Cetyltrimethylammonium Bromide Layer Research Articles

Label-free, liquid crystal-based aptasensor for detecting carbendazim at picomolar levels

We describe a simple and sensitive liquid–crystal (LC)-based method for quantifying carbendazim (CBZ) by exploiting aptamer-specific recognition at the aqueous-LC interface. The method relies on the interfacial interaction between an aptamer and cetyltrimethylammonium bromide (CTAB); this interaction varies depending on the amount of CBZ. In the absence of CBZ, the aptamer disrupts the CTAB monolayer through electrostatic attraction, leading to a transition from homeotropic to tilted ordering of the LCs. As CBZ concentrations rise, the formation of aptamer-CBZ complexes increases, preserving the vertical alignment of the LCs by reducing collapse of the CTAB layer caused by electrostatic interactions. Using these methods, we achieved a CBZ detection limit of 3.12 pM (0.000597 μg/L) over a linear range of 0.05–5 nM. Moreover, we quantified CBZ levels in peach, soil, and tap water samples. Our LC-based detection method has significant research potential, offering sensitive, and straightforward detection of CBZ.

Hybrid magnetic CoFe2O4@γ-Fe2O3@CTAB nanocomposites as efficient and reusable adsorbents for Remazol Brilliant Blue R dye

ABSTRACT The main goal of the present survey was to elaborate, characterize and evaluate the efficiency of ferrite-based nanoparticles modified with cetyltrimethylammonium bromide (CTAB) as potential magnetic nanoadsorbents to remove Remazol Brilliant Blue R (RBBR) from water. It is proposed an innovative nanomaterial architecture based on highly magnetic and chemically stable core@shell nanoparticles covered by an adsorptive surface layer of CTAB (CoFe2O4@γ-Fe2O3@CTAB). Samples of two different mean sizes (7.5 and 14.6 nm) were synthesized using a hydrothermal coprecipitation followed by surface treatment and functionalization. Batch tests were performed to evaluate the influence of contact time, temperature, pH, shaking rate, presence of interferents and mean size on the performance of the proposed nanomaterials. The kinetics of the adsorption process followed the pseudo-second-order model with an equilibrium time of 20 min. The adsorption capacity was estimated by the Langmuir isotherm model and was found to be 56.3 mg/g (smaller size) and 45.6 mg/g (larger size) at pH = 3 and a shaking rate of 400 rpm. The process was spontaneous, exothermic, and showed increased randomness. Sulphate ions negatively impacted the removal of RBBR. The best performance of the nanoadsorbent based on smaller mean sizes can be correlated to its larger surface area. Regeneration and readsorption tests showed that the nanoadsorbents retain more than 80% of their original removal capacity, therefore they can be effectively recycled and reused.

Modelling aggregates of cetyltrimethylammonium bromide on gold surfaces using dissipative particle dynamics simulations

ABSTRACT In this study, we developed a coarse-grained model based on the dissipative particle dynamics (DPD) method to investigate the aggregates of the cetyltrimethylammonium bromide (CTAB) molecules on gold surfaces including nanoparticles. We adopted the DPD model for CTAB solutions developed by Mao et al. [Modeling aggregation of ionic surfactants using a smeared charge approximation in dissipative particle dynamics simulations. J Phys Chem B. 2015;119:11673–11683] and introduced an attractive interaction between gold (Au) particles and bromide (Br) ions (i.e. Au-Br attraction) to bind CTAB molecules onto the gold surface via the electrostatic interactions between their cationic head groups and Br ions adsorbed on the gold surface. The proposed model with a proper Au-Br attraction can semi-quantitatively describe the structures of CTAB aggregates on a flat gold surface and around gold nanorods (AuNRs). As the Au-Br attraction and the CTAB concentration increase, the CTAB aggregates on the gold surface can change from micelles to a compact bilayer structure. In particular, our model predicts that in the CTAB layer, the inner sub-layer may have a higher ligand density than the outer sub-layer. The anisotropic distribution of CTAB molecules around AuNRs is also captured in our model.

