Biomedical subjects

Weiqing Xu

Publications and source records attributed to Weiqing Xu.

At least 19 recordsLinked to original sources

PubMed2006

Surface-enhanced Raman scattering on mercaptopyridine-capped CdS microclusters.

We obtained the high-quality Raman spectra of 4-mercaptopyridine (4-Mpy) adsorbed on CdS microclusters. The Raman signals were enhanced relative to the same molecules in solution. We compared the Raman spectra of 4-Mpy molecules adsorbed on CdS microclusters and Ag substrate. The difference of 4-Mpy molecules adsorbed on semiconductor and metal substrate was revealed. The results demonstrated that adsorbed species on semiconductor CdS can be detected by SERS spectroscopy.

Microscopy, Electron, Scanning↗

PubMed2006

Surface enhanced Raman scattering based on silver dendrites substrate.

A simple method of the reduction of AgNO3 by copper foil in aqueous medium was used to prepare silver dendrites, which can be used as a novel good reproducible surface enhanced Raman scattering (SERS) active substrate. The SERS spectra of 4-pyridinethiol on this novel substrate reflected the different SERS activities on the minuteness and strong Ag dendrites. The electromagnetic coupling enhancement and chemical enhancement mechanisms are used to explain the SERS effect.

Journal Article↗

PubMed2006

A simple method to synthesize triangular silver nanoparticles by light irradiation.

We describe a simple method to synthesize triangular silver nanoparticles by photoreducing the silver ions by citrate. A noteworthy difference of the present method as compared with the previous photo-induced methods is that good shape control over the nanoparticles can be realized in the absence of soft templates or polymer directing agents. The formation process of the silver nanoparticles was investigated by UV-vis spectroscopy and transmission electron microscopy (TEM). It was found that the concentration of reactant plays important role in the morphology control of produced silver nanoparticles. As one of the applications of these nanoparticles, they were used as surface-enhanced Raman scattering substrates and 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BVPP) was used as a Raman probe to evaluate the enhancement ability of the triangular silver nanoparticles.

Chemistry↗

PubMed2006

[A study of the level of serum leptin in patients with obstructive sleep apnea-hypopnea syndrome and obesity and patients with normal body mass].

OBJECTIVE: To explore the level of serum leptin in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) and obesity and patients with normal body mass. METHOD: Polysomnography (PSG) was performed in 53 patients with OSAHS and in 41 simple obesity and in 62 patients with normal body mass. The level of serum leptin was detected by radioimmunoassay. The stature, weight, neck collar, hip circumference, waistline were measured. RESULT: (1) Serum leptin level in patients with OSAHS and obesity was higher than patients with normal body mass. At the same time, serum leptin level in patients with OSAHS was higher than obesity ( P < 0.05). (2) Serum leptin levels were positive significantly correlated with BMI in both OSAHS patients and simple obesity, but only the leptin level in patients with OSAHS was significantly correlated with apnea and hypopnea index (AHI) and proportion of neck circumference and waist-hip ratio (WHR). CONCLUSION: The rise of the serum leptin level in obesity was resisted of leptin. The serum leptin level of patients with OSAHS correlated with AHI shows that OSAHS maybe one reason of arising serum leptin's rising. Leptin could stimulate aspirator centrum.

Adult↗

PubMed2005

Optical properties of Ag/CdTe nanocomposite self-organized by electrostatic interaction.

Ag/CdTe nanocomposite was prepared via self-organization process by electrostatic interaction between positively charged CdTe quantum dots and negatively charged Ag nanoparticles and examined with respect to their optical properties. The positively charged CdTe quantum dots and negatively charged Ag nanoparticles were synthesized separately by modifying nanoparticles surface with cationic and anionic thiol compounds, respectively. The result showed that the mixing ratio of Ag nanoparticles to CdTe quantum dots is an important parameter for controlling resulting composites. The resulting solution is optically transparent if one component is in excess. Photoluminescence of CdTe quantum dots undergoes considerably quenching if CdTe nanocrystals are in excess and SERS spectra of BVPP absorbed on Ag colloid became stronger if Ag nanoparticles are in excess. Nevertheless, while the ratio is approximately 1, micrometer-sized solid composite is obtained with the elapse of 1h after mixing. SERS spectra for solid composite only exhibit the signals of the CdS nanocrystal which reflected that prolonged refluxing during the synthesis leads to a partial hydrolysis of the thiols and to the incorporation of the sulfur from the thiol molecules into the the growing nanoparticles to form mixed CdTe(S) nanocrystal, similar to CdTe/CdS core/shell structure. From the results, we conclude that optical properties of Ag/CdTe are dependent on the mixing ratio of both nanoparticles.

