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ABSTRACT: Chemical imaging analysis holds great potential in probing the chemical heterogeneity of samples with high spatial resolution and molecular specificity. This paper demonstrates the implementation of Raman mapping for microscopic characterization of tablets containing chloramphenicol palmitate polymorphs with the aid of a new multivariate image segmentation approach based on spatial directed agglomeration clustering. This approach performs the agglomeration clustering by stepwise merging the pixels possessing both spatial closeness and spectral similarity into clusters that define the image segmentation. The incorporation of spatial closeness into the clustering process enables the approach to improve the robustness and avoid poorly defined image segmentation arising from clusters with highly separated pixels. Additionally, the stepwise merging of clusters offers an F-statistic-based procedure to automatically ascertain the number of image segments. Raman mapping analysis of tablets containing two polymorphs of chloramphenicol palmitate followed by multivariate image segmentation reveals that the proposed technique offers the identification of each polymorph and a quantitative visualization of the spatial distribution of the polymorphs identified. This technique holds promise in rapid, noninvasive, and quantitative polymorph analysis for pharmaceutical production processes.
Analytical Chemistry 10/2006; 78(17):6003-11. · 5.86 Impact Factor
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ABSTRACT: A quartz crystal microbalance (QCM) sensor was proposed for the detection of small molecule biotin based on the mixed self-assembled monolayer (SAM) of thiols on gold substrate and the bioaffinity difference between an analyte (biotin) and an analogue compound (HABA) in binding avidin. Avidin formed a metastable complex with 2-[(4-hydroxyphenyl)azo]benzoic acid (HABA) immobilized on the crystal surface. When the sensor contacts a sample solution containing biotin, the avidin was released from the sensor surface to form a more stable complex with biotin in solution. The frequency change recorded is proportional to the desorbed mass of avidin, and there is a clear mathematic relationship between the frequency change and the biotin concentration. The use of mixed SAMs allows the stable attachment of bioreceptor molecules on the QCM, and enhances the amount of the immobilized molecules on the QCM, as a longer "space arm" in the mixed SAMs makes this monolayer membrane more accessible to capture the immobilized molecules. The proposed bioaffinity sensor has nice response to biotin in the range of 0.017-1.67 microg/mL. The sensor could be regenerated under very mild conditions simply by reimmersion of the sensor into a biotin solution to desorb the surplus avidin.
Biosensors and Bioelectronics 03/2006; 21(8):1545-52. · 5.60 Impact Factor
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ABSTRACT: Nanosized flower-like ZnO was synthesized by a simple hydrothermal method which is a convenient, environment friendly, inexpensive and efficient process. Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to confirm the material structure and the crystallite microstructure. Then ZnO was dispersed in the chitosan solution to form a ZnO/chitosan composite matrix for the fabrication of H2O2 biosensor. This composite combined the advantages of inorganic species (ZnO) and organic polymer (chitosan). The parameters affecting the fabrication and experimental conditions of biosensors were optimized. Using hydroquinone as the mediator, the biosensor showed a fast response of less than 5s with the linear range of 1.0x10(-5) to 1.8x10(-3) M H2O2 with a correlation coefficient of 0.995 (n=20). The detection limit of the sensor was found to be 2.0 microM, based on a signal-to-noise ratio of 3. The biosensor exhibited satisfactory reproducibility and stability and retained about 78% of its original response after 40 days storage in a phosphate buffer at 4 degrees C.
Journal of Inorganic Biochemistry 11/2005; 99(10):2046-53. · 3.35 Impact Factor
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ABSTRACT: Phytic acid (IP6) and its salts are promising reagents to alleviate corrosion of metals, which are environmentally friendly and highly efficient, compared to some traditional inhibitors toxic to environment. This paper reports the studies of the structure and anticorrosion features of two kinds of the self-assembled monolayers (SAMs) of IP6 at the silver surface under various pH values, 1.27 and 13, by using electrochemical and surface enhanced Raman scattering (SERS) spectroelectrochemical measurements. On the basis of recorded ex situ SERS spectra, different adsorption modes of both resulted SAMs of IP6 at the silver surfaces have been postulated. In addition, based on in situ SERS electrochemical measurements, a tentative explanation for the difference in corrosion potentials of two kinds of the silver surfaces in the presence of SAMs formed from completely protonated or deprotonated IP6 molecules has also been presented.
