pH-responsive deoxyribonucleic acid capture/release by polydopamine functionalized magnetic nanoparticles

Polydopamine functionalized magnetic nanoparticles (PDA@Fe₃O₄) were prepared and characterized by transmission electron microscopy, scanning electron microscopy, zeta potential and vibrating sample magnetometry. They were found to enable highly efficient capture of genomic deoxyribonucleic acid (DNA). The adsorption capacity of PDA@Fe₃O₄ for genomic DNA can reach 161 mg g⁻¹. The extraction protocol used aqueous solutions for DNA binding to and releasing from the surface of the magnetic particles based on the pH inducing the charge switch of amino and phenolic hydroxyl groups on PDA@Fe₃O₄. The extracted DNA with high quality (A₂₆₀/A₂₈₀ = 1.80) can be directly used as templates for polymerase chain reaction (PCR) followed by capillary electrophoresis (CE) analysis. None of the toxic chemical reagents and PCR inhibitors was used throughout the whole procedure. PDA@Fe₃O₄ based magnetic solid phase extraction (MSPE) method was superior to those using commercial kit and traditional phenol–chloroform extraction methods in yield of DNA. The developed PDA@Fe₃O₄ based MSPE-PCR-CE method was applied for simultaneous and fast detection of Listeria monocytogenes and Escherichia coli O157:H7 in milk.     

Single probe nucleic acid immobilization on chemically modified single protein by controlling ionic strength and pH

In an effort toward determining the feasibility of single molecule analysis, we describe a case whereby the binding of one biotinylated DNA to one streptavidin molecule via electrostatic interactions was controlled by altering in pH 4.0-9.0 and 0.16 of the ion strength. The quantitative analysis of immobilized probe ssDNA was realized in real-time via a quartz crystal microbalance (QCM) and electrochemical (EC) measurement in the range 100 pM to 50 μM of probe oligonucleotide concentration. The variation amount of biotinylated ssDNA immobilized on the streptavidin-modified surface at pH 7.5 was about 0.16 pmol, giving a ratio of streptavidin to biotinylated ssDNA of about 1:1.1. On the other hand, at pH 4.9, it was immobilized about 0.29 pmol. From the shape of the Langmuir plot and QCM, the immobilization efficiency of biotinylated DNA via streptavidin at pH 4.9 was approximately twofold that at pH 7.5. In view points of the reaction velocity, it was increased with decreasing buffer solution pH, indicating a strong interaction of negatively charged probe DNA with the positively charged streptavidin. And also the EC response value of ΔI/I_streptavidin for the immobilized biotinylated ssDNA in pH 4.9 was about 49%, while the corresponding value for the pH 7.5 was approximately 34%. As DNA molecules possess negative charges, electrostatic repulsion occurred between streptavidin and biotinylated ssDNA at pH 7.5. At pH 4.9, the attraction between the biotinylated ssDNA and streptavidin resulted in increased adsorption which has an isoelectric point of about 5.9. It was deduced that the binding of biotinylated ssDNA to one or two of the four binding sites of streptavidin can be controlled by adjusting the pH-controlled electrostatic interaction.     

N-Methylimidazolium modified magnetic particles-assisted highly sensitive Escherichia coli detection based on polymerase chain reaction and capillary electrophoresis

Effective bacteria detection and quantification are essential prerequisite for the prevention and treatment of infectious diseases. Herein, we report a method for the detection and quantification of Escherichia coli (E. coli).N-Methylimidazolium modified magnetic particles (MIm-MPs) are synthesized successfully and used as an efficient magnetic material for the isolation and concentration of E. coli. The factors including pH of binding buffer, concentration of elution buffer and elution time which may affect the capture and elution efficiencies are optimized. The linear correlation between bacteria concentration and peak area of polymerase chain reaction (PCR) product analyzed by capillary electrophoresis (CE) is determined. Rapid preconcentration of trace amount of E. coli (10¹ cfu mL⁻¹) in large volume of aqueous sample (500 mL) is achieved, and the capture efficiency can reach 99%. The quantification of bacteria in large volume of spiked tap water and mineral water samples is realized. The recoveries for different concentrations of E. coli in tap and mineral water samples are in the range between 83% and 93%. The results demonstrate that this MIm-MPs-PCR-CE method can be applied to detect and quantify bacteria in real samples.     

