DNA Aptamer-Conjugated Magnetic Graphene Oxide for Pathogenic Bacteria Aggregation: Selective and Enhanced Photothermal Therapy for Effective and Rapid Killing.

Methicillin-resistant Staphylococcus aureus (MRSA), often called "superbug", is a nosocomial and multidrug resistance bacterium that shows resistance to ß-lactam antibiotics. There has been high demand to develop an alternative treatment model to antibiotics for efficiently fighting MRSA. Herein, we developed DNA aptamer-conjugated magnetic graphene oxide (Apt@MGO) as a multifunctional and biocompatible nanoplatform for selective and rapid eradication of MRSA and evaluated heat generation and cell death performance of Apt@MGO for the first time under dispersed and aggregated states. The aptamer sequence was specifically selected for MRSA and acted as a molecular targeting probe for selective MRSA recognition and antibiotic-free therapy. Magnetic graphene oxide (MGO) serves as a nanoplatform for aptamer conjugation and as a photothermal agent by converting near-infrared (NIR) light to heat. Iron oxide nanoparticles (Fe3O4 NPs) are formed on GO to prepare MGO, which shows magnetic properties for collecting MRSA cells in a certain area in the reaction tube by an external magnet. The collected MGO induces remarkably high local heating and eventual MRSA cell death under NIR laser irradiation. We demonstrate that Apt@MGO resulted in ∼78% MRSA and over >97% MRSA cell inactivation in dispersed and aggregated states, respectively, under 200 seconds (sn) exposure of NIR irradiation (808 nm, 1.1 W cm-2). An in vitro study highlights that Apt@MGO is considered a targeted, biocompatible, and light-activated photothermal agent for efficient and rapid killing of MRSA in the aggregated state under NIR light.

An automated system for preconcentration on imprinted polymer and laser diode spectrometric determination of uranium in mineral water samples.

A study, where uranium was online enriched and laser diode spectrometry was determined, was performed with some bottled mineral water samples. A uranium-imprinted polymer (PMDU) was synthesized and characterized for preparation of a specific adsorbent of UO22+ cations. The homemade system preconcentrated uranium in PMDU resin and determined using an Arsenazo III complex at 650 nm in a combined laser diode spectrometer. All analytical parameters of the system were optimized at 5.5 of the retention pH, 6.0 N HClO4 of eluent concentration, 0.05% of Arsenazo III complex, and a 40 mm coil length. The effect of interferent ions was also investigated and LOD and LOQ values were found to be 0.54 and 1.80 ng mL-1 respectively. Sample throughput was 12 h-1, the preconcentration factor was 50, and RSD% value was 1.1. Certified reference materials of TMDA 52.3 and TMDA 62.2 were quantitatively analyzed and the proposed method was successfully applied to the bottled mineral water samples.

A new fluorescence reagent: Synthesis, characterization and application for speciation of arsenic (III)/(VI) species in tea samples.

A sensitive and selective fluorimetric method for the rapid determination of trace amounts of As(III)/As(V) species in certain tea samples forms the basis of the study. 3',6'-bis(diethylamino)-2-{[(1E)-(4,5-dimethyl-2-furyl)methylene]amino}spiro[isoindole-1,9'-xanthen]-3(2H)-one (DMBD), was synthesized and characterized as a new fluorescence reagent for the speciation of As(III)/As(V) species. As(III) was quantitatively recovered with fluorescence reagent at concentrations between 0.5 and 1.5 mol L-1 of HNO3, while As(V) was not quantitatively recovered at any pH. The optimum conditions for the speciation of As(III)/As(V) species were investigated on certain commonly tested experimental parameters such as acidity and pH of the sample, amount of reagent, effects of temperature, and interfering ions etc. In order to determine trace amounts of total arsenic, KI and l(+) ascorbic acid were used to reduce As(V) to the trivalent state in the sample solution prior to determination. The concentration of As(V) in the sample solution were calculated by the difference in concentration between As(III) and the total arsenic in the sample solution. The study yielded a linear function of the concentration of As(III) in the 0-5 mg L-1 range with a detection limit of 0.22 µg L-1. The relative standard deviation was found to be 0.3% for the 0.5 mg L-1 As(III) level. The proposed method was successfully applied for the determination of trace amounts of As(III) and As(V) in certain tea samples. The results of analysis of the certified reference material (INCT-TL-1 tea sample) was found to be in good agreement with the certified value.

