Showing papers on "Detection limit published in 2018"

Metastable α-AgVO3 microrods as peroxidase mimetics for colorimetric determination of H2O2

Abstract: Single phase metastable α-AgVO3 microrods with high crystallinity, tetragonal rod-like microstructure, uniform particle size distribution, and good dispersion were synthesized by direct coprecipitation at room temperature. They are shown to be viable peroxidase mimics that catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine in the presence of H2O2. Kinetic analysis indicated typical Michaelis–Menten catalytic behavior. The findings were used to design a colorimetric assay for H2O2, best measured at 652 nm. The method has a linear response in the 60 to 200 μM H2O2 concentration range, with a 2 μM detection limit. Benefitting from the chemical stability of the microrods, the method is well reproducible. It also is easily performed and highly specific.

Cobalt nitride nanowire array as an efficient electrochemical sensor for glucose and H2O2 detection

Abstract: It is highly attractive to develop non-noble-metal nanoarray architecture as a high-active catalyst electrode for molecular detection due to its large specific surface area and easy accessibility to target molecules. In this paper, we demonstrate the development of cobalt nitride nanowire array on Ti mesh (Co 3 N NW/TM) as an efficient catalyst electrode for glucose oxidation in alkaline solutions and H 2 O 2 reduction in neutral solutions. Electrochemical tests suggest that such Co 3 N NW/TM possesses superior non-enzymatic sensing ability toward rapid glucose and H 2 O 2 detection. As a glucose sensor, this fabricated electrode offers a high sensitivity of 3325.6 μA mM −1 cm −2 , with a wide linear range from 0.1 μM to 2.5 mM, a low detection limit of 50 nM (S/N = 3), and satisfactory stability and reproducibility. Its application in determining glucose in human blood serum is also successful. Amperometric H 2 O 2 sensing can also been realized with a sensitivity of 139.9 μA mM −1 cm −2 , a linear range from 2 μM to 28 mM, and a detection limit of 1 μM (S / N = 3). This nanoarray architecture holds great promise as an attractive sensing platform toward electrochemical small molecules detection.

Effective Enrichment and Detection of Trace Polycyclic Aromatic Hydrocarbons in Food Samples based on Magnetic Covalent Organic Framework Hybrid Microspheres.

Abstract: The present study reported a facile, sensitive, and efficient method for enrichment and determination of trace polycyclic aromatic hydrocarbons (PAHs) in food samples by employing new core–shell nanostructure magnetic covalent organic framework hybrid microspheres (Fe3O4@COF-(TpBD)) as the sorbent followed by HPLC-DAD. Under mild synthetic conditions, the Fe3O4@COF-(TpBD) were prepared with the retention of colloidal nanosize, larger specific surface area, higher porosity, uniform morphology, and supermagnetism. The as-prepared materials showed an excellent adsorption ability for PAHs, and the enrichment efficiency of the Fe3O4@COF-(TpBD) could reach 99.95%. The obtained materials also had fast adsorption kinetics and realized adsorption equilibrium within 12 min. The eluent was further analyzed by HPLC-DAD, and good linearity was observed in the range of 1–100 ng/mL with the linear correlation being above 0.9990. The limits of detection (S/N = 3) and limits of quantitation (S/N = 10) for 15 PAHs were in ...

Nonenzymatic electrochemical sensor based on CuO-TiO2 for sensitive and selective detection of methyl parathion pesticide in ground water

Abstract: Detection of pesticides in ground water has become a very important and crucial research area due to the rapid expansion of agriculture and stringent environmental protection acts. In this paper, the as-prepared CuO-TiO 2 hybrid nanocomposites were decorated on the glass carbon electrode as the nonenzymatic electrochemical nanosensor for the sensitive and selective detection of methyl parathion. The electrochemical behavior of the modified electrode was investigated by cyclic voltammetry, showing that the modified electrode can be used for methyl parathion detection. Differential pulse voltammetry was applied to evaluate methyl parathion detection ability under optimized experimental conditions, and found the modified electrode can detect methyl parathion sensitively in a wide dynamic detection range from 0 ppb to 2000 ppb with a lower limit of detection (LOD) of 1.21 ppb. In addition, other interfering materials have no any influences on the detection of methyl parathion. Furthermore, the modified electrode has also been used for methyl parathion detection in the actual ground water samples, and showed efficient sensing ability. The electrochemical sensor developed would have great potentiality for methyl parathion sensing and provide new insights into the detection of other organophosphorous pesticides in the ground water.

