Raman intensity enhancement of molecules adsorbed onto HfS2 flakes up to 200 layers.

Newly emerging two-dimensional transition metal dichalcogenide HfS2 has received considerable attention recently due to its ultrahigh photoresponsivity, well-balanced carrier mobility and an appropriate band gap which offer potential in electronic and optoelectronic devices. In this work, HfS2 flakes up to 200 layers with varying color contrasts are fabricated and transferred on a SiO2/Si substrate. The Raman intensities of HfS2 flakes and Raman intensities of molecules adsorbed on HfS2 flakes are quantitatively studied both theoretically and experimentally by considering an optical interference effect. The effects of the main experimental factors: thickness of SiO2 and excitation wavelength on Raman intensities are also theoretically investigated. Due to the low absorption of HfS2, many strong high-order interference-induced enhancement peaks are observed which are different from high absorption materials like graphene and MoS2, in which only 2-4 interference-induced enhancement peaks exist. Due to the environmental instability of single layer HfS2 under ambient conditions, multi-layer HfS2 is a better choice than single layer HfS2 as a Raman scattering substrate which has a stronger Raman enhancement and a better environmental stability. The discovery here will expand the application of HfS2 flakes in molecular detection.

[The Synthesis, Luminescence and Energy Transmission of NaLa(MoO4) 2 : Eu3+/Tb3+/Tm3+ Materials].

A series of Eu3+ /Tb3+ /Tm3+ single/co-doped NaLa(MoO4)2 (NLM) phosphors have been synthesized by microemulsion-hydrothermal method. Phosphor crystal structure, morphology and luminescent properties were tested and studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectroscopy. The results show that the prepared samples are all tetragonal single crystals. By way of substitution, the sites of La3+ are replaced by Eu3+, Tb3+ and Tm3+. Morphology of the samples are tetragonal sheet structure and the size of particles is 1 - 1.5 µm. When the doping concentration of Eu3+ is 9%, NLM : 9%Eu3+ phosphor emission peak is the strongest at 616 nm, the critical transfer distance (R(c)) between Eu3+ in the NLM matrix is about 15.20 Å at this time. At the emission spectrum of NLM : 9%Eu3+, the peak at 591 nm is the magnetic dipole transition of 5D0 to 7F1 of Eu3+. The peak at 616 nm is the electric dipole transition of 5D0 to 7 F2 of Eu3+. Electric dipole transition emission intensity is about 10 times of the strength of the magnetic dipole transition. This indicates that Eu3+ is located at noninversion symmetry site. By Fixing Eu3+ (Tb3+) concentration and varying the concentration of Tb3+ (Eu3+), the energy transfer mechanism between Eu3+ and Tb3+ was studied. By adjusting the Eu3+, Tb3+ and Tm3+ doping concentrations, tunable luminescence of visible light region is implemented under the single matrix. The luminescence of NLM x%Eu3+, y%Tb3+, z%Tm3+ phosphors are translated from blue (0.205, 0.135) to pseudo-white (0.305, 0.266) under 360 nm irradiation.

[The Different Phase, Morphology Controllable Synthesis and Luminescent Properties Investigation of NaYF4: Yb, Er].

Using sodium fluoride and rare earth nitrate as raw materials and sodium citrate as surfactant, micron grade NaYF4 upconversion luminescent materials were prepared by hydrothermal method. By X-ray diffraction(XRD), scanning electron microscope(SEM) and fluorescence spectrometer, the crystal phase, morphology and luminescent characteristics of the prepared samples were investigated. The results showed that the phase of the samples could generate a transition from cubic phase to hexagonal phase by adjusting the proportion (5, 6, 7, 8, 9, 11) of NaF/RE , and the X ray diffraction peaks for the cubic and hexagonal phase of samples exactly matched with those of the standard card of PDF# 77-2042 and PDF# 16-0334, respectively. The SEM photographs showed that the crystallinity of samples was high and the dispersibility was favourable, the morphology were translated from microrods to hexagonal microplates. The samples upconversion luminescent spectra showed the intensity enhancement of red and green light emission peaks with increasement of the ratio of NaF/RE3+. The green emission peaks of samples at 520 and 539 nm corresponded to the ²H¹¹/²-4-->I15/2 and 4S3/2-->4I15/2 level transition of Er³âº ion, and the red light emission peaks of samples at 653 nm corresponded to the 4F9/2-->4I15/2 levelt ransition of Er+ ion. The chromaticity coordinate diagram exhibited that the change of the luminescent color of samples could be achieved by adjusting the ratio of NaF/RE³âº. With the increasing of NaF/RE³âº ratio, for the whole light-emitting colors of samples, the shift from yellow region to near red region could be realized. It can be concluded that through the relatively simple experimental procedure and lower cost materials, the change of phase and morphology, the moving of light-emitting color for sample NaYF4:Yb³âº, Er³âº could be well controlled only by changing the single component (NaF) molar ratio in the raw materials. The effect of phase and morphology of fluorescent materials on their upconversion luminescence has great potential applications in photonic devices and bioanalysis research.

