Electrostatic Self-assembly Technology Research Articles

SERS Taper-Fiber Nanoprobe Modified by Gold Nanoparticles Wrapped with Ultrathin Alumina Film by Atomic Layer Deposition.

A taper-fiber SERS nanoprobe modified by gold nanoparticles (Au-NPs) with ultrathin alumina layers was fabricated and its ability to perform remote Raman detection was demonstrated. The taper-fiber nanoprobe (TFNP) with a nanoscale tip size under 80 nm was made by heated pulling combined with the chemical etching method. The Au-NPs were deposited on the TFNP surface with the electrostatic self-assembly technology, and then the TFNP was wrapped with ultrathin alumina layers by the atomic layer deposition (ALD) technique. The results told us that with the increasing thickness of the alumina film, the Raman signals decreased. With approximately 1 nm alumina film, the remote detection limit for R6G aqueous solution reached 10−6 mol/L.

Label-free fiber optic biosensor based on thin-core modal interferometer

A label-free, cost-effective fiber optic biosensor (FOB) using electrostatic self-assembly (ESA) technology is presented and experimentally demonstrated. The FOB was constructed by sandwiching a thin-core single-mode fiber (TCSMF) between two single-mode fibers (SMFs). Firstly, we simulated the refractive index (RI) sensitivity of this fiber structure, and validated it using different concentrations of glycerol solutions. Then the diallyldimethyl ammonium chloride (PDDA) and styrenesulfonate sodium salt (PSS) were employed as polyelectrolyte self-assembled multilayers (PSAMs) deposition for surface functionalization of the fiber. We selected biotin–streptavidin as a bioconjugate pair for testing the effectiveness of the biosensor, and achieved a streptavidin detection limit of 0.02nM. The specificity was further verified by a comparison experiment conducted using bovine serum albumin (BSA) and gelatin. These results demonstrate the feasibility of this sensor for use in biological and chemical applications.

A sensitive and low toxicity electrochemical sensor for 2,4-dichlorophenol based on the nanocomposite of carbon dots, hexadecyltrimethyl ammonium bromide and chitosan

A novel and sensitive electrochemical sensor for 2,4-dichlorophenol (2,4-DCP) based on a nanocomposite of carbon dots (CDs), hexadecyltrimethyl ammonium bromide (CTAB) and chitosan (CS) was constructed through electrostatic self-assembly technology. The nanocomposite of CDs–CTAB–CS introduced a favorable access for the electron transfer and exhibited excellent electrocatalytic activity toward the oxidation of 2,4-DCP. Differential pulse voltammetry (DPV) was used for the quantitative determination of 2,4-DCP. Under the optimized experimental conditions, the oxidation peak currents of 2,4-DCP were proportional to its concentrations in the range from 0.04 to 8.0μmolL−1 with a detection limit as 0.01μmolL−1. The newly developed method was successfully applied for the determination of 2,4-DCP in waste water with satisfactory recoveries. This CDs–CTAB–CS modified electrochemical sensor provides an operational access to design simpler, low toxicity and environment-friendly sensors based on carbon dots.

Fabrication of hierarchical structured Fe3O4 and Ag nanoparticles dual-coated silk fibers through electrostatic self-assembly

In the present work, special hierarchical structured Fe3O4 nanoparticles (Fe3O4NPs)/Ag nanoparticles (AgNPs) dual-coated silk fibers have been prepared via a simple electrostatic self-assembly technology. Silk fibers were sequentially immersed in solutions of positively charged AgNPs and negatively charged Fe3O4NPs. As-prepared hierarchical structured silk fibers were characterized by XRD, FESEM, and VSM. XRD and SEM characterizations demonstrated that silk fibers were hierarchically and uniformly coated by high dense AgNPs and Fe3O4NPs. VSM analysis indicated that the as-prepared ternary composite fibers showed excellent magnetic property.

Remote detection of the surface-enhanced Raman spectrum with the optical fiber nanoprobe

Optical fiber nanoprobe with gold nanoparticles substrate on the surface was prepared by electrostatic self-assembly technology. Surface-enhanced Raman spectrum of the cells was measured using the optical fiber nanoprobe by remote detection method and direct detection method using confocal Raman micro-spectroscopy. The spectrum were analyzed with the detailed chemical components. The remote detection method using the optical fiber nanoprobe could make the probe inserting into the cells or tissue, and that may be helpful for the online SERS measurement of the cells in the biomedical research and diagnosis in the future.

