Concentration Of Buffer Solution Research Articles

Hydrogen-bonded organic frameworks as stationary phase for open-tubular capillary electrochromatography

BackgroundCapillary electrochromatography (CEC) stationary phases have always been the focus of attention. The selection of excellent stationary phases are the key to realize separate of different compounds. Hydrogen-bonded organic frameworks (HOFs) are porous materials connected by hydrogen bonds between molecules, which have the advantages of renewable, high specific surface area and mild synthesis conditions. At present, HOFs are used in gas adsorption and storage, catalysis and drug delivery. Because of its unique advantages, HOFs have a bright future as CEC stationary phases. ResultsUsing melamine (MA) and 1,3,6,8-tetra (4-carboxylphenyl)pyrene (H4TBAPy) as reaction monomers, a HOFs named MA/PFC-1 was synthesized by solvent evaporation at room temperature. The inner wall of the capillary column was coated with MA/PFC-1 by chemical bonding. Sulfonamides were used as the target analytes. The effects of pH, phosphate buffer solution concentration, organic additive content and applied voltage on sulfonamides separation were investigated. The MA/PFC-1-coated capillary column had good resolution (>1.5) and reproducibility. The intra-day, inter-day, column-to-column, and inter-batch precision of the retention times were 0.03%–0.09%, 0.04%–0.09%, 0.03%–0.14% and 0.06%–0.09%, respectively. The intra-day, inter-day, column-to-column, and inter-batch precision of the peak areas were 0.11%–0.25%, 0.13%–0.20%, 0.12%–0.15% and 0.08%–0.15%, respectively. The MA/PFC-1-coated capillary column was run 150 consecutive times, and the results showed no noticeable change, which proved that this method had good stability. SignificanceThis work applied HOFs to CEC. The results show the that MA/PFC-1-coated capillary column has good separation performance. The MA/PFC-1-coated capillary column has been successfully applied to the determination of sulfamethoxazole in tablets, which has practical application value. To open up the application of HOFs in CEC and provide a new idea for developing new CEC stationary phases.

A novel g-C3N4@La:Y2O3 nanocomposite fluorescence sensor for simultaneous determination and photocatalytic degradation of Ulipristal acetate and Tacrolimus using Doehlert design optimization

Graphitic carbon nitride nanocomposite doped with La:Y2O3 was used as a new sensor for detection and determination of two hazardous active pharmaceutical compounds, Tacrolimus and Ulipristal acetate, by fluorescence spectrophotometry. This novel nanosensor has a fantastic ability to detect these drugs quickly, accurately, and simultaneously. The effect of Tacrolimus on this nanosensor is the quenching of fluorescence emission intensity at the wavelength of 369 nm while the Ulipristal acetate increases the fluorescence emission at 433 nm. Doehlert design was used to optimize the effective factors to reach the maximum fluorescence emission intensity of the nanosensor. Factors including pH, buffer solution concentration and the ratio of La:Y2O3 dopant in the nanocomposite structure. Under optimal conditions, the limit of detection of 17 nM and the limit of qualification of 58 nM for Tacrolimus and the limit of detection of 11 nM and the limit of qualification of 36 nM for Uipristal acetate were obtained with good accuracy. The prepared g-C3N4@La:Y2O3 nanocomposite has a reasonable ability to photodegrade these two drugs. In this regard, the process of photocatalytic degradation of Tacrolimus and Ulipristal acetate was investigated under visible light irradiation. The effect of active species in photocatalytic degradation was evaluated in order to determine the exact degradation mechanism, and the effect of Fenton factors on analytes degradation was also investigated.

A Simple, Ecofriendly, and Fast Method for Nitrate Quantification in Bottled Water Using Visible Spectrophotometry.