A new turn-on fluorimetric method for the rapid speciation of Cr(III)/Cr(VI) species in tea samples with rhodamine-based fluorescent reagent.

A new fluorimetric method with rhodamine-based fluorescent agent was developed for the rapid speciation of Cr(III)/Cr(VI) in tea, soil and water samples. The system, which utilizes a fluorescent reagent, was used for the first time after synthesis/characterization of 3',6'-bis(diethylamino)-2-{[(1E)-(2,4-dimethoxyphenyl)methylene] amino}spiro[isoindole-1,9'-xanthen]-3(2H)-one (BDAS). The reagent responds instantaneously at room temperature in a 1:1 stoichiometric manner to the amount of Cr(III). The selectivity of this system for Cr(III) over other metal ions is remarkably high, and its sensitivity is below 0.01mgL-1 in aqueous solutions which enables a simplification without any pretreatment of the real sample. The method has a wide linear range of 0.1-10mgL-1 and a detection limit of 0.15µgL-1 for Cr(III) while the relative standard deviation was 0.1% for 0.1mgL-1 Cr(III) concentration. The results of detection and recovery experiments for Cr(III) in tea, soil and water were satisfactory, indicating that the method has better feasibility and application potential in the routine determination and speciation of Cr(III)/Cr(VI). The results of analysis of the certified reference material (INCT-TL-1 tea sample and CWW-TM-D waste water) are in good agreement with the certified value.

Synthesis, characterization and application of a new fluorescence reagent for the determination of aluminum in food samples.

A new sensitive fluorimetry method for the simple and rapid measurement of aluminum in some food samples, which used 3',6'-bis(diethylamino)-2-{[(1E)-(4-ethoxyphenyl) methylene] amino}spiro[isoindole-1,9'-xanthen]-3(2H)-one (DEMAX) for Al(III) chelation is described herein. The fluorescence intensity of the aluminum-DEMAX complex remains unaltered for over 24h at room temperature and is a linear function of the concentration of aluminum in the 0-1000mg/L range with a detection limit (LOD, defined as 3s/b) of 3.02µgL-1 and quantification limit (LOQ, defined as 10Sb/m) of 30µgL-1. The relative standard deviation (RSD) was 0.1% for a 1µgL-1 aluminum level. The influences of the analytical parameters such as pH, waiting time of aluminum-DEMAX complex, amount of reagent, effect of temperature etc. were investigated. The developed method was successfully used for assaying aluminum in some food samples and dialysis solution, measured by the new home-made fluorimetric system. The results of analysis of the certified reference material (INCT-TL-1) are in good agreement with the certified value.

DNA aptamer functionalized gold nanostructures for molecular recognition and photothermal inactivation of methicillin-Resistant Staphylococcus aureus.

In this work, we report the development of DNA aptamer-functionalized gold nanoparticles (Apt@Au NPs) and gold nanorods (Apt@Au NRs) for inactivation of Methicillin-resistant Staphylococcus aureus (MRSA) with targeted photothermal therapy (PTT). Although both Apt@Au NPs and Apt@Au NRs specifically bind to MRSA cells, Apt@Au NPs and Apt@Au NRs inactivated ∼5% and over 95% of the cells,respectively through PTT. This difference in inactivation was based on the relatively high longitudinal absorption of near-infrared (NIR) radiation and strong photothermal conversion capability for the Apt@Au NRs compared to the Apt@Au NPs. The Au NRs served as a nanoplatform for the loading of thiolated aptamer and also provided multivalent effects for increasing binding strength and affinity to MRSA. Our results indicate that the type of aptamer and the degree of multivalent effect(s) are important factors for MRSA inactivation efficiency in PTT. We show that the Apt@Au NRs are a very effective and promising nanosystem for specific cell recognition and in vitro PTT.

