Synergistic effects of binary surfactant mixtures in the adsorption of diclofenac sodium drug from aqueous solution by modified zeolite.

In this paper, the surfactant-modified clinoptilolite zeolite (with two methods) were used to remove diclofenac sodium (DFS) as a widely used drug in an aqueous solution. Clinoptilolite was modified by using pure cationic surfactant (cetyltrimethylammonium chloride, CTAC) and the mixed surfactants of CTAC + Triton-X100 (TX100). In the new approach, the synergistic effects between CTAC and TX100 were determined by surface tension measurements in different mole fractions and the optimum ratio (y1 ≈ 0.8) was identified with the maximum synergism. According to the mole fraction of this composition, the surface of clinoptilolite was modified by mixed surfactants (MSMZ) for the adsorption of DFS and then results compared with modified zeolite with pure cationic surfactant (SMZ). The raw and modified (SMZ and MSMZ) zeolites were characterized by Fourier transform infrared spectroscopy (FT-IR), BET analysis, the scanning electron microscopy (SEM) images, Zeta potential and X-ray. The experimental data of adsorption in equilibrium conditions were also analyzed using different adsorption isotherm models (Langmuir, Freundlich, Hill, Khan, Sips, Redlich-Peterson and Toth) in non-linear forms, and finally, the best model consistent with experimental data is determined (SMZ:Sips and MSMZ:Toth). According to the best isotherm model, the amount of absorption capacity in MSMZ was obtained almost 57% higher than SMZ. In addition, the kinetic adsorption data were correlated with eight various models in order to selection the best model for these systems. The kinetic adsorption data were well described by fractal-like pseudo-first-order (FL-PFO) and IKL models for SMZ and MSMZ adsorbents, respectively. Eight error functions were used to estimate the best fitted isotherm and kinetic models.

Development of an electrochemical sensor for the determination of antibiotic sulfamethazine in cow milk using graphene oxide decorated with Cu-Ag core-shell nanoparticles.

Determination and sensing of antibiotics in dairy products are the biggest challenges in the world. In continuation of our earlier study, a facile and novel determination method for the detection of sulfamethazine (SMZ) in cow milk has been developed using a glassy carbon electrode modified with graphene oxide decorated with Cu-Ag core-shell nanoparticles. The Cu-Ag core-shell nanoparticles and graphene oxide were synthesized and characterized via different techniques such as TEM, SEM, XRD and FTIR. The as-synthesized Cu-Ag core-shell nanoparticles were used for the decoration of the glassy carbon electrode modified with graphene oxide. The electroanalytical measurements including cyclic voltammetry and square wave voltammetry were performed and compared with HPLC, which was utilized for the determination of SMZ in cow milk. The experimental conditions were optimized to obtain a well-defined response signal. The concentration linear range was 10-1000 µM and the limit of detection was 0.46 µM for S/N = 3. The obtained results show good agreement with HPLC reported data.

Fabrication of a sensitive label free electrochemical immunosensor for detection of prostate specific antigen using functionalized multi-walled carbon nanotubes/polyaniline/AuNPs.

The aim of this research is to introduce a novel label free electrochemical immunosensor based on glassy carbon electrode (GCE) modified with carboxylated carbon nanotubes (COOH-MWCNTs)/polyaniline (PANI)/gold nanoparticles (AuNPs) for the detection of prostate specific antigen (PSA). The AuNPs were utilized as a connector for PSA antibody immobilization through NH2 groups on antibody. Investigations on modified electrode surface were performed by FT-IR spectrum, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) to evaluate the synthesized nanocomposite and modified electrode surface. As a sensitive analytical method for the detection of PSA, differential pulse voltammetry (DPV) was employed in different ranges of antigen concentration, 1.66 ag·mL-1 to 1.3 ng·mL-1. In addition, the detection limit was obtained 0.5 pg·mL-1, from the linear relationship between antigen concentration log and peak current. Also, the proposed immunosensor was carried out for the determination of PSA in human serum samples, indicating recoveries ranging from 92 to 104%. Finally, it should be noted that the reproducibility and specificity, along with the stability of the present immunosensor were examined, and satisfactory findings were obtained, thus proving it as a promising PSA immunosensor.