Capillary and microchip gel electrophoresis for simultaneous detection of Salmonella pullorum and Salmonella gallinarum by rfbS allele-specific PCR

We report the use of capillary gel electrophoresis (CGE) based on a rfbS allele-specific polymerase chain reaction (PCR) for the analysis and simultaneous detection of Salmonella pullorum and Salmonella gallinarum, which are the major bacterial pathogens in poultry. rfbS allele-specific PCR was used to concurrently amplify two specific 147- and 187-bp DNA fragments for the simultaneous detection of S. pullorum and S. gallinarum at an annealing temperature of 54 ± 1 °C and an MgCl₂ concentration of 2.8-5.6 mM. Under an electric field of 333.3 V/cm and a sieving matrix of 1.0% poly(ethyleneoxide) (M_r 600 000), the amplified PCR products were analyzed within 6 min by CGE separation. This CGE assay could be translated to microchip format using programmed field strength gradients (PFSG). In the microchip gel electrophoresis with PFSG, both of the Salmonella analyses were completed within 30 s, without decreasing the resolution efficiency. rfbS allele-specific PCR-microchip gel electrophoresis with the PFSG technique might be a new tool for the simultaneous detection of both S. pullorum and S. gallinarum, due to its ultra-speed and high efficiency.     

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets with high oxidase yield for analytical glucose and choline detections

A colloidal suspension of nanostructured poly(N-butyl benzimidazole)-graphene sheets (PBBIns-Gs) was used to modify a gold electrode to form a three-dimensional PBBIns-Gs/Au electrode that was sensitive to hydrogen peroxide (H₂O₂) in the presence of acetic acid (AcOH). The positively charged nanostructured poly(N-butyl benzimidazole) (PBBIns) separated the graphene sheets (Gs) and kept them suspended in an aqueous solution. Additionally, graphene sheets (Gs) formed “diaphragms” that intercalated Gs, which separated PBBIns to prevent tight packing and enhanced the surface area. The PBBIns-Gs/Au electrode exhibited superior sensitivity toward H₂O₂ relative to the PBBIns-modified Au (PBBIns/Au) electrode. Furthermore, a high yield of glucose oxidase (GOD) on the PBBIns-Gs of 52.3 mg GOD per 1 mg PBBIns-Gs was obtained from the electrostatic attraction between the positively charged PBBIns-Gs and negatively charged GOD. The non-destructive immobilization of GOD on the surface of the PBBIns-Gs (GOD-PBBIns-Gs) retained 91.5% and 39.2% of bioactivity, respectively, relative to free GOD for the colloidal suspension of the GOD-PBBIns-Gs and its modified Au (GOD-PBBIns-Gs/Au) electrode. Based on advantages including a negative working potential, high sensitivity toward H₂O₂, and non-destructive immobilization, the proposed glucose biosensor based on an GOD-PBBIns-Gs/Au electrode exhibited a fast response time (5.6 s), broad detection range (10 μM to 10 mM), high sensitivity (143.5 μA mM⁻¹ cm⁻²) and selectivity, and excellent stability. Finally, a choline biosensor was developed by dipping a PBBIns-Gs/Au electrode into a choline oxidase (ChOx) solution for enzyme loading. The choline biosensor had a linear range of 0.1 μM to 0.83 mM, sensitivity of 494.9 μA mM⁻¹ cm⁻², and detection limit of 0.02 μM. The results of glucose and choline measurement indicate that the PBBIns-Gs/Au electrode provides a useful platform for the development of oxidase-based biosensors.     

Surface plasmon resonance and electrochemistry characterization of layer-by-layer self-assembled DNA and Zr4+ thin films, and their interaction with cytochrome c

Through electrostatic layer-by-layer (LbL) assembly, negatively charged calf thymus double stranded DNA (CTds-DNA), and positively charged Zr⁴⁺ ions were alternately deposited on gold substrate modified with chemisorbed cysteamine. Thus-prepared three-dimensional DNA networks were characterized by surface plasmon resonance (SPR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS). SPR spectroscopy indicates that the effective thickness of DNA monolayer in the (DNA/Zr⁴⁺)₁ bilayer was 1.5 ± 0.1 nm, which corresponds to the surface coverage of 79% of its full packed monolayer. At the same time, a linear increase of film thickness with increasing number of layers was also confirmed by SPR characterizations. The data of XPS and IR-RAS show that Zr⁴⁺ ions interact with both the phosphate groups and nitrogenous bases of DNA and load into the framework of DNA. Furthermore, the interactions between this composite film and heme protein cytochrome c (Cyt c) were investigated by SPR spectroscopy and electrochemistry. Compared with the adsorption of Cyt c on DNA monolayer, this composite multilayer film can obviously enhance the amount of immobilized Cyt c confirmed by SPR reflectivity-incident angle (R-θ) curves. Cyclic voltammetry (CV) indicates the Cyt c adsorbed on the composite film is electroactive, and the enhancement of peak current in CV indirectly verifies the increase of the amount of immobilized Cyt c.     