Cadmium Compounds↗

PubMed2005

Surface-enhanced Raman activity and stability study of silver films prepared by reduction of Ag+ ions in N,N-dimethylformamide.

A new SERS-active silver film prepared by directly depositing silver nanoparticles on glass is reported. The spontaneous reduction of Ag+ ions in N,N-dimethylformamide (DMF) (in the absence of a protecting agent) leads to the deposition of silver nanoparticles on clean glass surfaces in contact with the solution. The observed optical micrographs and AFM images show that the arrangement of the nanoparticles is inhomogeneous and the particles appear to be closely packed. These films are shown to be excellent substrates for SERS measurements, demonstrating significant enhancement, good stability, and trace detection capability. The SERS enhancement of the silver films with different deposition times was compared and found that the 8-h film gives the largest enhancement ability with an enhancement factor estimated at about 10(9). It is also found that the silver films stored for 80 days in air show no significant degradation in their sensitivity.

Dimethylformamide↗

PubMed2005

The molecular structure and orientation of antiferroelectric liquid crystal using the density-functional theory and two-dimensional correlation-polarized infrared spectroscopy.

The structure and vibrational frequencies of the chiral antiferroelectric liquid-crystal molecule, 4-(1-methyheptyloxycarbonyl) phenyl-4-(4'-octyloxy) benzoate (MHOCPOOB), have been calculated using the density-functional theory (DFT) with the Becke-3 Lee-Yang-Parr/6-31G(d,p) level. The observed vibrational spectra have been resolved and assigned in detail by comparison to the computed values. The results indicate that the computed and observed spectra are in good agreement with each other. The stable molecular structure obtained with the DFT theory shows that the two hydrocarbon chains are all-trans zigzag conformer and nearly perpendicular to each other. The orientation of the mesogen part and the hydrocarbon chains for MHOCPOOB in the Sm-C*A phase are investigated by employing the polarization-angle-dependent infrared spectra in the electric-field induced and the two-dimensional correlation spectroscopy. After combining the experimental and theoretical results, it can be concluded that the azimuth of the achiral and chiral chains is opposite to each other, the orientation of the achiral chain is almost the same direction as the mesogen core, and the orientation of the chiral chain is nearly perpendicular to the mesogen part. The achiral and chiral CH2 chains are both a probable all-trans zigzag conformer.

Journal Article↗

PubMed2005

Effects of a central metal on the organization of 5,10,15,20-tetra-(p-chlorophenyl)-rare earth porphyrin hydroxyl compound at the air/water interface and in Langmuir-Blodgett films.

Langmuir monolayers and Langmuir-Blodgett (LB) films of 5,10,15,20-tetra-(p-chlorophenyl) terbium/gadolinium porphyrin hydroxyl compound (TbOH and GdOH) and their mixtures with stearic acid (SA) in a molar ratio of 1:1 were investigated by Brewster angle microscopy (BAM), ultraviolet-visible (UV-vis), and infrared (IR) spectroscopy and atomic force microscopy (AFM). pi-A isotherms showed that well-defined Langmuir monolayers were formed at an air/water interface for the porphyrins and their mixture with SA. The BAM observations suggest that the pi-pi interaction between the GdOH molecules is stronger than that between the TbOH molecules. This result can be further confirmed by the AFM measurements. After the introduction of SA, the pi-pi interaction between the TbOH molecules is broken and thus two phases formed in the mixed LB film. However, it cannot break the stronger pi-pi interaction between the GdOH molecules. Therefore, no phase separation is observed in the GdOH/SA LB film. IR reflection-absorption (RA) spectra showed that the COOH groups of SA are partly converted to COO(-) groups, suggesting that there is an interaction between MOH and SA in the films. This interaction leads the benzene rings of TbOH to rotate toward parallel to the substrate and those of GdOH to rotate toward perpendicular to the substrate. All these results have demonstrated that the central metal ions have great effects on the organization and formation of the films.

Journal Article↗

PubMed2005

Preparation of gold colloid monolayer by immunological identification.