Electrochemical molecularly bioimprinted siloxane biosensor on the basis of core/shell silver nanoparticles/EGFR exon 21 L858R point mutant gene/siloxane film for ultra-sensing of Gemcitabine as a lung cancer chemotherapy medication.

In search for improvements in bioanalysis electrochemical sensors, for better assessment of anti-cancer drugs, it is necessary for their detection limits to be minimized and the sensitivity and selectivity to be surpassed simultaneously; whereas, resolving any probable interfering with other medical treatments are considered. In this work, a novel approach was adopted for detection and assessment of Gemcitabine (GEM) as an anti-cancer drug based on evaluating its interaction with EGFR exon 21-point mutant gene. An electrochemical nanobiosensor was invented based on a new molecularly bioimprinted siloxane polymer (MBIS) strategy; in which the EGFR exon 21 acts as an identification probe. The roles of multi-walled carbon nanotubes and Ag nanoparticles (NPs) are to perform as a signal amplifier. The MBIS film was prepared by acid-catalysed hydrolysis/condensation of the sample solution, containing Ag NPs, ds-DNA of EGFR exon 21 point mutant gene, GEM as a template molecule, 3-(aminopropyl) trimethoxysilane (APTMS) and tetraethoxysilane. The interaction between the dsDNA and GEM was investigated by employing the modified biosensor and monitoring oxidation signal of guanine and adenine. The produced biosensor was characterized by XRD, FE-SEM, EDS, FT-IR and differential pulse voltammetry. The oxidation signals of adenine and guanine were in linear range when the device was subjected to various concentrations of GEM, from 1.5 to -93 µM, where a low detection limit 12.5 nmol L-1, and 48.8 nmol L-1 were recorded by guanine and adenine respectively. The developed biosensor did perform very well when employed for the actual samples; the stability was also approved which was acceptable for a reasonable time.

An electrochemical immunosensor for the prostate specific antigen based on the use of reduced graphene oxide decorated with gold nanoparticles.

The authors describe an immunosensor for the prostate specific antigen (PSA). It was obtained by modifying a glassy carbon electrode (GCE) first modified with gold nanoparticles and then with reduced graphene oxide that was decorated with gold nanoparticles. The AuNPs on reduced graphene oxide provide a suitable surface for attachment of antibodies. On binding of the antigen, the square wave voltammetric signal (measured by using hexacyanoferrate as a probe) reduced. This method has two logarithmically linear analytical ranges that extend from 25 to 55 fg.mL-1 and from 1 to 36 ng.mL-1, respectively. The lowest detection limit is 2 pg.mL-1. Electrochemical impedance spectroscopy was also carried out for PSA determination. EIS works in the 0.0018 to 41 ng.mL-1 concentration range and has an LOD of 60 pg.mL-1. This method was applied to the determination of PSA in (spiked) human serum samples. In order to survey the selectivity of immunosensor, determination of PSA was performed in human serum samples, and finally sensitivity and reproducibility were examined. Graphical abstract Facile label free immunosensor based on reduced graphene oxide decorated with gold nanoparticles for early diagnosis prostate cancer via ultrasensitive detection of PSA biomarker: application in human serum.

Fixed bed adsorption column studies and models for removal of ibuprofen from aqueous solution by strong adsorbent Nano-clay composite.

In this study, ibuprofen was removed using a strong nano-clay-composite based on cloisite 15A, PVP and ß-cyclodextrin (CD@clay-PVP) adsorbent through a fixed-bed column system. Chemically modified nano-clay was characterized by using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and XRD. Different input situations were evaluated and included adsorbent bed height, initial concentrations, and the impact of the flow rate on the adsorbent. The various mathematical models employed to predict the breakthrough curve and model parameters include Thomas, bed-depth service time (BDST), Yoon-Nelson, and Clark. The characteristics of parameters related to the models were obtained by linear and nonlinear regression to design the process for the columns. Based on error analysis and adsorption conditions, all of the models are identical in describing the adsorption fixed-bed columns.

A novel molecularly imprinted sensor for imidacloprid pesticide based on poly(levodopa) electro-polymerized/TiO2 nanoparticles composite.

