Linear Calibration Range Research Articles

N,N-dimethyl-2-phenylpropan-1-amine quantification in urine: application to excretion study following single oral dietary supplement dose.

N,N-dimethyl-2-phenylpropan-1-amine (NN-DMPPA) is a new designer stimulant prohibited in sport in-competition according to the List of Prohibited Substances and Methods published by the World Anti-Doping Agency (WADA). The first published data on the excretion study of NN-DMPPA to support the knowledge of NN-DMPPA in routine anti-doping control have been presented. The reliable gas chromatography-mass spectrometry quantitative method (GC-MS) has been validated and applied to the excretion study of NN-DMPPA. The validation parameters of the GC-MS method for determination of NN-DMPPA in human urine were the linear calibration range of 100 to 7500ng/mL, the LOD of 13.9ng/mL and the LOQ of 42.2ng/mL. According to the obtained repeatability, intermediate precision, and trueness, the applied GC-MS method was precise and accurate. Urine samples from three volunteers in the excretion study were collected for 5days after single oral administration of the supplement NOXPUMP containing NN-DMPPA. The obtained results showed the maximum concentration of NN-DMPPA (189-303ng/mL) in urine samples ata time of 2-3h post-administration. The NN-DMPPA concentration in urine samples was higher than 50ng/mL until 22-23h after the dietary supplement ingestion. This means that according to the WADA rules the use of a supplement containing NN-DMPPA may be related to a positive case when athletes took this supplement in-competition. Moreover, excretion results demonstrate also that NN-DMPPA may be detected in urine samples by the applied GC-MS method till 46h after supplement administration. Additionally, the excretion study of β-methylphenethylamine as the second prohibited substance present in the supplement NOXPUMP has been investigated. Graphical Abstract Excretion study of new designer stimulant, N,N-dimethyl-2-phenylpropan-1-amine, and β-methylphenethylamine following single oral NOXPUMP supplement dose.

A single laboratory-validated LC-MS method for the analysis of tulathromycin residues in bison and deer sera and selected tissues of white-tailed deer.

The performance characteristics of a newly developed liquid chromatography-mass spectrometry (LC-MS) method were validated and demonstrated to be fit for purpose in a pharmacokinetic and tissue depletion study of white-tailed deer and bison. Tulathromycin was extracted from bison and deer sera with acetonitrile or trifluoroacetic acid and K2 HPO4 (pH 6.8) buffer solution and cleaned up on a conditioned Bond-Elut cartridge. Tulathromycin, retained on the cartridge; it was eluted with methanol containing 2% formic acid, dried, re-constituted in methanol/1% formic acid, and analyzed by LC-MS. The limit of quantification (LOQ) of the method was 0.6 ng/mL in serum and 0.6 ng/g in tissue with RSDs ≤ 10% and accurate over the linear calibration range of 0.8-100 ng/mL for bison serum, 0.6-50 ng/mL for deer serum, 100-2500 ng/g for deer muscle tissue, and 500-5000 ng/g for deer lung tissue, all with coefficients of determination, r(2) ≥0.99. The validated method was used to quantify the concentration of tulathromycin residues in serum of bison and deer and selected tissue (lung and muscle tissue) samples obtained from 10 healthy, white-tailed deer that were administered the therapeutic dose approved for cattle (i.e., a single 2.5 mg/kg subcutaneous injection of tulathromycin in the neck). The deer were included in a tulathromycin drug depletion study. © 2016 Her Majesty the Queen in Right of Canada. Drug Testing and Analysis © 2016 John Wiley & Sons, Ltd.