There are many works associating the presence of nitrate in water and the occurrence of cancer in humans. The most common method for quantifying nitrate in water is based on the use of toxic cadmium as a reductant. In this work, a new approach was developed for the quantification of nitrate in bottled water with indirect spectrophotometry using Zn0 as a reductant. Nitrate is reduced to nitrite using Zn0 in a buffered medium (acetate/acetic acid) and quantified with visible spectrophotometry using the Griess reaction between sulfanilamide and N-(1-naphthyl)-ethylenediamine. The influence of pH, buffer solution (constitution and concentration), Zn0 (mass and granulometry), and agitation time on the efficiency of nitrite generation was evaluated. The optimal conditions were an acetate-acetic acid buffer solution with a concentration and pH of 0.75 mol L-1 and 6.00, respectively, and a Zn0 particle size of 20 MESH and Zn0 mass of 300 mg. The limits of detection and quantification (LoD and LoQ) were 0.024 and 0.08 mg L-1, respectively. The method's accuracy and precision were evaluated using the analysis of commercial bottled water. In conclusion, the use of Zn0 instead of cadmium provided a green method with excellent LoD/LoQ. Further, the method proved to be simple and easy to apply during outdoor analysis.

Toward effect of buffer system composition in dehydrogenase activity of Escherichia coli and its electrochemical activity in mediated bioanode

The impact of composition, concentration, and pH of buffer solution on the activity and viability of Escherichia coli BB cells has been studied. Potassium/sodium phosphates with different composition and pH and TRIS buffer solutions used for microbiological and biotechnological applications as well as in microbial bioanodes were compared. The optimal buffer solution to achieve the highest dehydrogenase activity was 50 мМ potassium phosphate buffer solution, KH2PO4, isotonized by sodium chloride either with pH 7.4 for freshly obtained E. coli cells or with pH 7.8 to maintain the activity and viability of the microorganisms while storing. The cells concentration in solution was important to achieve the highest dehydrogenase activity, viz. 0.6–0.8 mg of cells (in terms of the dry weight) per mL of buffer solution with 0.2 M dextrose (substrate) was optimal. The good correlation between dehydrogenase activity and electrochemical current responses of bioanodes with E. coli and methyl orange as a redox mediator was shown.

Effect of ionic strength on DNA–dye interactions of Victoria blue B and methylene green using UV–visible spectroscopy

Abstract Victoria blue and methylene green dyes have both been extensively studied due to their numerous applications, including their ability to bind to DNA. Dyes are very important in everyday life with applications in textile, cosmetics, food and pharmaceutical industries. It has been found that some of them adversely affect human health causing severe abnormalities. Among these abnormalities, cancer is of great concern due to its fatal and almost non-recoverable nature. In this work we have studied the binding of two dyes namely Victoria blue B (VBB) and Methylene green (MG) with double stranded DNA (Salmon sperm). The interactions were studied in the presence of different concentrations of buffer solutions at a constant pH. The selected dyes showed interactions with double-stranded DNA through intercalation and electrostatic modes. Upon increasing ionic strength of the buffer the binding constant (K b ) value for MG was decreased whereas increased for VBB, which conclude that, at higher ionic strength (0.5 M) the DNA–MG interactions is lower and DNA–VVB interactions is maximum. The carcinogenicity of a given dye is indicated from its binding constants in the current study. Based on the recorded K b values of the selected dyes it was concluded that proper disposing and precautions should be taken while utilizing/dealing these dyes in order to minimize/avoid their impact on environment and human health.

Beef quality monitoring using immobilization lipase on modified polypropylene non-woven fabric based on time-temperature indicator

A lipase-based time-temperature indicator (TTI) was developed via the immobilization of lipase on polyethylene imine/glutaraldehyde/polypropylene non-woven fabric for the catalytic hydrolysis of glyceryl triacetate. pH of the reaction system gradually decreased and the color changed from green to orange or salmon pink. Four TTIs were selected by changing the concentration of glyceryl triacetate methanolic solution, the concentration of lipase-phosphate buffer solution, and the amount of phosphate buffer added, storing at 5–25 °C and measuring the coloration difference every 24 h. The Arrhenius activation energy (Ea) of obtained TTIs was calculated as 26.28, 47.98, 38.87, and 42.00 kJ/mol. For the application of TTIs to fresh beef monitoring, the kinetic properties of beef were studied and an Ea value of 37.60 kJ/mol was obtained. The similarity of these Ea shows accuracy in the prediction of beef quality with TTI color development.