Dynamics of Competitive Adsorption of Lipase and Ionic Surfactants at the Water-Air Interface.

Lipase is one of the most important enzymes playing a key role in many biological and chemical processes, in particular for fat hydrolysis in living systems and technological applications such as food production, medicine, and biodiesel production. As lipase is soluble in water, the major hydrolysis process occurs at the water-oil interface, where lipase can get in contact with the oil. To provide optimum conditions, the emulsification of the oil is essential to provide a large interfacial area which is generally done by adding surfactants. However, the presence of surfactants can influence the lipase activity and also cause competitive adsorption, resulting in a removal of lipase from the interface or its conformational changes in the solution bulk. Here we have studied the dynamics of competitive adsorption and interfacial elasticity of mixed solutions containing lipase and the anionic surfactant sodium dodecyl sulfate (SDS) or the cationic surfactant cetyltrimethylammonium bromide (CTAB), respectively, at the water-air interface. The experiments were performed with a special coaxial double capillary setup for drop bulk-interface exchange developed for the drop profile analysis tensiometer PAT with two protocols: sequential and simultaneous adsorption of single components and mixed systems. The results in terms of dynamic surface tension and dilational viscoelasticity illustrate fast and complete desorption of a preadsorbed CTAB and SDS layers via subphase exchange with a buffer solution. In contrast, the preadsorbed lipase layer cannot be removed either by SDS or CTAB from the interface during drop bulk exchange with a buffer solution due to the unfolding process and conformation evolution of the protein molecules at the interface. In the opposite case, lipase can remove preadsorbed SDS and CTAB. The dynamic surface tension and viscoelasticity data measured before and after subphase exchange show joint adsorption of lipase and CTAB in the form of complexes, while SDS is adsorbed in competition with lipase. The results are in good correlation with the determined surface charges of the lipase gained by computational simulations which show a dominant negatively charged surface for lipase that can interact with the cationic CTAB while partial positively charged regions are observed for the interaction with the anionic SDS.

Colloidal stability of nanoparticles stabilized with mixed ligands in solvents with varying polarity.

Colloidal stability of nanoparticles (NPs) strongly influences their synthesis, processing, and applications. For gold NPs stabilized with cetyl trimethylammonium bromide (CTAB) and polymer ligands we show that gradual increase in polarity of the water/aprotic solvent mixture leads to stabilization-aggregation-stabilization-aggregation transitions. We propose that these transitions are mediated by structural rearrangements of the CTAB layer on the NP surface.

Influence of the CTAB surfactant layer on optical properties of single metallic nanospheres.

We evaluate experimentally and theoretically the role of the residual ligands and ambient environment refractive index in the optical response of a single spherical gold nanoparticle on a substrate and demonstrate the changes in the near- and far-field properties of its hybridized modes in the presence of the cetyltrimethylammonium bromide (CTAB) layer. Particularly, we show that the conventional bilayer scheme for CTAB is not relevant for colloidal nanoparticles deposited on a substrate. We show that this CTAB layer considerably changes the amplitude and localization of the confinement of the electric field, which is of prime importance in the design of plasmonic complex systems coupled to emitters. Moreover, we numerically study the influence of the CTAB layer on the modification of sensitivity of plasmonic resonances of a gold nanopshere to local refractive index changes.

Self-assembly and wetting properties of gold nanorod-CTAB molecules on HOPG.

The formation of self-assembled superstructures of cetyltrimethylammonium bromide (CTAB) after drying on a nonwetting highly ordered pyrolytic graphite (HOPG) surface have been investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Although SEM did not reveal coverage of CTAB layers, AFM showed not only CTAB assembly, but also the dynamics of the process on the surface. The self-assembled layers of CTAB molecules on the HOPG terraces prior to nanorod deposition were shown to change the wettability of the surface, and as a result, gold nanorod deposition takes place on nonwetting HOPG terraces.

