Showing papers on "Detection limit published in 2010"

Colorimetric Detection of Pb2+ Using Glutathione Functionalized Gold Nanoparticles

Abstract: A facile, cost-effective and sensitive colorimetric detection method for Pb2+ has been developed by using glutathione functionalized gold nanoparticles (GSH-GNPs). The sensitivity and selectivity of detection were investigated in detail. The GSH-GNPs could be induced to aggregate immediately in the presence of Pb2+, especially after the addition of 1 M NaCl aqueous solution. The Pb2+ could be detected by colorimetric response of GNPs that could be monitored by a UV−vis spectrophotometer or even naked eyes, and the detection limit could reach 100 nM. The GSH-GNPs bound by Pb2+ showed excellent selectivity compared to other metal ions (Hg2+, Mg2+, Zn2+, Ni2+, Cu2+, Co2+, Ca2+, Mn2+, Fe2+, Cd2+, Ba2+, and Cr3+), which led to prominent color change. This provided a simple and effective colorimetric sensor (no enzyme or DNA) for on-site and real-time detection of Pb2+. Most importantly, this probe was also applied to determine the Pb2+ in the lake samples with low interference and high sensitivity.

Highly Sensitive, Colorimetric Detection of Mercury(II) in Aqueous Media by Quaternary Ammonium Group-Capped Gold Nanoparticles at Room Temperature

Abstract: We provide a highly sensitive and selective assay to detect Hg2+ in aqueous solutions using gold nanoparticles modified with quaternary ammonium group-terminated thiols at room temperature. The mechanism is the abstraction of thiols by Hg2+ that led to the aggregation of nanoparticles. With the assistance of solar light irradiation, the detection limit can be as low as 30 nM, which satisfies the guideline concentration of Hg2+ in drinking water set by the WHO. In addition, the dynamic range of detection is wide (3 × 10−8−1 × 10−2 M). This range, to our best knowledge, is the widest one that has been reported so far in gold nanoparticle (AuNP)-based assays for Hg2+.

Lab-on-paper with dual electrochemical/colorimetric detection for simultaneous determination of gold and iron.

Abstract: A novel lab-on-paper device combining electrochemical and colorimetric detection for the rapid screening of Au(III) in the presence of a common interference, Fe(III), in industrial waste solutions is presented here. With dilute aqua regia (0.1 M HCl + 0.05 M HNO3) as the supporting electrolyte, square wave voltammetry on paper provided a well-defined reduction peak for Au(III) at ∼287 ± 12 mV vs Ag/AgCl. Under the optimized working conditions, the calibration curve showed good linearity in the concentration range of 1−200 ppm of Au(III) with a correlation coefficient of 0.997. The limit of detection (LOD) of the proposed method is 1 ppm. Interferences from various cations were also studied. Fe(III) is the only metal that affects the electrochemical determination of Au(III) when present above a 2.5-fold excess concentration of that of the Au(III). To overcome this limitation, a colorimetric method was used to simultaneously detect Fe(III) as a screening tool. The procedure was then successfully applied to ...

A Simple and Highly Sensitive Colorimetric Detection Method for Gaseous Formaldehyde

Abstract: A colorimetric detection method using amine-functionalized polymer films doped with a pH indicator has been developed for the rapid, sensitive, and quantitative detection of gaseous formaldehyde at concentrations well below the immediately dangerous to life or health (IDLH) limit. In 1 min, visible color changes are easily observed, even down to the permissible exposure limit (PEL) at 750 ppb. The limit of detection is below 50 ppb (7% of the PEL) after 10 min of exposure. This sensor is essentially unaffected by changes in humidity or temperature (4 to 50 degrees C) and is not sensitive to common interferents.

Colorimetric detection of mercury(II) ion using unmodified silver nanoparticles and mercury-specific oligonucleotides.

Abstract: A sensitive and selective colorimetric detection method for mercury(II) has been well-established in this paper. It was based on the conformation change of mercury-specific oligonucleotides (MSO) from random coil structure to hairpin structure upon the addition of Hg2+ and the phenomenon of salt-induced unmodified silver nanoparticles (AgNPs) aggregation. The calibration curve showed that the net absorption ratio value at 395 and 570 nm increased linearly over the Hg2+ concentration range of 25−500 nM with a limit of detection of 17 nM. The other environmentally relevant metal ions did not interfere with the determination of Hg2+.

Highly selective fluorescent sensors for Hg2+ based on bovine serum albumin-capped gold nanoclusters

Abstract: In this paper, we report a new homogeneous assay for rapid, highly selective and sensitive detection of Hg2+ in aqueous solution based on the induced photoluminescence (PL) quenching of BSA-modified gold nanoclusters (BSA-Au NCs). There was a linear correlation between the expression (I0 − I)/I0 and the concentrations of Hg2+ over the ranges of 0.4–43.2 μM, and the corresponding limit of detection (LOD) was 80 nM. The relative standard deviation of 5 replicate measurements was 1.4% for 1.0 × 10−5 mol L−1 Hg2+. Moreover, this method has excellent selectivity over metal ions and anions. The feasibility of the BSA-Au NCs sensor for Hg2+ in different aqueous samples was demonstrated with satisfactory results. Moreover, the possible sensing Hg2+ mechanism was also discussed.