A New Turn-On Fluorometric Detection Method for the Determination of Ag(I) in Some Food and Water Samples.

A new sensitive and selective turn-on fluorometry procedure for the determination of silver using a laboratory-built fluorometry system is described herein. After synthesis and characterization, a [2-((E)-{[3',6'-bis(ethylamino)-2',7'-dimethyl-3-oxospiro[isoindole-1,9'-xanthen]-2(3H)-yl]imino}methyl)cyclopenta-2,4-dien-1-yl] (cyclopenta-2,4-dien-1-yl)iron (DKMS) fluorescent reagent was used for the first time. Ag(I) was complexed with the new fluorescent reagent, and direct measurements were made using fluorometry without any separation/preconcentration. The fluorescence intensity of the Ag(I)-DKMS complex remained unchanged for over 18 h at room temperature and was a linear function of the concentration of Ag(I) in the 0-2.5 mg/L range. The optimum determination conditions were established by testing different reagent quantities, the acidity and pH of the sample, and the effect of temperature and interfering ions. The LOD of the method was 1.00 µg/L whereas the RSD was 0.1% for 0.1 mg/L Ag(I) concentration. "The developed method was applied successfully for the Ag(I) determination of silver in burn cream, anode slime, some food and water samples". Results of the analysis of Certified Reference Materials (NCS DC73349 Bush Branches and Leaves - Trace Elements, and CWW-TM-D Certified Wastewater and Trace Metals) are in good agreement with the certified values.

DLLME-spectrophotometric determination of glyphosate residue in legumes.

A new separation and pre-concentration method for spectrophotometric determination of glyphosate herbicide was developed. Glyphosate was converted into dithiocarbamic acid with CS2, followed by copper in the presence of ammonia to promote complex formation. This complex was collected in a CH2Cl2 organic drop and absorbance measured at 435nm. The analytical parameters, such as the amount of NH3, Cu(II) and CS2, type of extraction solutions, and the ratio of dispersive and organic liquids were optimized. The calibration curve was linear in the range 0.5-10mgl-1. The limits of detection and quantification were calculated from 3s to 10s criterions as 0.21mgl-1 and 0.70mgl-1, respectively. The developed method was applied to legume samples with the satisfactory recovery values of 98±4-102±3%.

Dispersive Liquid-Liquid Microextraction of Bismuth in Various Samples and Determination by Flame Atomic Absorption Spectrometry.

A dispersive liquid-liquid microextraction method for the determination of bismuth in various samples by flame atomic absorption spectrometry is described. In this method, crystal violet was used as counter positive ion for BiCl4 (-) complex ion, chloroform as extraction solvent, and ethanol as disperser solvent. The analytical parameters that may affect the extraction efficiency like acidity of sample, type and amount of extraction and disperser solvents, amount of ligand, and extraction time were studied in detail. The effect of interfering ions on the analyte recovery was also investigated. The calibration graph was linear in the range of 0.040-1.00 mg L(-1) with detection limit of 4.0 µg L(-1) (n = 13). The precision as relative standard deviation was 3% (n = 11, 0.20 mg L(-1)) and the enrichment factor was 74. The developed method was applied successfully for the determination of bismuth in various water, pharmaceutical, and cosmetic samples and the certified reference material (TMDA-64 lake water).

Determination of some metal ions in various meat and baby food samples by atomic spectrometry.

