Showing papers on "Detection limit published in 2015"

Preparation of highly photoluminescent sulfur-doped carbon dots for Fe(III) detection

Abstract: Sulfur-doped carbon dots (S-doped C-dots)were synthesized using a simple and straightforward hydrothermal method. The as-prepared S-doped C-dots exhibit significant fluorescence quantum yield (67%) and unique emission behavior. The spherical S-doped C-dots have an average diameter of 4.6 nm and the fluorescence of S-doped C-dots can be effectively and selectively quenched by Fe3+ ions. Thus, S-doped C-dots were applied as probes toward Fe3+ detection, exhibiting a limit of detection of 0.1 μM.

Green preparation of carbon dots by Jinhua bergamot for sensitive and selective fluorescent detection of Hg2+ and Fe3+

Abstract: Green, low-cost, and water-soluble fluorescent carbon dots were prepared under hydrothermal conditions, with a plant of Jinhua bergamot as a carbon source. The as-synthesized C-dots have better stability and relatively high photoluminescence with a quantum yield of 50.78%, along with the fluorescence lifetime of ca. 3.84 ns. Their photoluminescence can be significantly quenched by simply using the buffer solution of HAC–NaAC for Hg 2+ and Tris–HCl for Fe 3+ . Based on this, we explored for selective detection of Hg 2+ and Fe 3+ with high selectivity, fast response, low cost, and broad linear ranges of 0.01–100 μM for Hg 2+ and 0.025–100 μM for Fe 3+ , as well as low detection limits of 5.5 nM (Hg 2+ ) and 0.075 μM (Fe 3+ ) (S/N = 3).

Colorimetric detection and removal of copper(II) ions from wastewater samples using tailor-made composite adsorbent

Abstract: The nitrogen donor ligand was functionalized with polarable mesoporous silica as composite adsorbent, by a cost-effective and environmentally friendly procedure, for highly selective copper (Cu(II)) ions detection and removal from water. The nitrogen donor ligand of N , N (octane-1,8-diylidene)di(2-hydroxy-3,5-dimethylaniline) was synthesized to be specific to Cu(II) ions. The composite adsorbent permitted fast and specific Cu(II) ions capturing via colorimetric naked-eye detection based on stable complexation [Cu(II)–ligand] n + mechanism. The effect of pH value, interferential metal ions, initial Cu(II) concentration, and contact time on adsorption capability were investigated systematically. The adsorbent was selective toward Cu(II) as shown by a light yellow to green color change. This was characterized by UV–vis spectroscopy and the color change was observed for the visual detection of Cu(II) ions. The ions selectivity of the adsorbent toward Cu(II) was determined by changes in UV–vis reflectance spectra. However, the presence of competing ions showed no interference for the detection of Cu(II) ion by the composite adsorbent. The results demonstrated that the composite adsorbent exhibited excellent sorption performance for Cu(II) ions. The low detection limit and sorption capacity of the adsorbent were 0.10 μg/L and 200.80 mg/g, respectively. The adsorbed Cu(II) was eluted with suitable eluent and simultaneously regenerated into the initial form for next operation without significant deterioration in its nanostructure case cavities. The data also confirmed that the adsorbent is a cost-effective and environmentally friendly procedure for Cu(II) treatment. Therefore, the composite adsorbent can be considered as a potential adsorbent for Cu(II) ions monitoring and removal from wastewater.

Simultaneous Capture, Detection, and Inactivation of Bacteria as Enabled by a Surface-Enhanced Raman Scattering Multifunctional Chip†

Abstract: Herein, we present a multifunctional chip based on surface-enhanced Raman scattering (SERS) that effectively captures, discriminates, and inactivates pathogenic bacteria. The developed SERS chip is made of a silicon wafer decorated with silver nanoparticles and modified with 4-mercaptophenylboronic acid (4-MPBA). It was prepared in a straightforward manner by chemical reduction assisted by hydrogen fluoride etching, followed by the conjugation of 4-MPBA through AgS bonds. The dominant merits of the fabricated SERS chip include excellent reproducibility with a relative standard deviation (RSD) value smaller than 11.0 %, adaptable bacterial-capture efficiency (ca. 60 %) at low concentrations (500–2000 CFU mL−1), a low detection limit (down to a concentration of 1.0×102 cells mL−1), and high antibacterial activity (an antibacterial rate of ca. 97 %). The SERS chip enabled sensitive and specific discrimination of Escherichia coli and Staphylococcus aureus from human blood.

