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Selected papers from the latest issue:
Flow injection analysis of nanomolar silicate using long pathlength absorbance spectroscopy
09 November 2011, 22:36:33
Publication year: 2011
Source: Talanta, Available online 9 November 2011
Jian Ma, Robert. H. Byrne
Determination of silicate at low concentrations (i.e., nanomolar levels) is an important analytical objective for both marine science and the semiconductor industry. Here we report the use of flow injection analysis (FIA) in combination with long pathlength liquid core waveguide (LCW) spectrometry to achieve detection limits for dissolved silica on the order of 10 nM. Sample throughput for the simple, automated analytical apparatus used in this work is 12 hat low levels of dissolved silica; this rate can be increased by a factor of three for higher (micromolar) levels of dissolved silica. The analytical protocol is based on the reaction of silicate with ammonium molybdate to form a yellow silicomolybdate complex, which is subsequently reduced to silicomolybdenum blue by ascorbic acid. Optimization of the FIA procedure included consideration of the compositions and concentrations of reagents, volume of the injection loop, flow rate conditions, and lengths of mixing coils. The interference by phosphate was examined and eliminated through addition of oxalic acid. The dissolved silica detection limit of 7.2 nM in pure water is consistent with the strictest standard for the semiconductor industry, and the 9.0 nM detection limit for seawater shows that this analytical method is also suitable for oligotrophic ocean waters. The targeted analytical range of 10 nM to 5 μM can be easily extended to higher concentrations without altering the experimental hardware—i.e., by simply changing flow rates or selecting alternative analytical wavelengths. Compared to previously published LCW-based spectrophotometric methods, this analytical system exhibits improved sensitivity, reduced sample consumption, and higher sample throughput.
Source: Talanta, Available online 9 November 2011
Jian Ma, Robert. H. Byrne
Determination of silicate at low concentrations (i.e., nanomolar levels) is an important analytical objective for both marine science and the semiconductor industry. Here we report the use of flow injection analysis (FIA) in combination with long pathlength liquid core waveguide (LCW) spectrometry to achieve detection limits for dissolved silica on the order of 10 nM. Sample throughput for the simple, automated analytical apparatus used in this work is 12 hat low levels of dissolved silica; this rate can be increased by a factor of three for higher (micromolar) levels of dissolved silica. The analytical protocol is based on the reaction of silicate with ammonium molybdate to form a yellow silicomolybdate complex, which is subsequently reduced to silicomolybdenum blue by ascorbic acid. Optimization of the FIA procedure included consideration of the compositions and concentrations of reagents, volume of the injection loop, flow rate conditions, and lengths of mixing coils. The interference by phosphate was examined and eliminated through addition of oxalic acid. The dissolved silica detection limit of 7.2 nM in pure water is consistent with the strictest standard for the semiconductor industry, and the 9.0 nM detection limit for seawater shows that this analytical method is also suitable for oligotrophic ocean waters. The targeted analytical range of 10 nM to 5 μM can be easily extended to higher concentrations without altering the experimental hardware—i.e., by simply changing flow rates or selecting alternative analytical wavelengths. Compared to previously published LCW-based spectrophotometric methods, this analytical system exhibits improved sensitivity, reduced sample consumption, and higher sample throughput.
Highlights
► Flow injection analysis of silicate at nanomolar levels ► Silicate analyses using liquid core waveguide and CCD spectrometer ► Ten nM detection limit with twelve sample per hour analysis rate ► Silicate analysis of pure water, salt solutions and seawaterDNA G-Quadruplex-Templated Formation of the Fluorescent Silver Nanocluster and Its Application to Bioimaging
09 November 2011, 22:36:33
Publication year: 2011
Source: Talanta, Available online 9 November 2011
Jun Ai, Weiwei Guo, Bingling Li, Tao Li, Dan Li, ...