Preparation of porous organic cage and its use as chiral stationary phase for capillary electrochromatography

Porous organic cages (POCs) are a unique type of microporous materials composed of discrete molecules with internal cavities that are accessible to various compounds. In this study, a prismatic chiral POC with good thermochemical stability was synthesized by condensing (1R,2R)-diaminocyclohexane and 3,3',5,5'-teturonic-4,4'-biphenediol via the Schiff base reaction and characterized by proton nuclear magnetic resonance spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy. The IR spectrum of the POC revealed a strong characteristic absorption peak at 1635 cm-1, indicating that it formed imine bonds (C=N). The absorption peak at 3425 cm-1 was attributed to the stretching vibrations of -OH, the absorption peaks at 2925 and 2858 cm-1 were attributed to the stretching vibrations of N=C-H and C-H, and the absorption peaks at 1446 and 1383 cm-1 were attributed to the stretching vibrations of C=C-H and C=C in the benzene ring. High-resolution mass spectral analysis of the POC showed a molecular ion peak at m/z 1363.7228, indicating its successful synthesis. TGA was performed from 25 to 800 ℃ at a rate of 10 ℃/min, and the results of this analysis showed that the POC was stable up to approximately 300 ℃. The POC was dissolved in dichloromethane and uniformly coated on the inner wall of a quartz capillary via the dynamic coating method to prepare a capillary electrochromatographic column. The experimental results revealed that the chiral electrochromatographic column could not only resolve ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol but also separate the isomers of o-, m-, and p-toluidine and o-, m-, and p-chloroaniline, indicating its good chiral separation ability. Investigation of the optimal separation conditions for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol revealed that the voltage, buffer solution concentration, and pH significantly affected their separation degree. In particular, the optimal separation voltage for ofloxacin, Troger's base, and 2-amino-1-butanol was 15 kV, while that for 1-phenyl-1-amyl alcohol was 17 kV. The optimal buffer concentration and pH for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol were 0.100 mol/L and 7.5. Under optimal chromatographic conditions, the resolution values for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-pentanol were 1.80, 3.33, 1.69, and 1.18, respectively. The results collectively demonstrate that the prepared POC may serve as a good chiral stationary phase for capillary electrochromatography with a certain chiral resolution ability and has good application prospects in chromatographic separation.

Analytical studies on some pesticides with antifungal effects: Simultaneous determination by HPLC, investigation of interactions with DNA and DNA damages

A simple, and fast method was developed for the simultaneous determination of five fungicides, namely thiram (THR), epoxiconazole (EPO), hexaconazole (HEX), tebuconazole (TEB), and diethofencarb (DIE), in different matrices by HPLC-UV. Parameters influencing the peak shape and resolution, such as the composition of mobile phase, pH and concentration of buffer solution, and column temperature, were examined and optimized. The proposed method was validated in terms of linearity, sensitivity, precision, and accuracy. Forced degradation studies were carried out for all analytes to demonstrate the specificity of the method and to evaluate the stability of analytes under different conditions. DNA interaction and DNA damage studies were conducted by HPLC and comet assay, respectively. All fungicides were found to bind DNA, except for DIE. While the binding coefficients for EPO, HEX, and TEB were of the order of 104, THR was found to interact more strongly with DNA with a binding coefficient of higher than 106. DIE did not induce DNA damage at any concentration tested. On the other hand, TEB, HEX, and EPO induced DNA damage up to 30 µg/mL. THR showed cytotoxic effects at 20 and 30 µg/mL and caused significant DNA damage at lower concentrations.