The design and initial characterization of the self-assembled gold colloid monolayer by a sandwich structure via the immunological identification are reported. The 13 nm gold colloid nanoparticles and the silicon or quartz substrates have been modified with the mouse polyclonal antibody against hepatitis B virus surface antigen (PAb) and the mouse monoclonal antibody against hepatitis B virus surface antigen (MAb), respectively. They can be linked by a special reaction with their corresponding hepatitis B virus surface antigen (Antigen) as a sandwich structure. Thus, the density of gold nanoparticles self-assembled on the substrate can be readily controlled by the amount of the antigen added. The resulting substrates have been characterized by atomic force microscopy (AFM) and surface-enhanced Raman scattering (SERS) spectroscopy when the gold nanoparticles were modified with SERS-active probe molecules of 4-mercaptobenzoic acid (MBA) after silver enhancement. These data show that the gold nanoparticles are separately fixed onto the substrate and form a uniform monolayer, which possess a set of features that make them very attractive for both basic and applied uses, including roughness, high stability, and biocompatibility.

Animals↗

PubMed2005

Structure and phase transition in self-assembled films of an anti-ferroelectric liquid crystal studied by two-dimensional correlation FTIR spectroscopy.

The FTIR spectra were measured for a self-assembled film of the anti-ferroelectric liquid crystal (AFLC) molecules over a temperature range of 40-150 degrees C. The frequency and intensity variations of the infrared spectra were discussed in terms of changes in molecular orientation, conformation and intra- and/or inter-molecular interaction during phase transitions. The two-dimensional (2d) correlation analysis revealed that two hydrocarbon chains have different orientation behaviors, the shorter hydrocarbon chain is parallel to molecular long axis and the longer one is perpendicular to it. The splitting of the C=O stretching band indicated that the s-cis and the s-trans conformers of the ester group coexist in the self-assembly film. During the phase transitions, in mesogen part the C=O group adjacent to the chiral part is first response with temperature changing, following the C=O group between two phenyl rings, and eventually the phenyl rings; and the respondence with temperature of methyl is slower than that of methylene in alkyl chains.

Phase Transition↗

PubMed2004

Formation and stability of rare earth metalloporphyrin monolayer films on amino-terminated silanized quartz surfaces studied by ultraviolet-visible and X-ray photoelectron spectroscopy.

We investigated the fabrication of self-assembled monolayers of 5,10,15,20-tetra-(p-chlorophenyl)-porphyrin metal hydroxyl compounds (MOH; M=Gd, Tb, Er, Lu) on amino-terminated silanized quartz surfaces using ultraviolet-visible (UV-vis) and X-ray photoelectron spectroscopy (XPS). The orientation of MOH molecules in the films, the kinetics of the adsorption of MOH from a chloroform solution on an amino-terminated quartz substrate, and the stability of the metalloporphyrin films under natural light, UV light, and acidic and basic conditions were studied by UV-vis spectroscopy. The results indicate that the central metal is crucial in the formation of self-assembled porphyrin films and that the stability of the MOH SAMs also depends on the central metal. Under natural and UV light irradiation conditions, the stability of the MOH SAMs depends on the strength of the M-N bonds between the central metal and pyrrole nitrogens or between the central metal and the axial ligand. In the acidic conditions, the UV-vis spectra of the MOH SAMs show decreases in the absorbance and blue shifts. These spectral changes lead us to suggest that the four M-N bonds between the central metal and the pyrrole nitrogens of the porphyrins are cleaved and the resulted porphyrins are protonated under acidic conditions. Thus, it is likely that the protonated porphyrins and MOH form pi-pi complexes with a parallel stacking of the macrocycles through the electrostatic attractive interaction in the SAMs, resulting in the blue shifts of the Soret bands of the SAMs.

Journal Article↗

PubMed2004

Self-assembled metal colloid films: two approaches for preparing new SERS active substrates.

