Surface Of Gold Colloids Research Articles

Raman and surface enhanced Raman scattering study of the orientation of cruciform 9,10-anthracene thiophene and furan derivatives deposited on a gold colloidal surface

The 9,10-di(thiophen-2-yl)anthracene (TAT), 9,10-di(furan-2-yl)anthracene (FAF) and 2-[(10-(thiophen-2-yl)anthracen-9-yl)]furan (TAF) cruciform molecular systems were synthesized using one-step coupling reactions and structurally characterized via Raman, infrared, 1H NMR, 13C NMR and mass spectroscopies. The orientation of the analytes on a gold colloidal surface was inferred from a surface-enhanced Raman scattering (SERS) study. The metal surface interaction was driven by the S and O atoms of the thiophene and furan α-substituents, and the plane of the anthracene fragment remained parallel to the surface. Theoretical calculations based on a simplified molecular model for the analyte-surface interaction provide a good representation of the experimental data.

Raman and SERS study of N-acetyl-5-methoxytryptamine, melatonin—The influence of the different molecular fragments on the SERS effect

In this work a detailed experimental Raman and SERS study on melatonin is reported. Additional density functional theory (DFT) with the hybrid exchange-correlation functional B3LYP, in combination with the 6-311++G(d,p) basis set have been performed. Scaled quantum mechanical force field (SQM FF) method for the prediction of the vibrational spectra is used to determine the geometrical, energetic and vibrational characteristics of the molecule. The DFT-computed structural parameters and harmonic vibrational wavenumbers reproduce the experimental data very well and help to characterize the vibrational behaviour of the adsorbed species. The assignment of the normal modes obtained by calculations was supported by previous vibrational studies on the distinct functional groups present in melatonin. The SERS study was carried out with particular emphasis on the interaction and adsorption of the different parts of the molecule to the gold colloidal surface. Furthermore, the adsorption behavior of melatonin on colloidal Au surface is deduced from the SERS selection rules and analysis of the calculated molecular electrostatic potential (MEP).

Reversible peptide oligomerization over nanoscale gold surfaces

A selective oligomeric formation of amyloid beta 1-40 (Ab 1-40 ) monomers over a nanogold colloidal surface was investigated. An unfolded Ab 1-40 monomer is considered to construct a dimer or trimer based oligomeric form with its hydrophobic segment placing outward under an acidic condition. Under a basic condition, a conformation of Ab is expected to take a folded monomeric form with its hydrophilic segment folded inward, avoiding the networking with residual colloidal particles. The most probable oligomeric form constructed over a 20 nm gold colloidal surface within a 25 ℃ to 65 ℃ temperature range is a dimer based unit and that over 30 or 40 nm gold colloidal surface below 15 ℃ is concluded to be a trimer based unit. However, selective oligomerization was not successfully reproduced under the rest of the conditions. A dipole-induced dipole interaction must cause a flexible structural change between folded and unfolded forms.

Interaction of N‐benzylamino(boronphenyl)methylphosphonic acid analogs with the gold colloidal surface under different concentration and pH conditions