Self-Assembly of Cetyltrimethylammonium Bromide and Lamellar Zeolite Precursor for the Preparation of Hierarchical MWW Zeolite

Construction of hierarchical zeolite catalysts from lamellar zeolite precursor is challenging and promising for industrial catalysis. Although numerous efforts have been dedicated to control the organization of zeolite nanosheets by postsynthetic approaches or employing complex surfactants in hydrothermal synthesis, there is still no successful case that the hierarchical lamellar zeolite is hydrothermally synthesized by the self-assembly of the commercially available simple surfactant cetyltrimethylammonium bromide (CTAB) and inorganic zeolite precursor. In traditional syntheses, the self-assembly of simple surfactants and the growth of microporous framework are hardly compatible from both thermodynamic and kinetic viewpoints, preferring to cause phase separation. Herein, we approach for the first time the hydrothermal synthesis of a mesostructured multilamellar zeolite ECNU-7P, consisting of an alternative stacking of inorganic MWW zeolite nanosheets and organic CTAB layers with large interlayer spacing ...

Structure and Interaction of Graphene Oxide– Cetyltrimethylammonium Bromide Complexation

Complexation of graphene oxide (GO) and cetyltrimethylammonium bromide (CTAB), a model amphiphile, was quantitatively studied to elucidate the governing forces and resulting structures of their self-assembly. We systematically varied pertinent self-assembly parameters, including GO size, mixing ratio, salt, and osmotic stress, and quantified the nanoscale structures of GO:CTAB using X-ray diffraction. Multilamellar stacking of GO and CTAB layers persists in all GO:CTAB assemblies exhibiting structural order. While driven by hydrophobic interactions between the hydrocarbon tails, the CTAB layer displays a series of structural transitions from a bilayer with in-plane ordering to a more fluidic bilayer and to an interdigitated monolayer. Interaction between GO and CTAB layers shows domination by electrostatics, and osmotic stress studies indicate the absence of continuous hydration layers in GO:CTAB assemblies. Adding salt increases the interlayer spacing by intercalating between GO and CTAB layers, and this...

A cleaning method with centrifugation for removing surfactants from gold nanoparticles and its mechanism

We developed an effective cleaning method based on a centrifugal effect to remove the surfactant cetyltrimethylammonium bromide (CTAB) from the surfaces of noble metallic such as 50 nm gold nano-octahedrons. The cleaned surface can be obtained by choosing the proper centrifugal speed and times under the appropriate temperature and humidity conditions. Thermal gravimetric analysis (TGA), surface-enhanced Raman scattering (SERS) and Fourier transform infrared spectroscopy (FTIR) are conducted to systematically investigate the adsorbed CTAB layer structure on gold nano-octahedrons surface. The results indicate that CTAB molecules bind to gold surface via their long hydrophobic tail and form a (sub) monolayer on the gold surface, and the bromide ions chemisorbed at the gold surface are desorbed. The dilution effect of water can act on the transformation of CTAB on gold surface during the cleaning procedure. Additionally, a localized solution flow is induced by the polarization of the electrical double layer gold nanoparticle with high speed in a centrifugal field. Mass transfer around the gold nanoparticle is occurring, and thus to be the influences on the surface cleaning of gold nanoparticles. We also performed the cyclic voltammetry (CV) studies in 0.5 mol/L sulfuric acid solution and alkaline solution contained with 0.1 mol/L NaOH + 1.0 m mol/L Pb(NO3)2, used the gold nano-octahedrons film as electrode. The results suggest that, after the cleaning procedures with centrifugation, the surface of gold nano-octahedrons can be purified enough to be used for electrochemical studies instead of traditional gold (111) facets.

