentration, pH, temperature) affecting size control were evaluated.

Synthesis and evaluation of a diethylammonio-propylsulfate amphoteric ionic column for the high-performance liquid chromatography-mass spectrometric separation and detection of amino acids.

A diethylammonio-propylsulfate amphoteric ionic resin was synthesized and employed as the stationary phase for high-performance liquid chromatography-mass spectrometry (LC-MS) separation and detection of amino acids. The influence of experimental conditions such as mobile phase composition, column length and temperature upon the amino acid separations was evaluated. However, temperature, addition of water-miscible organic solvent to the mobile phase and mobile phase gradients were not effective at improving the separations. In contrast, the use of an unbuffered pure water mobile phase proved successful for the separation and detection of amino acids. The observed order of elution seems to parallel the isoelectric points of the respective amino acids and suggests that this diethylammonio-propylsulfate stationary phase column functions as an amphoteric ion-exchanger. Under optimized chromatographic conditions, the detection limits for the amino acids were in range of 0.07-0.44 pmol (pico-mole). The method was also successfully applied for the analysis of an actual commercial sample.

Nanoparticle induced formation of self-assembled zwitterionic surfactant microdomains which mimic microemulsions for the in situ fabrication and dispersion of silver nanoparticles.

The effective synthesis of highly concentrated and stable spherical silver nanoparticles (Ag-NPs) enclosed within microdomains formed by the Ag-NP induced self-assembly of zwitterionic surfactants is described. In this paper, the rapid and efficient synthesis of dispersed and stable Ag-NPs in zwitterionic surfactants, such as 3-(nonyldimethylammonio)- or 3-(decyldimethyl-ammonio)-propyl sulfate (C9- or C10-APSO4) that self-assemble in the presence of the Ag-NPs to form microdomains akin to microemulsions (ME) without the need of any organic solvent, co-surfactant or polymer is presented. Essentially all (>99.9%) of the synthesized Ag-NPs (TEM diameter 16.8 ± 4.3 nm) were incorporated and dispersed within the ME microdomains (213.5 ± 48.0 nm). A mechanism for formation of ME and its enclosing of the Ag-NPs in the ME is proposed.

One-pot synthesis with in situ preconcentration of spherical monodispersed gold nanoparticles using thermoresponsive 3-(alkyldimethylammonio)-propyl sulfate zwitterionic surfactants.

Homogeneous solutions of thermoresponsive zwitterionic 3-(alkyldimethylammonio)-propyl sulfate surfactants at elevated temperatures were employed for the synthesis of gold nanoparticles (AuNPs) by the citrate reduction method. Upon cooling at completion of the reaction, the mixture phase separates with the monodispersed AuNPs condensed and concentrated in the small volume surfactant-rich phase.

Fluorescence method using on-line sodium cholate coacervate surfactant mediated extraction for the flow injections analysis of Rhodamine B.

An on-line surfactant mediated extraction method in a flow injection analysis format with fluorescence detection was developed for the determination of Rhodamine B (RhB) in food condiments. The sample was extracted using the phase separation behavior exhibited by the bile salt surfactant, sodium cholate (NaC), upon addition of sodium dodecylsulfate (SDS) in the presence of acid at room temperature. The RhB in the sample was incorporated into the NaC/SDS coacervate phase which was then collected on a glass-wool packed mini column from which it was subsequently eluted using a 1.00 mol L(-1) HCl solution. The inherent fluorescence (λex=555 nm; λem=575 nm) of RhB was employed for detection. Good linearity (r(2)=0.9933) was obtained over the concentration range 0.4-4794-479.0 µg L(-1) RhB. The detection (LOD) and quantification (LOQ) limits were 0.12 and 0.40 µg L(-1), respectively. The method was successfully applied for analysis of RhB in food condiments and spiked samples. The average recoveries ranged from 95.3% to 118.9% at spiked concentration levels of 1.19 and 2.39 µg L(-1). Under optimized conditions, a throughput of 50 samples per hour was achieved. The proposed method may be a valuable tool not only for quality control of food condiments and similar food confectioneries but for the analysis of a variety of other RhB-containing samples as well.

"Turn-on" fluorescent polymeric microparticle sensors for the determination of ammonia and amines in the vapor state.