Gold Nanoparticles-Modified Tapered Fiber Nanoprobe for Remote SERS Detection

This letter presents a surface-enhanced Raman scattering (SERS) nanoprobe based on gold nanoparticles-modified tapered optical fiber and demonstrates its ability to perform remote Raman detection. The nanoscale tapered fiber with the tip size of 40.7 nm was made by heated pulling and chemical etching methods. The gold nanoparticles, prepared beforehand by the Frens method with a microwave heating process, were deposited on the tapered surface of the nanoprobe with the electrostatic self-assembly technology. Raman spectra of Rhodamine 6G (R6G) molecules were measured, using this SERS nanoprobe in an optrode remote detection mode. Considerably high signal-to-noise ratio and high sensitivity were achieved. The detection limit for R6G aqueous solution reaches 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> mol/L.

Structural Characterization, Adsorption and Dispersion Properties of Sodium Lignosulfonate by Horseradish Peroxidase Incubation†

A novel and efficient polymerization of lignosulofonate(by-products from sulfite pulping process) was investigated in the present study. The ability of commercial horseradish peroxidase(HRP) for polymerizing sodium lignosulfonate(SL) was investigated in aqueous solution at room temperature. The gel permeation chromatography(GPC),potentiometric titration,infrared spectroscopy(IR),and1H nuclear magnetic resonance(1H NMR) were used the structural characterization of SL. GPC results showed a significant increase in molecular weight(Mw) of SL. With different dosages of HRP added,SLs with different Mwcould be obtained. When 6 g/L HRP was added,the Mwof SL could increase by 155%. During the HRP incubation,phenolic groups were oxidized to phenoxyl radicals. These radicals could undergo radical-couplings directly. On the other hand,unbound electron could transfer to the para- and ortho-carbon of the phenols and β-carbon of the branch,undergoing radical-couplings. Among the radical-couplings,β-O-4' and β-β' were the predominant. Moreover,the sulfonic group increased by 27% after HRP incubation. The adsorption of SL by HRP incubation was studied by electrostatic self-assembly technology. After HRP incubation,the adsorption amount of SL increased significantly. Further,because of the increase of Mwand sulfonic group content,resulting in the stronger steric hindrance and electronic repulsion,the dispersion ability of SL on TiO2slurry was improved.

A sensitive electrochemical chlorophenols sensor based on nanocomposite of ZnSe quantum dots and cetyltrimethylammonium bromide

In this work, a very sensitive and simple electrochemical sensor for chlorophenols (CPs) based on a nanocomposite of cetyltrimethylammonium bromide (CTAB) and ZnSe quantum dots (ZnSe–CTAB) through electrostatic self-assembly technology was built for the first time. The composite of ZnSe–CTAB introduced a favorable access for the electron transfer and gave superior electrocatalytic activity for the oxidation of CPs than ZnSe QDs and CTAB alone. Differential pulse voltammetry (DPV) was used for the quantitative determination of the CPs including 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP). Under the optimum conditions, the peak currents of the CPs were proportional to their concentrations in the range from 0.02 to 10.0μM for 2-CP, 0.006 to 9.0μM for 2,4-DCP, and 0.06 to 8.0 for PCP. The detection limits were 0.008μM for 2-CP, 0.002μM for 2,4-DCP, and 0.01μM for PCP, respectively. The method was successfully applied for the determination of CPs in waste water with satisfactory recoveries. This ZnSe–CTAB electrode system provides operational access to design environment-friendly CPs sensors.

The Influence of Laccase Modification on the Adsorption of Lignosulfonate

The ability of commercial laccase to improve the adsorption of sodium lignosulfonate (SL) without any mediator was studied. When SL are modified by laccase, gel permeation chromatography (GPC) shows an initial decrease followed by an extensive increase in molecular weight (Mw). Furthermore, the decrease in Mw is accompanied by an increase in phenolic hydroxyl groups, while the increase in Mw is accompanied by the decrease in phenolic hydroxyl groups. The laccase modification does not affect the content of the sulfonic group. Furthermore, the electrostatic self-assembly technology indicates that the adsorbed amount and the root-mean-square (RMS) of SL/PDAC multilayers increase obviously with the increase of the incubation time, which might be due to the influence of the Mw and the adsorption configuration.