Synthesis of stable ultra-small Cu nanoparticles for direct writing flexible electronics

In this study, pure Cu nanoparticles (NPs) have been successfully synthesized and the Cu nano-ink was prepared for direct writing on photo paper using a roller pen. The tri-sodium citrate was used as initial reducing-cum-surfactant agent followed by hydrazine as a second massive reducing agent and cetyltrimethylammonium bromide (CTAB) as extra surfactant agent. From the XRD, TEM, and HR-TEM analyses, the synthesized particles are confirmed to be Cu in spherical shape with sizes range of 2.5±1.0nm. By analyzing the FT-IR spectroscopy and TGA curves, it was found that the obtained particles capped with tri-sodium citrate and CTAB layers are stable to oxidation up to the temperature 228°C. The reduced size and enhanced air-stability of the Cu NPs result in an improved particle density upon sintering, which is mainly responsible for the increased conductivity of the Cu patterns. The resistivity of Cu patterns sintered in Ar at 160°C for 2h is 7.2±0.6μΩcm, which is 4.40 times the bulk Cu resistivity. The drawn Cu lines exhibited excellent integrity and good conductivity, which were experimentally tested. Moreover, a Cu electrode and a sample RFID antenna were successfully made.

Effects of successive additions of two capping ligands on the structural properties of PbO nanoparticles

A cost-effective approach to the synthesis of lead oxide (PbO) nanoparticles by successive additions of two capping ligands using a simple method of precipitation is reported herein. The successive additions of polyvinyl pyrrolidone (PVP) and cetyltrimethyl ammonium bromide (CTAB) cap the Pb(OH)2 with a primary layer of PVP and a secondary layer of CTAB, forming a bilayer system around Pb(OH)2. PVP controls the PbO particle size, while CTAB enhances the particle size of the PVP-treated PbO by seeding growth process. The effects of the successive additions of these two capping ligands were studied by varying the relative percentages of PVP and CTAB from 0 to 100 %. From transmission electron microscopy and X-ray diffraction results, it was confirmed that the size of the PbO nanoparticles decreased with a relative increase in the percentage of PVP (and corresponding decrease in the percentage of CTAB). Furthermore, X-ray diffraction results demonstrated the formation of a pure α-PbO phase. Field emission scanning electron microscopy images showed the increase in grain size with the decrease in the percentage of PVP. Infrared spectroscopy depicted the formation of PbO along with the presence of PVP and CTAB covering the particle surface. Thermogravimetric analysis and differential thermal analysis revealed the decomposition of lead oxalate to α-PbO at around 370 °C.

A Nanodiagnostic Colorimetric Assay for 18S rRNA of Leishmania Pathogens using Nucleic Acid Sequence-Based Amplification and Gold Nanorods

We describe here a nanodiagnostic colorimetric assay for 18S rRNA of Leishmania pathogens that uses nucleic acid sequence-based amplification (NASBA) and gold nanorods (GNRs). NASBA primers targeting 18S rRNA were used for amplification of RNA in an isothermal process. The electrostatic interactions between the phosphate groups of the RNA amplicons and the cetyl trimethylammonium bromide layer on the GNRs resulting in their aggregation. This phenomenon changes the color of the GNR solution from red to purple. Our data showed 100% sensitivity and 80% specificity with the colorimetric assay compared with results using reverse transcription polymerase chain reaction. The nanodiagnostic method we describe simplifies the detection of NASBA amplicons without the need for gel electrophoresis.

Time Dependence of Interactions between a Surfactant-Coated Substrate and a Uniformly Charged Surface

Using the surface force balance (SFB), we recorded the changes with time of the adhesion, normal, and shear interactions between a monolayer of cetyltrimethylammonium bromide (CTAB) on mica and a bare mica surface across surfactant-free water. In this asymmetric case, the bare mica acts a stable probe of the interactions between the two surfaces as the CTAB-coated one undergoes changes with time. As previously demonstrated, when a CTAB monolayer on mica is immersed in water, it reorganized to form bilayer patches, exposing the bare mica surface, followed by a gradual release of free surfactants to the bulk. We probe how this degradation with time affects both the normal force vs distance interaction profiles, and adhesion between the CTAB-coated surface and a bare mica surface. We demonstrate that the CTAB layer leads to a reduction in the sliding friction relative to that between bare mica surfaces, which is reversed only at advanced degradation levels, whereupon an abrupt increase in the friction occurs. This change is ascribed to adhesion between exposed bare mica surfaces, which sets on when the density of CTAB patches is low. The reproducibility of the normal force profiles and of adhesion forces on sequential approaches at the same contact spot indicates that there is no substantial transfer of materials between the surfaces while they are in adhesive contact.