Development of a sensitive and selective kojic acid sensor based on molecularly imprinted polymer modified electrode in the lab-on-valve system

In this work, a kojic acid electrochemical sensor, based on a non-covalent molecularly imprinted polymer (MIP) modified electrode, had been fabricated in the lab-on-valve system. The sensitive layer was synthesized by cyclic voltammetry using o-phenylenediamine as the functional monomer and kojic acid as the template. The template molecules were then removed from the modified electrode surface by washing with NaOH solution. Differential pulse voltammetry method using ferricyanide as probe was applied as the analytical technique, after extraction of kojic acid on the electrode. Chemical and flow parameters associated with the extraction process were investigated. The response recorded with the imprinted sensor exhibited a response in a range of 0.01-0.2 μmol L⁻¹ with a detection limit of 3 nmol L⁻¹. The interference studies showed that the MIP modified electrode had excellent selectivity. Furthermore, the proposed MIP electrode exhibited good sensitivity and low sample/reagent consumption, and the sensor could be applied to the determination kojic acid in cosmetics samples.     

Ferric nanoparticle-based resonance light scattering determination of DNA at nanogram levels

A novel assay of DNA has been proposed by using ferric nanoparticles as probes coupled with resonance light scattering (RLS) detection. At pH 7.40, the RLS intensity of ferric nanoparticles can be greatly enhanced by the aggregation of positively charged ferric nanoparticles through electrostatic interaction with negatively charged DNA. The enhanced intensity of RLS at 452 nm is proportional to the concentration of DNA in the range of 0.01-0.8 μg ml⁻¹ for calf thymus and salmon sperm DNA and in the range of 0.005-0.3 μg ml⁻¹ for E. coli K12 genomic DNA. Detection limits are 3.6 ng ml⁻¹ for calf thymus DNA, 4.4 ng ml⁻¹ for salmon sperm DNA, and 1.9 ng ml⁻¹ for E. coli K12 genomic DNA, respectively. Compared with the chromophores previously used in RLS assay, the ferric nanoparticles have offered several advantages in easy preparation, good photostability and high sensitivity without being modified or functionalized.     

Application of a new hybrid organic-inorganic monolithic column for efficient deoxyribonucleic acid purification

A new hybrid organic-inorganic monolithic column for efficient deoxyribonucleic acid (DNA) extraction was prepared in situ by polymerization of N-(β-aminoethyl)-γ-aminopropyltriethoxysilane (AEAPTES) and tetraethoxysilane (TEOS). The main extraction mechanism was based on the Coulombic force between DNA and the amino silica hybrid monolithic column. DNA extraction conditions, such as pH, ion concentration and type, and loading capacity, were optimized online by capillary electrophoresis with laser-induced fluorescence detection. Under optimal condition, a 6.0-cm monolithic column provided a capacity of 48 ng DNA with an extraction efficiency of 74 ± 6.3% (X ± RSD). The DNA extraction process on this monolithic column was carried out in a totally aqueous system for the successful purification of DNA and removal of proteins. The PBE2 plasmid could be extracted from Bacillus subtilis (B. subtilis) crude lysate within 25 min, and the purified DNA was suitable for the amplification of a target fragment by polymerase chain reaction. This study demonstrates a new attractive solid-phase support for DNA extraction to meet the increasingly miniaturized and automated trends of genetic analyses.     

Adduct formation in LC-ESI-MS of nonylphenol ethoxylates: mass spectrometrical, theoretical and quantitative analytical aspects

