Daqian Song

Study on the interaction mechanism between DNA and the main active components in Scutellaria baicalensis Georgi

Abstract Binding of baicalein, wogonin and baicalin to fish sperm DNA was studied by using ethidium bromide dye as a fluorescence probe. To study the binding mechanism, the absorption, fluorescence, melting temperature and viscosity measurement were carried out. The experimental results indicated that the planar of flavonoids intercalated to the DNA helix. When bound to DNA, flavonoids showed hyperchromic and blue shift in the absorption spectra and fluorescence quenching (>50%) in the fluorescence spectra. Furthermore, the intercalative binding was consistent with the red shift in the position of λ max in the fluorescence spectra. It was also found that ionic strength had little or no effect on the binding of flavonoids and DNA. Stern–Volmer plots at 25 and 37°C showed that the quenching of fluorescence by flavonoids was a combined quenching process. The binding site number n, apparent binding constant K A at 25 and 37°C, and the corresponding thermodynamic parameters ΔG, ΔH, ΔS at 25°C were obtained. The interaction of flavonoid–metal complexes with DNA was also studied by spectral methods, and the results suggested that the complexes intercalated into DNA.

A novel surface plasmon resonance biosensor based on graphene oxide decorated with gold nanorod-antibody conjugates for determination of transferrin.

A surface plasmon resonance (SPR) biosensor based on graphene oxide (GO) decorated with gold nanorod (AuNR)-antibody conjugates was developed. Compared with traditional SPR biosensor, GO sheets were assembled on the amino-modified Au film via electrostatic interaction, and then AuNR-antibody conjugates were immobilized via carbodiimide-assisted amidation reaction. The abundant oxygen-containing functional groups, large specific surface area and friendly biocompatibility of GO sheets are beneficial to the immobilization of AuNR-antibody conjugates. Meanwhile, AuNRs are anchored to the GO surface through antibody and function as enhancers for the transferrin determination, which greatly enhance the sensitivity of the detection. As a result, the present biosensor shows a satisfactory response to transferrin in the concentration range of 0.0375-40.00 μg mL(-1). The lowest concentration of transferrin that can be determined by this method is about 32-fold lower than that obtained with the sensor based on Au film. This design affords a facile method of controlling the assembly of AuNRs on the GO sheets and can be easily extended to other protein detection by preparing corresponding AuNR-antibody conjugates.

A novel sandwich immunosensing method for measuring cardiac troponin I in sera.

Common methods for monitoring human cardiac troponin I (cTn I) are based on using antibodies against cTn I labeled with horseradish peroxidase, radioactive isotopes, or other labels. In this study, a novel label-free sandwich immunosensing method for measuring cTn I was developed. Three monoclonal antibodies (mAbs 9F5, 2F11, and 8C12) against human cTn I were generated by the commonly used hybridoma technique and characterized by a surface plasmon resonance (SPR) biosensor. An optimal pair of mAbs for measuring human cTn I was selected, as both mAbs have high affinities for cTn I and do not compete against each other for cTn I binding. An optical immunosensor for measuring cTn I in sera based on SPR was developed by using avidin as an intermediate layer and biotinylated-2F11 as the capturing antibody. Two detection methods for cTn I with the immunosensor were performed: (1) the direct detection of cTn I with a detection range of 2.5 to 40 microg/L and (2) the sandwich immunosensing method. In the sandwich assay mode, the second antibody 9F5 biologically amplified the sensor response. As a result, the sandwich assay showed a sensitivity of 0.25 microg/L and a detection range of 0.5 to 20 microg/L with within-run variation of 4.9 to 6.7% and between-run variation of 5.2 to 8.4%. This method has greatly enhanced the sensitivity for detection compared to that previously reported in the literatures.