[Morphology and Spectral Properties Study of LaCeF3:Tb Microcrystalline].

LaCeF3:Tb microcrystalline was synthesized by microemulsion method, oleic acid-assisted solvothermal method, ultrasonic-assisted solvothermal method separately. LaCeF3:Tb microcrystalline synthesized by ultrasonic-assisted solvothermal method is rarely reported. Using X-ray diffraction (XRD), scanning electron microscope (SEM), fluorescence spectroscopy (PL) method such as the crystal phase, morphology and luminescence properties of the samples have been characterized. XRD results show that the crystallization product is good, microcrystalline and standard card PDF# 38-0452 (the six-party LaCeF3) is corresponding, SEM images showing the product has uniform size and morphology, under 250 nm excitation nanoparticlesshows strong green light, the main emission peaks respectively belonged to 5D4-->7F6 (489 nm), 5D4-->7F5 (545 nm), 5D4-->7F4 (585 nm) and 5D4-->7F3 (621 nm) transition of Tb³âº. Through LaCeF3 and LaCeF3:Tb spectral studies prove the existence of the Ce-Tb energy transfer. Calculated the critical doping concentration of Tb in LaCeF3microcrystalline synthesized by different methods.

[Study of fast pretreatment method in detection of melamine in liquid milk using liquid chromatography and Raman spectroscopy].

The present paper proposed for the first time the flocculation-filtration method for separation of interfering substances in milk, such as fat. In this method only two steps were carried out. Firstly, aluminum chloride (PAC, Al2 (OH)nCl6-n,) is used to flocculate the milk; Secondly, water filter was used to filter the mixture. Then the clear filtrate could be used for the detection of melamine. The whole preprocessing would not take more than one minute. The pretreatment process was optimized. Experiments show that the adding proportion of PAC should be about 2%-3% for best filtration efficiency, and that it would have the best flocculation effect when the mixture was mildly alkaline. High performance liquid chromatography experiments show that the melamine recovery of this method is more than 90%. Samples pretreated by the flocculation--filtration method were clearer and the baselines of spectral curve obtained by sensitizing Raman method were more smooth which means better purification compared to those samples pretreated by centrifugal pretreatment method. The pretreatment method proposed can be used in HPLC and Raman spectroscopy methods for rapid detecting melamine in liquid milk. This method shows better separation effect, simpler operation, and lower time and money cost than those pretreatment processes in the existing standard melamine detection method for milk. By use of this pretreatment method, the melamine rapid detection efficiency would be greatly improved.

[Detection of Plasmodium falciparum by using magnetic nanoparticles separation-based quantitative real-time PCR assay].

OBJECTIVE: To establish a magnetic nanoparticles separation-based quantitative real-time PCR (RT-PCR) assay for fast and accurate detection of Plasmodium falciparum and providing a technical support for improving the control and prevention of imported malaria. METHODS: According to the conserved sequences of the P. falciparum genome 18SrRNA, the species-specific primers and probe were designed and synthetized. The RT-PCR was established by constructing the plasmid standard, fitting the standard curve and using magnetic nanoparticles separation. The sensitivity and specificity of the assay were evaluated. RESULTS: The relationship between the threshold cycle (Ct) and logarithm of initial templates copies was linear over a range of 2.5 x 10(1) to 2.5 x 10(8) copies/µl (R2 = 0.999). Among 13 subjects of entry frontier, a P. falciparum carrier with low load was detected by using the assay and none was detected with the conventional examinations (microscopic examinations and rapid tests). CONCLUSION: This assay shows a high sensitivity in detection of P. falciparum, with rapid and accurate characteristics, and is especially useful in diagnosis of P. falciparum infectors with low parasitaemia at entry-exit frontier ports.