This research reports the first application of poly(levodopa) in the development of a molecularly imprinted sensor. A novel electrochemical sensor with high selectivity and sensitivity was developed for imidacloprid (IMD) determination based on an imprinted poly(levodopa) electro-polymerized on electrodeposited TiO2 nanoparticles (TiO2NPs) modified glassy carbon electrode (GCE). High affinity of IMD imprinted poly(levodopa) to IMD provided a very selective response of the electrode to IMD and electrodeposited TiO2NPs at the electrode surface resulted in the electrocatalytic reduction of IMD and consequently high sensitivity of the modified electrode. IMD imprinted poly(levodopa) electro-polymerized on TiO2NPs was well characterized by FT-IR, SEM, and EDX techniques. Sensor response to IMD was investigated by using square wave voltammetry (SWV), cyclic voltammetry (CV), and differential pulse voltammetry (DPV) techniques. The sensor showed a really vast linear range of 2-400 µM, completely low detection limit (LoD) of 0.3 µM, and limit of quantitation (LoQ) of 1 µM by SWV measurements that are very acceptable in comparison to other reported IMD sensors. Sensor application in real samples for IMD determination showed good applicability of the developed sensor. Response time is very short and the sensor showed suitable repeatability and stability after use several times. Graphical abstract ᅟ.

Polythiophene supported MnO2 nanoparticles as nano-stabilizer for simultaneously electrostatically immobilization of d-amino acid oxidase and hemoglobin as efficient bio-nanocomposite in fabrication of dopamine bi-enzyme biosensor.

A novel, highly selective and sensitive voltammetric bi-enzyme biosensor for sensing dopamine (DA), in presence of H2O2 which resulted as d-alanine enzymatic oxidation, was fabricated on the basis of simultaneously electrostatically immobilization of d-amino acid oxidase (DAAO) and hemoglobin (Hb) on MnO2 nanoparticles (MnO2 NPs) enriched poly thiophene (PTh). Cyclic voltammetry (CV), technique was applied for electropolymerization of thiophene on glassy carbon electrode (GCE) surface and MnO2 NPs dispersed on PTh network by soaking PTh/GCE in potassium permanganate (KMnO4) solution. Excellent catalytic properties and large surface area of MnO2 NPs/PTh composite caused it was used as an enzymes immobilization host in this developed bi-enzyme biosensor. The developed biosensor was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and CV. The performance of the modified bi-enzyme biosensor was investigated in terms of its response time, detection limit, sensitivity, stability and selectivity in a lab environment. The composite of DAAO-Hb/MnO2 NPs/PTh to construct a bi-enzyme biosensor in this study showed a linear response with DA in the concentration range of 0.04-9.0µM with R-squared value of 0.994 (for S/N=3) and its sensitivity and detection limite were about 12.801µA/µM and 41nM respectively. Also this bi-enzyme biosensors exhibited high selectivity, rapid response (5s) and long-term stability (42days). At the end, the proposed biosensor was applied successfully in human serum as real sample.

Enzymatic biosensor based on entrapment of d-amino acid oxidase on gold nanofilm/MWCNTs nanocomposite modified glassy carbon electrode by sol-gel network: Analytical applications for d-alanine in human serum.

Sensing and determination of d-alanine is studied by using an enzymatic biosensor which was constructed on the basis of d-amino acid oxidase (DAAO) immobilization by sol-gel film onto glassy carbon electrode surface modified with nanocomposite of gold nanofilm (Au-NF) and multiwalled carbon nanotubes (MWCNTs). The Au-NF/MWCNT nanocomposite was prepared by applying the potentiostatic technique for electrodeposition of Au-NF on the MWCNT immobilized on glassy carbon electrode surface. The modified electrode is investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), linear sweep voltammetry (LSV) and cyclic voltammetry(CV) techniques. The linear sweep voltammetry was used for determination of d-alanine and the results showed an excellent linear relationship between biosensor response and d-alanine concentration ranging from 0.25µM to 4.5µM with correction coefficient of 0.999 (n=20). Detection limit for the fabricated sensor was calculated about 20nM (for S/N=3) and sensitivity was about 56.1µAµM-1cm-2. The developed biosensor exhibited rapid and accurate response to d-alanine, a good stability (4 weeks) and an average recovery of 98.9% in human serum samples.