Gold Nanorods Performing as Dual-Modal Nanoprobes via Metal-Enhanced Fluorescence (MEF) and Surface-Enhanced Raman Scattering (SERS)

The integration of metal-enhanced fluorescence (MEF) and surface-enhanced Raman scattering (SERS) onto single plasmonic nanoparticles is highly desirable to boost up accuracy and sensitivity in spectroscopic investigations. In this work, we demonstrate the feasibility of performing both MEF and SERS analysis on gold nanorods (GNRs) decorated with a unique molecular probe, here Rose Bengal (RB) fluorophore. While the cetyltrimethylammonium bromide layer on GNRs captures RB molecules preventing fluorescence quenching, the selective excitation of the two surface plasmon resonances of GNRs can trigger either the enhancement of fluorescence emission or Raman scattering. Both fluorescence enhancement mechanisms, i.e. increase of excitation rate and increase of quantum efficiency, promote an average 2.2-fold enhancement. For excitation with 785 nm laser line an average SERS enhancement of 1.7 × 105 is estimated and compared with the electromagnetic enhancement provided by finite-difference time-domain (FDTD) simulations. An extended dual-modal response of RB–GNRs conjugate is demonstrated by resonant excitation of both RB and GNRs with 532 nm laser line, which allows the surface-enhanced resonance Raman scattering (SERRS) and MEF signals to be detected simultaneously. The reporting abilities in SERS are demonstrated by conveying the Raman fingerprints of two molecular species concomitantly adsorbed on the surface of GNRs.

Ethanol-Induced Formation of Silver Nanoparticle Aggregates for Highly Active SERS Substrates and Application in DNA Detection

A controllable silver nanoparticle aggregate system has been synthesized by adding different amounts of ethanol to cetyltrimethylammonium bromide (CTAB) capped silver nanoparticles (Ag-nps), which could be used as highly efficient surface-enhanced Raman scattering (SERS) active substrates. This ethanol-induced aggregation can be attributed to preferential dissolution of CTAB into ethanol, which leads a partial removal of the protective CTAB layer on Ag-nps. The optical and morphological properties of these aggregates under various volumes of ethanol were explored via UV−vis spectroscopy and atomic force microscopy. Two common probe molecules, Rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) were used for testing the SERS activity on these substrates at very low concentrations. It was found that the SERS enhancement ability is dependent on the ethanol volume used. The SERS enhancement factors of 4-ATP were estimated to be as large as 8.1 × 108 for b2 vibration modes and 6.8 × 106 for a1 vibration modes. Good stability of the substrates was demonstrated by measuring the Raman activity with time. The optimized SERS-active substrate with the largest enhancement ability shown in this study could be used to detect double-strand DNA. The great advantage for this SERS-based DNA detection is that a dye label is not needed. It showed the potential of this Ag-nps aggregate system as a convenient and powerful SERS-active substrate for DNA detection.

Adsolubilization of dihydroxybenzenes into CTAB layers on silica particles

The adsolubilization of dihydroxybenzenes (catechol and hydroquinone) into cetyltrimethylammonium bromide (CTAB) layers on silica particles have been investigated by dye method and UV spectrum. It is found that the adsolubilization amount of catechol increases with increasing the concentration of CTAB, reaches a maximum value at the critical micelle concentration (CMC), and then decreases with further increment of CTAB concentration. For hydroquinone, different phenomenon is observed. The maximum adsolubilization amount reaches at critical surface aggregation concentration (CSAC) instead of CMC of the CTAB and then decreases to constant values. In order to analyze the adsolubilization difference between catechol and hydroquinone, we determined the interaction between them and CTAB in the bulk solution by measuring the diffusion coefficient of dihydroxybenzenes with ultramicroelectrode (UME). The individual contributions to the overall apparent diffusion coefficient of dihydroxybenzenes in CTAB solutions were also calculated. The results indicate that more hydroquinone than catechol could interact with CTAB molecules. However, rarely hydroquinone could interact with CTAB micelles compared with catechol. It is suggested that the substitution positions of hydroxyl lead to the difference of the interaction between dihydroxybenzenes and CTAB, which is responsible for the difference of the adsolubilization.