Three-dimensional fluorinated covalent organic frameworks coated capillary for the separation of fluoroquinolones by capillary electrochromatography

In this work, a three-dimensional fluorinated covalent organic frameworks (3D FCOFs) JUC-515 was synthesized from tetra(4-aminophenyl)methane (TAM) and 2,3,5,6-tetrafluoroterephthalol (TFA) by an ionic liquid method. JUC-515 was introduced into the capillary column and bonded to the inner wall of the capillary column by chemical bonding. Through a variety of characterization results, JUC-515 was successfully synthesized and introduced into the capillary column. The effects of buffer solution concentration, organic additive content and pH of the buffer solution on the separation of fluoroquinolones (FQs) were investigated in detail. The JUC-515-coated capillary column showed good resolution (>1.5) and reproducibility. The relative standard deviations (RSDs) of the retention time for intraday, interday, column-to-column and interbatch precision were less than 0.88%, 2.45%, 2.74% and 3.32%, respectively. The RSDs of the peak area for intraday, interday, column-to-column and interbatch precision were less than 3.79%, 4.31%, 3.33% and 5.62%, respectively. The JUC-515-coated capillary column could be used no less than 150 times. The results showed that the JUC-515-coated capillary column had good separation performance. In addition, by separating fluorinated β-phenylalanine analogs, β-phenylalanine and trifluoromethyl β-phenylalanine analogs, the separation mechanism based on fluorine interactions was discussed. In conclusion, JUC-515 had good potential as a stationary phase for capillary electrochromatography.

Development of the DNA-based voltammetric biosensor for detection of vincristine as anticancer drug.

In the article presented herein, a deoxyribonucleic acid (DNA) biosensor is introduced for Vincristine determination in pharmaceutical preparations based on the modification of screen printed electrode (SPE) with double-stranded DNA (ds-DNA), polypyrrole (PP), peony-like CuO:Tb3+ nanostructure (P-L CuO:Tb3+ NS). The developed sensor indicated a wide linear response to Vincristine concentration ranged from 1.0 nM to 400.0μM with a limit of detection as low as .21nM. The intercalation of Vincristine with DNA guanine led to the response. The optimized parameters for the biosensor performance were ds-DNA/Vincristine interaction time, DNA concentration and type of buffer solution. The docking investigation confirm the minor groove interaction between guanine base at surface of or ds-DNA/PP/P-L CuO:Tb3+ NS/SPE and Vincristine. The proposed sensor could successfully determine Vincristine in Vincristine injections and biological fluids, with acceptable obtains.

Palm kernel fatty acid distillate-based bulk liquid membrane for Cu(II) separation: Design and its operating parameters

This study focus on the development of palm kernel fatty acid distillate (PKFAD) based on a bulk liquid membrane (BLM) as a green membrane for the separation of Cu(II) from wastewater. PKFAD was used as a sole membrane solution without the addition of extractant and/or modifier, which reduced the consumption of hazardous chemicals and favoured the environment. The effects of design (number of stirrer blades and baffles) and operating (stirring speed, buffer solution concentration, and operating time) parameters on the simultaneous extraction and stripping of Cu(II) across PKFAD-based BLM, as well as its overall recovery were investigated to get optimal metal ions recovery. To examine the practical applicability, the selectivity of PKFAD-based BLM in separating Cu(II) was tested using electroplating industry wastewater. The results showed high percentages of extraction (93%), stripping (94%), recovery (87%), and enrichment factor (1.74) of Cu(II) using the best design (four stirrer blades and no baffles) and operating (stirring speed of 220 rpm, buffer solution concentration of 0.2 M, and operating time of 7 h) parameters of PKFAD-based BLM. The separation factor values of ≥1 for Cu(II) over the coexisting metal ions from actual electroplating wastewater have been accomplished with PKFAD-based BLM. Hence, PKFAD-based BLM is a potential BLM with a sole green membrane phase for separating Cu(II) selectively from wastewater.