Non-enzymatic detection of glucose using poly(azure A)-nickel modified glassy carbon electrode

A simple, sensitive and selective non-enzymatic glucose sensor was constructed in this paper. The poly(azure A)-nickel modified glassy carbon electrode was successfully fabricated by the electropolymerization of azure A and the adsorption of Ni2+. The Ni modified electrode, which was characterized by scanning electron microscope, cyclic voltammetry, electrochemical impedance spectra and X-ray photoelectron spectroscopy measurements, respectively, displayed well-defined current responses of the Ni(III)/Ni(II) couple and showed a good activity for electrocatalytic oxidation of glucose in alkaline medium. Under the optimized conditions, the developed sensor exhibited a broad linear calibration range of 5 μM–12mM for quantification of glucose and a low detection limit of 0.64μM (3σ). The excellent analytical performance including simple structure, fast response time, good anti-interference ability, satisfying stability and reliable reproducibility were also found from the proposed amperometric sensor. The results were satisfactory for the determination of glucose in human serum samples as comparison to those from a local hospital.

Determination of Polycyclic Aromatic Hydrocarbons in Mosses by Ultrasonic-Assisted Extraction and Gas Chromatography–Tandem Mass Spectrometry

ABSTRACTA facile method for the determination of polycyclic aromatic hydrocarbons in mosses is reported using ultrasonic-assisted extraction and gas chromatography–tandem mass spectrometry. The efficiency of ultrasonic-assisted extraction and the reagents was optimized. Tandem mass spectrometry with selective reaction monitoring was used to enhance the selectivity to reduce matrix interferences and simplify the purification protocol. The detection limits were from 0.1 to 2.0 ng/mL. The linear calibration range was two orders of magnitude and the coefficients of linear correlation exceeded 0.9992 for all analytes. The relative standard deviations within 1 day and 3 days were less than 9.0%. Recoveries from 56.8 to 109.0% were obtained in fortified mosses. The rapid, low solvent gas chromatography–tandem mass spectrometry method was used to determine polycyclic aromatic hydrocarbons in mosses.

Development of a Microbiosensor for Acetate Detection in Biofilms

We developed an amperometric acetate microbiosensor capable of measuring in situ sub-micromolar concentration of acetate inside biofilms. The operating principle of the microbiosensor utilized electrochemically active biofilms (EABs) to convert acetate to electrons on the microelectrode tip. The acetate microbiosensor consisted of a 30 µm glass-covered carbon wire working electrode with G.sulfurreducens biofilm on the tip recessed into a glass outer case approximately 200 μm and a Ag/AgCl reference electrode, as shown in Figure 1. The glass outer case terminated to a 30 µm tip diameter where acetate could flow into and diffuse up to the active tip. Acetate-free G.sulfurreducens growth medium served as electrolyte. The microbiosensor showed a linear response between 50 µM and 1.6 mM acetate concentration with a 79 ± 8 µM limit of detection (S/N=2). The operating potential of the microbiosensor was selected as +300 mVAg/AgCl satisfying the limiting current condition. The microbiosensor also demonstrated a higher specificity to acetate over other possible metabolites that could interfere with acetate measurements. To test the microbiosensor, we measured local acetate concentration inside G. sulfurreducens biofilms grown on a 1 in2 electrode in a three-electrode bioreactor operated in fed-batch mode. Measuring acetate profiles in G.sulfurreducens biofilms is critical to understand acetate limitations and acetate diffusion and to test the developed microbiosensor in G.sulfurreducens biofilms which utilizes acetate as the electron donor. The microbiosensor was used to measure acetate depth profiles within ~225 µm thick G.sulfurreducens biofilm under no current generation (open circuit potential) and current generation (at +300 mVAg/AgCl) conditions. For depth profile measurements, bulk acetate concentration in the bioreactor was set to 1.5 mM by considering the linear calibration range of the microbiosensor. The acetate concentration remained at bulk values throughout the biofilm at open circuit potential when the biofilm was not respiring. However, the acetate concentration decreased from the bulk values to below the detection limit within 200 μm when current was allowed to pass at +300 mVAg/AgCl. This showed that the biofilm was acetate-limited due to the zero acetate concentration at the bottom of the biofilm. Figure 1

Dual-responsive competitive immunosensor for sensitive detection of tumor marker on g-CN/rGO conjugation