10/2004;
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ABSTRACT: Multilayered thin films were prepared by a layer-by-layer (LbL) deposition of sulfonated β-cyclodextrin (s-β-CD) and cationic poly(allylamine) hydrochloride (PAH) on the surface of a quartz slide. A self-assembled fluorescent host, s-β-CD/neutral red was formed by the inclusion interaction of neutral red (NR) with the s-β-CD immobilized on the multilayered films. An optical sensor for lithocholic acid (LA), based on the fluorescence quenching of s-β-CD/NR complex immobilized on the multilayered films, has been developed, in which NR served as a sensitive fluorescence indicator probe. The decrease of fluorescence intensity of s-β-CD/NR complex in the presence of LA was attributed to the formation of an inclusion complex between s-β-CD and LA, which has been utilized as the basis of the fabrication of a LA-sensitive fluorescence sensor. The response mechanism of sensor has been discussed in detail. The analytical performance characteristics of the proposed LA-sensitive sensor were investigated. The sensor can be applied to the quantification of LA with a linear range covering from 2 uM to 60 uM and a detection limit of 1 uM. The sensor exhibits excellent reproducibility, reversibility and selectivity.
Journal of Photochemistry and Photobiology A: Chemistry. 171(2):137-144.
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ABSTRACT: The effect of Pt on gas sensing properties of nano-crystalline CdSnO3, a semiconducting oxide with perovskite structure, was studied. CdSnO3 was prepared by solid-state reaction of inorganic reagents 3CdSO4·8H2O, SnCl4·5H2O and NaOH. The thermal analysis was detected by means of thermogravimetric-differential thermal analysis (TG-DTA). XRD was used to confirm the material structure and TEM to depict the crystallite microstructure and the specific surface area was measured by Brunaur–Emmett–Teller (BET) method. Noble metal additive Pt of different concentrations from 0.1 to 2 at.% was incorporated into CdSnO3 by impregnation technique. Conductance responses of the nano-crystalline CdSnO3 thick films were measured by exposing the films to C2H5OH, CO, CH4, C4H10, gasoline and LPG at different operating temperatures. It was found that sensors doped with Pt exhibited good sensitivity and selectivity to the vapor of C2H5OH and the optimum sensitivity is obtained with the sensor doped with 1.5 at.% Pt.
Analytica Chimica Acta. 527(1):21-26.
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ABSTRACT: n-Type semi-conductive nanometer material MgFe2O4 was synthesized by solid-state reaction of inorganic reagents MgSO4, Fe(NO3)3·9H2O, and NaOH. The process was a convenient, environment friendly, inexpensive and efficient preparation method for MgFe2O4 nanomaterial. X-ray diffraction (XRD) was used to confirm the material structure and transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) to depict the crystallite microstructure. Conductance responses of the nanocrystalline MgFe2O4 thick film were measured by exposing the film to reducing gases like methane (CH4), hydrogen sulfide (H2S), liquefied petroleum gas (LPG) and ethanol gas (C2H5OH). It was found that the sensor exhibited various sensing responses to these gases at different operating temperature. Furthermore, the sensor exhibited a fast response and a good recovery. Successive on and off responses could be repeated without observing major changes in the response signal.
Sensors and Actuators B: Chemical.
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ABSTRACT: The paper reports the preparation and gas sensing characteristic of NiFe2O4 nanopowder with and without different noble metal dopants such as Au, Pt, Pd. Ultrafine NiFe2O4 powders were prepared by solid-state reaction of inorganic reagents, Ni(Ac)2, Fe(NO3)3, and NaOH. XRD and Raman spectrometer were used to confirm the material structure and TEM to depict the crystallite microstructure. Au, Pd and Pt with different concentration were incorporated into NiFe2O4 by impregnation technique. The electrical resistance response to H2S gas of the sensors based on the materials was investigated at different operating temperature and different gas concentrations. The results show that NiFe2O4 is a p-type semiconductor and the sensor response of the doped NiFe2O4 sensors was superior to that of the undoped ones. The sensor response increased linearly with the H2S gas concentration up to 100 ppm. The sensor with the 1.5 wt.% Au doped NiFe2O4 showed excellent electrical resistance response towards 5 ppm H2S gas and the sensor response was up to 35.8 at 300 °C. The 1.5 wt.% Pt doped one was less sensitive to H2S but work at lower temperature, 240 °C. The gas-sensing behavior of these materials with respect to various reducing gases like liquefied petroleum gas (LPG), methane (CH4), carbon monoxide (CO), butane (C4H10) and hydrogen gas (H2) suggested that the H2S gas sensor developed possesses an excellent selectivity. The interaction mechanism and correlations between the electrical resistance response and noble metal dopants were discussed.