Layered Black Phosphorus as a Selective Vapor Sensor

Abstract: Black phosphorus is a layered material that is sensitive to the surrounding atmosphere. This is generally considered as a disadvantage, especially when compared to more stable layered compounds, such as graphite or MoS2. This sensitivity is now turned into an advantage. A vapor sensor that is based on layered black phosphorus and uses electrochemical impedance spectroscopy as the detection method is presented; the device selectively detects methanol vapor. The impedance phase measured at a constant frequency is used as a distinctive parameter for the selective quantification of methanol, and increases with the methanol concentration. The low detection limit of 28 ppm is well below the approved exposure limit of 200 ppm. The results are highly reproducible, and the vapor sensor is shown to be very selective in the presence of other vapors and to have long-term stability.

Construction of three-dimensional flower-like α-MoO3 with hierarchical structure for highly selective triethylamine sensor

Abstract: Novel flower-like α-MoO3 with hierarchical structure was synthesized via a facile solvothermal route without any surfactant or template, and subsequent calcination at 400 °C in air for 2 h. The α-MoO3 flowers with the diameters about 3–5 μm consist of microrods with average diameters of 150–200 nm growing radially from the center of the hierarchical flower-like structure, and the microrods are assembled from nanoplates. The sensors based on α-MoO3 flowers are highly sensitive and distinctively selective to triethylamine (TEA). The response of this sensor to 100 ppm TEA attains 416 and the detection limit is 0.5 ppm at the operating temperature of 250 °C. The change of the surface status of α-MoO3 flowers before and after exposure to TEA at 250 °C was investigated by using XPS technique and the TEA sensing mechanism over α-MoO3 was proposed.

Noncovalently functionalized monolayer graphene for sensitivity enhancement of surface plasmon resonance immunosensors.

Abstract: A highly efficient surface plasmon resonance (SPR) immunosensor is described using a functionalized single graphene layer on a thin gold film. The aim of this approach was two-fold: first, to amplify the SPR signal by growing graphene through chemical vapor deposition and, second, to control the immobilization of biotinylated cholera toxin antigen on copper coordinated nitrilotriacetic acid (NTA) using graphene as an ultrathin layer. The NTA groups were attached to graphene via pyrene derivatives implying π–π interactions. With this setup, an immunosensor for the specific antibody anticholera toxin with a detection limit of 4 pg mL–1 was obtained. In parallel, NTA polypyrrole films of different thicknesses were electrogenerated on the gold sensing platform where the optimal electropolymerization conditions were determined. For this optimized polypyrrole-NTA setup, the simple presence of a graphene layer between the gold and polymer film led to a significant increase of the SPR signal.

Three-dimensional nitrogen-doped graphene as an ultrasensitive electrochemical sensor for the detection of dopamine

Abstract: Three-dimensional nitrogen-doped graphene (3D N-doped graphene) was prepared through chemical vapor deposition (CVD) by using porous nickel foam as a substrate. As a model, a dopamine biosensor was constructed based on the 3D N-doped graphene porous foam. Electrochemical experiments exhibited that this biosensor had a remarkable detection ability with a wide linear detection range from 3 × 10−6 M to 1 × 10−4 M and a low detection limit of 1 nM. Moreover, the fabricated biosensor also showed an excellent anti-interference ability, reproducibility, and stability.

Iodine-Mediated Etching of Gold Nanorods for Plasmonic ELISA Based on Colorimetric Detection of Alkaline Phosphatase.