A new dual mode competitive immunosensing platform for sensitive determination of α-fetoprotein (AFP) combined photoelectrochemical and electrochemical methods was designed on graphite carbon nitride and reduced graphene oxide (g-CN/rGO) conjugate support. To construct such versatile support, polyamidoamine dendrimer (PAAD) decorated graphene oxide (GO) as substrate was reduced via potentiostatic technology, and the prepared rGO-PAAD nanocomposite was utilized as matrix to immobilize g-CN and capture antigen, and as electron transporter to mediate electron transfer for enhancement of photoelectrochemical and electrochemical signals. And then, horseradish peroxidase labeled antibody was competitively captured onto sensing interface with free antigen in incubated solution. Photoelectrochemical signal originated from g-CN, an excellent photoactive material with large photo-induced electric response, and was amplified by rGO-PAAD nanocomposite. The resultant concentration positively related linear calibration range was from 1pg/mL to 40ng/mL with ultralow detection limit of 1pg/mL. On the other hand, the enzyme-induced electrocatalytical signal amplification was produced by using hydroquinone as reactive substrate and horseradish peroxidase as reactive enzyme in existence of H2O2, which displayed a wide dynamic linear range from 0.1ng/mL to 160ng/mL with low detection limit of 0.1ng/mL. Additionally, the satisfying selectivity, good reproducibility and high consistency of dual-signal outputs of this designed dual-responsive immunosensor demonstrated the promising application in developing sensitive and accurate immunosensor for clinical test and disease diagnosis.

Polyelectrolyte-free layer by layer self-assembled multilayer films of cationic phthalocyanine cobalt(II) and carbon nanotube for the efficient detection of 4-nitrophenol

4-Nitrophenol (4-NP) sensors with high sensitivity and reproducibility are desirable for biosafety and environmental monitoring. Herein, cationic tetra-β-(N,N,N-trimethylaminoethoxy) phthalocyanine cobalt(II)/acid-treated carbon nanotubes multilayer films, marked as (tmaePcCo/CNT)n films (n represents the bilayer number), were successfully constructed on glassy carbon electrode (GCE) by a facile, effective layer by layer (LBL) electrostatic assembly method without the assistant of polyelectrolyte. Because CNTs within the multilayer films are beneficial to collect and transfer charges, and polyelectrolyte-free assembly ensures active sites exposing, the obtained (tmaePcCo/CNT)10/GCE exhibits excellent 4-NP electrocatalytic performance with good reproducibility and acceptable stability, a wide linear calibration range over 3 orders of magnitude of 4-NP concentrations (1μM–1.8mM) and a low detection limit of 0.2μM (S/N=3), and it can be applied to the quantification analysis of 4-NP under optimum conditions. This work shows that the LBL multilayer films fabricated without polyelectrolyte can provide a valid way to improve the sensitivity and reproducibility of 4-NP sensors.

Synthesis and characterization of gold nanoparticles incorporated bentonite clay for electrocatalytic sensing of arsenic(III)

In the present manuscript, a simple and easy route to synthesize bentonite (bt) clay-supported gold nanoparticles (Au NPs) is reported (represented as Au-bt). Application of this new environmentally benign material in electrocatalytic determination of arsenite (As(III)) was studied. The successful synthesis and incorporation of Au NPs into the bt clay is supported by spectroscopic, microscopic and electrochemical methods. The synthesized Au-bt material was used to modify glassy carbon electrode (GC) by the evaporation of Au-bt aqueous suspension dropped on the surface of the GC (GC/Au-bt). Cyclic voltammetry and chronoamperometry studies of As(III) solutions were performed with this GC/Au-bt electrode which act as efficient platform for the electro-oxidation of As(III) to As(V) at a very low overpotential. Kinetic parameters were evaluated for the oxidation of As(III) at the GC/Au-bt platforms. A wide linear calibration range for the determination of As(III) from 1 to 1700 μM was obtained with high reproducibility and stability. A limit of detection, 0.1 μM was achieved with high sensitivity. Additionally, it showed a good selectivity for the determination of As(III) in the presence of copper(II) and other interfering ions suggesting a promising new route for trace level determination of As(III) in neutral conditions.