Herein, a novel kind of silver nanocluster is synthesized simply by mixing G-quadruplex template with silver ions and reduction reagent (NaBH4, here). AS1411 (a G-quadruplex that can bind nucleolin overexpressed in cancer cells) is used as the main model template to prove the synthesis protocol and its potential application. We used fluorescence assay, CD, MALDI TOF MS, and TEM to characterize the silver nanocluster. It is found that after formation of the silver nanocluster, AS1411 still keeps its structure and is able to bind with nucleolin in cancer cell. Meanwhile, this binding behavior can greatly enhance the fluorescence intensity of the silver nanocluster. This property can be directly employed into bioimaging HeLa cells. The cell toxicity (3-[4,5-dimethylthiazolyl-2]-2, 5 -diphenyltetrazolium bromide, MTT) assay demonstrated that the silver nanocluster has only little affect on the cytotoxicity to the cells, which further proves the applicability of the method in tumor cell imaging. At last, the universality of the synthesis protocol is verified by using a series of other G-quadruplex sequences as templates. For a lot of functional nucleic acids, such as human telomeres and certain aptamers, are with G-rich sequences and can fold into G-quadruplexes in functioning conditions, our method displays a promising application space in future researches.
Source: Talanta, Available online 9 November 2011
Jun Ai, Weiwei Guo, Bingling Li, Tao Li, Dan Li, ...
Herein, a novel kind of silver nanocluster is synthesized simply by mixing G-quadruplex template with silver ions and reduction reagent (NaBH4, here). AS1411 (a G-quadruplex that can bind nucleolin overexpressed in cancer cells) is used as the main model template to prove the synthesis protocol and its potential application. We used fluorescence assay, CD, MALDI TOF MS, and TEM to characterize the silver nanocluster. It is found that after formation of the silver nanocluster, AS1411 still keeps its structure and is able to bind with nucleolin in cancer cell. Meanwhile, this binding behavior can greatly enhance the fluorescence intensity of the silver nanocluster. This property can be directly employed into bioimaging HeLa cells. The cell toxicity (3-[4,5-dimethylthiazolyl-2]-2, 5 -diphenyltetrazolium bromide, MTT) assay demonstrated that the silver nanocluster has only little affect on the cytotoxicity to the cells, which further proves the applicability of the method in tumor cell imaging. At last, the universality of the synthesis protocol is verified by using a series of other G-quadruplex sequences as templates. For a lot of functional nucleic acids, such as human telomeres and certain aptamers, are with G-rich sequences and can fold into G-quadruplexes in functioning conditions, our method displays a promising application space in future researches.
Highlights
► G-quadruplex stabilized silver nanoclusters were utilized as novel fluorescent probes for cell bioimaging. ► The characteristic of silver nanocluster were investigated using CD, MALDI TOF MS, and TEM analysis. ► The cell toxicity MTT assay demonstrated that the silver nanocluster has only little affect on the cytotoxicity.Evaluation of seven cosubstrates in the quantification of horseradish peroxidase enzyme by square wave voltammetry
09 November 2011, 22:36:33
Publication year: 2011
Source: Talanta, Available online 9 November 2011
Silvina V. Kergaravat, Maria Isabel Pividori, Silvia R. Hernandez
The electrochemical detection for horseradish peroxidase-cosubstrate-H2O2systems was optimized. O-phenilendiamine, phenol, hydroquinone, pyrocatechol, p-chlorophenol, p-aminophenol and 3-3′-5-5′-tetramethylbenzidine were evaluated as cosubstrates of horseradish peroxidase (HRP) enzyme. Therefore, the reaction time, the addition sequence of the substrates, the cosubstrate: H2O2ratio and the electrochemical techniques were elected by one-factor optimization assays while the buffer pH, the enzymatic activity and cosubstrate and H2O2concentrations for each system were selected simultaneously by response surface methodology. Then, the calibration curves for seven horseradish peroxidase-cosubstrate-H2O2systems were built and the analytic parameters were analyzed. O-phenilendiamine was selected as the best cosubstrate for the HRP enzyme. For this system the reaction time of 60 seconds, the phosphate buffer pH = 6.0, and the concentrations of 2.5 × 10 mol Lo-phenilendiamine and of 1.25 × 10 mol LH2O2were chosen as the optimal conditions. In these conditions, the calibration curve of horseradish peroxidase by square wave voltammetry showed a linearity range from 9.5 × 10to 1.9 × 10 mol Land the limit of detection of 3.8 × 10 mol Lwith R.S.D.% of 0.03% (n = 3).
