Chiral ionic liquid monolayer-stabilized gold nanoparticles: synthesis, self-assembly, and application to SERS

Biomass-assisted fabrication of rGO-AuNPs as surface-enhanced Raman scattering substrates for in-situ monitoring methylene blue degradation

Reduced graphene oxide-gold nanoparticles nanocomposites (rGO-AuNPs) with high surface-enhanced Raman scattering (SERS) activity was created by biomass-assisted green synthesis with Lilium casa blanca petals biomass for the first time, and its application for methylene blue (MB) degradation was explored through in-situ monitoring. Lilium casa blanca petals biomass was used as a reducing agent to reduce GO and chloroauric acid successively when carrying out rGO-AuNPs in-situ synthesis while it also acted as a capping agent. The produced rGO had oxygen-containing functional groups which had an outstanding performance in enhancing the SERS effect. Characterization results confirmed that the AuNPs were grafted onto the rGO sheet, and the mechanism study showed that total flavonoids in Lilium casa blanca petals biomass were the main biological compounds involved in the reduction. rGO-AuNPs had a high Raman enhancement factor (EF) which could reach 3.88 × 10⁷. The synthesized nanocomposite also had a good catalytic activity that could be employed as catalyst in MB degradation, and it could complete degradation within 15min. The reaction rate increased linearly with the amount of rGO-AuNPs, and the degradation could be in-situ monitored both by UV and SERS.

Hydrated Ionic Liquids Boost the Trace Detection Capacity of Proteins on TiO2 Support

Trace detection based on surface-enhanced Raman scattering (SERS) has attracted considerable attention, and exploiting efficient strategies to stretch the limit of detection and understanding the mechanisms on molecular level are of utmost importance. In this work, we use ionic liquids (ILs) as trace additives in a protein-TiO2 system, allowing us to obtain an exceptionally low limit of detection down to 10-9 M. The enhancement factors (EFs) were determined to 2.30 × 104, 6.17 × 104, and 1.19 × 105, for the three systems: one without ILs, one with ILs in solutions, and one with ILs immobilized on the TiO2 substrate, respectively, corresponding to the molecular forces of 1.65, 1.32, and 1.16 nN quantified by the atomic force microscopy. The dissociation and following hydration of ILs, occurring in the SERS system, weakened the molecular forces but instead improved the electron transfer ability of ILs, which is the major contribution for the observed excellent detection. The weaker diffusion of the hydrated IL ions immobilized on the TiO2 substrate did provide a considerably greater EF value, compared to the ILs in the solution. This work clearly demonstrates the importance of the hydration of ions, causing an improved electron transfer ability of ILs and leading to an exceptional SERS performance in the field of trace detection. Our results should stimulate further development to use ILs in SERS and related applications in bioanalysis, medical diagnosis, and environmental science.

Insights in the Diffusion Controlled Interfacial Flow Synthesis of Au Nanostructures in a Microfluidic System

Continuous segmented flow interfacial synthesis of Au nanostructures is demonstrated in a microchannel reactor. This study brings new insights into the growth of nanostructures at continuous interfaces. The size as well as the shape of the nanostructures showed significant dependence on the reactant concentrations, reaction time, temperature, and surface tension, which actually controlled the interfacial mass transfer. The microchannel reactor assisted in achieving a high interfacial area, as well as uniformity in mass transfer effects. Hexagonal nanostructures were seen to be formed in synthesis times as short as 10 min. The wettability of the channel showed significant effect on the particle size as well as the actual shape. The hydrophobic channel yielded hexagonal structures of relatively smaller size than the hydrophilic microchannel, which yielded sharp hexagonal bipyramidal particles (diagonal distance of 30 nm). The evolution of particle size and shape for the case of hydrophilic microchannel is also shown as a function of the residence time. The interfacial synthesis approach based on a stable segmented flow promoted an excellent control on the reaction extent, reduction in axial dispersion as well as the particle size distribution.

Plasmonic behavior of ionic liquid stabilized gold nanoparticles in molecular solvents

In this paper, we have demonstrated the facile synthesis of stable gold nanoparticles (AuNPs) using imidazolium ionic liquids (ImILs) as a stabilizer as well as a surfactant and their surface plasmon resonance (SPR) in different molecular solvents with varying dielectric properties.