A simple approach for simultaneous detection of cadmium(II) and lead(II) based on glutathione coated magnetic nanoparticles as a highly selective electrochemical probe

Abstract: We introduce the synthesis and electrochemical application of a glutathione functionalized magnetic nanocomposite (GSH@Fe3O4) for the development of a simple, stable and selective sensor for heavy metal ion detection in real-life samples for the first time. The monitoring method is based on electrochemical preconcentration/reduction of metal ions onto a GSH@Fe3O4 modified magnetic glassy carbon electrode, followed by subsequent anodic stripping. This method allows the detection of Pb2+ and Cd2+ ions with high sensitivity (calculated detection limits of 0.182 μgL−1 and 0.172 μgL−1), low cost, and great convenience in operation and was tested for different water samples. The results infer that the GSH@Fe3O4 nanocomposite can be an alternative candidate for practical applications in electrochemical detection of metal ions.

Printed Graphene Electrochemical Biosensors Fabricated by Inkjet Maskless Lithography for Rapid and Sensitive Detection of Organophosphates

Abstract: Solution phase printing of graphene-based electrodes has recently become an attractive low-cost, scalable manufacturing technique to create in-field electrochemical biosensors. Here, we report a graphene-based electrode developed via inkjet maskless lithography (IML) for the direct and rapid monitoring of triple-O linked phosphonate organophosphates (OPs); these constitute the active compounds found in chemical warfare agents and pesticides that exhibit acute toxicity as well as long-term pollution to soils and waterways. The IML-printed graphene electrode is nano/microstructured with a 1000 mW benchtop laser engraver and electrochemically deposited platinum nanoparticles (dia. ∼25 nm) to improve its electrical conductivity (sheet resistance decreased from ∼10 000 to 100 Ω/sq), surface area, and electroactive nature for subsequent enzyme functionalization and biosensing. The enzyme phosphotriesterase (PTE) was conjugated to the electrode surface via glutaraldehyde cross-linking. The resulting biosensor was able to rapidly measure (5 s response time) the insecticide paraoxon (a model OP) with a low detection limit (3 nM), and high sensitivity (370 nA/μM) with negligible interference from similar nerve agents. Moreover, the biosensor exhibited high reusability (average of 0.3% decrease in sensitivity per sensing event), stability (90% anodic current signal retention over 1000 s), longevity (70% retained sensitivity after 8 weeks), and the ability to selectively sense OP in actual soil and water samples. Hence, this work presents a scalable printed graphene manufacturing technique that can be used to create OP biosensors that are suitable for in-field applications as well as, more generally, for low-cost biosensor test strips that could be incorporated into wearable or disposable sensing paradigms.

Sensitive colorimetric assay for uric acid and glucose detection based on multilayer-modified paper with smartphone as signal readout.

Abstract: In this work, a multilayer-modified paper-based colorimetric sensing platform with improved color uniformity and intensity was developed for the sensitive and selective determination of uric acid and glucose with smartphone as signal readout. In detail, chitosan, different kinds of chromogenic reagents, and horseradish peroxidase (HRP) combined with a specific oxidase, e.g., uricase or glucose oxidase (GOD), were immoblized onto the paper substrate to form a multilayer-modified test paper. Hydrogen peroxide produced by the oxidases (uricase or GOD) reacts with the substrates (uric acid or glucose), and could oxidize the co-immoblized chromogenic reagents to form colored products with HRP as catalyst. A simple strategy by placing the test paper on top of a light-emitting diode lamp was adopted to efficiently prevent influence from the external light. The color images were recorded by the smartphone camera, and then the gray values of the color images were calculated for quantitative analysis. The developed method provided a wide linear response from 0.01 to 1.0 mM for uric acid detection and from 0.02 to 4.0 mM for glucose detection, with a limit of detection (LOD) as low as 0.003 and 0.014 mM, respectively, which was much lower than for previously reported paper-based colorimetric assays. The proposed assays were successfully applied to uric acid and glucose detection in real serum samples. Furthermore, the enhanced analytical performance of the proposed method allowed the non-invasive detection of glucose levels in tear samples, which holds great potential for point-of-care analysis.