Preparation of surface plasmon resonance biosensor based on magnetic core/shell Fe3O4/SiO2 and Fe3O4/Ag/SiO2 nanoparticles

In this paper, surface plasmon resonance biosensors based on magnetic core/shell Fe(3)O(4)/SiO(2) and Fe(3)O(4)/Ag/SiO(2) nanoparticles were developed for immunoassay. With Fe(3)O(4) and Fe(3)O(4)/Ag nanoparticles being used as seeding materials, Fe(3)O(4)/SiO(2) and Fe(3)O(4)/Ag/SiO(2) nanoparticles were formed by hydrolysis of tetraethyl orthosilicate. The aldehyde group functionalized magnetic nanoparticles provide organic functionality for bioconjugation. The products were characterized by scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), FTIR and UV-vis absorption spectrometry. The magnetic nanoparticles possess the unique superparamagnetism property, exceptional optical properties and good compatibilities, and could be used as immobilization matrix for goat anti-rabbit IgG. The magnetic nanoparticles can be easily immobilized on the surface of SPR biosensor chip by a magnetic pillar. The effects of Fe(3)O(4)/SiO(2) and Fe(3)O(4)/Ag/SiO(2) nanoparticles on the sensitivity of SPR biosensors were also investigated. As a result, the SPR biosensors based on Fe(3)O(4)/SiO(2) nanoparticles and Fe(3)O(4)/Ag/SiO(2) nanoparticles exhibit a response for rabbit IgG in the concentration range of 1.25-20.00 μg ml(-1) and 0.30-20.00 μg ml(-1), respectively.

Magnetic ionic liquid-based dispersive liquid–liquid microextraction for the determination of triazine herbicides in vegetable oils by liquid chromatography

Magnetic ionic liquid-based dispersive liquid-liquid microextraction (MIL-based DLLME) was developed for extracting triazine herbicides from vegetable oils. The MIL, 1-hexyl-3-methylimidazolium tetrachloroferrate ([C6mim] [FeCl4]), was used as the microextraction solvent. The magnetic separation time was shortened by simply mixing carbonyl iron powder with the MIL in the sample after DLLME. The effects of several important experimental parameters, including the amount of MIL, the time of ultrasonic extraction, the type and the volume of cleanup solvent were investigated. The MIL-based DLLME coupled with liquid chromatography gave the limits of detection of 1.31-1.49ngmL(-1) and limits of quantification of 4.33-4.91 ng mL(-1) for triazine herbicides. When the present method was applied to the analysis of vegetable oil samples, the obtained recoveries were in the range of 81.8-114.2% and the relative standard deviations were lower than 7.7%. Compared with existing methods, the performances achieved by the present method were acceptable.

Determination of affinities and antigenic epitopes of bovine cardiac troponin I (cTnI) with monoclonal antibodies by surface plasmon resonance biosensor.

A surface plasmon resonance (SPR) biosensor based on wavelength modulation was used for real-time detection of the interaction of three monoclonal antibodies and antigens of bovine cardiac troponin I (cTnI). In order to recognize antigenic epitopes of bovine cTnI, two experimental modes were applied. In the first experimental mode, three monoclonal antibodies were divided into three groups and three experiments were performed on biosensor surfaces prepared with protein A. In the second experimental mode, antigen was immobilized on the biosensor surface prepared by the amine-coupling method and three monoclonal antibodies were detected in turn. The results obtained by the two modes are consistent. In addition, the affinities of the monoclonal antibodies for the antigen were also determined by the association rate and the disassociation rate in real-time. These results validate the biosensor technology and illustrate how biosensors based on wavelength modulation can be used to study the interaction of monoclonal antibodies and antigens in real time.

Magnetic solid-phase extraction of five pyrethroids from environmental water samples followed by ultrafast liquid chromatography analysis

In this study, the polystyrene-coated magnetic nanoparticles (MNPs/PSt) were successfully prepared and characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometry. The as-prepared MNPs/PSt were used as the adsorbent in magnetic solid phase extraction of five pyrethroids, including lambda-cyhalothrin, deltamethrin, esfenvalerate, permethrin, bifenthrin, in environmental water samples. The five pyrethroids were determined by ultra fast liquid chromatography-ultraviolet spectrometry. The influencing factors, including amount of MNPs/Pst, extraction time, pH value, type and volume of desorption solvent and desorption time, were examined and optimized. The extraction recoveries obtained with merely 50mg of MNPs/Pst were very satisfactory. The whole extraction process could be completed within 0.5h. The MNPs/PSt can be reused after an easy washing process. Thus, a simple, green, economical, time saving and effective method for pyrethroids analysis in environmental water samples was established. A high enrichment factor of 500 was achieved and the limits of detection for lambda-cyhalothrin, deltamethrin, esfenvalerate, permethrin, bifenthrin were 0.015±0.001 ng mL(-1), 0.012±0.001 ng mL(-1), 0.026±0.001 ng mL(-1), 0.020±0.001 ng mL(-1), 0.013±0.001 ng mL(-1), respectively. Recoveries obtained by analyzing spiked water samples at three concentration levels (0.100±0.001 ng mL(-1), 1.000±0.001 ng mL(-1), 10.000±0.001 ng mL(-1)) were between 78.97±8.38% and 96.05±8.38%. The standard curves for the five pyrethroids showed good linearity with the correlation coefficients in the range of 0.9994-0.9999. The intra-day and inter-day precision were satisfactory with the RSDs in the range of 2.05-5.52% and 2.73-8.38%, respectively.