Source: Talanta, Available online 9 November 2011
Silvina V. Kergaravat, Maria Isabel Pividori, Silvia R. Hernandez
The electrochemical detection for horseradish peroxidase-cosubstrate-H2O2systems was optimized. O-phenilendiamine, phenol, hydroquinone, pyrocatechol, p-chlorophenol, p-aminophenol and 3-3′-5-5′-tetramethylbenzidine were evaluated as cosubstrates of horseradish peroxidase (HRP) enzyme. Therefore, the reaction time, the addition sequence of the substrates, the cosubstrate: H2O2ratio and the electrochemical techniques were elected by one-factor optimization assays while the buffer pH, the enzymatic activity and cosubstrate and H2O2concentrations for each system were selected simultaneously by response surface methodology. Then, the calibration curves for seven horseradish peroxidase-cosubstrate-H2O2systems were built and the analytic parameters were analyzed. O-phenilendiamine was selected as the best cosubstrate for the HRP enzyme. For this system the reaction time of 60 seconds, the phosphate buffer pH = 6.0, and the concentrations of 2.5 × 10 mol Lo-phenilendiamine and of 1.25 × 10 mol LH2O2were chosen as the optimal conditions. In these conditions, the calibration curve of horseradish peroxidase by square wave voltammetry showed a linearity range from 9.5 × 10to 1.9 × 10 mol Land the limit of detection of 3.8 × 10 mol Lwith R.S.D.% of 0.03% (n = 3).
Highlights
► Its scope will include the following topics: The activity of horseradish peroxidase reaction was related to phenolic compounds. ► The electrochemical enzymatic response was obtained by square wave voltammetry. ► Square wave voltammetry coupled to the univariate calibration was used to quantify the HRP acivity. ► o-phenilendiamine can be considered as the most efficient cosubstrate.Fabrication of DNA/graphene/polyaniline nanocomplex for label-free voltammetric detection of DNA hybridization
09 November 2011, 22:36:33
Publication year: 2011
Source: Talanta, Available online 9 November 2011
Meng Du, Tao Yang, Xiao Li, Kui Jiao
A novel DNA electrochemical biosensor was described for the detection of specific gene sequences. Electrochemically reduced graphene oxide (ERGNO) was prepared on polyaniline (PAN) nanofibers modified glassy carbon electrode (GCE). Compared with the electrochemical reduction of graphene oxide directly on bare GCE (reduction potential: ca. -1.3 V), more positive reduction potential (ca. -1 V) for graphene oxide was observed with the PAN membrane existing. The formed ERGNO/PAN nanocomposites were applied to bind ssDNA probe via the non-covalent assembly. The surface density of ssDNA was calculated by voltammetric studies of redox cations ([Ru(NH3)6]), which were bound to the surface via electrostatic interaction with negative charged phosphate backbone of the DNA. After the hybridization of ssDNA probe with complementary DNA, the response of surface-bound [Ru(NH3)6]changed obviously, which could been adopted to recognize the DNA hybridization. Under optimal conditions, the dynamic range of the DNA biosensor for detecting the sequence-specific DNA of cauliflower mosaic virus (CaMV35S) gene was from 1.0 × 10to 1.0 × 10 mol L, with a detection limit of 3.2 × 10 mol L. This biosensor also showed a high degree of selectivity.
Source: Talanta, Available online 9 November 2011
Meng Du, Tao Yang, Xiao Li, Kui Jiao
A novel DNA electrochemical biosensor was described for the detection of specific gene sequences. Electrochemically reduced graphene oxide (ERGNO) was prepared on polyaniline (PAN) nanofibers modified glassy carbon electrode (GCE). Compared with the electrochemical reduction of graphene oxide directly on bare GCE (reduction potential: ca. -1.3 V), more positive reduction potential (ca. -1 V) for graphene oxide was observed with the PAN membrane existing. The formed ERGNO/PAN nanocomposites were applied to bind ssDNA probe via the non-covalent assembly. The surface density of ssDNA was calculated by voltammetric studies of redox cations ([Ru(NH3)6]), which were bound to the surface via electrostatic interaction with negative charged phosphate backbone of the DNA. After the hybridization of ssDNA probe with complementary DNA, the response of surface-bound [Ru(NH3)6]changed obviously, which could been adopted to recognize the DNA hybridization. Under optimal conditions, the dynamic range of the DNA biosensor for detecting the sequence-specific DNA of cauliflower mosaic virus (CaMV35S) gene was from 1.0 × 10to 1.0 × 10 mol L, with a detection limit of 3.2 × 10 mol L. This biosensor also showed a high degree of selectivity.
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