[Color-tunable nano-material alpha-NaYF4 : Yb, Er, Tm prepared by microemulsion-hydrothermal method].

NaYF4 : Yb3+, Er3+, Tm3+ nanoparticles were prepared by microemulsion-hydrothermal method. Crystal phase, morphology and structure of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The luminescence properties were studied by up-conversional fluorescence spectroscopy. The XRD patterns of as-prepared samples were in agreement with the PDF # 77-2042 of cubic NaYF4. SEM images of the particles showed that the samples were cotton-like spherical in shape and which were assembled by smaller nano-particles. The average size was 120 nm, while the shape was regular and the particle size was homogeneous. Under the excitation of 980 nm, the as-prepared particles could emit blue (438 and 486 nm), green (523 and 539 nm) and red (650 nm) light simultaneously. It can be seen from the color coordinates figure (CIE) that when doping concentration ratio of Tm3+ and E3+ increased from 0 to 2, the whole emitting light color of samples movedto green region. While the ratio was 1 : 1, pseudo white light was obtained. As the ratio changed from 2 to 7, the luminous color was moved to red region.

[Influence of Bi3+ doping on properties of CaMoO4 : Eu3+ phosphors].

Europium doped CaMoO4 and bismuth co-doped CaMoO4 : Eu3+ phosphors were prepared via microemulsion-hydrothermal method. The structure, morphology and luminescence properties of samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fluorescence spectroscopy, respectively. The XRD patterns of as-prepared samples were in agreement with the PDF # 29-0351 of CaMoO4, which indicated that the phosphor possessed tetragonal crystal structure. SEM images showed that the samples were basically flake in shape and their average size was 1.5-2.5 microm. The critical molar concentration of activator (Eu3+) in CaMoO4 : Eu3+ was 5%, and the predominant peak of CaMoO4 : Eu3+ located at 616 nm, corresponding to the 5D0 -->7 F2 electronic dipole transition of Eu3+. The photoluminescence color can be tuned from orange-yellow (0.514, 0.537) to white (0.339, 0.333) by adjusting the doping concentrations of Eu3+ ions. To enhance the red emission intensity of Eu3+, Bi3+ was used to co-dope CaMoO4 : Eu3+ as sensitizers. When the concentration of Bi3+ is 3%, luminescence intensity was maximum. The chromaticity coordinates (CIE) varied from orange (0.497, 0.347) to red (0.585, 0.349) with increasing the content of Bi3+.

[Research progress in Raman spectra and its test sample pretreatment].

It is generally accepted that Raman spectroscopy is an advanced method with simple operation, small amount of specimens needed as well as rapid on-line screening, detection and identification. However, in the technology of determination, sample preparation is also an significant factor during analysis process. It would affect the accuracy and precision of the results, and normally involved complicated procedure. Developing a rapid and effective sample preparation method coupled with Raman detective technology is a method worth study. In the present paper, the simply basic principle, the origin and development of generating Raman spectra were introduced, some Raman technology, such as the surface-enhanced Raman spectroscopy, tip-enhanced Raman spectroscopy, shell-isolated nanoparticle enhanced Raman spectroscopy and the sample preparation were discussed.

An immunosensor based on magnetic relaxation switch and polystyrene microparticle-induced immune multivalency enrichment system for the detection of Pantoea stewartii subsp. Stewartii.

A rapid, sensitive, and simple immunosensor has been developed for the detection of Pantoea stewartii subsp. Stewartii (Pss). This immunosensor combines magnetic relaxation switch (MRS) assay with polystyrene microparticle-induced immune multivalency enrichment system. Comparing to conventional enzyme-linked immunosorbent assay (ELISA), the immunosensor developed in this study provides higher sensitivity and requires less analysis time. The detection limit of Pss obtained by immunosensor was determined to be 10(3)cfu/mL, 50 times lower than that by ELISA (5×10(4)cfu/mL), while the analysis time required by immunosensor is 30min much shorter than that by ELISA. The average recoveries studied with Pss at various spiking levels ranged from 85.5% to 93.4% with a relative standard deviation (RSD) below 6.0%. No cross-reaction with the other five strains was found, demonstrating a good specificity of Pss detection. The results showed that the MRS immunosensor combined with PS-induced immune multivalency enhancement system is a promising platform for the determination of large biological molecules due to its high sensitivity, specificity, homogeneity, and speed.