In this study, we present surface‐enhanced Raman spectroscopy (SERS) investigations of five analogs of a novel group of N‐benzylamino(boronphenyl)methylphosphonic acids: N‐benzylamino‐(3‐boronphenyl)‐S‐methylphosphonic acid (m‐PhS), N‐benzylamino‐(4‐boronphenyl)‐S‐methylphosphonic acid (p‐PhS), N‐benzylamino‐(2‐boronphenyl)‐R‐methylphosphonic acid (o‐PhR), N‐benzylamino‐(3‐boronphenyl)‐R‐methylphosphonic acid (m‐PhR), and N‐benzylamino‐(4‐boronphenyl)‐R‐methylphosphonic acid (p‐PhR) deposited onto 10‐nm gold nanoparticles in an aqueous solution at physiological pH (pH = 7). In addition, for the p‐PhR molecule, the SERS spectra in the various conditions of pH levels of the solutions (from pH = 3 to 11) and phosphonic acid concentration (10−3–10−5 M) were measured. In general, the SERS spectral profiles indicate that at pH = 7, all of the aforementioned molecules interact with the colloidal gold surface via a boronphenyl ring. However, the orientation of the boronphenyl ring onto the substrate surface is different for each of the studied molecules. The boronic acid group of p‐PhS and p‐PhR binds to the gold nanoparticles, whereas the phosphonic acid group assists in the interaction with the substrate for p‐PhR only. For all the molecules, the –CLCα(P)N– fragment distinctly influences the molecule/gold interactions, especially in the case of o‐PhR. The previous differences in the compound behavior at the gold/liquid interface underline the role of an absolute configuration (–R and –S) and a type of isomer (orto‐, meta‐, and para‐) on the SERS signals, which means their influence on the adsorbate geometry. Additionally, based on the SERS results for p‐PhR in various environmental conditions, we draw conclusions about spectral changes (adsorbate geometry changes) as a result of the pH of solution and molecule concentration alternations. Copyright © 2014 John Wiley & Sons, Ltd.

Surface-enhanced Raman spectroscopic analysis of maleic hydrazide adsorbed on gold surface

In this paper, surface-enhanced Raman scattering (SERS) spectra of maleic hydrazide (MH, 6-hydroxy-3(2H)-pyridazinone) were studied by using citrate-reduced gold colloidal nanoparticles. Comparisons between the prominent SERS bands and the precise mode descriptions predicted through density functional theory (DFT) simulations at the B3LYP/6-311++g(d,p) level allowed an in-depth orientation analysis of the adsorbed species on gold surfaces. And main forms of hydrogen bonds in the solid state of MH were also determined to be OH⋯O. Furthermore, the effects of concentration and pH on the SERS spectra of the molecule were discussed. It is found that with the different adsorbate concentration, the SERS spectra of MH show significant changes in their features, indicating different orientations and adsorption sites of the molecule on the gold colloidal surface. The SERS and absorption spectra under different pH conditions show that a basic environment leads to the deprotonation of N2 and the nearly parallel orientation of the MH molecule on the gold surface. Moreover, the enhanced characteristic bands were observed at MH concentrations down to about 1ppm with the gold colloids, demonstrating a potential of the technique in the analysis of MH residues.

Self-Assembly of Amyloid Beta Peptide Over Dialkoxy Disulfide Functionalized Nano Gold Colloidal Particles

Aiming to more stably produce an oligomer form of amyloid beta (i.e., a key intermediate of fibrillogenesis which eventually leads to Alzheimer’s disease), the surface of gold colloids were functionalized with nitro-, phenyl-, chloro-, and methoxy-dibenzyloxy disulfide, and molecular interactions were investigated in a dimethyl sulfoxide environment. The transition of color change was observed at pHo as the pH value was lowered externally. As evidence of disulfide being adsorbed on the colloidal surface, the pHo values were dependent of each substituent of the dibenzyloxy disulfide compounds. The trend of pHo exhibited a parabolic relationship as a function of F-value (Swain-Lupton Field constant). Functionalization of gold colloidal surface with methoxy-dibenzyloxy disulfide achieved larger amplitude in repetitive peak shift between pH 4 and 10 implying a formation of an oligomer under the reversible process

Direct determination of benzo[ a]pyrene in water samples by a gold nanoparticle-based solid phase extraction method and laser-excited time-resolved Shpol'skii spectrometry

The strong affinity between polycyclic aromatic hydrocarbons (PAH) and the surface of gold colloids is investigated to device an extraction method for water samples. Within the 20–100 nm particle diameter range, the 20 nm gold nanoparticles showed the best extraction efficiencies for all the studied analytes. The new approach is combined to laser-excited time-resolved Shpol'skii spectrometry for the direct analysis of benzo[ a]pyrene in drinking water samples. For a 500 μL sample volume, the analytical figures of merit demonstrate precise and accurate analysis at the parts-per-trillion level. The extraction efficiencies are statistically equivalent to 100% with relative standard deviations lower than 2%. The average recoveries were varied from 87.5% to 96.5% for different concentration of analytes. The simplicity of the experimental procedure, the low analysis cost, and the excellent analytical figures of merit demonstrate the potential of this approach for routine analysis of drinking water samples.