Cross-linked acrylic ester microparticles (EG50OH) with absorbed fluorescent probe molecules, such as fluorescein and acridine orange were successfully fabricated and employed as "turn-on" fluorescent sensors for the detection and determination of ammonia and organic amine vapor concentrations. Using EG50OH microparticles that had fluorescein (fluorescein fluorescent microparticle, FL-FMP sensor) incorporated as the fluorescent probe molecule (with lambda(ex) = 450 nm; lambda(em) = 528 nm), the detection limit achieved for ammonia vapor was 0.73 ppm, the response being linearly dependent on concentration over the range of 1.0-250 ppm gaseous ammonia. The FL-FMP responded to organic amines with the relative signal response following the order: triethylamine > tert-butylamine > diethylamine > n-propylamine > ammonia. A limit of detection of 0.048 ppm triethylamine vapor was achieved using this FL-FMP sensor. The sensor response is based on the acid-base properties of the fluorescent probe molecules. The fluorescent probes immobilized in/on the EG50OH are in a microenvironment such that they are in their neutral or protonated states and only exhibit weak fluorescence. Upon exposure to ammonia or amine vapor, the fluorescent species are deprotonated and exhibit much greater fluorescence emission ("turned-on" due to exposure to these basic analytes). The ease of fabrication and aforementioned properties of these fluorescent microparticle sensors are such that they should be amenable for use in a variety of situations requiring the detection or monitoring of ammonia and amines in the vapor state.

Cloud point extraction with surfactant derivatization as an enrichment step prior to gas chromatographic or gas chromatography-mass spectrometric analysis.

Cloud point extraction (CPE) using Triton X-114 was successfully applied as an extractive preconcentration step prior to gas chromatographic-mass spectrometric analysis. No liquid chromatographic or back-extraction steps were required to remove the target analyte(s) from the surfactant-rich extractant phase. Instead a post-extraction derivatization step is employed in which the surfactant of the surfactant-rich phase is reacted with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) prior to injection into the gas chromatograph. Such derivatization of the Triton X-114 surfactant following CPE was found to provide improved chromatographic performance yielding a reasonable elution time window that is free of derivatized surfactant signals, reproducible analyte retention times, and quantitative results. Mixtures of polycyclic aromatic hydrocarbons (PAHs), herbicides, and profens were utilized to demonstrate the feasibility and performance of this approach. The retention times of six PAHs (acenaphthene, acenaphthylene, anthracene, biphenyl, dibenzofuran, and fluorene) were found to be very reproducible with relative standard deviations (RSDs) in the range of 0.5-0.8%. Quantitative gas chromatography-mass spectrometry (GC/MS) analysis of a herbicide test mixture (composed of alachlor, atrazine, butachlor, hexachlorocyclopentadiene, metolachlor, and simazine) following their CPE from spiked water samples yielded detection limits in the range of 6.6-97 ng/L (except for that of hexachlorocyclopentadiene which was 482 ng/L). The enrichment factors achieved for these herbicides ranged from 17 to 33. The recovery of the herbicides from spiked water samples ranged from 90 to 100% except for simazine and atrazine which were 50% and 74%, respectively. The BSFTA derivatization step can serve not only to derivatize the surfactant but also appropriate nonvolatile (or less volatile) analytes. An ibuprofen and flurbiprofen test mix was utilized to demonstrate this feature. The proposed protocol offers an attractive alternative means by which surfactant-mediated extractions can be utilized as an enrichment step prior to gas chromatographic or gas chromatographic-mass spectrometric analysis of analytes which should serve to expand the scope of CPE in gas chromatographic (GC) analysis.

Evaluation of the potential of chitosan hydrogels to extract polar organic species from nonpolar organic solvents: application to the extraction of aminopyridines from hexane.

The extraction of a series of aminopyridines (APs) utilizing chitosan hydrogels in hexane was investigated. The chitosan hydrogel was prepared using glutaraldehyde as a cross-linking agent. Experiments were carried out to determine the maximum extraction efficiency, distribution coefficient, sorption capacity, and adsorption and desorption mechanisms. The efficiency of extraction of aminopyridines attained a maximum value of ca. 100% with the distribution coefficients for the transfer of the aminopyridines from hexane to chitosan hydrogel increasing in the order of ortho-