Immunosensor based on magnetic relaxation switch and biotin-streptavidin system for the detection of Kanamycin in milk.

A rapid, sensitive, and simple immunosensor was developed for the detection of Kanamycin (KM) in milk. This immunosensor is based on magnetic relaxation switch (MRS) assay and biotin-streptavidin system (B-SA system). The target analyte (KM) competed with those on the surface of the superparamagnetic iron oxide (SPIO) nanoparticles and hence affected the formation of SPIO aggregates. The dispersed and aggregated states of SPIO can modulate the spin-spin relaxation time (T(2)) of the neighboring water molecule. T(2) was then changed as an effect of the target analyte. The B-SA system was used to amplify the SPIO binding, thus enhance the sensitivity. The detection working was 1.5 to 25.2ng mL(-1) and limit of detection (LOD) was determined to be 0.1ng mL(-1). The LOD of the immunosensor decreased tenfold, and its analysis time (45min) was much shorter than that of enzyme-linked immunosorbent assay (6h to 8h). The average recoveries of the KM at various spiking levels ranged from 80.2% to 85.6% with a relative standard deviation (RSD) below 4.0%. The results showed that the MRS immunosensor was a promising platform for the determination of small molecular residues because of its high sensitivity, specificity, homogeneity, and speed.

[Detection and analysis of several kinds of oils with Raman spectrum].

Applying Raman spectrometry to detect several kinds of oils such as petrol, diesel oil, naphtha and KHF (aviation fuel hydro treating), the authors can explore the regular laws existing among these oils. The authors detected 150 cases of oils using Raman spectrometer developed by ourselves with 785 nm excitation wavelength miniature portable, and dealed with these spectra-paragraphs of the oils on level and SNV (normalization method) methods. The spectrograms of four categories of oils including petrol, diesel oil, naphtha and KHF and also the additives of them have different characteristics and rules. According to the alkenes peak's location and intensity we can distinguish petrol and naphtha, and then screen out some unqualified petrol. Raman spectrometry is very simple and has advantages that it needs a small amount of oil samples, at the same time, it also has no damage to test samples. The spectra-paragraphs show that different kinds of samples have different character on location and intensity of Raman peak. The Raman spectrometry method has great potential on establishing a rapid oil screening detection and identification method.

[Quality analysis of olive oil and quantification detection of adulteration in olive oil by near-infrared spectrometry and chemometrics].

Discriminant analysis was used to classify 20 olive oil samples based on their near-infrared (NIR) spectra. The samples were successfully classified into two categories which are consistent with extra virgin olive oil and ordinary olive oil defined in the products. The NIR spectra of olive-oil mixtures containing colza oil, corn oil, peanut oil, camellia oil, sunflower oil, and poppy seed oil were collected, respectively. The volume percent of adulterants ranged from 0 to 100%. The best spectrum bands for analysis were selected before developing partial least-squares (PLS) calibration models. The relative errors of prediction ranged from -5.67% to 5.61%. Results showed that the method combined with chemometrics methods and near-infrared spectrometry is simple, fast and credible for qualitative and quantitative analyses of olive oil samples.

Rapid authentication of olive oil adulteration by Raman spectrometry.

The authentication of olive oil and its adulteration with lower priced oils are still serious problems in the olive oil industry. In this study, a method based on the intensity ratio of the Raman spectroscopy vibration bands, especially on the intensity ratio of the cis ( ==C-H) and cis (C=C) bonds normalized by the band at 1441 cm(-1) (CH(2)), was established to authenticate genuine/fake olive oil. These intensity ratios of the vibration bands given in the form of a two-dimensional chart allow first the discrimination between the various grades of olive oil and the seed oils and then the detection of olive oil fraud by the line of y = 0.7, which is observed under most experiments and dot charts. This method can reliably distinguish the genuine olive oils from the olive oils containing 5% (volume percentage) or more of other edible oils, such as soybean oil, rapeseed oil, sunflower seed oil, or corn oil. Compared to the traditional principal component analysis method, this method is more intuitive, more precise, and easier to use. Moreover, this method also has the advantages of simplicity efficiency and has no need for sample preprocessing, being especially suitable for on-site testing in field applications.