Bioconjugation and characterisation of gold colloid-labelled proteins

Colloidal metal particles, in particular gold, have found many biological applications often as probes in light and electron microscopy, and more recently since the 1980s in membrane-based rapid immunoaffinity tests. The surface plasmon resonance absorbance properties in the visible spectroscopy region of gold colloids make them useful tools in medical devices, as the colloids are directly visible to the naked eye. Despite the relative ease with which gold-protein conjugates can be prepared a major issue is the manufacture of poor-quality and poorly characterised bioconjugates that can result in the under performance of subsequent diagnostic tests. This paper describes the preparation of good-quality conjugates for use in immunoassays by optimising the adsorption of antibodies onto the surface of gold colloids, followed by their subsequent characterisation. The conjugates were characterized for size, aggregation and quality using a range of techniques: UV-visible (UV/Vis) absorption spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The biological activities of the conjugated products were also assessed using an immunoassay format and electrochemical measurements. By utilising a number of measurement techniques we aimed to gain a better understanding of the extent of particle aggregation, and the resulting stability and activity of the biological molecule on the surfaces of nanoparticles. The tools developed will enable researchers and companies to ensure the sensitivity, quality and reproducibility of batches of nanoparticle bio-conjugates.

A Localized Surface Plasmon Resonance Light-Scattering Assay of Mercury (II) on the Basis of Hg2+−DNA Complex Induced Aggregation of Gold Nanoparticles

It is known that localized surface plasmon resonance (LSPR) is responsible for the surface-enhanced spectroscopic processes of metallic nanoparticles and thus LSPR spectroscopy has become a powerful technique for chemical and biological purposes. In this contribution, we present a simple homogeneous Hg2+ assay by measuring enhanced LSPR scattering signals resulted from Hg(2+)-DNA complex induced aggregation of gold nanoparticles (AuNPs). In a medium of pH 7.4 tris-HCl buffer containing 0.05 M NaCl, single-stranded oligonucletides with the sequence of 5'-d(T6)-3' (poly-T6 ssDNA), can be selectively adsorbed onto the surface of gold colloids, stabilizing the AuNPs against aggregation. If Hg(2+)-DNA complex via Hg(2+)-mediated thymine-Hg(2+)-thymine (T-Hg(2+)-T) is formed, however, the adsorption of poly-T6 ssDNA onto the surface of gold colloids gets reduced, and then aggregation of the AuNPs occurs owing to the decrease of the electrostatic repulsion between AuNPs. Consequently, strong LSPR scattering signals resulting from the aggregates of AuNPs could be visually observed under a dark field microscope and easily be measured with a common spectrofluorometer. The LSPR scattering intensities characterized at 556.0 nm were found to be proportional to the concentration of Hg2+ ions in the range of 4.0 x 10(-8) to 6.0 x 10(-7) M with the limit of determination (3sigma) of 1.0 nM. Compared with reported colorimetric methods, our present approaches display the advantages of higher sensitivity.

The conjugation of amyloid beta protein on the gold colloidal nanoparticles’ surfaces

The conjugation of various sequences of amyloidβ proteinsolution (Aβ); Aβ1−11, Aβ12−28,Aβ31−35,Aβ1−40,and Aβ1−42 with gold colloidal suspension of 20 nm size was examined. Absorption spectroscopywas utilized to identify changes in the optical properties of gold colloid for pHs,ranging from pH 2 to pH 10. Colour changes were seen for all tested proteins in thisstudy at a higher pH than where bare gold colloid exhibits its colour change atpH = 3.09 ± 0.02. All testedAβ sequencesexcept for Aβ1−42 exhibited colour changes around pI values ofAβ1−40, aboutpH 5.2. The Aβ1−42 exhibited precipitants in all pH lower than pH 7 and showed the colour change aroundpH 3.96 ± 0.05. The colour change observed at a pH lower than 5 is attributed to the unfoldedAβ monomer units around the gold colloidal surface. Interestingly, onlyAβ1−40-coated gold colloidal nanoparticles exhibited a reversible colour change as the pHwas externally altered between pH 4 and 10. This reversibility is an importantimplication of the observation of a reversible step reported for the fibrillogenesis.It was interpreted that the reversible process takes place when hydrophilicAβ possesses a three-dimensional network containing bothβ-sheetand α-helices.