Influence of cetyltrimethylammonium bromide aqueous solutions on the surface strength of quartz glass under conditions of pH variation

A mechanism of the combined influence of solutions of electrolytes with various pHs (in 10−3 N KCl solution) and cetyltrimethylammonium bromide (CTAB) cationic surfactant on the surface strength of quartz glass in a mechanical contact is studied. A similar cation-active medium is shown to embrittle quartz glass in neutral and alkaline pH ranges. The brittle strength of a near-surface layer of a material decreases owing to adsorption and electrocapillary reduction of its surface energy. The surface strength of the glass decreases to the largest extent at the CTAB critical micellization concentration. At low concentrations (10−6M), a protective effect of forming chemisorbed CTAB layers prevails that is manifested in the hydrophobization of the surface of quartz glass by CTAB molecules and its screening from direct contact with an electrolyte solution. At the CTAB concentrations that are higher than the CMC, a formed micellar structure of CTAB has a lubricating effect, leading to softer boundary conditions of a frictional contact and a decreased probability of the damage of the near-surface layer of quartz glass. In acidic electrolyte solutions, CTAB cations or molecules did not affect the surface strength of quartz glass.

Capping effect of CTAB on positively charged Ag nanoparticles

A facial synthesis process of silver nanoparticles (NPs) capped by cetyltrimethylammonium bromide (CTAB) is reported with exploration for the capping effect of CTAB on particles’ stability and surface properties in aqueous medium. Multidisciplinary approaches including electrophoresis, UV-visible absorption spectroscopy, Fourier-transformed infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA) and small angle X-ray scattering (SAXS) are conducted to systematically investigate surface charge and the adsorbed CTAB layer structure on Ag clusters. Obtained results indicate that CTAB molecules bind strongly to silver surface via their headgroups and form a bilayer shell. Detailed analysis of SAXS and NMR data and discussion on the interaction between CTAB molecules and NPs’ surface, provide a clearer model of capped molecules on Ag clusters.

Templated Surfactant Readsorption on Polyelectrolyte-Induced Depleted Surfactant Surfaces

Changes in the structure of a surfactant adsorbed on oxidized silicon arising from interaction with a polyelectrolyte have been studied using polarized infrared attenuated total reflection spectroscopy. Specifically, the cationic surfactant cetyltrimethylammonium bromide (CTAB) was found to form a highly ordered layer on oxidized silicon at a concentration of 5.5 x 10(-5) M and a pH of 9.6. Addition of a solution of the anionic polyelectrolyte poly(styrenesulfonate) to the ordered CTAB layer resulted in a rapid and dramatic decrease in the surface excess of CTAB. Interestingly however, the interfacial order of the residual surfactant was retained for a time period greater than 1 h, before decreasing. Reintroduction of a surfactant solution prior to destabilization of the residual interfacial CTAB resulted in the readsorption of the surfactant, the recovery of the initial equilibrium coverage, and the maintenance of an ordered CTAB conformation. This desorption/readsorption process may be subsequently repeated without destroying the order of the CTAB on the surface. If however sufficient time is allowed for the residual interfacial surfactant to destabilize prior to readdition of CTAB, the degree of surfactant order remains low, despite the rapid reobtainment of a surface excess equal to or greater than that initially measured. These results are interpreted in terms of polymer/surfactant interfacial complexation and the removal of adsorbed surfactant into solution. The ordering behavior of the residual surfactant suggests that CTAB is left on the surface in isolated patches of highly ordered species that maintain their order until two-dimensional diffusion leads to a more homogeneous surfactant surface distribution and hence the loss of conformational order. The degree of orientation order assumed by surfactant readsorbing on a depleted surface appears to be templated by the order of the residual interfacial surfactant, suggestive of a two-dimensional epitaxial growth mechanism for CTAB readsorption.