Sensors and Actuators B: Chemical.
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ABSTRACT: An amperometric immunosensor was developed based on immobilizing antibody on the surface of modified CdFe2O4 magnetic nanoparticles. The goat anti-human IgG antibody (anti-IgG) was first covalently immobilized to core–shell (CdFe2O4–SiO2) magnetic nanoparticles, which were surface-modified with amino groups on the surface. The resulting bio-magnetic nanoparticles were attached to the surface of carbon paste electrode (CPE) with the help of a permanent magnet. A sandwich immunoassay was performed on the bio-magnetic nanoparticles monolayer supported by CPE. The assay comprised first loading of IgG on the bio-magnetic nanoparticles monolayer, then blocking in BSA solution, followed by incubation in anti-IgG-HRP conjugate, and finally the amperometric detection with hydroquinone as a mediator. The linear range for IgG assay was 0.51–30.17 μg ml−1 and the detection limit was 0.18 μg ml−1. The simple manipulations of construction and low cost were main advantages of proposed immunosensing method.
Sensors and Actuators B: Chemical.
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ABSTRACT: A compound material of multi-walled carbon nanotubes (MWNTs) coated with SnO2 was synthesized at ambient conditions. The Raman spectra, X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed that the existence of SnO2 nanoparticles were on the outside of the MWNTs. The gas sensing properties of the material were studied. It was found that the sensor exhibited nice sensing responses to liquefied petroleum gas (LPG) and ethanol gas (C2H5OH) and a fast response and recovery within seconds. Furthermore, the gas sensor responses increased linearly with the increment of the gas concentrations of LPG and ethanol.
Thin Solid Films.
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ABSTRACT: An optical sensor for cetyltrimethylammonium chloride (CTAC), based on the fluorescence quenching of berberine/butylated β-cyclodextrin (HDB-β-CD) complex immobilized in plasticized poly(vinyl chloride) (PVC) membrane has been developed, in which berberine served as a sensitive fluorescence indicator probe. The decrease of fluorescence intensity of berberine/HDB-β-CD complex upon the addition of CTAC was attributed to the formation of an inclusion complex between HDB-β-CD and CTAC, which has been utilized as the basis of the fabrication of a CTAC-sensitive fluorescence sensor. The response mechanism of sensor has been discussed in detail. The analytical performance characteristics of the proposed CTAC-sensitive sensor were investigated. The sensor can be applied to the quantification of CTAC with a linear range covering from 7.0 × 10−11 to 4.0 × 10−9 mol L−1 with a detection limit of 3.0 × 10−11 mol L−1. The sensor exhibits excellent reproducibility, reversibility and selectivity. The recommended method was successfully used for the determination of CTAC in water samples.
Sensors and Actuators B: Chemical.
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ABSTRACT: An approach to prepare novel glass-coated gold core-shell nanoparticles embedded with Raman active molecules has been developed. This strategy eliminates the need of a coupling agent and enables efficient embedding of most of commercially available Raman active dyes, even those with weak affinity to a gold surface. Our experiments have demonstrated the hypothesis that the glass encapsulation chemistry is based on the reaction between silanol groups hydrolyzed by TEOS and citrate anion groups adsorbed onto the gold nanoparticles leading to the formation of a silica layer through further reaction with silanol groups of other hydrolyzed TEOS. Furthermore, it has been demonstrated the potential of these novel nanoparticls as Raman tags in ultrasensitive immunoassays for human IgG antigen with a detection limit of 4.9 ng/ml.
Analytica Chimica Acta.