In this paper, we report a simple and rapid solid phase extraction system for the separation/preconcentration and determination of Cd(II), Co(II), Cu(II), Fe(III), Cr(III), Pb(II), and Zn(II) ions by flame atomic absorption spectrometry (FAAS). This method is based upon the retention of metal ions on a column packed with poly[N-(3-methyl-1H-indole-1-yl)]-2-methacrylamide-co-2-acrylamido-2-methyl-1-propane sulphonic acid-co divinylbenzene] (MMAD) resin as a solid-phase extraction (SPE) sorbent at pH 8. At the optimized conditions, the limits of detection (3 s/b) between 0.12 and 1.6 µg L(-1), preconcentration factor of 100, and the relative standard deviation of ⩽1.8% were achieved (n=10). The accuracy of the method was verified by analyzing certified reference materials (CRMs) and performing recovery experiments. The developed method was successfully applied to the various natural water, meat products and baby food samples. The recoveries of analyte ions were found in added real samples and CRMs from 95% to 102%.

A solid phase extraction procedure for the determination of Cd(II) and Pb(II) ions in food and water samples by flame atomic absorption spectrometry.

A relatively rapid, accurate and precise solid phase extraction method is presented for the determination of cadmium(II) and lead(II) in various food and water samples. Quantitation is carried out by flame atomic absorption spectrometry (FAAS). The method is based on the retention of the trace metal ions on Dowex Marathon C, a strong acid cation exchange resin. Some important parameters affecting the analytical performance of the method such as pH, flow rate and volume of the sample solution; type, concentration, volume, flow rate of the eluent; and matrix effects on the retention of the metal ions were investigated. Common coexisting ions did not interfere on the separation and determination of the analytes. The detection limits (3 σb) for Cd(II) and Pb(II) were found as 0.13 and 0.18 µg L(-1), respectively, while the limit of quantification values (10 σb) were computed as 0.43 and 0.60 µg L(-1) for the same sequence of the analytes. The precision (as relative standard deviation was lower than 4% at 5 µg L(-1) Cd(II) and 10 µg L(-1) Pb(II) levels, and the preconcentration factor was found to be 250. The accuracy of the proposed procedure was verified by analysing the certified reference materials, SPS-WW2 Batch 108 wastewater level 2 and INCT-TL-1 tea leaves, with the satisfactory results. In addition, for the accuracy of the method the recovery studies (⩾ 95%) were carried out. The method was applied to the determination of the analytes in the various natural waters (lake water, tap water, waste water with boric acid, waste water with H2SO4) and food samples (pomegranate flower, organic pear, radish leaf, lamb meat, etc.), and good results were obtained. While the food samples almost do not contain cadmium, they have included lead at low levels of 0.13-1.12 µg g(-1).

On-line solid-phase separation/preconcentration for the determination of copper in urine by flame atomic absorption spectrometry.

A new on-line separation/preconcentration system was developed for the determination of Cu(II) ions by flame atomic absorption spectrometry in urine samples. A newly synthesized chelating resin, by anchoring eriochrome blue black R reagent to Amberlite XAD-16 resin, was used as a packing material for the selective separation/preconcentration of Cu(II) ions. The influence of the parameters on the determination of Cu(II) ions such as pH of sample solution, amount of the resin, eluent type, interfering ions and flow variables was studied. The detection limit of the method was 1.0 µg L(-1) while precision was 2.3% (n=15) at 50 µg L(-1) Cu(II) level. The adsorption capacity of the resin was 217 µg g(-1) Cu(II). The accuracy of the method was proven using TMDA-64 standard lake water and synthetic urine sample. The developed method has been applied successfully to the determination of copper in urine with satisfactory results.

Development of a new on-line system for the sequential speciation and determination of chromium species in various samples using a combination of chelating and ion exchange resins.