Fiber-optic biochemical sensing with a colloidal gold-modified long period fiber grating

A novel class of fiber-optic evanescent-wave sensor, which is simple to construct and easy to use, is presented and analyzed. This fiber-optic sensor is based on the modification of the grating portion of a long-period fiber grating with self-assembled gold colloids. The transmission spectra and optical properties of gold colloids change with the different refractive index of the environment near the surface of gold colloids. The sensor response of gold colloids increases linearly with solvents of increasing refractive index. When the colloidal gold surface was modified with a dinitrophenyl compound (DNP), experimental results show that the signal increase linearly with increasing concentration of the analyte, and the detection limit of the sensor for anti-DNP is 1.4 × 10 −7 g/mL or 9.5 × 10 −10 M.

Immunoassay using probe-labelling immunogold nanoparticles with silver staining enhancement via surface-enhanced Raman scattering.

This paper reports a novel immunoassay based on surface-enhanced Raman scattering (SERS) and immunogold labelling with silver staining enhancement. Immunoreactions between immunogold colloids modified by a Raman-active probe molecule (e.g., 4-mercaptobenzoic acid) and antigens, which were captured by antibody-assembled chips such as silicon or quartz, were detected via SERS signals of Raman-active probe molecule. All the self-assembled steps were subjected to the measurements of ultraviolet-visible (UV-vis) spectra to monitor the formation of a sandwich structure onto a substrate. The immunoassay was performed by a sandwich structure consisting of three layers. The first layer was composed of immobilized antibody molecules of mouse polyclonal antibody against Hepatitis B virus surface antigen (PAb) on a silicon or quartz substrate. The second layer was the complementary Hepatitis B virus surface antigen (Antigen) molecules captured by PAb on the substrate. The third layer was composed of the probe-labelling immunogold nanoparticles, which were modified by mouse monoclonal antibody against Hepatitis B virus surface antigen (MAb) and 4-mercaptobenzoic acid (MBA) as the Raman-active probe on the surface of gold colloids. After silver staining enhancement, the antigen is identified by a SERS spectrum of MBA. A working curve of the intensity of a SERS signal at 1585 cm(-1) due to the [small nu](8a) aromatic ring vibration of MBA versus the concentration of analyte (Antigen) was obtained and the non-optimized detection limit for the Hepatitis B virus surface antigen was found to be as low as 0.5 [micro sign]g mL(-1).

Colloidal Gold-Modified Optical Fiber for Chemical and Biochemical Sensing

A novel class of fiber-optic evanescent-wave sensor was constructed on the basis of modification of the unclad portion of an optical fiber with self-assembled gold colloids. The optical properties and, hence, the attenuated total reflection spectrum of self-assembled gold colloids on the optical fiber changes with different refractive index of the environment near the colloidal gold surface. With sucrose solutions of increasing refractive index, the sensor response decreases linearly. The colloidal gold surface was also functionalized with glycine, succinic acid, or biotin to enhance the selectivity of the sensor. Results show that the sensor response decreases linearly with increasing concentration of each analyte. When the colloidal gold surface was functionalized with biotin, the detection limit of the sensor for streptavidin was 9.8 x 10(-11) M. Using this approach, we demonstrate proof-of-concept of a class of refractive index sensor that is sensitive to the refractive index of the environment near the colloidal gold surface and, hence, is suitable for label-free detection of molecular or biomolecular binding at the surface of gold colloids.