Colorimetric detection of polycyclic aromatic hydrocarbons by using gold nanoparticles

The existence and content of polycyclic aromatic hydrocarbons (PAHs) in the environment have gradually received attention because PAHs are widely detected in many sources. Therefore, an effective detection method for PAHs is necessary for further treatment. This study proposes a novel colorimetric detection method based on AuNPs to determine the contents of phenanthrene (Phe) and pyrene (Pyr). Trisodium citrate was used as a reducing agent to synthesize gold nanoparticles, and ammonium nitrate (NH4NO3) was added as a reactant to detect the analyte content. Some assay parameters, such as the concentration of NH4NO3 solution, the volume of NH4NO3 solution, the concentration of MES buffer solution, the volume of MES buffer solution, and the reaction time influenced the analyte detection ability of AuNPs and were optimized. The limits of detection for Phe and Pyr are 0.06 mg/L and 0.087 mg/L, respectively. In addition, the detection method has good selectivity and anti-interference ability for the target analytes. This colorimetric method was used to detect target analytes in real water (tap water and mineral water) with acceptable results.

Development of Simple Analytical Method for B-Group Vitamins in Nutritional Products: Enzymatic Digestion and UPLC-MS/MS Quantification.

A method for the simultaneous determination of seven B-group vitamers including thiamine, riboflavin, nicotinamide, niacin, pyridoxine, pyridoxal, and pyridoxamine in nutritional products by using enzymatic digestion followed by LC-MS/MS quantification was studied. The LC-MS/MS conditions such as MS transitions, mobile phase programs, and ammonium formate buffer concentrations, and sample treatment procedures (e.g., concentrations of buffer solution, digestion temperature, and digestion time) were investigated. The analytical method performance was evaluated by multiple criteria such as selectivity, linearity, detection and quantification limits, repeatability, reproducibility, and recovery by using real sample matrices. The validated method was successfully applied to analyze vitamin B concentrations in different nutritional products like ultra-heat-treated milk, powdered milk, and nutritional powder. Vitamin B concentrations varied over a wide range from lower than detection limits to about 9000 µg/100 g, depending on vitamin groups, compound forms, and sample types. The measured concentrations of B-group vitamins in our samples were generally in good agreement with values of label claims.

Electrostatic and Hydrogen Bond Immobilization of Trypsine onto pH-Sensitive N-Vinylpyrrolidone and 4-Vinylpyridine Radical co-Grafted Chitosan Based on Hydrogel

The present investigation of new hydrogel based on chitosan was prepared by radical graft copolymerization of N-vinylpyrrolidone and 4-vinylpyridine with chitosan and cross-linking by N, N′-methylen-bis-acrylamide. The swelling behavior of the prepared hydrogel, with the optimal amount of gelator, was investigated. The hydrophilicity, and pH sensitivity of gel was suitable for trypsin carry. Trypsin was loaded onto the hydrogel enternal pores and surfaces by electrostatic interaction and hydrogen bond attachment. Several parameters, such as adsorbtion of pH value, loading time, and buffer solution concentration on trypsin loading amount, also enzyme activity were examined. According to the kinetic and FTIR, SEM spectroscopy analysis data trypsin was combination by the hydrogen bond and electrostatic interaction to the chitosan based structure. The hydrogen bonds were formed between -NH2, -CH2OH, >C=O, pyridine ring, -OH, and -NH- groups of carrier with -NH2, -COOH, -OH, >C=O, -NH-, disulfide bridge, ester groups of trypsine. In additional, at pH=5–8, the functional groups in the gel are partially ionized and take the form of -NH3+, -OH2+, >COH+. The protein is the same degree ionized in that medium, and the protein interacts electrostatically with the carrier.

Tensile Properties and Surface Treatment of Fiber Composites with the Concentration of Polydopamine and Buffer Solution

This study investigates the mechanical properties of composites with the fiber surface treatment of polydopamine (PDA). The test material was composite laminated with carbon fiber, aramid fiber, and glass fiber. The mechanical properties were evaluated by tensile testing. The tensile strength of the aramid and glass composites generally did not increase effectively with surface treatment. In carbon composites, both strength and toughness properties were improved by surface modification. In aramid composites, the toughness showed the best effect with surface treatment, but glass composites had no effect. When the deposited PDA was properly and evenly distributed, the composites showed excellent tensile properties.