A new on-line flow injection (FI) procedure for the sequential separation, preconcentration and speciation of Cr(III)/Cr(VI) species in different matrices is described based on the combining of solid phase extraction and flame atomic absorption spectrometry (FAAS). Poly 2-(5-methylisoxazol)methacrylamide-co-2-acrylamido-2-methyl-1-propanesulfonic acid-co-divinyl-benzene and Dowex 21K resins were used as chelating and ion-exchange materials for the separation/preconcentration of Cr(III) and Cr(VI) ions, respectively. Trace amounts of chromium retained on the resins were eluted sequentially with HNO3 and then introduced directly to the nebulizer-burner system of FAAS. The optimum conditions such as pH of the sample solution, amount of the resin, volume of the sample and interfering ions, which are effective on the quantitative recovery of the analytes, were investigated for sequential determination of Cr(III) and Cr(VI) ions. The preconcentration factors were found to be 48 and 30 for Cr(III) and Cr(VI), and the detection limits corresponding to three times the standard deviation of the blank (3s/b) were 0.05 and 0.3 µg L(-1), respectively. The method was verified by analyzing a certified reference material. The proposed method was applied to the determination based on the speciation of chromium in various real samples with satisfactory results.

Synthesis/characterization of a new chelating resin and on-line solid phase extraction for the determination of Ag(I) and Pd(II) from water, cream, anode slime and converter samples by flow injection flame atomic absorption spectrometry.

On-line preconcentration procedures for the determination of Ag(I) and Pd(II) by flame atomic absorption spectrometry have been described. A new chelating resin, poly (N,N'-dipropionitrilemethacrylamide-co-divinylbenzene-co-2-acrylamido-2-methyl-1-propane sulfonic acid) was synthesized and used as a new adsorbent material. The resin was characterized by Fourier transform infrared spectroscopy and elemental analysis. Ag(I) was adsorbed on the chelating resin at pH 5.0 and eluted with 1.0 mol L(-1) HNO3. Pd(II) was retained at pH 9.5 and eluted with 1.5 mol L(-1) HCl. The experimental parameters (pH, type and concentration of eluent, flow rates of sample and eluent solutions, elution time and the effect of interfering ions) for both Ag(I) and Pd(II) were investigated in detail. The detection limit for Ag(I) was 2.4 µg L(-1) and the relative standard deviation was 2.9% for 0.2 µg mL(-1) Ag(I). The detection limit for Pd(II) was 1.7 µg L(-1) and the relative standard deviation was 2.8% for 0.3 µg mL(-1) Pd(II). Accuracy was confirmed by analyzing a certified reference material (TMDA-70), recovery studies on real samples and comparison with electrothermal atomic absorption analysis. The proposed methods were successfully applied to the on-line determination of Ag(I) in bottled water, pharmaceutical cream and anode slime samples and Pd(II) in bottled water and catalytic converter samples.

On-line preconcentration/determination of zinc from water, biological and food samples using synthesized chelating resin and flame atomic absorption spectrometry.

An on-line flow injection pre-concentration-flame atomic absorption spectrometry method was developed to determine trace zinc in water (tap, dam, and well water), biological (hair and nail), and liver samples. As a solid phase extractant, a synthesized new chelating resin, poly(2-thiozylmethacrylamide-co-divinylbenzene-co-2-acrylamido-2-methyl-1-propane sulfonic acid) was used. The resin was characterized by Fourier transform infrared spectroscopy, elemental analysis, and surface area by nitrogen sorption. A pre-concentration factor of 40-fold for a sample volume of 12.6 mL was obtained by using the time-based technique. The detection limit for the pre-concentration method was found to be 2.2 µg L(-1). The precision (as RSD,%) for 10 replicate determinations at the 0.04 µg mL(-1) Zn concentration was 1.2%. The calibration graph using the pre-concentration system for zinc was linear with a correlation coefficient of 0.998 in the concentration range from 0.005 to 0.05 µg mL(-1). The applicability and accuracy of the developed method were estimated by the analysis spiked water, biological, liver samples (83-105%), and also certified reference material TMDA-70 (fortified lake water) and SPS-WW1 Batch 111-Wastewater. The results were in agreement with the certified values.

