Showing papers on "Detection limit published in 2016"

Ultrasensitive surface-enhanced Raman scattering detection in common fluids

Abstract: Detecting target analytes with high specificity and sensitivity in any fluid is of fundamental importance to analytical science and technology. Surface-enhanced Raman scattering (SERS) has proven to be capable of detecting single molecules with high specificity, but achieving single-molecule sensitivity in any highly diluted solutions remains a challenge. Here we demonstrate a universal platform that allows for the enrichment and delivery of analytes into the SERS-sensitive sites in both aqueous and nonaqueous fluids, and its subsequent quantitative detection of Rhodamine 6G (R6G) down to ∼75 fM level (10(-15) mol⋅L(-1)). Our platform, termed slippery liquid-infused porous surface-enhanced Raman scattering (SLIPSERS), is based on a slippery, omniphobic substrate that enables the complete concentration of analytes and SERS substrates (e.g., Au nanoparticles) within an evaporating liquid droplet. Combining our SLIPSERS platform with a SERS mapping technique, we have systematically quantified the probability, p(c), of detecting R6G molecules at concentrations c ranging from 750 fM (p > 90%) down to 75 aM (10(-18) mol⋅L(-1)) levels (p ≤ 1.4%). The ability to detect analytes down to attomolar level is the lowest limit of detection for any SERS-based detection reported thus far. We have shown that analytes present in liquid, solid, or air phases can be extracted using a suitable liquid solvent and subsequently detected through SLIPSERS. Based on this platform, we have further demonstrated ultrasensitive detection of chemical and biological molecules as well as environmental contaminants within a broad range of common fluids for potential applications related to analytical chemistry, molecular diagnostics, environmental monitoring, and national security.

Turn-off fluorescence sensor for the detection of ferric ion in water using green synthesized N-doped carbon dots and its bio-imaging.

Abstract: This paper reports turn-off fluorescence sensor for Fe3 + ion in water using fluorescent N-doped carbon dots as a probe. A simple and efficient hydrothermal carbonization of Prunus avium fruit extract for the synthesis of fluorescent nitrogen-doped carbon dots (N-CDs) is described. This green approach proceeds quickly and provides good quality N-CDs. The mean size of synthesized N-CDs was approximately 7 nm calculated from the high-resolution transmission electron microscopic images. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy revealed the presence of –OH, –NH2, –COOH, and –CO functional groups over the surface of CDs. The N-CDs showed excellent fluorescent properties, and emitted blue fluorescence at 411 nm upon excitation at 310 nm. The calculated quantum yield of the synthesized N-CDs is 13% against quinine sulfate as a reference fluorophore. The synthesized N-CDs were used as a fluorescent probe towards the selective and sensitive detection of biologically important Fe3 + ions in water by fluorescence spectroscopy and for bio-imaging of MDA-MB-231 cells. The limit of detection (LOD) and the Stern–Volmer quenching constant for the synthesized N-CDs were 0.96 μM and 2.0958 × 103 M of Fe3 + ions. The green synthesized N-CDs are efficiently used as a promising candidate for the detection of Fe3 + ions and bio-imaging.

Three-Dimensional Ni2P Nanoarray: An Efficient Catalyst Electrode for Sensitive and Selective Nonenzymatic Glucose Sensing with High Specificity

Abstract: It is highly attractive to construct a natural enzyme-free electrode for sensitive and selective detection of glucose. In this Letter, we report that a Ni2P nanoarray on conductive carbon cloth (Ni2P NA/CC) behaves as an efficient three-dimensional catalyst electrode for glucose electrooxidation under alkaline conditions. Electrochemical measurements demonstrate that the Ni2P NA/CC, when used as a nonenzymatic glucose sensor, offers superior analytical performances with a short response time of 5 s, a wide detection range of 1 μM to 3 mM, a low detection limit of 0.18 μM (S/N = 3), a response sensitivity of 7792 μA mM–1 cm–2, and satisfactory selectivity, specificity, and reproducibility. Moreover, it can also be used for glucose detection in human blood serum, promising its application toward determination of glucose in real samples.

Colorimetric Detection of Escherichia coli Based on the Enzyme-Induced Metallization of Gold Nanorods.