Determination of five pyrethroids in tea drinks by dispersive solid phase extraction with polyaniline-coated magnetic particles.

The polyaniline-coated magnetic particles with bowl-shaped morphology (Fe3O4/C/PANI microbowls) were successfully prepared and characterized by scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry. The prepared microbowls were used as the magnetic adsorbent in dispersive solid phase extraction of five pyrethroids, including cyhalothrin, beta-cypermethrin, esfenvalerate, permethrin and bifenthrin in plain tea drinks. The effects of experiment factors, including amount of Fe3O4/C/PANI microbowls, pH value, ultrasound extraction time and desorption conditions, were investigated. The extraction recoveries obtained with 8 mg of magnetic microbowls were satisfactory, and the microbowls can be reused after easy washing. Thus, a simple, selective and effective method for the determination of the pyrethroids was established successfully. The results showed that the method had good linearity (r=0.9992-0.9998), and the limits of detections (LODs) were from 0.025 to 0.032 ng mL(-1). The intra-day and inter-day relative standard deviations (RSDs) were in the range of 2.4-6.1% and 3.5-8.8%, respectively. Recoveries obtained by analyzing the real tea drinks were in the range of 72.1-118.4%.

Water-soluble ZnO-Au nanocomposite-based probe for enhanced protein detection in a SPR biosensor system

A surface plasmon resonance biosensor based on ZnO-Au nanocomposites was developed for the detection of rabbit IgG. The ZnO-Au nanocomposites can bind protein by covalent attachment to construct a probe for target analyte. The probe with unique optical properties and good biocompatibility could enhance the sensitivity of SPR biosensor. Under the optimized conditions, the biosensor based on ZnO-Au nanocomposites exhibits a satisfactory response to rabbit IgG in the concentration range of 0.15-20.00 μg ml(-1). For comparison, the biosensor based on Au film and the biosensor based on Au nanoparticles were also studied for the detection of rabbit IgG. The biosensor based on Au film shows a response to rabbit IgG in the concentration range of 2.50-20.00 μg ml(-1). The biosensor based on Au nanoparticles shows a response in the concentration range of 0.30-20.00 μg ml(-1). The biosensor based on ZnO-Au nanocomposites was therefore found to be the most sensitive of the three types of biosensors. The lowest concentration of rabbit IgG that can be determined by the proposed biosensor is about 16-fold lower than that of the biosensor based on Au film alone.

Preparation and application of novel nanocomposites of magnetic-Au nanorod in SPR biosensor.

A novel nanocomposite Fe(3)O(4)-Au nanorod (AuNR) was prepared and used as the substrate in the surface plasmon resonance (SPR) biosensor to detect goat IgM. Fe(3)O(4)-AuNR nanocomposites were synthesized by a method of seed-mediated growth, and further characterized by molecular absorption spectroscopy, transmission electronic microscopy (TEM), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The nanocomposites exhibit both magnetic property and exceptional optical property, which are beneficial to the antibody immobilization and the sensitivity of detection. The sensing membrane can be regenerated easily and the experimental procedure is simplified. Moreover, the Au nanorods show two plasmon resonance wavelengths defined as transverse mode and longitudinal mode, and the longitudinal plasmon wavelengths are more sensitive to the changes in the dielectric properties of the surroundings. Fe(3)O(4)-AuNR nanocomposites got a high sensitivity in detection of antibody-antigen immunoassay. In the optimal conditions, the biosensor based on Fe(3)O(4)-AuNR nanocomposites exhibits a satisfactory response to goat IgM in the concentration range of 0.15-40.00 μg mL(-1). However, the biosensor without Fe(3)O(4)-AuNR nanocomposites shows a response to goat IgM in the concentration range of 1.25-40.00 μg mL(-1). As a result, the sensitivity of the biosensor based on Fe(3)O(4)-AuNR nanocomposites is enhanced significantly.