Large-Volume Sample Staking of Rice Polyphenols Prior to Their Determination by Non-aqueous Capillary Electrophoresis

A rapid non-aqueous capillary electrophoretic (NACE) method for the separation of (−)-epicatechin (EPI), (+)-catechin (−CAT), kaempferol (KAE), quercetin (QUR), naringanin (NAR), ferulic acid (FA), and p-coumaric acid (p-CA) has been developed and applied to the determination of these compounds in different rice varieties. All seven compounds were separated on capillary of 50 μm × 68 cm (60-cm effective length) using 20 mmol L−1 borate buffer of pH 9.0 and 5 % acetonitrile in methanol. Large-volume sample stacking (LVSS) technique was optimized and used to preconcentrate non-detectable polyphenols of white polished rice. Rice extracts were concentrated on-line by LVSS prior to separation by non-aqueous capillary electrophoresis. An improvement of 10–55 times in detectability was achieved with injection at 50 mbar for 30 s followed by voltage inversion (−20 kV) for 5 s. Linear calibration range of 1–300 μg L−1 and 0.01–60 μg L−1 was observed for NACE and NACE-LVSS method respectively, with the detection limit of 0.33–2.0 and 0.006–0.19 μg L−1. Good reproducibility with standard deviations of less than 5 % was achieved. Polyphenol contents of different rice varieties were determined using developed method.

Construction of an electrochemical sensing platform based on platinum nanoparticles supported on carbon for tetracycline determination

In this paper, we report the construction of an electrochemical sensing platform based on platinum nanoparticles supported on carbon (PtNPs/C) for the determination of the antibiotic tetracycline (TTC). Initially, the PtNPs/C was synthesized and characterized by powder X-ray diffraction spectroscopy and transmission electron microscopy. The effect of experimental parameters on the electrochemical behavior of the PtNPs/C coated glassy carbon electrode (PtNPs/C/GCE), including the amount of PtNPs and electroactive area, scan rate and pH, were evaluated. The electrooxidation of TTC on the PtNPs/C/GCE was investigated by cyclic voltammetry and differential pulse voltammetry, with the determination of TTC electrooxidation mechanism. Under optimum experimental conditions, the linear calibration range, detection limit, quantification and sensitivity of the PtNPs/C/GCE were 9.99–44.01μmolL−1, 4.28μmolL−1, 14.3μmolL−1 and 3.32μALμmol−1cm−2, respectively. Finally, the proposed electrochemical sensing platform was successfully applied to determine low TTC concentrations in urine samples, suggesting its great applicability in clinical analysis and quality control.

Development of an Eco-Friendly Method for Iron Extraction and Determination in Pharmaceuticals Using Ciprofloxacin Drug as Chelating agent

A method is developed for the determination of iron (III) in pharmaceutical preparations by coupling cloud point extraction (CPE) and UV-Vis spectrophotometry. The method is based on the reaction of Fe(III) with excess drug ciprofloxacin (CIPRO) in dilute H2SO4, forming a hydrophobic Fe(III)- CIPRO complex which can be extracted into a non-ionic surfactant Triton X-114, and iron ions are determined spectrophotometrically at absorption maximum of 437 nm. Several variables which impact on the extraction and determination of Fe (III) are optimized in order to maximize the extraction efficiency and improve the sensitivity of the method. The interferences study is also considered to check the accuracy of the procedure. The results have shown that the preconcentration factor of 71 fold leading to obtain a limit of detection of 2.67 ng mL-1 with linear calibration range of 5-150 ng mL-1 (r=0.9998) and a superb sensitivity in terms of molar absorptivity of 1.13x106 L.mol-1.cm-1 . The mean percent recovery of 99.78±0.53% and the precision (RSD %) ranged from 1.96 to 0.76 are achieved. The developed method is applied to the determination of iron in four selected pharmaceutical drugs. The experimental values agree statistically with the quoted values stated by the manufacturer’ companies.