The analysis of nonylphenol ethoxylate (A₉PEO_n) surfactants with LC-ESI-MS was investigated in a detailed study of the formation of different types of adducts. Part of the observations was explained by calculating their relative stabilities using molecular dynamics techniques.Strong differences in adduct formation behaviour were found for different oligomers.Beside the common sodium adducts, surfactant dimer adducts [2 × A₉PEO_1,2 + Na]⁺, adducts including a solvent molecule [A₉PEO_1,2 + MeOH + Na]⁺ and doubly charged adducts [A₉PEO_>11 + 2 × Na]²⁺ were found.Molecular dynamics calculations showed that the A₉PEO_n molecule wraps itself around the complexing sodium ion in a way that negative electronic charges on oxygen have optimum electrostatic interaction with this ion. van der Waals interactions between alkyl chains are of less importance for the stability of these adducts. Both [2 × A₉PEO_2,5 + Na]⁺ dimer and [A₉PEO_2,5 + Na]⁺ monomer adducts turned out to be stable from an energetic point of view with adducts of A₉PEO₅ being more stable than adducts of A₉PEO₂. Only for the monomer adduct the latter is in accordance with experimental observations.Consequences of the formation of several adducts per A₉PEO_n oligomer for the quantitative analysis of environmental samples were evaluated. In clean samples, it was found that the presence of short-chain A₉PEO_1,2 can cause an overestimation of long-chain A₉PEO_>2. In real environmental extracts, other processes like matrix effects have a stronger influence on the quantitative result, and therefore no significant influence of adduct formation processes could be observed. However, inclusion of [A₉PEO_1,2 + MeOH + Na]⁺ adduct signals does improve the detection limits of the two short-chain oligomers.Correct quantitative results are obtained when A₉PEO₁ and A₉PEO₂ are quantified separately, and longer oligomers with a molar calibration followed by correction of the average molar weight of the A₉PEO_>2 in the sample.     

Selective membrane alternative to the recovery of zinc from hot-dip galvanizing effluents

This work reports the study of the kinetics of zinc recovery from spent pickling solutions by means of emulsion pertraction technology (EPT) in order to reuse the metal in electrolytic processes. Tributyl phosphate (TBP) and service water were used as extraction (EX) and back-extraction (BEX) agents, respectively. Kinetic experiments were carried out in hollow fiber membrane contactors in order to analyse the influence of several operation variables on the rate of zinc recovery. A mathematical model that considers the mass transfer resistance shared between the organic liquid membrane and the organic phase boundary layer was developed; the mass transfer coefficients were estimated by means of the parameter estimation tool ASPEN CUSTOM MODELER (from ASPENTECH) to obtain the values k_m = 2.68 × 10⁻⁷ m/s and A_Vk_o = 0.0125 s⁻¹. Simulated results agreed satisfactorily well with experimental data. Consequently, the kinetic model and parameters were confirmed. Finally, a comparison between EPT and non-dispersive solvent extraction (NDSX) was carried out in order to evaluate the advantages and disadvantages of both membrane configurations.     

Langmuir-Blodgett film of p-tert-butylthiacalix[4]arene modified glassy carbon electrode as voltammetric sensor for the determination of Hg(II)

The π-A isotherms and UV-vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Hg²⁺ at the air-water surface. From these observations, a glassy carbon electrode coated with Langmuir-Blodgett film of p-tert-butylthiacalix[4] arene as a new voltammetric sensor is designed for the determination of trace amounts of Hg²⁺. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir-Blodgett film-modified electrode can greatly improve the measuring sensitivity of Hg²⁺. Under the selected conditions, the Langmuir-Blodgett film-modified electrode in 0.1 mol L⁻¹ H₂SO₄ + 0.01 mol L⁻¹ KCl solution shows a linear voltammetric response for Hg²⁺ in the range of 5.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹, with a detection limit of 2.0 × 10⁻¹⁰ mol L⁻¹. The proposed method was also applied to determine Hg²⁺ in water samples (tap, lake and river water). In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility and good stability.     

Layer by layer assembly of catalase and amine-terminated ionic liquid onto titanium nitride nanoparticles modified glassy carbon electrode: Study of direct voltammetry and bioelectrocatalytic activity

A novel, simple and facile layer by layer (LBL) approach is used for modification of glassy carbon (GC) electrode with multilayer of catalase and nanocomposite containing 1-(3-Aminopropyl)-3-methylimidazolium bromide (amine terminated ionic liquid (NH₂-IL)) and titanium nitride nanoparticles (TiNnp). First a thin layer of NH₂-IL is covalently attached to GC/TiNnp electrode using electro-oxidation method. Then, with alternative self assemble positively charged NH₂-IL and negatively charged catalase a sensitive H₂O₂ biosensor is constructed, whose response is directly correlated to the number of bilayers. The surface coverage of active catalase per bilayer, heterogeneous electron transfer rate constant (k_s) and Michaelis–Menten constant (K_M) of immobilized catalase were 3.32 × 10⁻¹² mol cm⁻², 5.28 s⁻¹ and 1.1 mM, respectively. The biosensor shows good stability, high reproducibility, long life-time, and fast amperometric response with the high sensitivity of 380 μA mM⁻¹ cm⁻² and low detection limit of 100 nM at concentration range up to 2.1 mM.     