L-cysteine functionalized gold nanoparticles for the colorimetric detection of Hg2+ induced by ultraviolet light.

Abstract: A simple, cost-effective yet rapid and sensitive colorimetric sensor for the detection of Hg(2+) using L-cysteine functionalized gold nanoparticles induced by ultraviolet radiation was developed. The sensitivity and selectivity of detection was also investigated. The L-cysteine modified gold nanoparticles can be induced to aggregate quickly in the presence of Hg(2+), especially with the assistance of ultraviolet radiation. The presence of Hg(2+) can be monitored by the colorimetric response of gold nanoparticles. The detection of Hg(2+) could be realized, after measuring the UV-vis spectra, with a detection limit of 100 nM. The selectivity of this method has been investigated by other divalent metal ions. The effective colorimetric sensor can be used for on-site and real-time Hg(2+) detection.

Detection of melamine in liquid milk using surface‐enhanced Raman scattering spectroscopy

Abstract: Melamine, a nitrogen-rich chemical, has recently caused enormous economic losses to the food industry due to the cases of milk products adulterated by melamine. This has led to an urgent need of rapid and reliable methods for detection of melamine in food. In this study, surface-enhanced Raman scattering (SERS) spectroscopy was used to detect melamine in liquid milk. The sample preparation with liquid milk is very easy; it has to be only diluted with double-distilled water followed by centrifugation. By using a silver colloid, at least a 105-fold enhancement of the Raman signal was achieved for the measurement of melamine. The limit of detection by this method was 0.01 µg ml−1 for melamine standard samples. Based on the intensity of the Raman vibrational bands normalised to that of the band at 928 cm−1 (CH2), an external standard method was employed for quantitative analysis. The linear regression square (R2) of the curve was 0.9998; the limit of quantitation using this approach was 0.5 µg ml−1 of melamine in liquid milk; the relative standard deviation was ≤10%; and recoveries were from 93 to 109%. The test results for SERS were very precise and as good as those obtained by liquid chromatography/tandem mass spectrometry. The method was simple, fast(only needs about 3 min), cost effective, and sensitive for the detection of melamine in liquid milk samples. Therefore, it is more suitable for the field detection of melamine in liquid milk. Copyright © 2010 John Wiley & Sons, Ltd.

Amperometric biosensor for direct blood lactate detection.

Abstract: An amperometric sensor for lactate quantification is presented. The developed biosensor requires only 0.2 U of lactate oxidase, which is immobilized in a mucin/albumin hydrogel matrix. By protecting the platinum surface with a Nafion membrane, typical interference related to negatively charged species such as ascorbic acid has been minimized to practically undetectable levels. Electrochemical properties associated with the Nafion membrane are assessed as a function of Nafion concentration. In a phosphate buffer solution of pH 7.0, linear dependence of the catalytic current upon lactate bulk concentration was obtained between 2 and ∼1000 μM. A detection limit of 0.8 μM can be calculated considering 3 times the standard deviation of the blank signal divided by the sensitivity of the sensor. The lactate biosensor presents remarkable operational stability and sensitivity (0.537 ± 0.007) mA.M−1, where the error is the standard deviation of the slope calculated from the linear regression of the calibration curv...

Nanoparticle-based immunoassays for sensitive and early detection of HIV-1 capsid (p24) antigen

Abstract: We evaluated the feasibility of using nanoparticle (NP)-based assays for improving detection sensitivity of human immunodeficiency virus type 1 (HIV-1) p24 antigen. One assay that was evaluated is a gold NP-based biobarcode amplification (BCA) assay, which can detect HIV-1 p24 antigen at levels as low as 0.1 pg/mL. The lower limit of detection for an enzyme-linked immunosorbent assay (ELISA) is 10-15 pg/mL. These results demonstrate that the HIV-1 p24 BCA assay offers 100-150-fold enhancement in the detection limit over the traditional colorimetric ELISA. Furthermore, the BCA assay detected HIV-1 infection 3 days earlier than did ELISA in samples from patients who had experienced seroconversion. The other assay that we tested is the europium NP-based immunoassay, which uses europium NPs to replace gold NPs in the BCA assay to further simplify the detection method and decrease the incubation time. For detection of HIV-1 p24, the lower limit of detection for the europium NP-based immunoassay was 0.5 pg/mL. These results indicate that the universal labeling technology based on NPs and its application may provide a rapid and sensitive testing platform for clinical diagnosis and laboratory research.