A linear molecule functionalized multi-walled carbon nanotubes with well dispersed PtRu nanoparticles for ethanol electro-oxidation

The performance-enhanced PtRu electrocatalysts derived from polyoxyethylene bis(amine) functionalized multi-walled carbon nanotubes (POB-MWCNTs) were fabricated by electrostatic self-assembly technology, in which Pt and Ru precursors were first uniformly distributed on the POB-functionalized MWCNT surface via the electrostatic interaction and then reduced in situ to PtRu nanoparticles in ethylene glycol-water solution. In this process, POB as the wrapping molecule not only preserves the integrity and well dispersion of MWCNTs, but also facilitates the even distribution of PtRu nanoparticles on the surface of MWCNTs. The structure and catalytic properties of the PtRu catalysts were characterized by various spectroscopic techniques such as FT-IR, Raman, TGA, XPS, TEM and XRD spectrometry, and the electrocatalytic properties for ethanol oxidation were investigated by cyclic voltammetry and chronoamperometry. It was revealed that the as-prepared PtRu catalysts possess a high electrocatalytic activity and stability for the electro-oxidation of ethanol, and it provides a facile and eco-friend approach to large-scale production of high performance fuel cell eletrocatalysts.

Preparation of the Layer-by-Layer Deposited Silver Nanoparticles Multilayer Films on Poly(ethylene Terephalate) Substrate

This research presented the preparation of multilayer films on poly(ethylene terephalate) (PET) Substrate by electrostatic self-assembly technology. The silver nanoparticles were characterized by UV–vis spectrometry and scanning electron microscopy (SEM). The sequential dipping of hydrolyzed PET substrate in dilute solutions of poly(diallyldimethyl ammonium chloride)(PDDA) and silver nanoparticles to fabricate multilayer films. The multilayer films were monitored by UV–vis spectrometry, the surface plasmon resonance (SPR) obtained at 420 nm confirmed the existence of nanosilver on the PET film. The silver nanoparticles were also verified by the Inductively Coupled Plasma Spectrometry (ICP) and thermogravimetric analysis of the multilayer film. The transmission spectra indicated that the PET films contained silver nanoparticles have better UV protection property.

Self-assembly of Pt nanoparticles on highly graphitized carbon nanotubes as an excellent oxygen-reduction catalyst

Platinum nanoparticles/graphitic carbon nanotubes (GCNTs) nanocomposites are fabricated with electrostatic self-assembly technology. Pt precursors are uniformly distributed on poly(diallyldimethylammonium chloride)-functionalized GCNTs surface (PDDA-GCNTs) via the electrostatic interaction and then in situ reduced to Pt nanoparticles in ethylene glycol, where PDDA is not only used as the wrapping polymer for GCNTs to preserve the integrity and the electronic structure of GCNTs, but also facilitates the uniform distribution of Pt nanoparticles on the surface of GCNTs. X-ray diffraction patterns and transmission electron microscope images reveal that Pt nanoparticles with an average size of ∼2.7nm are uniformly dispersed on highly graphitized GCNTs. Significant enhancement in the electrocatalytic activity on Pt/PDDA-GCNTs catalyst towards oxygen reduction reaction (ORR) has been demonstrated. In addition, this catalyst also shows enhanced electrochemical durability due to the high graphitization degree of GCNTs. This provides a facile and eco-friendly approach to large-scale production of high performance fuel cell eletrocatalysts.

The interaction of a novel ruthenium (II) complex with self-assembled DNA film on silicon surface

Calf thymus DNA (ct-DNA) films were immobilized onto patterned silicon wafers through electrostatic self-assembly technology and interacted with a novel dinuclear ruthenium (II) complex, [(bpy) 2 Ru(H 2 bpi)Ru(bpy) 2 ](ClO 4 ) 4 , which were demonstrated by using a confocal optical microscope. The morphology of the DNA film was measured by atomic force microscopy and the results show that the DNA strands have been folded into coiled conformations and aggregated into circles with diameters between 18 and 55 nm. The interaction process was also monitored by UV-visible and fluorescence spectra and investigated by X-ray photoelectron spectra. The results show that the Ru (II) complex interacts with ct-DNA by the intercalative mode as it behaves in aqueous solutions.

Self-assembly of small molecules: An approach combining electrostatic self-assembly technology with host–guest chemistry

A fluorescence probe study, surface tension and dye solubilization tests indicate that the water-soluble calixarene, 5,11,17,23,29,35,41,47-octosulfonato-49,50,51,52,53,54,55,56-octododecyloxycalix[8]arene (18-C12) acts as a “unimolecular” micelle in water. By forming guest–host-type complexes with 18-C12, lipophilic dyes, such as methyl yellow (MY), p-hydroxyazobenzene (HAB) and 1-(p-phenylazophenylazo)-2-naphthol (Sudan III), dissolve in aqueous solution. By dipping a charged substrate in the 18-C12–dye solution and a cationic polyelectrolyte solution alternately, these small molecular dyes were successfully self-assembled into multilayer films.