In this paper, we propose two new approaches for preparing active substrates for surface-enhanced Raman scattering (SERS). In the first approach (method 1), one transfers AgI nanoparticles capped by negatively charged mercaptoacetic acid from a AgI colloid solution onto a quartz slide and then deoxidizes AgI to Ag nanoparticles on the substrate. The second approach (method 2) deoxidizes AgI to Ag nanoparticles in a colloid solution and then transfers the Ag nanoparticles capped by negatively charged mercaptoacetic acid onto a quartz slide. By transfer of the AgI/Ag nanoparticles from the colloid solutions to the solid substrates, the problem of instability of the colloid solutions can largely be overcome. The films thus prepared by both approaches retain the merits of metal colloid solutions while they discharge their shortcomings. Accordingly, the obtained Ag particle films are very suitable as SERS active substrates. SERS active substrates with different coverages can be formed in a layer-by-layer electrostatic assembly by exposing positively charged surfaces to the colloid solutions containing oppositely charged AgI/Ag nanoparticles. The SERS active substrates fabricated by the two novel methods have been characterized by means of atomic force microscopy (AFM) and ultraviolet-visible (UV-vis) spectroscopy. The results of AFM and UV-vis spectroscopy show that the Ag nanoparticles grow with the increase in the number of coverage and that most of them remain isolated even at high coverages. Consequently, the surface optical properties are dominated by the absorption due to the isolated Ag nanoparticles. The relationship between SERS intensity and surface morphology of the new active substrates has been investigated for Rhodamine 6G (R6G) adsorbed on them. It has been found that the SERS enhancement depends on the size and aggregation of the Ag particles on the substrates. Especially, we can obtain a stronger SERS signal from the substrate prepared by method 1, implying that for the metal nanoparticles capped with stabilizer molecules such as mercaptoacetic acid, the in situ deoxidization in the film is of great use in preparing SERS active substrates. Furthermore, we have found that the addition of Cl- into the AgI colloid solution changes the surface morphology of the SERS active substrates and favors stronger SERS enhancement.

Journal Article↗

PubMed2004

Novel method for preparing controllable and stable silver particle films for surface-enhanced Raman scattering spectroscopy.

A new surface-enhanced Raman scattering (SERS) active substrate has been developed based on our previous study. Small silver nanoparticles on a quartz slide can be enlarged by using a mixture of commercially available reagents called Silver Enhancer and Initiator. The optical properties and characteristics of the new substrate have been investigated by ultraviolet-visible (UV-Vis) spectroscopy and atomic force microscopy (AFM). The results indicate that the small silver nanoparticles grow and some silver aggregates emerge on the quartz slide after the slide is immersed into the Silver Enhancer and Initiator Mixture (SEIM). The average diameter of the silver nanoparticles on the substrate becomes approximately double after the immersion into SEIM for 20 s. 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BPENB) was used as a Raman probe to evaluate the enhancement ability of the new silver substrate. It has been found that the SERS intensity can be increased about 10 times by using the substrate treated by SEIM compared with that without being treated by SEIM. Interestingly enough, the SERS enhancement increases with time. This may be due to the reorganization of silver nanoparticles on the quartz surface. The new substrate can remain active for more than 90 days. The adsorption mode of BPENB on the new substrate and the dependence of the BPENB configurations on the concentration of BPENB in methanol solution have also been investigated by SERS or UV-Vis spectroscopy. The SERS spectra of a self-assembled monolayer (SAM) BPENB film adsorbed on a silver substrate treated by SEIM show that BPENB molecules are chemically absorbed through the Ag-N bond. Consequently, a nearly perpendicular orientation of BPENB on the silver surface is proposed. The SERS spectra of BPENB SAMs on the new substrates fabricated from methanol solutions with different concentrations are compared. The concentration dependence of the SERS spectra reveals that the BPENB molecules are adsorbed on the silver film as monomers when the film is prepared from the solution with a lower concentration (<4 x 10(-6) M) and as aggregates when it is prepared from the solution with a higher concentration (>1 x 10(-5) M).

Journal Article↗

PubMed2004

Ultraviolet-visible and surface-enhanced Raman scattering spectroscopy studies on self-assembled metalloporphyrin films on organic monolayer-modified ultra-thin silver substrates.

A self-assembled monolayer (SAM) film of 5,10,15,20-tetra-(para-chlorophenyl)-porphyrin terbium (or lutetium) hydroxy compound (TbOH/LuOH) fabricated on a silver substrate premodified with a SAM of 4-mercaptopyridine (PySH) was studied by ultraviolet-visible (UV-Vis) spectroscopy and surface-enhanced Raman scattering (SERS) spectroscopy. PySH can modify the substrate and deliver its pyridyl group pointing out from the silver surface. Thus, we can investigate the effects of the central metals of the metalloporphyrins in the formation of the composite films. For the TbOH-PySH composite film, a new absorption band arising from TbOH appears at 425 nm, and a band at 512 nm due to the PySH-modified silver substrate shifts to a longer wavelength (538 nm). The results suggest that TbOH is successfully assembled on the top of PySH-modified silver film and that there is an interaction between TbOH and PySH in the film. The frequency shifts and relative intensity changes of bands due to PySH in the SERS spectra imply the coordination of the pyridyl group on Tb in the SAM. As for the LuOH-PySH composite film, its SERS spectrum shows bands arising from both the LuOH and PySH moieties, indicating that LuOH is assembled on the PySH-modified silver film. Furthermore, a band at 1221 cm(-1) due to the in-plane C-H bending mode of PySH disappears, implying that the pyridyl moiety of PySH becomes more parallel to the silver surface upon the formation of the LuOH-PySH composite film. Additionally, an absorption band at 515 nm shifts to a longer wavelength (541 nm) and becomes broad upon the formation of the composite film, suggesting an interaction between LuOH and PySH in the film. By comparing the spectral changes between the two self-assembled composite films, we find that the central metal is crucial in the formation of the composite films. The structure and orientation of the composite films depend on the central metal of the metalloporphyrin compounds.