Structural studies of cerium tantalates

Structural data obtained from neutron diffraction studies of some cerium tantalate phases are presented, including the first report of the high temperature structure of a CeTaO₄ phase, Ce_0.85TaO_3.84 deduced from in situ data recorded at 900°C in vacuum. It was found that this material transformed from the low temperature LaTaO₄ type phase to the orthorhombic A2₁am structure reported here, with a unit cell of a=5.64062(2) Å, b=14.81609(6) Å and c=3.93482(1) Å. This data agrees well with the previously proposed structural transformations.     

Non-chromatographic screening method for the determination of mercury species. Application to the monitoring of mercury levels in Antarctic samples

A simple non-chromatographic method for the determination of mercury (Hg²⁺), methylmercury (MeHg⁺), dimethylmercury (Me₂Hg), and phenylmercury (PhHg⁺) employing atomic fluorescence spectrometry (AFS) as detection technique was developed. Mercury species showed a particular behavior in the presence of several reagents. In a first stage SnCl₂ was employed for Hg²⁺ determination; in a second step, [Hg²⁺ + PhHg⁺] concentration was determined using SnCl₂ and UV radiation. MeHg⁺ decomposition was prevented adding 2-mercaptoethanol. In a third stage, [Hg²⁺ + PhHg⁺ + MeHg⁺] concentration was determined using K₂S₂O₈. Finally, the four species were determined employing NaBH₄. Reagents concentration and flow rates were optimized. The extraction technique of mercury species involved the use of 2-mercaptoethanol as ion-pair reagent. The limits of detection for Hg²⁺, PhHg⁺, MeHg⁺, and Me₂Hg were 1, 40, 68, and 99 ng L⁻¹ with a relative standard deviation of 1.5, 3.1, 4.7 and 5.8%, respectively. Calibration curve was linear with a correlation factor equal to 0.9995. The method was successfully applied to the determination of the mercury species in two Antarctic materials: IRMM 813 (Adamussium colbecki) and MURST-ISS-A2 (Antarctic Krill).     

Determination of bisphenol A, 4-n-nonylphenol, and 4-tert-octylphenol by temperature-controlled ionic liquid dispersive liquid-phase microextraction combined with high performance liquid chromatography-fluorescence detector

Present study described a simple, sensitive, and viable method for the determination of bisphenol A, 4-n-nonylphenol and 4-tert-octylphenol in water samples using temperature-controlled ionic liquid dispersive liquid-phase microextraction coupled to high performance liquid chromatography-fluorescence detector. In this experiment, 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈MIM][PF₆]) was used as the extraction solvent, and bisphenol A, 4-n-nonylphenol and 4-tert-octylphenol were selected as the model analytes. Parameters affecting the extraction efficiency such as the volume of [C₈MIM][PF₆], dissolving temperature, extraction time, sample pH, centrifuging time and salting-out effect have been investigated in detail. Under the optimized conditions, good linear relationship was found in the concentration range of 1.0-100 μg L⁻¹ for BPA, 1.5-150 μg L⁻¹ for 4-NP, and 3-300 μg L⁻¹ for 4-OP, respectively. Limits of detection (LOD, S/N = 3) were in the range of 0.23-0.48 μg L⁻¹. Intra day and inter day precisions (RSDs, n = 6) were in the range of 4.6-5.5% and 8.5-13.3%, respectively. This method has been also successfully applied to analyze the real water samples at two different spiked concentrations and excellent results were obtained.     

Electrocatalytic oxidation behavior of guanosine at graphene, chitosan and Fe3O4 nanoparticles modified glassy carbon electrode and its determination

A graphene, chitosan and Fe₃O₄ nanoparticles (nano-Fe₃O₄) modified glassy carbon electrode (graphene-chitosan/nano-Fe₃O₄/GCE) was fabricated. The modified electrode was characterized by scanning electron microscope and electrochemical impedance spectroscopy. The electrochemical oxidation behavior of guanosine was investigated in pH 7.0 phosphate buffer solution by cyclic voltammetry and differential pulse voltammetry. The experimental results indicated that the modified electrode exhibited an electrocatalytic and adsorptive activities towards the oxidation of guanosine. The transfer electron number (n), transfer proton number (m) and electrochemically effective surface area (A) were calculated. Under the optimized conditions, the oxidation peak current was proportional to guanosine concentration in the range of 2.0 × 10⁻⁶ to 3.5 × 10⁻⁴ mol L⁻¹ with the correlation coefficient of 0.9939 and the detection limit of 7.5 × 10⁻⁷ mol L⁻¹ (S/N = 3). Moreover, the modified electrode showed good ability to discriminate the electrochemical oxidation response of guanosine, guanine and adenosine. The proposed method was further applied to determine guanosine in spiked urine samples and traditional Chinese medicines with satisfactory results.     