Determination of salivary cotinine through solid phase extraction using a bead-injection lab-on-valve approach hyphenated to hydrophilic interaction liquid chromatography

Cotinine, the first metabolite of nicotine, is often used as a biomarker in the monitoring of environmental tobacco smoke (ETS) exposure due to its long half-life. This paper reports on the development of an at-line automatic micro-solid phase extraction (μSPE) method for the determination of salivary cotinine followed by its analysis via hydrophilic interaction liquid chromatography (HILIC). The SPE methodology is based on the bead injection (BI) concept in a mesofluidic lab-on-valve (LOV) flow system to automatically perform all SPE steps. Three commercially available reversed-phase sorbents were tested, namely, Oasis HLB, Lichrolut EN and Focus, and the spherically shaped sorbents (i.e., Oasis HLB and Focus) provided better packing within the SPE column and hence higher column efficiency. An HILIC column was chosen based on its potential for achieving higher sensitivity and better retention of polar compounds such as cotinine. The method uses an isocratic program with acetonitrile:100mM ammonium acetate buffer, pH 5.8 in 95:5v/v ratio as the mobile phase at a flow rate of 1.0mLmin−1. Using this approach, the linear calibration range was from 10 to 1000ng which corresponded to 5–500μgL−1. The corresponding μSPE-BI-LOV system was proven to be reliable in the handing and analysis of viscous biological samples such as saliva, achieving a sampling rate of 6h−1 and a limit of detection and quantification of 1.5 and 3μgL−1, respectively.

Development of an Analytical Method Based on Temperature Controlled Solid-Liquid Extraction Using an Ionic Liquid as Solid Solvent

At the present paper, an analytical method based on temperature controlled solid-liquid extraction (TC-SLE) utilizing a synthesized ionic liquid, (N-butylpyridinium hexafluorophosphate, [BPy]PF6), as solid solvent and phenanthroline (PT) as an extractant was developed to determine micro levels of Fe2+ in tea by PT spectrophotometry. TC-SLE was carried out in two continuous steps: Fe2+ can be completely extracted by PT-[BPy]PF6 or back-extracted at 80 °C and the two phases were separated automatically by cooling to room temperature. Fe2+, after back-extraction, needs 2 mol/L HNO3 as stripping agent and the whole process was determined by PT spectrophotometry at room temperature. The extracted species was neutral Fe(PT)mCl2 (m = 1) according to slope analysis in the Fe2+-[BPy]PF6-PT TC-SLE system. The calibration curve was Y = 0.20856X − 0.000775 (correlation coefficient = 0.99991). The linear calibration range was 0.10–4.50 μg/mL and the limit of detection for Fe2+ is 7.0 × 10−2 μg/mL. In this method, the contents of Fe2+ in Tieguanyin tea were determined with RSDs (n = 5) 3.05% and recoveries in range of 90.6%–108.6%.

Electrochemical determination of nanomolar levels of isoniazid in pharmaceutical formulation using silver nanoparticles decorated copolymer

A copolymer of methyl methacrylate and 2-acrylamido-2-methylpropane sulfonic acid (P(MMA-co-AMPS)) and silver nanoparticles (Ag NPs) incorporated P(MMA-co-AMPS) (Ag-P(MMA-co-AMPS)) are used to construct efficient electrochemical sensing platforms (ESPs) to quantitatively determine isoniazid (INZ) at neutral pH conditions. Cyclic voltammetry, amperometry and electrochemical impedance spectroscopy are used as diagnostic tools for INZ determination at these ESPs in pH 7.0 phosphate buffer solution. It has been found that P(MMA-co-AMPS) copolymer facilitates the INZ oxidation with improved electrochemical behaviors. At Ag-P(MMA-co-AMPS), electrochemical characteristics of INZ is much improved than at P(MMA-co-AMPS) due to the interaction of INZ with Ag NPs. Based on the linear increase in oxidation current, a sensitive INZ electrochemical sensor is constructed. The sensor displays a linear calibration range from 50.0nM to 150.0μM for INZ determination. Detection limit (based on three times standard deviation of the blank) and sensitivity of this sensor is 10.0nM and 197nAμM⿿1cm⿿2, respectively. Further, P(MMA-co-AMPS) and Ag-P(MMA-co-AMPS) materials are successfully applied for analysis of INZ in presence of other biologically important molecules and also in a pharmaceutical formulation. The obtained results are very much consistent with the INZ amount originally present in the pharmaceutical formulation.