Polyoxovanadate fabricated gold nanoparticles: Application in SERS

This article reports a surface modification of gold nanoparticles with water soluble polyoxometalate, V₁₀O₂₈^6- (decavanadate, V10). Two sizes of citrate-capped gold nanoparticles AuNP-Citrate-S (∼11nm) and AuNP-Citrate-L (∼46nm) were modified with V10 in aqueous media to form AuNP-V10-S and AuNP-V10-L, respectively. Both AuNP-V10-S and AuNP-V10-L were found to be significantly better than their citrate counterparts in strengthening Raman vibrational signals of analyte molecule. All the nanoparticles were characterized by UV-visible and Fourier transform infrared (FTIR) spectroscopies, dynamic light scattering (DLS), transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) line analysis. We demonstrate that AuNP-V10-L is excellent surface-enhanced Raman scattering (SERS) substrate for a Raman-active analyte molecule at nanomolar concentrations.

Poly(dopamine) assisted in situ fabrication of silver nanoparticles/metal–organic framework hybrids as SERS substrates for folic acid detection

A novel and simple in situ strategy for the preparation of AgNPs/MIL-101(Cr) hybrids as SERS substrates for folic acid detection was developed.

Crystalline-like structures and multilayering in Langmuir films of ionic liquids at the air–water interface

Langmuir films of [C₁₈mim][NTf₂] ionic liquid exhibited, for the first time, the reversible formation of crystalline-like structures at the surface of water, compatible with the formation of multilayers.

Interaction of the CLPFFD peptide with gold nanospheres. A Raman, surface enhanced Raman scattering and theoretical study

In a previous work we demonstrated that toxic aggregates of the protein β-amyloid (ATAβ) involved in the Alzheimer's disease (AD) can be destabilized upon electromagnetic irradiation of the peptide Cys-Leu-Pro-Phe-Phe-Asp (CLPFFD) adsorbed on gold nanospheres (AuNSs). For a selective recognition of the therapeutic target (i.e. ATAβ) of AD by the conjugates peptide-nanoparticle it is relevant to understand how the interaction between attached ligands and nanoparticles occurs. In this work a surface enhanced Raman scattering spectroscopy (SERS) study of the interactions of CLPFFD with AuNSs of 10nm average diameter was carried out. The SERS data suggest that phenylalanine displays its aromatic ring coplanar to the surface which is supported by theoretical data obtained from molecular mechanics (MM) and Extended Hückel Theory (EHT) calculations.

Facile synthesis of silver and bimetallic silver–gold nanoparticles and their applications in surface-enhanced Raman scattering

Monometallic and bimetallic core–shell colloids reported here demonstrate significant SERS signals for a hydrophobic dye molecule at as low as 10 nM and AEF lies within the highest literature values.

A surface-enhanced Raman scattering strategy for detection of peanut allergen Ara h 1 using a bipyramid-shaped gold nanocrystal substrate with an improved synthesis

We report an improved synthesis of branched gold nanocrystals for detection of peanut allergen Ara h 1 through use of sodium dodecylbenzene sulfonate. The method allows reduction of CTAB to 0.05 M and accelerates growth of gold seeds.

One-phase synthesis of surface modified gold nanoparticles and generation of SERS substrate by seed growth method

In this study, we report a novel and facile single-phase synthesis of stable AuNP-CTAB(NA) conjugates with good dispersibility, bearing a bilayer of cationic surfactant, cetyltrimethylammonium bromide (CTAB) supported by N-nonylamine (NA) as a cosurfactant. We investigated AuNP-CTAB(NA) conjugates by (1)H NMR spectroscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and transmission electron microscopy (TEM). These studies suggest the presence of a CTAB bilayer on the nanoparticles surface forming an admicelle and NA embedded in the hydrophobic core of that bilayer. AuNP-CTAB(NA) conjugates remain dispersed in water even in the presence of high concentrations of salt and over a wide range of solution pHs. These conjugates further grow bigger when treated with additional AuCl(4)(-), CTAB, and NA in the presence of the mild reducing agent, hydroquinone (HQ). The larger AuNP-CTAB(NA)-1 conjugates serve as SERS (surface-enhanced Raman Scattering) substrate of Raman active dye even at nanomolar concentrations.

