Microwave-assisted rapid preparation of monodisperse superhydrophilic resin microspheres as adsorbent for triazines in fruit juices
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An indirect competitive immunoassay using quantum dots (QDs) as the fluorescent label has been developed for detection of melamine in milk products. The method exhibited a response for melamine with IC 50 value of 11.3 ng mL -1 and a detection limit of 0.27 ng mL -1 . Milk and milk powder samples spiked with melamine have been analyzed, and the method provided recoveries ranging from 84.2% to 108.0%, and a CV of 12.8%. The implementation of QDs provides for at least 30 fold improvement of detection limit when compared with optically-based ELISA screening methods that have been reported. The analytical performance in combination with simplicity of sample and antibody preparation provides the basis for a practical method for melamine detection.
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Polyvinyl Alcohol
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A simple electrochemical approach, which does not require any expensive and complex instruments, is established for the selective and quantitative recognition of melamine in diary products and pet foods. During a preconcentration step (at 1.8 V versus Ag/AgCl), the formation of a polymer film from melamine on a preanodized screen-printed carbon electrode was identified by SEM and XPS. The as-formed polymer was found to be electroactive with a reversible redox peak, and hence square-wave voltammetry was applied to further increase the detection sensitivity to meet the detection limit for application in real sample analysis. Simply with a medium exchange procedure, melamine was selectively detected with a detection limit (S/N = 3) of 0.8 μM (i.e., 98.3 ppb) by square-wave voltammetry. Lower than 1 ppm of melamine in real samples can be easily detected with good recoveries of 98.7–100.9% by the proposed approach. The recovery tests established for external calibration and standard addition techniques verified that the analysis can be done in a single-run measurement.
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In this paper, we develop a simple design for simultaneous detection of melamine (MEL) and cyromazine (CYR) by surface-enhanced Raman scattering (SERS) with the formation of well-defined MEL or CYR-aptamer-AgNPs. This detection will take only 10 min, and SERS signals generated by MEL-aptamer-AgNPs exhibits a linear dependence on melamine (R2 = 0.998) concentration ranging from 0.1 to 0.5 ppm on melamine. The detection limit is sensitive down to 43.5 ppb. SERS signals generated by CYR-aptamer-AgNPs exhibits a linear dependence on cyromazine (R2 = 0.997) concentration ranging from 0.1 to 0.5 ppm on cyromazine. The detection limit is sensitive down to 23.6 ppb. This SERS biosensor was first reported for the simultaneous detection of melamine and cyromazine by using aptamer-based in situ silver nanoparticles synthesis. So we expected that the development of this biosensor could provide a good platform for the rapid detection of other pollutants in raw milk.
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Silver nanoparticle
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In this paper, we developed a simply designed detection method for logic gates by using aptamers, cetyltrimethyl ammonium bromide, together with melamine and cyromazine to control the aggregation and dispersion of gold nanoparticles (AuNPs). First, either melamine or cyromazine can induce the aggregation of AuNPs, supporting an OR gate to detect whether they were present or not. Second, based on the fact that aptamer T31 can specifically bind with melamine, preventing the aggregation of AuNPs, an improved INHIBIT gate was also fabricated to find whether there was melamine. It has a detection limit of 0.12 ppm by the naked eye for the detection of melamine, and the limit of detection (LOD) by spectrophotometer is 2.2 ppb. Third, with the adsorption of aptamer Tcy1 on AuNPs and the strong coordination of Tcy1 with cyromazine, the addition of cyromazine and CTAB immediately resulted in the aggregation of AuNPs, giving rise to an AND gate. This gate has a detection limit of 0.17 ppm by the naked eye and the limit of detection (LOD) is 9.0 ppb by spectrophotometer. The system provided a good platform for the development of functional logic systems.
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Ammonium bromide
Drug Detection
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The present study reported a facile method for the determination of melamine in milk powder products based on the aggregation of reactant-free 5 nm gold nanoparticles (AuNPs). The strong electrostatic attraction between the positively charged exocyclic amine groups present in the melamine molecule and the negatively charged ions bound to the AuNPs induced aggregation of the AuNPs, resulting in visible color changes that could be seen with the naked eye and monitored by ultraviolet–visible (UV–Vis) absorbance spectra. The method shows high sensitivity with detection limits of 1 × 10−9 M for visual detection and 1 × 10−11 M for UV–Vis analysis, which is far below the safety limit of melamine ingestion in infant formula (1 ppm = 7.9 × 10−6 M) and the detection limit acquired by most AuNP-based melamine detection methods. Good recoveries were obtained over the range of 94.7–95.5% with a relative standard deviation of mean recovery (RSD) ranging from 1.40 to 5.81. The method provides a simple, feasible, fast and real-time detection of melamine adulterants in infant formula by the naked eye, without the aid of advanced instruments.
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Through infant milk powder samples of the known results,according to high performance liquid chromatography(HPLC) method in melamine testing method of GB/T22388-2008 raw milk and dairy products,the samples were analyzed.Method detection limit of melamine in infant milk powder by HPLC was calculated through the analysis of 12 samples.The results showed that the method detection limit was 0.6 mg/kg.
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Small particle size (46.6 nm) and monodisperse (P=0.1060.2) polystyrene particles was prepared using K_2S_2O_8 as initiator in the O/W microemulsion of H_2O-APG0810-ST. The influence of APG0810 concentration,initiator concentration and salt concentration on particle size and polydispersity of polystyrene has been discussed. The result is that the particle size become small (44.3 nm) with the APG0810 concentration increasing, and the monodispersity become weak; while with the salt concentration increasing the particle size become small(45.2 nm) , but when salt concentration is more than a certain concentration, the particle size has a tendency to big. The particle size become small(41.2 nm) with initiator concentration increasing.
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Polystyrene
Microemulsion
Particle (ecology)
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Although aptamer-functionalized AuNPs technology exhibits great potential in analytical and biological chemistry, direct analysis of molecules at a low concentration using colorimetric assay remains challenging. The development of intuitive methods has attracted interest for promising detection of melamine in milk samples due to a demand for stable and understandable process. In this study, we propose a rapid and facile colorimetric measurement method of melamine combined aptamer-functionalized AuNPs in contaminated milk samples. To realize the high stability and the lower limit of detection, the aptamer-functionalized surface of AuNPs via a coordinated bond was used in combination with ultra-sonication. The kinetics of this colorimetric assay based on aptamer-functionalized AuNPs was analyzed to illustrate that the higher the concentration of melamine, the faster the aggregation of AuNPs induced. The sensitivity, selectivity, limit of detection and recovery rate were sufficiently validated to understand the measurement principle of melamine using aptamer-functionalized AuNPs. The calibration curve established by the absorption peak ratio (A640 /A520) was linear in the concentration range of 0~1μM of melamine in aqueous solutions with the correlation coefficient (R2) of 0.986 and the limit of detection (LOD) of 22 nM, whereas, the correlation coefficient (R2) of 0.998 and the LOD of 14.9 nM were achieved at the concentration of melamine below 0.5 μM in milk samples. The optimized performance of this colorimetric assay of melamine using aptamer-functionalized AuNPs in milk samples was obtained with 100 μL of 13 nm AuNPs solution, 40 μL of 1 μM (100 dilutions) aptamers and the pre-reaction time of 30 min. This simple colorimetric measurement of melamine using aptamer-functionalized AuNPs provides a promising target for various applications of the sample source with complex sample matrices.
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