Abstract: A novel enzyme-induced metallization colorimetric assay is developed to monitor and measure beta-galactosidase (β-gal) activity, and is further employed for colorimetric bacteriophage (phage)-enabled detection of Escherichia coli (E. coli). This assay relies on enzymatic reaction-induced silver deposition on the surface of gold nanorods (AuNRs). In the presence of β-gal, the substrate p-aminophenyl β-d-galactopyranoside is hydrolyzed to produce p-aminophenol (PAP). Reduction of silver ions by PAP generates a silver shell on the surface of AuNRs, resulting in the blue shift of the longitudinal localized surface plasmon resonance peak and multicolor changes of the detection solution from light green to orange-red. Under optimized conditions, the detection limit for β-gal is 128 pM, which is lower than the conventional colorimetric assay. Additionally, the assay has a broader dynamic range for β-gal detection. The specificity of this assay for the detection of β-gal is demonstrated against several protein competitors. Additionally, this technique is successfully applied to detect E. coli bacteria cells in combination with bacteriophage infection. Due to the simplicity and short incubation time of this enzyme-induced metallization colorimetric method, the assay is well suited for the detection of bacteria in low-resource settings.

Fabrication of potato-like silver molybdate microstructures for photocatalytic degradation of chronic toxicity ciprofloxacin and highly selective electrochemical detection of H 2 O 2

Abstract: In the present work, potato-like silver molybdate (Ag2MoO4) microstructures were synthesized through a simple hydrothermal method. The microstructures of Ag2MoO4 were characterized by various analytical and spectroscopic techniques such as XRD, FTIR, Raman, SEM, EDX and XPS. Interestingly, the as-prepared Ag2MoO4 showed excellent photocatalytic and electrocatalytic activity for the degradation of ciprofloxacin (CIP) and electrochemical detection of hydrogen peroxide (H2O2), respectively. The ultraviolet-visible (UV-Vis) spectroscopy results revealed that the potato-like Ag2MoO4 microstructures could offer a high photocatalytic activity towards the degradation of CIP under UV-light illumination, leads to rapid degradation within 40 min with a degradation rate of above 98%. In addition, the cyclic voltammetry (CV) and amperometry studies were realized that the electrochemical performance of Ag2MoO4 modified electrode toward H2O2 detection. Our H2O2 sensor shows a wide linear range and lower detection limit of 0.04–240 μM and 0.03 μM, respectively. The Ag2MoO4 modified electrode exhibits a high selectivity towards the detection of H2O2 in the presence of different biological interferences. These results suggested that the development of potato-like Ag2MoO4 microstructure could be an efficient photocatalyst as well as electrocatalyst in the potential application of environmental, biomedical and pharmaceutical samples.

Fluorescence Determination of Nitrite in Water Using Prawn-Shell Derived Nitrogen-Doped Carbon Nanodots as Fluorophores

Abstract: In this work, we report the synthesis of nitrogen (N)-doped carbon nanodots (N-CNDs) with an N doping level of 3.6 at. % by hydrothermal treatment of prawn shell and their application as fluorophores for selective and sensitive fluorescence detection of NO2– in water. The results demonstrate that NO2– detection by directly fluorescent quenching at N-CNDs fluorophores can achieve an analytical detection linear range up to 1.0 mM with a detection limit of 1.0 μM. The obtained detection limit of NO2– using N-CNDs fluorophores is dramatically lower than the maximum limit value of 3.0 mg L–1 (namely, 65 μM) for NO2– in drinking water ruled by the World Health Organization (WHO), which is very important for a practical application of the developed analytical method. The interference experiments indicate that only I– ions among all common anions and cations investigated show very adverse influence on selective detection of NO2– by this developed N-CNDs based fluorescent determination method. Further, the fluores...

A novel glucose sensor based on immobilization of glucose oxidase on the chitosan-coated Fe3O4 nanoparticles and the luminol–H2O2–gold nanoparticle chemiluminescence detection system

Abstract: A novel and efficient glucose biosensor based on the chemiluminescence (CL) detection of enzymatically generated H2O2 was constructed by the effective immobilization of glucose oxidase (GOX) on the Fe3O4–chitosan (Fe3O4–CS) nanoparticles support. The covalent immobilization of enzyme was performed using glutheraldehyde (GA) as a cross-linking agent. (H2O2 was constructed by one covalent immobilization of glucose oxidase in glutaraldehyde-functionalized glass cell). In addition to catalyzes the luminol CL reaction, gold NPs offer excellent catalytic activity toward hydrogen peroxide generation as a result of enzymatic reaction between glucose oxidase and glucose. Based on response surface methodology (RSM), the optimal immobilization conditions for glucose oxidase were obtained as: enzyme to support ratio, 0.7; Immobilization pH, 6; cross-linking time, 75 min; and glutaraldehyde (GA) concentration, 0.2%. The characterization of Fe3O4, Fe3O4–chitosan and Au nanoparticles was analyzed by XRD, FT-IR and SEM. The linear range of this novel method is 1 × 10−4 to 8.5 × 10−7 mol L−1 (R2 = 0.9956). The detection limit is 4.3 × 10−7 mol L−1. The relative standard deviation (RSD)