Protein-decorated reduced oxide graphene composite and its application to SERS

A globular protein, β-lactoglobulin (BLG), was used to decorate reduced graphene oxide sheets (RGO) and the obtained BLG-RGO composite can be dispersed in aqueous solution with pH-sensitive solubility. The morphology of the BLG-RGO composite was studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results indicate that BLG-RGO is effectively exfoliated with an average thickness of 2.5 nm. UV-vis spectra were performed to examine the reduction degree and determine the optimum concentration of β-lactoglobulin and appropriate pH value. Furthermore, Raman spectra demonstrate that β-Lactoglobulin promotes the chemical reduction process of graphene oxide and benefits to repair the crystal defects. Due to the adsorption of β-Lactoglobulin on the surface of graphene sheets, the BLG-RGO composite was further used as template for Au nanoparticles assembly. These Au nanoparticles assembled on the BLG-RGO composite were shown to yield a large SERS enhancement for Rhodamine 6G.

The effects of the π-π stacking interactions on the patterns of gold nanoparticles formed at the air-water interface

Benzyl-n-hexadecyl dimethylammonium chloride (BHDC) monolayer-stabilized gold nanoparticles were synthesized in a two-phase liquid-liquid system and found to self-assemble into varied structures under the control of temperature at the air-water interface. It has been demonstrated that the π-π stacking interactions between the capping agent molecules significantly affect the formation of the unique patterns. A possible mechanism based on Marangoni-Bénard convection in the evaporating droplets and π-π stacking interactions was proposed. Four surfactants with similar structures: N-hexadecyl-N-methylpyrrolidinium bromide (C(16)MPB), 1-hexadecyl-3-methylimidazolium bromide (C(16)mimBr), 1-(2,4,6-trimethylphenyl)-3-hexadecylimidazolium bromide (C(16)pimBr) and hexadecyltrimethylammonium bromide (CTAB) were also used to further verify the formation mechanism mentioned above.

An approach for fabricating self-assembled monolayer of gold nanoparticles on NH2(+) ion implantation modified indium tin oxide as the SERS-active substrate

In this paper, an approach for fabricating an active surface-enhanced Raman scattering (SERS) substrate was adopted. This approach was based on the assembling of gold nanoparticles (AuNPs) film on NH(2)(+) ion implantation modified indium tin oxide (NH(2)/ITO) substrate. Scanning electron microscopy (SEM) was used to investigate the surface morphology of the active SERS substrate, which showed that large quantities of AuNPs were coated on the substrate. Rhodamine 6G (R6G) was used as probe molecules for SERS experiments, showing that this new active substrate had sensitivity to SERS response. The substrate efficiency was strictly related to the AuNPs morphology, which depended on the pH value of the Au colloid used in the assembly process.

Nanoparticles in liquid crystals and liquid crystalline nanoparticles

Combinations of liquid crystals and materials with unique features as well as properties at the nanoscale are reviewed. Particular attention is paid to recent developments, i.e., since 2007, in areas ranging from liquid crystal-nanoparticle dispersions to nanomaterials forming liquid crystalline phases after surface modification with mesogenic or promesogenic moieties. Experimental and synthetic approaches are summarized, design strategies compared, and potential as well as existing applications discussed. Finally, a critical outlook into the future of this fascinating field of liquid crystal research is provided.

Patterns of gold nanoparticles formed at the air/water interface: effects of capping agents

Gold nanoparticles stabilized with different capping agents were synthesized in a two-phase liquid-liquid system and found to self-assemble into various patterns at the air/water interface. The shapes of the patterns are closely related to the molecule structures of the capping agents. Systems with mixed capping agents were also investigated, and honeycomb patterns can be obtained in this way. T-shape and H-shape patterns were also observed. A possible mechanism based on Marangoni-Benard convection in evaporating droplets is proposed.