Electrospun Polyacrylonitrile/Polythiophene Fibers for Phosphate Anion Sensing

Electrospun fibers are widely used in various applications such as tissue engineering, wound healing, drug delivery, materials science, chemical industry, energy storage, and sensor thanks to their combination of unique properties such as large surface area, high mechanical stability, high porosity, and great electrical conductivity. In addition, conducting polymers (CPs) used in fiber structures offer an extraordinary range of materials due to their diverse properties such as electrical and optical properties, the possibility of both chemical and electrochemical synthesis, and ease of processing.
 Among CPs, polythiophene (PTh) is highly important due to its unique redox electrical behavior, ease of synthesis, and application in many fields.
 In this study, 10 wt% polyacrylonitrile (PAN) fibers (P1), 10 wt% PAN/1 wt% PTh fibers (P2), and 10 wt% PAN/3 wt% PTh fibers (P3) were produced using an electrospinning technique. The structures, the morphologies and the electroactivities of the electrospun fibers were characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), Thermogravimetric analysis (TGA), and Cyclic voltammetry (CV). FTIR, SEM-EDX and TGA results supported the presence of PTh in PAN fibers.
 The electrochemical behaviors of indium-tin-oxide (ITO) glasses coated with the P1, P2, and P3 fibers in phosphate buffer solution (PBS) at various concentrations were assessed by CV. These electrospun fibers containing PTh were used for phosphate anion sensing. For all fiber samples, the oxidation potential increased with a decreasing concentration of phosphate buffer solution. The obtained results indicated that the thermal stability and electrical conductivity of the fibers were affected by PTh. This study shows that PAN fibers containing PTh as anionic sensors can be used as new recognition models.

Eco-friendly Indigo Reduction by Using Dietzia sp. KDB1 Strain : Some Variables Required to Develop Process Technology

This study was aimed to develop the reduction process of natural indigo (Indigo/era tinctoria) by using bacterial strain (Dietzia sp. KDB1) separated from Korean traditional fermentation bath. In detail, changes in pH, oxidation reduction potential (ORP), and color intensity (K/S) of dyed ramie fabric were evaluated by using some of alkaline mediums, pH adjustments, and concentrations of KDB1 and indigo, respectively. In terms of pH control and reducing power, buffer solution of NaHCO3/NaOH was the most effective among the mediums used. In the baths with buffer solution, initial pH 10.7 exhibited faster initiation of reduction and higher K/S than other initial pH values. The bath adjusted at pH 10.0 showed higher K/S and more negative ORP, than the baths adjusted at pH 10.5 and 10.7. Better reducing power was obtained at higher indigo and KDB1 concentrations. With the combination of buffer solution, scale-up, repeat dyeing, and higher KDB1 concentration, K/S range of 9.5–16.0 was obtained at days of 4–6. Use of single bacterial strain for indigo reduction attains a simple, reliable and eco-friendly dyeing process which can be applied as an alternative to sodium dithionite reduction.

Alkaline Hydrolysis and Dyeing Characteristics of Sea-Island-Type Ultramicrofibers of PET Tricot Fabrics with Black Disperse Dye.

In this study, we investigated conditions for the alkaline hydrolysis and black-disperse dyeing of sea-island-type polyethylene terephthalate (PET) ultramicrofiber tricot fabric. We examined the weight loss ratios and tensile strengths according to the NaOH content (10–30% on mass of fabric (omf)) during treatment; the optimal conditions used 25% omf NaOH for 30 min at 100 °C for an average weight loss ratio of 23.47%. By scanning electron microscope (SEM) analysis, the ‘sea’ components are extracted with increasing NaOH concentration until 25% omf NaOH, and damage of the ‘island’ components above 25% omf NaOH leads to a reduction in tensile strength. The dyeing conditions, including temperature (95–135 °C), time (20–60 min), pH buffer solution concentration (1–9 g/L), and contents of dispersant (1–9 g/L) and UV-absorbent (5–25% omf) were also explored. The optimal dyeing conditions were established as a dye concentration of 8% omf with 1 g/L dispersant, 1 g/L pH buffer solution concentration, and 10% omf UV-absorbent at 135 °C for 40 min at a 1:10 goods-to-liquor ratio. The rubbing colorfastness values for the fabrics dyed with the black disperse dye spanned four grades under dry and wet conditions. The light colorfastness values of the dyed fabrics were good to excellent in the range of 4–5 grades.