First report on hemoglobin electrostatic immobilization on WO3 nanoparticles: application in the simultaneous determination of levodopa, uric acid, and folic acid.

This work describes the first report about the simultaneous determination of levodopa (L-DOPA) with folic acid (FA) and uric acid (UA) based on electrocatalytic oxidation of L-DOPA with peroxidase properties of hemoglobin (Hb) in the presence of H2O2 as Hb activator. Bovine Hb was electrostatically immobilized on WO3 nanoparticles (WO3NPs) in pH between Hb and WO3NP isoelectric points, and subsequently, a carbon paste electrode (CPE) was modified with the obtained WO3NPs-Hb and multiwalled carbon nanotubes (MWCNTs). The resulting biosensor supplied a sensitive and suitably stable biosensor for the simultaneous determination of L-DOPA, UA, and FA. The obtained linear range and detection limit for L-DOPA, UA, and FA were completely acceptable, and the biosensor response time for these molecules was relatively short so that it reaches about 95 % of its maximum response in less than 10 s. The applicability of the current biosensor was confirmed with the determination of L-DOPA in the presence of fixed amounts of FA and UA in some real samples by the standard addition method.

Glassy carbon electrode modified with horse radish peroxidase/organic nucleophilic-functionalized carbon nanotube composite for enhanced electrocatalytic oxidation and efficient voltammetric sensing of levodopa.

A novel and selective enzymatic biosensor was designed and constructed for voltammetric determination of levodopa (L-Dopa) in aqueous media (phosphate buffer solution, pH=7). Biosensor development was on the basis of to physically immobilizing of horse radish peroxidase (HRP) as electrochemical catalyst by sol-gel on glassy carbon electrode modified with organic nucleophilic carbon nanotube composite which in this composite p-phenylenediamine (pPDA) as organic nucleophile chemically bonded with functionalized MWCNT (MWCNT-COOH). The results of this study suggest that prepared bioorganic nucleophilic carbon nanotube composite (HRP/MWCNT-pPDA) shows fast electron transfer rate for electro oxidation of L-Dopa because of its high electrochemical catalytic activity toward the oxidation of L-Dopa, more--NH2 reactive sites and large effective surface area. Also in this work we measured L-Dopa in the presence of folic acid and uric acid as interferences. The proposed biosensor was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), FT-IR spectroscopy and cyclic voltammetry (CV). The differential pulse voltammetry (DPV) was used for determination of L-Dopa from 0.1 µM to 1.9 µM with a low detection limit of 40 nM (for S/N=3) and sensitivity was about 35.5 µA/µM. Also this biosensor has several advantages such as rapid response, high stability and reproducibility.

Optimization of modified carbon paste electrode with multiwalled carbon nanotube/ionic liquid/cauliflower-like gold nanostructures for simultaneous determination of ascorbic acid, dopamine and uric acid.

We describe the modification of a carbon paste electrode (CPE) with multiwalled carbon nanotubes (MWCNTs) and an ionic liquid (IL). Electrochemical studies by using a D-optimal mixture design in Design-Expert software revealed an optimized composition of 60% graphite, 14.2% paraffin, 10.8% MWCNT and 15% IL. The optimal modified CPE shows good electrochemical properties that are well matched with model prediction parameters. In the next step, the optimized CPE was modified with gold nanostructures by applying a double-pulse electrochemical technique. The resulting electrode was characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and electrochemical impedance spectroscopy. It gives three sharp and well-separated oxidation peaks for ascorbic acid (AA), dopamine (DA), and uric acid (UA). The sensor enables simultaneous determination of AA, DA and UA with linear responses from 0.3 to 285, 0.08 to 200, and 0.1 to 450 µM, respectively, and with 120, 30 and 30 nM detection limits (at an S/N of 3). The method was successfully applied to the determination of AA, DA, and UA in spiked samples of human serum and urine.

Amperometric sensing of anti-HIV drug zidovudine on Ag nanofilm-multiwalled carbon nanotubes modified glassy carbon electrode.

