Large-scale, rapid synthesis and application in surface-enhanced Raman spectroscopy of sub-micrometer polyhedral gold nanocrystals

Macromolecule-protected sub-micrometer polyhedral gold nanocrystals have been facilely prepared by heating an aqueous solution containing poly (N-vinyl-2-pyrrolidone) (PVP) and HAuCl4 without adding other reducing agents. Scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), ultraviolet-visible-near-infrared spectroscopy (UV-vis-NIR), and x-ray diffraction (XRD) were employed to characterize the obtained polyhedral gold nanocrystals. It is found that the 10:1 molar ratio of PVP to gold is a key factor for obtaining quasi-monodisperse polyhedral gold nanocrystals. Furthermore, the application of polyhedral gold nanocrystals in surface-enhanced Raman scattering (SERS) was investigated by using 4-aminothiophenol (4-ATP) as a probe molecule. The results indicated that the sub-micrometer polyhedral gold nanocrystals modified on the ITO substrate exhibited higher SERS activity compared to the traditional gold nanoparticle modified film. The enhancement factor (EF) on polyhedral gold nanocrystals was about six times larger than that obtained on aggregated gold nanoparticles (similar to 25 nm).

Wet-chemical approach to three-dimensional gold nanocorallines: Synthesis and application in surface-enhanced Raman spectroscopy

The shape-con trolled synthesis of micrometer- sized gold nanocoralline was simply realized via a wet-chemical approach. The as-prepared hierarchical gold nanocorallines (HGNs) on the solid substrate were initially applied in SERS analysis with 4-aminothiophenol (4-ATP) as the probe molecule. The HGN-modified glass substrate exhibits a higher SERS effect (one order of magnitude higher) than the aggregated gold nanoparticle (similar to 25 nm)-modified glass substrate.

Density functional studies of diatomic LaO to LuO

Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies and dipole moments of the title molecules in neutral, positively and negatively charged ions were studied by use of density functional method. Ground electronic state was assigned for each molecule. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides ionic component, covalent bonds are formed between the metal s, d and f orbitals and oxygen p orbitals. Contrary to the well known lanthanide contraction, the bond distance is not regular from LaO to LuO for both neutral and charged molecules. An obvious population at 5d orbital was observed through the lanthanide series. 4f electrons also participate the chemical bonding for CeO to NdO and TbO to TmO. For EuO, GdO, YbO and LuO, 4f electrons tend to be localized. The spin multiplicity is regular for neutral and charged molecules. The spin multiplicity of the charged molecules can be obtained by -1 (or +1 for TbO+, DyO+, YbO- and YbO+) compared with the corresponding neutral molecules.

Kinetic study of DNA/DNA hybridization with electrochemical impedance spectroscopy

The hybridization of immobilized oligonucleotides probe strands with solution phase targets is the underlying principle of microarraybased techniques for the analysis of DNA variation. To study the kinetics of DNA/DNA hybridization, target DNA is often prior labeled with markers. A label-free method of electrochemical impedance spectra (EIS) for study the hybridization in process was reported. The Langmuir model was used to determine the association rate constant (K-on), the dissociation rate constant (K-off) and the affinity rate constant (K-A), for perfect matched DNA hybridization. The results show that, EIS is a successful technique possessing high effectivity and sensitivity to study DNA/DNA hybridization kinetics. This work can provide another view on EIS for the studying of DNA/DNA hybridization.

Solvent effects on spectrophotometric titrations and vibrational spectroscopy of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin in aqueoius DMF

The spectrophotometric titration by sodium hydroxide of 5,10,15-triphenyl-20-(4-hydroxyphenyl)porphyrin ((OH)(1)PH2) is studied as a function of solvent composition of DMF-H2O binary solvent mixture ([OH-] = 0.04 M). Combining the structure changes of the porphyrin and the "four orbital" model of Gouterman, many features of the optical spectra of this deprotonated para-hydroxy-substituted tetraphenylporphyrin in different composition of binary solvent mixtures can be rationalized. In highly aqueous solvents, the changes of the titration curves are shown to be mainly due to hydrogen-bonding of the oxygen of the phenoxide anion group by the hydroxylic solvent, Which decreases the energy of the phenoxide anion pi orbital. Thus the phenoxide anion pi orbital cannot cross over the porphyrin Tr orbital being a different HOMO. However, its energy is close to that of the porphyrin pi orbitals. As a result, in the visible region, no charge-transfer band is observed, while in the visible-near region, the Soret peak split into two components. In nonaqueous solvents, the changes are mainly attributed to further deprotonation of pyrrolic-Hs of (OH) 1PH2 by NaOH and coordination with two sodium ions to form the sodium complex of (OH) 1PH2, which turns hyperporphyrin spectra of deprotonated of phenolic-H of (OH)(1)PH2 into three-banded spectra of regular metalloporphyrin.