Evaluation of graphene-based sorbent in the determination of polar environmental contaminants in water by micro-solid phase extraction-high performance liquid chromatography

A facile method of extraction using porous membrane protected micro-solid phase extraction (μ-SPE) with a graphene-based sorbent followed by high performance liquid chromatography–ultraviolet detector was developed. The reduced graphene oxide (r-GO) (1mg), synthesized from graphite oxide, was enclosed in a polypropylene bag representing the μ-SPE device, which was used for the extraction of estrogens such as estrone, 17β-estradiol, 17α-ethynylestradiol and diethylstilbestrol in water. The r-GO obtained was identified and characterized by Fourier transform infrared, transmission electron microscopy, scanning electron microscopy and thermogravimetric analysis. The sorbent was loaded with sodium dodecyl sulfate by sonication to prevent agglomeration in aqueous solution. With this method, low limits of detection of between 0.24 and 0.52ngL−1 were achieved. For estrogen analysis a linear calibration range of 0.01–100μgL−1 was obtained, with the coefficients of determination (r2) higher than 0.992. This proposed method was successfully applied to determine estrogens in water.

All-in-one bioprobe devised with hierarchical-ordered magnetic NiCo2O4 superstructure for ultrasensitive dual-readout immunosensor for logic diagnosis of tumor marker

A new enzyme-free all-in-one bioprobe, consisted of hematin decorated magnetic NiCo2O4 superstructure (ATS–MNS–Hb), was designed for ultrasensitive photoelectrochemical and electrochemical dual-readout immunosensing of carcinoembryonic antigen (CEA) on carbon nanohorns (CNH) support. Herein, the MNS, possessed hierarchical-ordered structure, good porosity and magnetism, acted as nanocarrier to absorb abundant Hb molecular after functionalization, providing a convenient collection means by magnetic control as well as enhanced dual-readout sensing performances. CNH superstructures were employed as support to immobilize abounding captured antibodies, and then as-designed dual mode bioprobe, covalent binding with secondary antibody of CEA, was introduced for ultrasensitive detection of CEA by sandwich immunosensing. Photoelectrochemical response originated from plentiful hematin molecular, a excellent photosensitizer with good visible light harvesting efficiency, absorbed by functionalized porous MNS. The resultant concentration dependant linear calibration range was from 10fg/mL to 1ng/mL with ultralow detection limit of 10fg/mL. For electrochemical process, catalase-like property of MNS was validated, moreover, MNS–Hb hybrid exhibited much higher mimic enzyme catalytic activity and evidently amplified electrocatalytic signal, performing a wide dynamic linear range from 1ng/mL to 40ng/mL with low detection limit of 1ng/mL. Additionally, due to the improved accuracy of dual signals detection, the exact diagnoses of serum samples were gotten by operating resulting dual signals with AND logic system. This work demonstrated the promising application of MNS in developing ultrasensitive, cost-effective and environment friendly dual-readout immunosensor and accurate diagnoses strategy for tumor markers.

Determination of silicon and aluminum in silicon carbide nanocrystals by high-resolution continuum source graphite furnace atomic absorption spectrometry

The determination of Al contaminant and the main component Si in silicon carbide (SiC) nanocrystals with the size-distribution of 1–8nm dispersed in an aqueous solution was developed using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS). The vaporization/atomization processes were investigated in a transversally heated graphite atomizer by evaporating solution samples of Al and Si preserved in various media (HCl, HNO3). For Si, the best results were obtained by applying a mixture of 5µg Pd plus 5µg Mg, whereas for Al, 10µg Mg (each as nitrate solution) was dispensed with the samples, but the results obtained without modifier were found to be better. This way a maximum pyrolysis temperature of 1200°C for Si and 1300°C for Al could be used, and the optimum (compromise) atomization temperature was 2400°C for both analytes. The Si and Al contents of different sized SiC nanocrystals, dispersed in aqueous solutions, were determined against aqueous (external) calibration standards. The correlation coefficients (R values) of the calibrations were found to be 0.9963 for Si and 0.9991 for Al. The upper limit of the linear calibration range was 2mg/l Si and 0.25mg/l Al. The limit of detection was 3µg/l for Si and 0.5µg/l for Al. The characteristic mass (m0) was calculated to be 389pg Si and 6.4pg Al. The Si and Al content in the solution samples were found to be in the range of 1.0–1.7mg/l and 0.1–0.25mg/l, respectively.