Abstract: Here, we propose a plasmonic enzyme-linked immunosorbent assay (ELISA) based on highly sensitive colorimetric detection of alkaline phosphatase (ALP), which is achieved by iodine-mediated etching of gold nanorods (AuNRs). Once the sandwich-type immunocomplex is formed, the ALP bound on the polystyrene microwells will hydrolyze ascorbic acid 2-phosphate into ascorbic acid. Subsequently, iodate is reduced to iodine, a moderate oxidant, which etches AuNRs from rod to sphere in shape. The shape change of AuNRs leads to a blue-shift of longitudinal localized surface plasmon resonance. As a result, the solution of AuNRs changes from blue to red. Benefiting from the highly sensitive detection of ALP, the proposed plasmonic ELISA has achieved an ultralow detection limit (100 pg/mL) for human immunoglobulin G (IgG). Importantly, the visual detection limit (3.0 ng/mL) allows the rapid differential diagnosis with the naked eye. The further detection of human IgG in fetal bovine serum indicates its applicability to the determination of low abundance protein in complex biological samples.

Magnetic nanoparticle based dispersive micro-solid-phase extraction for the determination of malachite green in water samples: optimized experimental design

Abstract: This paper presents an extraction method based on dispersive-nanoparticle-solid phase microextraction (DNSPME) for the preliminary preconcentration and subsequent spectrophotometric determination of trace amounts of malachite green (MG). The application of nanoparticles permits the easy separation and extraction of MG from trout fish water and natural water samples. The analyte was accumulated on a γ-Fe2O3 nanomaterial loaded on activated carbon (γ-Fe2O3-NPs–AC) that was identified by FESEM, XRD, FTIR, EDS and UV-Vis techniques. The influence of the expectable parameters on the extraction recovery, according to p < 0.05, was investigated and judged using a two-level Plackett–Burman screening design with 7 variables (adsorbent mass, centrifugation time, eluent volume, ionic strength, pH, ultrasonication temperature and ultrasonication time). It was found that three significant variables namely adsorbent mass, eluent volume and pH have a great influence on optimization using a central composite design combined with a desirability function. The results showed that the semi-empirically obtained second-order model was able to efficiently predict the ER% for MG adequately with a coefficient of determination of 99.7% (p < 0.001); the higher efficiency of the model was obtained through a good compromise between the experimental and predicted data. Working under the optimum conditions, specified as 0.6 mg of adsorbent and 120 μL of eluent volume at pH 6.0, led to the achievement of a high and reasonable linear range over 1–4000 ng mL−1 (R2 = 0.999) with a detection limit of 0.175 ng mL−1 and an obtained quantification limit of 0.583 ng mL−1. The relative standard deviation (RSD) for ten replicates was less than 3.50%. The proposed method was successfully applied for the determination of MG in trout fish water and natural water samples with excellent recoveries corresponding to spiked samples. All these results prove the suitability of the present method in terms of simplicity, easy operation conditions, efficiency and sensitivity for the determination of MG in real samples.

Synthesis of a carbon-dot-based photoluminescent probe for selective and ultrasensitive detection of Hg2+ in water and living cells

Abstract: A nitrogen and sulphur co-doped carbon dot (NSCD) based highly selective photoluminescent probe for mercury detection has been designed. The NSCDs with a PL quantum yield of 69% are easily prepared from a single polymeric molecular precursor. The turn on-off fluorescence change upon mercury addition is attributed to the nonradiative electron transfer from the excited state to the d-orbital of the metal ion. The soft–soft acid–base interaction between the sulphur part of the NSCD and Hg2+ makes the fluorescence probe more specific and selective towards Hg2+ in contrast to other metal ions. The limit of detection of mercury ions is found to be 0.05 nM. Due to their high photostability, low toxicity and low detection limit, these carbon dots are demonstrated to be excellent probes for the detection of Hg2+ in the living cell.

A colorimetric sensor for the sequential detection of Cu(2+) and CN(-) in fully aqueous media: practical performance of Cu(2+).