Journal Article↗

PubMed2004

Ultrasensitive detection of 1,4-Bis(4-vinylpyridyl)phenylene in a small volume of low refractive index liquid by surface-enhanced Raman scattering-active light waveguide.

This paper reports a novel surface-enhanced Raman scattering (SERS)-active light waveguide method for ultrasensitive detection of a sample dissolved in a small volume of low refractive index liquid. The SERS-active light waveguide demonstrated in this study was constructed via the light-guiding silica capillary. The surface of its inner wall was modified with SERS-active silver nanoparticles that can remarkably enhance Raman signals. The capillary with SERS-active modified layer was filled with the sample solution to form the SERS-active liquid core (LC) fiber. The incident laser beam travels through the waveguide in a totally reflective mode within the fiber wall and penetrates a small distance into the sample solution by the evanescent wave field. The Raman scattering of the analytes adsorbed onto the surface of the SERS-active modified layer can be excited by the laser beam and refracted into the fiber wall. Thus, a sample dissolved in low index liquid, e.g., methanol, can be quantitatively monitored by Raman spectroscopy and detection limit of its concentration is lower than 10(-9) mol/L.

Light↗

PubMed2003

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).

Animals↗

PubMed2003

Comparison of molecular orientation and phase transition behaviors in the two kinds of ordered ultrathin films of reversed duckweed polymer ES-3 studied by infrared grazing reflection-absorption spectroscopy.

A multilayer LB film and a casting film of reversed duckweed polymer ES-3 on Au-evaporated glass slides were investigated by Fourier Transform infrared grazing reflection-absorption spectroscopy. It is found that the two kinds of ordered ultrathin films have different orientation of alkyl chains, nearly perpendicular to the substrate surface for the LB film while rather tilted for the casting film. The studies on their thermal transition behaviors indicate that both of the films have three phase transition processes, respectively, occurring near 65, 105 and 140 degrees C for the former while near 80, 105 and 140 degrees C for the latter, but show different transition behavior in the each corresponding transition process. It is referred that at room temperature there are island-like domain structures formed in the LB film, but no ones in the casting film; however, the latter can form the domain structures between the first two transition points due to the desorption of solvents. The formation of domain structure seems to play two important roles, one of which is to make alkyl chains more perpendicular to the substrate surface, and the other to make alkyl chains more packed closely. Thermal cyclic experiments reveal that neither of the films could return to its original state after thermal cyclic treatment up to the temperature, which is above the third transition point, although its alkyl chain becomes highly ordered again.

Polymers↗

PubMed2003

Raman spectroscopic investigation of the single-monolayer Langmuir-Blodgett film of C16NaphOH and C10AzoNaphC4N-SDS.

Raman spectra were measured for Langmuir-Blodgett (LB) films of C(16)NaphOH and C(10)AzoNaphC(4)N-SDS on Calcium Fluorite substrate for the first time. In order to find out favorable excitation condition, Raman spectra of the single and multi-monolayer LB films excited at different lines at 244, 514, 633 and 778 nm are recorded and compared in the present study. Raman spectrum of the monolayer LB film of C(16)NaphOH excited by 244 nm demonstrate that excellent signal to noise is achieved even for one monolayer LB film with an extremely short integrating time as 60 s because of being resonantly enhanced, while no meaningful spectra were recorded under the same condition for the monolayer LB film of C(10)AzoNaphC(4)N-SDS because of burning. Using a HeNe 633 nm excitation the problem with strong substrate fluorescence was partially solved, since under these conditions this fluorescence is mainly outside the fingerprint region of the LB film molecules (1000-2000 cm(-1)). Therefore by using the HeNe laser excitation, Raman spectra with high signal to noise ratio of LB films of C(16)NaphOH were collected and shown in this paper. These findings stress again the necessity to define an appropriate Raman system for this special application of LB film diagnosis.

Alkanes↗