Synthesis, characterization and application of a new chelating resin for on-line separation, preconcentration and determination of Ag(I) by flame atomic absorption spectrometry.

A simple and reliable on-line separation/preconcentration procedure was developed for the determination of trace levels of Ag(I) by flame atomic absorption spectrometry. Poly[N-(3-methyl-1H-indol-1-yl)-2-methacrylamide-co-2-acrylamido-2-methyl-1-propane sulfonic acid-co-divinylbenzene] was synthesized and characterized as a new chelating resin for the first time. Ag(I) was sorbed on the chelating resin, from which it could be eluted with 3 mol L(-1) HCl and then introduced directly to the nebulizer-burner system for flame atomic absorption spectrometry. The parameters influential on the determination of Ag(I) ions such as the pH of the sample solution, amount of resin, eluent type, interfering ions and flow variables were studied. Under the optimum conditions, the calibration graph obtained was linear over the concentration range of 2-20 µg L(-1). The detection limit of the method (3σ) was 0.3 µg L(-1) while precision was 1.5% (n=25) at the level of 10 µg L(-1) Ag(I). The limit of quantification for the method, based on 20 σ, was 2.0 µg L(-1). The enrichment factor was found to be 65 while the optimized sample volume was 13.6 mL. The accuracy of the method was performed by analyzing certified reference materials. The developed method was applied successfully for the determination of silver in different water samples with satisfactory results.

An on-line preconcentration/separation system for the determination of bismuth in environmental samples by FAAS.

An on-line preconcentration procedure for the determination of bismuth by flame atomic absorption spectrometry (FAAS) has been described. Lewatit TP-207 chelating resin, including iminodiacetate group, packed in a minicolumn was used as adsorbent material. Bi(III) was sorbed on the chelating resin, from which it could be eluted with 3 mol L(-1) HNO(3) and then introduced directly to the nebulizer-burner system of FAAS. Best preconcentration conditions were established by testing different resin quantities, acidity of sample, types of eluent, sample and eluent solution volumes, adsorption and elution flow rates, and effect of interfering ions. The detection limit of the method was 2.75 microg L(-1) while the relative standard deviation was 3.0% for 0.4 microg mL(-1) Bi(III) concentration. The developed method has been applied successfully to the determination of bismuth in pharmaceutical cream, standard reference materials and various natural water samples with satisfactory results.

Determination of heavy metals at sub-ppm levels in seawater and dialysis solutions by FAAS after tetrakis(pyridine)-nickel(II)bis(thiocyanate) coprecipitation.

A coprecipitation method has been developed for the determination of Cr(III), Mn(II), Fe(III), Co(II), Cu(II), Cd(II) and Pb(II) ions in aqueous samples by flame atomic absorption spectrometry (FAAS) with the combination of pyridine, nickel(II) as a carrier element and potassium thiocyanate as an auxiliary complexing agent. The obtained coprecipitates were dissolved with nitric acid and measured by FAAS. The coprecipitation conditions, such as the effect of the pH, amounts of nickel, pyridine and potassium thiocyanate, sample volume, and the standing time of the precipitate formation were examined in detail. It was found that the metal ions studied were quantitatively coprecipitated with tetrakis(pyridine)-nickel(II)bis(thiocyanate) precipitate (TP-Ni-BT) in the pH range of 9.0 - 10.5. The reliability of the results was evaluated by recovery tests, using synthetic seawater solutions spiked with the analyte metal ions. The obtained recoveries ranged from 96 to 101% for all of the metal ions investigated. The proposed method was validated by analyses of two certified reference materials (NIST SRM 2711 Montana soil and HPS Certified Waste Water Trace Metals Lot #D532205). It was also successfully applied to seawater and dialysis solution samples. The detection limits (n = 25, 3s) were in the range of 0.01-2.44 microg l(-1) for the studied elements and the relative standard deviations were < or =6%, which indicated that this method could fully satisfy the requirements for analysis of such samples as seawater and dialysis solution having high salt contents.