A rapid method for the detection of foodborne pathogens by extraction of a trace amount of DNA from raw milk based on amino-modified silica-coated magnetic nanoparticles and polymerase chain reaction

A method based on amino-modified silica-coated magnetic nanoparticles (ASMNPs) and polymerase chain reaction (PCR) was developed to rapidly and sensitively detect foodborne pathogens in raw milk. After optimizing parameters such as pH, temperature, and time, a trace amount of genomic DNA of pathogens could be extracted directly from complex matrices such as raw milk using ASMNPs. The magnetically separated complexes of genomic DNA and ASMNPs were directly subjected to single PCR (S-PCR) or multiplex PCR (M-PCR) to detect single or multiple pathogens from raw milk samples. Salmonella Enteritidis (Gram-negative) and Listeria monocytogenes (Gram-positive) were used as model organisms to artificially contaminate raw milk samples. After magnetic separation and S-PCR, the detection sensitivities were 8 CFU mL⁻¹ and 13 CFU mL⁻¹ respectively for these two types of pathogens. Furthermore, this method was successfully used to detect multiple pathogens (S. Enteritidis and L. monocytogenes) from artificially contaminated raw milk using M-PCR at sensitivities of 15 CFU mL⁻¹ and 25 CFU mL⁻¹, respectively. This method has great potential to rapidly and sensitively detect pathogens in raw milk or other complex food matrices.     

Visual and surface plasmon resonance sensor for zirconium based on zirconium-induced aggregation of adenosine triphosphate-stabilized gold nanoparticles

Owing to its high affinity with phosphate, Zr(IV) can induce the aggregation of adenosine 5′-triphosphate (ATP)-stabilized AuNPs, leading to the change of surface plasmon resonance (SPR) absorption spectra and color of ATP-stabilized AuNP solutions. Based on these phenomena, visual and SPR sensors for Zr(IV) have been developed for the first time. The A_660 nm/A_518 nm values of ATP-stabilized AuNPs in SPR absorption spectra increase linearly with the concentrations of Zr(IV) from 0.5 μM to 100 μM (r = 0.9971) with a detection limit of 95 nM. A visual Zr(IV) detection is achieved with a detection limit of 30 μM. The sensor shows excellent selectivity against other metal ions, such as Cu²⁺, Fe³⁺, Cd²⁺, and Pb²⁺. The recoveries for the detection of 5 μM, 10 μM, 25 μM and 75 μM Zr(IV) in lake water samples are 96.0%, 97.0%, 95.6% and 102.4%, respectively. The recoveries of the proposed SPR method are comparable with those of ICP-OES method.     

Sensitive DNA biosensor improved by Luteolin copper(II) as indicator based on silver nanoparticles and carbon nanotubes modified electrode

A novel and sensitive electrochemical DNA biosensor has been developed for the detection of DNA hybridization. The biosensor was proposed by using copper(II) complex of Luteolin C₃₀H₁₈CuO₁₂ (CuL₂) as an electroactive indicator based on silver nanoparticles and multi-walled carbon nanotubes (Ag/MWCNTs) modified glassy carbon electrode (GCE). In this method, the 4-aminobenzoic acid (4-ABA) and Ag nanoparticles were covalently grafted on MWCNTs to form Ag/4-ABA/MWCNTs. The proposed method dramatically increased DNA attachment quantity and complementary ssDNA detection sensitivity for its large surface area and good charge-transport characteristics. DNA hybridization detection was performed using CuL₂ as an electroactive indicator. The CuL₂ was synthesized and characterized using elemental analysis (EA) and IR spectroscopy. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction between CuL₂ and ds-oligonucleotides (dsDNA). It was revealed that CuL₂ presented high electrochemical activity on GCE, and it could be intercalated into the double helices of dsDNA. The target ssDNA of the human hepatitis B virus (HBV) was quantified in a linear range from 3.23 × 10⁻¹² to 5.31 × 10⁻⁹ M (r = 0.9983). A detection limit of 6.46 × 10⁻¹³ M (3σ, n = 11) was achieved.