Abstract: A new highly selective colorimetric chemosensor 1 (E)-9-(((5-mercapto-1,3,4-thiadiazol-2-yl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol was designed and synthesized for the sequential detection of Cu2+ and CN−. This sensor 1 exhibited an obvious color change from yellow to orange in the presence of Cu2+ in a fully aqueous solution. The detection limit (0.9 μM) of 1 for Cu2+ is far lower than the WHO limit (31.5 μM) for drinking water. In addition, the resulting Cu2+-2·1 complex can be further used to detect toxic cyanide through a color change from orange to yellow, indicating the recovery of 1 from Cu2+-2·1. Importantly, chemosensor 1 could be used to detect and quantify Cu2+ in water samples, and a colorimetric test strip of 1 for the detection of Cu2+ could be useful for all practical purposes.

Aptamer based fluorescence recovery assay for aflatoxin B1 using a quencher system composed of quantum dots and graphene oxide

Abstract: Aflatoxin B1 (AFB1), a secondary fungal metabolite of Aspergillus flavus, was employed as a model mycotoxin to establish an aptamer based assay that exploits the quenching of the fluorescence of CdTe quantum dots (Q-dots) by graphene oxide (GO). A thiolated aptamer specific for AFB1 was linked to the surface of Q-dots via ligand exchange. The fluorescence of the aptamer modified-Q-dots is strongly quenched by GO. If, however, AFB1 is added, fluorescence is restored depending on the quantity of AFB1 added. The system was evaluated both in phosphate buffer solution and in peanut oil. If performed in an aqueous system, the assay possesses good selectivity, a wide dynamic range (from 3.2 nM to 320 μM) and a low limit of detection (1.0 nM). If performed in peanut oil solution, the dynamic range is from 1.6 nM to 160 μM, and the limit of detection is 1.4 nM. In our perception, this is a simple, sensitive and selective method for the determination of AFB1 that also may be extended to the analysis of other mycotoxins.

Colorimetric determination of nitrite in clinical, food and environmental samples using microfluidic devices stamped in paper platforms

Abstract: This study reports the use of microfluidic paper-based analytical devices (μPADs) associated with colorimetric detection for the determination of nitrite in clinical, food and environmental samples. μPADs were fabricated by a simple and fast stamping process in a geometry containing eight circular detection zones and one central zone to sample inlet interconnected by microfluidic channels. The colorimetric determination of nitrite was performed through the modified Griess reaction. Detection zones were spotted with a 0.75 μL aliquot of a solution containing 50 mM sulfanilamide, 1.2 M hydrochloric acid and 4 mM N-(1-naphthyl)ethylenediamine. The monitoring of the background colorimetric response revealed good stability over 12 h for devices stored in the absence of light. After the addition of standard or real samples, the resulting images were captured with a scanner, converted to a color scale and analyzed in the magenta channel. The analytical sensitivity and the limit of detection achieved after a preconcentration stage were 0.56 (AU μM−1) and 5.6 μM, respectively. The preconcentration provided an enrichment factor of ca. 3.2 times. The concentration levels of nitrite were successfully determined in saliva, preservative water, ham, sausage and river water samples. The concentration levels attained for each sample using μPADs were compared to the values found by spectrophotometry and there was no significant difference from one another at a confidence level of 95%.

An ultra-sensitive impedimetric immunosensor for detection of the serum oncomarker CA-125 in ovarian cancer patients

Abstract: Effective treatment of ovarian cancer depends upon the early detection of the malignancy. Here, we report on the development of a new nanostructured immunosensor for early detection of cancer antigen 125 (CA-125). A gold electrode was modified with mercaptopropionic acid (MPA), and then consecutively conjugated with silica coated gold nanoparticles (AuNP@SiO2), CdSe quantum dots (QDs) and anti-CA-125 monoclonal antibody (mAb). The engineered MPA|AuNP@SiO2|QD|mAb immunosensor was characterised using transmission electron microscopy (TEM), atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Successive conjugation of AuNP@SiO2, CdSe QD and anti-CA-125 mAb onto the gold electrode resulted in sensitive detection of CA-125 with a limit of detection (LOD) of 0.0016 U mL(-1) and a linear detection range (LDR) of 0-0.1 U mL(-1). Based on the high sensitivity and specificity of the immunosensor, we propose this highly stable and reproducible biosensor for the early detection of CA-125.