Lable-free quadruple signal amplification strategy for sensitive electrochemical p53 gene biosensing.

A versatile label-free quadruple signal amplification biosensing platform for p53 gene (target DNA) detection was proposed. The chitosan-graphene (CS-GR) modified electrode with excellent electron transfer ability could provide a large specific surface for high levels of AuNPs-DNA attachment. The large amount of AuNPs could immobilize more capture probes and enhance the electrochemical signal with the excellent electrocatalytic activity. Furthermore, with the assist of N.BstNB I (the nicking endonuclease), target DNA could be reused and more G-quadruplex-hemin DNAzyme could be formed, allowing significant signal amplification in the presence of H2O2. Such strategy can enhance the oxidation-reduction reaction of adsorbed methylene blue (MB) and efficiently improve the sensitivity of the proposed biosensor. The morphologies of materials and the stepwise biosensor were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cyclic voltammetry (CV). Differential pulse voltammetry (DPV) signals of MB provided quantitative measures of the concentrations of target DNA, with a linear calibration range of 1.0 × 10(-15)-1.0 × 10(-9)M and a detection limit of 3.0 × 10(-16)M. Moreover, the resulting biosensor also exhibited good specificity, acceptable reproducibility and stability, indicating that the present strategy was promising for broad potential application in clinic assay.

A novel electrochemical immunosensor using β-cyclodextrins functionalized silver supported adamantine-modified glucose oxidase as labels for ultrasensitive detection of alpha-fetoprotein

In this work, a novel sandwich-type electrochemical immunosensor based on host-guest interaction was fabricated for the detection of alpha-fetoprotein (AFP). Due to the large specific surface area of multiwalled carbon nanotubes and the unique supramolecular recognition ability of β-cyclodextrins, ferrocenecarboxylic acid (Fc) was incorporated into this sensor platform by host-guest interaction to generate an electrochemical signal. And β-cyclodextrins functionalized silver supported adamantine-modified glucose oxidase (GOD-CD-Ag), was used as a label to improve the analytical performance of the immunosensor by the dual amplification strategy. The obtained GOD-CD-Ag conjugates could convert glucose into gluconic acid with the formation of hydrogen peroxide (H2O2). And then silver nanoparticles could in situ catalyze the reduction of the generated H2O2, dramatically improving the oxidation reaction of Fc. The developed immunosensor shows a wide linear calibration range from 0.001 to 5.0 ng/mL with a low detection limit (0.2 pg/mL) for the detection of AFP. The method, with ideal reproducibility and selectivity, has a wide application prospect in clinical research.

A CdTe/CdS quantum dots amplified graphene quantum dots anodic electrochemiluminescence platform and the application for ascorbic acid detection in fruits

Herein, a CdTe/CdS QDs (with a CdTe core and a CdS shell) amplified electrogenerated chemiluminescence (ECL) of nitrogen functional graphene quantum dots (NGQDs) platform is reported. The utilization of CdTe/CdS QDs could facilitate the production of NGQDs radical, and then, a high yield of NGQDs* was formed due to the interaction of NGQDs radical with O2−, leading to an ∼21-fold ECL enhancement. This ECL enhancing system does not require the addition of coreactant and modification of electrode which is carried out in homogeneous solution. Benefiting from the remarkable ECL enhancement effect, a feasible and sensitive ECL sensor was constructed for ascorbic acid (AA) quantification. The proposed method features a detection limit of 70nM with a linear calibration range from 100nM to 100μM, and exhibits good stability, practicability, and acceptable fabrication reproducibility, showing promising application in real-sample.