The zidovudine (ZDV) is the first drug approved for the treatment of HIV virus infection. The detection and determination of this drug are very importance in human serum because of its undesirable effects. A new ZDV sensor was fabricated on the basis of nanocomposite of silver nanofilm (Ag-NF) and multiwalled carbon nanotubes (MWCNTs) immobilized on glassy carbon electrode (GCE). The modified electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) techniques. Results showed that the electrodeposited silver has a nanofilm structure and further electrochemical studies showed that the prepared nanocomposite has high electrocatalytic activity and is appropriate for using in sensors. The amperometric technique under optimal conditions is used for the determination of ZDV ranging from 0.1 to 400ppm (0.37µM-1.5mM) with a low detection limit of 0.04ppm (0.15µM) (S/N=3) and good sensitivity. The prepared sensor possessed accurate and rapid response to ZDV and shows an average recovery of 98.6% in real samples.

Canonical Monte Carlo simulation of adsorption of O2 and N2 mixture on single walled carbon nanotube at different temperatures and pressures.

Adsorption of pure and mixtures of O(2) and N(2) on isolated single-walled carbon nanotube (SWCNT) have been investigated at the subcritical (77 K) and different supercritical (273, 293, and 313 K) temperatures for the pressure range between 1 and 31 MPa using (N,V,T) Monte Carlo simulation. Both O(2) and N(2) gravimetric storage capacity exhibit similar behaviors, gas adsorption is higher on outer surface of tube, compared to the inner surface. Results are consistent with the experimental adsorption measurements. All adsorption isotherms for pure and mixture of O(2) and N(2) are characterized by type I (Langmuir shape), indicating enhanced solid-fluid interactions. Comparative studies reveal that, under identical conditions, O(2) adsorption is higher than N(2) adsorption, due to the adsorbate structure. Excess amount of O(2) and N(2) adsorption reach to a maximum at each temperature and specified pressure which can be suggested an optimum pressure for O(2) and N(2) storage. In addition, adsorptions of O(2) and N(2) mixtures have been investigated in two different compositions: (i) an equimolar gas mixture and (ii) air composition. Also, selectivity of nanotube to adsorption of O(2) and N(2) gases has been calculated for air composition at ambient condition.

Effect of the adsorption of oxygen on electronic structures and geometrical parameters of armchair single-wall carbon nanotubes: a density functional study.

We investigated the effect of atomic and molecular oxygen adsorption on the geometries and electronic properties of small and large armchair single-walled carbon nanotubes (SWCNTs) by means of the density functional theory (DFT). We calculated the equilibrium geometries, energetics, and electronic properties of the nanotubes as well as the tube-molecules. Global indices such as electronic chemical potential and hardness were calculated using the Kopmann's theorem. Our investigation involved the physisorption of molecular oxygen, chemisorption of atomic oxygen, and formation of epoxide-like structures. The adsorption energies of the oxygen molecules physisorbed to different sites were determined by calculating the short-range interactions. The effect of the tube diameter on the stability of the tube-O(2) system was studied for the different sites. Also we considered the orientation of O(2) molecule during adsorption of O(2) molecule on the outer surface of tubes. Adsorption of oxygen atom on top of the carbon atom of the tubes was also considered. We found out that O atoms bind to the outer surface of the SWCNTs to give stable epoxide-like structures. The most stable epoxide-like structure on the outer surface of the nanotubes was the (4,4)-O system with a calculated adsorption energy of -2.944 eV.

Study of surface tension and surface properties of binary alcohol/n-alkyl acetate mixtures.

The Butler equation is employed to describe quantitatively the nature, properties, and compositions of surface layers in binary liquid mixtures. Bulk mole fraction, surface molar area, and surface tension of pure components are necessary inputs for this equation. In addition, the UNIFAC group contribution method is applied to account for the nonideality of the bulk liquid as well as that of the surface layer. The average relative error obtained from the comparison of experimental and calculated surface tension values for 12 binary systems is less than 1%. Therefore, the model has good accuracy in comparison with other predictive equations. In addition to finding more information about the surface structure of binary mixtures, surface mole fraction was calculated using relative Gibbs adsorption values and an extended Langmuir model (EL). The obtained results show a good consistency between two models employed, i.e., the Gibbs adsorption model and EL model, based on the UNIFAC method.