A facile optosensing protocol based on molecularly imprinted polymer coated on CdTe quantum dots for highly sensitive and selective amoxicillin detection

Abstract: A facile method for coating a molecularly imprinted polymer onto CdTe quantum dots (MIP-QDs) was successfully formulated and for the first time used as a highly selective and sensitive photoluminescence probe for the determination of trace amoxicillin. The MIP-QDs were prepared using a sol-gel process with 3-aminopropylethoxysilane as a functional monomer, tetraethoxysilane as a cross-linker and amoxicillin as a template molecule. After removal of the template molecule from the polymer layer, MIP-QDs containing cavities specific to amoxicillin were obtained. The hydrogen bonding between the amino group of 3-aminopropylethoxysilane and functional groups of amoxicillin and the specific size and shape of the cavity provided good selectivity. The photoluminescence intensity of MIP-QDs was more strongly quenched by amoxicillin compared to a non-imprinted polymer (NIP-QDs) with an imprinting factor of 43.6. Under optimum conditions, the photoluminescence intensity of MIP-QDs was decreased in response to increase amoxicillin concentration with good linearity in the range of 0.20–50.0 μg L −1 . The limit of detection and the limit of quantitation were 0.14 μg L −1 and 0.46 μg L −1 , respectively. The developed method showed good repeatability and reproducibility with the relative standard deviation being less than 6%. This developed method was successfully applied for the determination of amoxicillin in egg, milk and honey samples with a satisfactory recovery of 85–102% being achieved.

Fluorescent Nanoprobes with Oriented Modified Antibodies to Improve Lateral Flow Immunoassay of Cardiac Troponin I.

Abstract: Performance of nanoprobes can often determine the detection level of Lateral immunochromatography. Traditional probes were limited by the quantity and orientation of antibodies, immune activity of the Fab region or binding strength between protein and substrate. This study developed a new efficient and robust technology to construct fluorescent nanoprobes with oriented modified antibodies, based on specific binding of the Fc region of antibody with streptococcal protein G (SPG) on the surface of polystyrene microspheres (MS) and subsequent covalent cross-linking at binding sites to firm them. Lateral flow immunoassay using these probes was applied for the detection of cardiac troponin I (cTnI). The significantly improved detection sensitivity demonstrated that antibody orientation on MS surfaces effectively enhanced immunological activities of probes compared with random immobilizing methods. Furthermore, performance evaluation results of lateral flow test strips met clinical requirements perfectly, inclu...

Sensitive detection of pesticides by a highly luminescent metal-organic framework

Abstract: This work reports a highly luminescent metal-organic framework (MOF) with high surface area of 4073.9 m2 g−1, exhibiting an excellent adsorption ability and sensing performance in rapidly detecting parathion-methyl. This is an excellent example of luminescent MOFs to sensitively detect pesticides by fluorescent quenching with satisfactory results. This sensor provides a very wide linear detection range from 1.0 μg kg−1 to 10 mg kg−1, and low limit of detection 0.12 μg kg−1 (0.456 nM) for parathion-methyl. This low detection limit is much lower than the maximum residue limits (MRL) in the European Union pesticides database (0.01 mg kg−1 for fruits and vegetables, 0.02 mg kg−1 for tree nuts), as well as those of previous assays. The quenching effect of parathion-methyl is attributed to the electron-rich chemical group of nitroaromatics which might lead to photo-induced electron transfer. The fluorescent method has been reliably used for the determination of parathion-methyl in spiked irrigation water with satisfactory results, which suggests its potential for rapid detection of pesticides in food and environmental sample.