Metabolic profiling of serum from gadolinium chloride-treated rats by H-1 NMR spectroscopy

Metabolic profiling of serum from gadolinium chloride (GdCl3, 10 and 50 mg/kg body weight, intraperitoneal [i.p.])-treated rats was investigated by the NMR spectroscopic-based metabonomic strategy. Serum samples were collected at 48, 96, and 168 h postdose (p.d.) after exposure to GdCl3. H-1 NMR spectra of serum were analyzed by pattern recognition using principal components analysis. The studies showed that there was a dose-related biochemical effect of GdCl3 treatment on the levels of a range of low-molecular weight compounds in serum. The liver damage induced by GdCl3 was characterized by the elevation of lactate, pyruvate, and creatine as well as the decrease of branched-chain amino acids (valine and isoleucine), alanine, glucose, and trimethylamine-N-oxide concentration in serum samples. The biochemical effects of GdCl3 in rats could be consulted when evaluating the biochemical profile of gadolinium-containing compounds that are being developed for nuclear magnetic resonance imaging.

Measuring the electronic decay constant of alkanedithiols by electrochemical impedance spectroscopy

Several methods have been used for the measurement of the electronic decay constant (beta) of organic molecules. However, each of them has some disadvantages. For the first time, electrochemical impedance spectroscopy (EIS) was used to obtain the 18 value by measuring the tunneling resistance through alkanedithiols. The tunneling resistance through alkanedithiols increases exponentially with the molecular length in terms of the mechanism of coherent nonresonant tunneling. beta was 0.51 +/- 0.01 per carbon.

Interaction of echinomycin with guanine: electrochemistry and spectroscopy studies

The interaction of antitumor antibiotic, echinomycin (Echi) with guanine (Gua) was thoroughly investigated by adsorptive transfer stripping cyclic voltammetry, ultraviolet and visible adsorption spectra (UV/Vis) and Fourier-transform infrared spectroscopy (FTIR). Electrochemistry provided a simple tool for verifying the occurrence of interaction between Echi and Gua. Echi could be accumulated from the solution and give well-defined electrochemical signals in 0.1 M phosphate buffer solution (pH 7.0) only when Gua was present on the surface of the electrochemically pretreated glass carbon electrode (GCE), suggesting a strong binding of Echi to Gua. All the acquired spectral data showed that a new adduct between Echi and Gua was formed, and two pairs of adjacent intermolecular hydrogen bonds between the Ala backbone atoms in Echi and Gua (Ala-NH to Gua-N3 and Gua-NH2 to Ala-CO) played a dominating role in the interaction. Electrochemistry coupled with spectroscopy techniques could provide a relatively easy way to obtain useful insights into the molecular mechanism of drug-DNA interactions, which should be important in the development of new anticancer drugs with specific base recognition.

Application of impedance spectroscopy for monitoring colloid Au-enhanced antibody immobilization and antibody-antigen reactions

We used colloidal An to enhance the amount of antibody immobilized on a gold electrode and ultimately monitored the interaction of antigen-antibody by impedance measurement. Self-assembly of 6 nm (diameter) colloidal An onto the self-assembled monolayers (SAMs) of 4-aminothiophenol modified gold electrode resulted in an easier attachment of antibody. The redox reactions of [Fe(CN)(6)](4-)/[Fe(CN)(6)](3-) on the gold surface were blocked due to the procedures of self-assembly of 4-aminothiophenol and antibody immobilization, which were investigated by cyclic voltammetry and impedance spectroscopy. The interaction of antigen with grafted antibody recognition layers was carried out by soaking the modified electrode into a phosphate buffer at pH 7.4 with various concentrations of antigen at 37 degreesC for 30 min. The antibody recognition layers and their interactions with various concentrations of antigen could be detected by measurements of the impedance change. The results show that this method has good correlation for detection of Hepatitis B virus surface antigen in the range of 0.5-200 mug/l and a detection limit of about 50 ng/l.