Analysis of drugs of abuse in biofluids by low temperature plasma (LTP) ionization mass spectrometry

Abstract: Low temperature plasma (LTP) ionization is an ambient plasma ionization method that permits the direct mass analysis of samples in their native atmospheric environment with little or no sample preparation. In this work, the low temperature plasma probe is used in the direct and rapid mass spectrometric analysis of aqueous phase samples including biofluids (saliva, urine, and hair extract). A detailed trace qualitative examination of 14 drugs of abuse has been performed. The relative standard deviation on average was ∼16% for the LTP analysis of the drugs of abuse standards. Eleven of the fourteen drugs of abuse were detected in the low ng mL−1 (3 pg absolute detection) to the mid µg mL−1 (∼30 ng absolute detection) concentration range. One drug, cannabidiol, could not be detected until supplemental heating of the substrate was incorporated into the experimental protocol. The addition of supplemental heating improved the detection limits by at least an order of magnitude to ∼0.5 ng mL−1 to 0.5 µg mL−1 (1.5 pg–1.5 ng absolute) for twelve of the fourteen drugs of abuse, so extending the linear dynamic range which for most analytes was four orders of magnitude. Quantitative capabilities were evaluated using the particular example of benzoylecgonine in urine by employing a deuterated internal standard. Matrix effects observed during the analysis of the drugs in complex biological fluids are also discussed. In addition, low temperature plasma ionization was applied to the examination of real (not spiked) biological samples and these results were confirmed using standard LC/MS methodology. The main advantages observed for this ambient desorption/ionization technique include the capabilities for direct analysis of liquid surfaces for in situ detection and the remarkable sensitivity in the examination of the drugs of abuse investigated here. The disadvantages of the method include the modest quantitative accuracy making LTP most useful as a rapid but semi-quantitative screening method.

Electrochemical sensor for 2,4-dichlorophenoxy acetic acid using molecularly imprinted polypyrrole membrane as recognition element

Abstract: An electrochemical sensor based on molecularly imprinted polypyrrole membranes is reported for the determination of 2,4-dichlorophenoxy acetic acid (2,4-D). The sensor was prepared by electropolymerization of pyrrole on a glassy carbon electrode in the presence of 2,4-D as a template. The template was removed by overoxidation at +1.3 V in buffer solution. The sensor can effectively improve the reductive properties of 2,4-D and eliminate interferences by other pesticides and electroactive species. The peak current at -0.78 V is linear with the concentration of 2,4-D from 1.0 to 10 µM, the detection limit is 0.83 µM (at 3σ), and the relative standard deviation is 3.9% (at 5.0 µM of 2,4-D; n = 7). The method has been successfully applied to the determination of 2,4-D in environmental water samples, with recovery rates ranging from 92% to 108%.

Development of an Electrochemical Biosensor for the Detection of Aflatoxin M1 in Milk

Abstract: We have developed an electrochemical immunosensor for the detection of ultratrace amounts of aflatoxin M1 (AFM1) in food products. The sensor was based on a competitive immunoassay using horseradish peroxidase (HRP) as a tag. Magnetic nanoparticles coated with antibody (anti-AFM1) were used to separate the bound and unbound fractions. The samples containing AFM1 were incubated with a fixed amount of antibody and tracer [AFM1 linked to HRP (conjugate)] until the system reached equilibrium. Competition occurs between the antigen (AFM1) and the conjugate for the antibody. Then, the mixture was deposited on the surface of screen-printed carbon electrodes, and the mediator [5-methylphenazinium methyl sulphate (MPMS)] was added. The enzymatic response was measured amperometrically. A standard range (0, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.3, 0.4 and 0.5 ppb) of AFM1-contaminated milk from the ELISA kit was used to obtain a standard curve for AFM1. To test the detection sensitivity of our sensor, samples of commercial milk were supplemented at 0.01, 0.025, 0.05 or 0.1 ppb with AFM1. Our immunosensor has a low detection limit (0.01 ppb), which is under the recommended level of AFM1 [0.05 µg L-1 (ppb)], and has good reproducibility.

Stripping voltammetric determination of mercury(II) and lead(II) using screen-printed electrodes modified with gold films, and metal ion preconcentration with thiol-modified magnetic particles

Abstract: A novel approach to the electrochemical determination of heavy metals in tap water using anodic stripping voltammetry was developed using screen-printed electrodes modified with gold films. After optimisation of the experimental conditions, the screen-printed electrodes modified with gold films displayed excellent linear behaviour in the examined concentration range from 2 to 16 µg L-1 mercury and lead in 50 mM HCl with a detection limit of 1.5 µg L-1 and 0.5 µg L-1 for mercury and lead, respectively. In order to decrease the working range down to less than 1 µg L-1, a preconcentration step based on the use of magnetic particles modified with thiols was introduced into the protocol. Applying optimum binding conditions, the assay using screen-printed electrodes modified with gold films displayed excellent linear behaviour in the concentration range 0.1 to 0.8 µg L-1 in 50 mM HCl. The detection limit after a 120 s deposition time for mercury and lead were 0.08 µg L-1 and 0.02 µg L-1, respectively. The method has been applied to the determination of mercury and lead traces in tap water