Quartz Crystal Microbalance Aptasensor for the Molecular Detection of Dengue Virus

Introduction Dengue fever is the major public health concern in the Philippines and is endemic in all regions of the country in which all serotypes are present[1]. Despite the widespread nature of the virus transmitted by mosquitos, molecular diagnostics have significant limitations. An early diagnosis of dengue may prevent severe clinical complications associated with the infection. A novel genosensor using an aptamer for the detection of dengue virus serotypes 1-4 was demonstrated in this study. Method This genosensor composed of a thiolated aptamer immobilized on a 10MHz gold electrode QCM targeting the 3’ untranslated region of all complete genome sequences of dengue virus available in GenBank[2]. Aptamer concentration, buffer pH and ionic strength of buffer solutions were optimized to achieve the highest sensitivity of the QCM genosensor. Atomic force microscopy [3], electrochemical impedance spectrum (EIS) measurements and cyclic voltammetry (CV) were used to characterize the surface of the QCM electrode prepared[4]. Evaluation of binding kinetics and affinity study of the Aptamer-dengue genome was determined by surface plasmon resonance (SPR)[5]. Results and Conclusions Atomic Force Microscopy (AFM), Electrochemical Impedance (EIS) and Cyclic Voltammetry (CV) have been used to characterize the surface of the PQC electrode. The AFM results indicate that the thiolated aptamer onto the electrode has decreased the roughness of gold surface by forming a uniform layer on the electrode surface. The EIS and CV results indicate that the charge transfer resistance is increased after immobilization of the aptamer onto the bare gold electrodes, indicating that direct S-Au bonding via disulfide moieties and the negative charge of protein have blocked the electrode reaction between Fe (II) and Fe (III). The results showed that the developed aptamer QCM sensor has an optimum concentration range of the target dengue genome is 20–100 mg/ml for hybridization. This work demonstrated the possibility of using an immobilized aptamer on a QCM and other sensor platforms for the direct detection of the RT-PCR products of dengue virus serotypes 1-4.

Quantifying the factors limiting performance and rates in microbial fuel cells using the electrode potential slope analysis combined with electrical impedance spectroscopy

Improving power generation of microbial fuel cells (MFCs) requires better methods to quantify the impact of the solution chemistry on performance. While buffer concentration and conductivity have been indicated to impact performance of flat (carbon cloth) anodes, we were able for the first to time to quantitatively determine the impact of the phosphate buffer solution (PBS) concentration separate from conductivity on electrode resistances of commonly used brush anodes and activated carbon cathodes. Using the electrode potential slope (EPS) method, we showed that the anode resistance decreased by 64% (from 14.6 ± 0.1 mΩ m2 to 5.3 ± 0.1 mΩ m2) by increasing the PBS concentration from 50 to 200 mM. There was no appreciable change in the cathode resistance (17.0 ± 0.1 mΩ m2, 50 mM; 18.9 ± 0.2 mΩ m2, 200 mM) although overall performance increased due to a larger cathode experimental working potential (ECat,e0-50= 268.9 ± 0.9 mV, ECat,e0-200= 370 ± 1 mV). Adding phosphate buffer to low conductivity synthetic wastewater containing 0.25 g L−1 sodium acetate decreased the anode resistance by 52% (from 59.1 ± 0.2 mΩ m2 to 28.1 ± 0.1 mΩ m2), but increasing only conductivity by adding NaCl or acetate had little impact on electrode resistances. Using electrochemical impedance spectroscopy (EIS), we determined the reasons for these responses. The cathode was limited by oxygen reduction reaction (ORR) kinetics, while the brush anode was limited by mass transfer (proton diffusion), consistent with the impact of buffer concentration on performance. These results have important implications for operation of MFCs as increasing solution conductivity alone, for example, by adding seawater, will not be sufficient to improve anode performance.