Surfactantless synthesis of multiple shapes of gold nanostructures and their shape-dependent SERS spectroscopy

A useful method for the synthesis of various gold nanostructures is presented. The results demonstrated that flowerlike nanoparticle arrays, nanowire networks, nanosheets, and nanoflowers were obtained on the solid substrate under different experimental conditions. In addition, surface-enhanced Raman scattering (SERS) spectra of 4-aminothiophenol (4-ATP) on the as-prepared gold nanostructures of various shapes were measured, and their shape-dependent properties were evaluated. The intensity of the SERS signal was the smallest for the gold nanosheets, and the flowerlike nanoparticle arrays gave the strongest SERS signals.

Surface-enhanced resonance Raman spectroscopy and spectroscopy study of redox-induced conformational equilibrium of cytochrome c adsorbed on DNA-modified metal electrode

The redox-induced conformational equilibrium of cytochrome c (cyt c) adsorbed on DNA-modified metal electrode and the interaction mechanism of DNA with cyt c have been studied by electrochemical, spectroscopic and spectroelectrochemical techniques. The results indicate that the external electric field induces potential-dependent coordination equilibrium of the adsorbed cyt c between its oxidized state (with native six-coordinate low-spin and non-native five-coordinate high-spin heme configuration) and its reduced state (with native six-coordinate low-spin heme configuration) on DNA-modified metal electrode. The strong interactions between DNA and cyt c induce the self-aggregation of cyt c adsorbed on DNA. The orientational distribution of cyt c adsorbed on DNA-modified metal electrode is potential-dependent, which results in the deviation from an ideal Nernstian behavior of the adsorbed cyt c at high electrode potentials. The electric-field-induced increase in the activation barrier of proton-transfer steps attributed to the rearrangement of the hydrogen bond network and the self-aggregation of cyt c upon adsorption on DNA-modified electrode strongly decrease the interfacial electron transfer rate.

Application of electrochemical impedance spectroscopy for monitoring allergen-antibody reactions using gold nanoparticle-based biomolecular immobilization method

Gold nanoparticles were used to enhance the immobilization amount and retain the immunoactivity of recombinant dust mite allergen Der f2 immobilized on a glassy carbon electrode (GCE). The interaction between allergen and antibody was studied by electrochemical impedance spectroscopy (EIS). Self-assembled Au colloid layer (Phi = 16 nm) deposited on (3-mercaptopropyl)trimethoxysilane (MPTS)-modified GCE offered a basis to control the immobilization of allergen Der f2. The impedance measurements were based on the charge transfer kinetics of the [Fe(CN)(6)](3-/4-) redox pair, compared with bare GCE, the immobilization of allergen Der f2 and the allergen-antibody interaction that occurred on the electrode surface altered the interfacial electron transfer resistance and thereby slowed down the charge transfer kinetics by reducing the active area of the electrode or by preventing the redox species in electrolyte solution from approaching the electrode. The interactions of allergen with various concentrations of monoclonal antibody were also monitored through the change of impedance response. The results showed that the electron transfer resistance increased with increasing concentrations of monoclonal antibody.

In vitro study on the binding of neutral red to bovine serum albumin by molecular spectroscopy

In this paper, the binding of neutral red (NR) to bovine serum albumin (BSA) under physiological conditions has been studied by spectroscopy method including fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy. The Stern-Volmer fluorescence quenching constant (K-SV), binding constant (K-b) and the number of binding sites (It) were measured by fluorescence quenching method. Fluorescence experiments were also performed at different ionic strengths. It was found K-SV was ionic strength dependent, which indicated the electrostatic interactions were part of the binding forces. The distance r between donor (BSA) and acceptor (NR) was obtained according to Foster's non-radiative energy transfer theory. CD spectroscopy and FT-IR spectroscopy were used to investigate the structural information of BSA molecules on the binding of NR, and the results showed no change of BSA conformation in our experimental conditions.