High sensitivity and specificity simultaneous determination of lead, cadmium and copper using μPAD with dual electrochemical and colorimetric detection

Abstract: A bismuth-modified electrode can increase the sensitivity of lead and cadmium detection. However, use of a bismuth-modified electrode in the detection of copper remains limited because the bismuth signal overlaps with the signal for copper. In this study, we developed a new microfluidic paper-based analytical device (μPAD) coupled with dual electrochemical and colorimetric detection to obtain high sensitivity and specificity for the simultaneous determination of lead, cadmium and copper. The μPAD is divided into two parts. The first part is electrochemical detection for the determination of lead and cadmium using a bismuth-modified, boron-doped diamond electrode (Bi-BDDE). The limit of detection was 0.1 ng mL−1 (for both metals). The second part is colorimetric detection for the determination of copper based on the catalytic etching of silver nanoplates (AgNPls) by thiosulfate (S2O32−). The color of AgNPls on μPAD changed from pinkish violet to colorless after the addition of copper; this change can be monitored by naked eyes and its detection limit was5.0 ng mL−1 by the Image J analysis. The proposed method was applied for the simultaneous determination of these three metals in real samples and no significant differences in accuracy and precision were observed compared to the standard method.

An eco-friendly molecularly imprinted fluorescence composite material based on carbon dots for fluorescent detection of 4-nitrophenol

Abstract: We on report an eco-friendly molecularly imprinted material based on carbon dots (C-dots) via a facile and efficient sol–gel polymerization for selective fluorescence detection of 4-nitrophenol (4-NP). The amino-modified C-dots were firstly synthesized by a hydrothermal process using citric acid as the carbon source and poly(ethyleneimine) as the surface modifier, and then after a sol–gel molecular imprinting process, the molecularly imprinted fluorescence material was obtained. The material (MIP-C-dots) showed strong fluorescence from C-dots and high selectivity due to the presence of a molecular imprint. After the detection conditions were optimized, the relative fluorescence intensity (F0/F) of MIP-C-dots presented a good linearity with 4-NP concentrations in the linear range of 0.2 − 50 μmol L-1 with a detection limit (3σ/k) of 0.06 μmol L-1. In addition, the correlation coefficient was 0.9978 and the imprinting factor was 2.76. The method was applicable to the determination of trace 4-NP in Yangtze River water samples and good recoveries from 92.6–107.3 % were obtained. The present study provides a general strategy to fabricate materials based on C-dots with good fluorescence property for selective fluorescence detection of organic pollutants.

Electrochemical Detection of Trace Arsenic(III) by Nanocomposite of Nanorod-Like α-MnO2 Decorated with ∼5 nm Au Nanoparticles: Considering the Change of Arsenic Speciation.

Abstract: It has been reported that the majority of groundwater shows weak alkaline in which the As(III) species would be present as neutral H3AsO3 species and ionized H2AsO3- species. However, as most reported previously, electrochemical detection of As(III) has been operated under acidic conditions and the nonionic As(III) (H3AsO3) is the dominant species. Therefore, considering the change of As(III) speciation in different pH conditions, to develop a reliable method for the detection of As(III) in alkaline media might be more meaningful for practical applications. Here, combined the multilayer adsorption of nanorod-like α-MnO2 with the excellent electrocatalytic ability of ∼5 nm Au nanoparticles (AuNPs), an efficient and ultrahigh anti-interference electrochemical detection of As(III) with AuNPs/α-MnO2 nanocomposite in alkaline media (nearly real water environment) was developed. Notably, we have provided a thorough electrochemical analytical investigation to confirm the advantage of As(III) detection in alkaline media. The system was evaluated by a series of interference tests, and no obvious interference from commonly coexisting substances (referring to the groundwater, Togtoh region, Inner Mongolia, China) was observed in alkaline media. Furthermore, electrodes robust stability and excellent reproducibility were obtained. Under the optimized conditions, the limit of detection (3σ method) toward As(III) was 0.019 ppb, and the obtained sensitivity was 16.268 ± 0.242 μA ppb-1 cm-2. Finally, the proposed method has been successfully employed for detection of As(III) in a real water sample.

Fe3O4 and MnO2 assembled on halloysite nanotubes: A highly efficient solid-phase extractant for electrochemical detection of mercury(II) ions

Abstract: In this study, a novel and simple magnetic electrochemical sensing protocol for the sensitive detection of Hg(II) in aqueous media was demonstrated. For this purpose, the halloysite nanotubes-iron oxide–manganese oxide nanocomposite (HNTs-Fe 3 O 4 –MnO 2 ) was successfully synthesized for the first time. The synthesis process involves the deposition of Fe 3 O 4 nanoparticles on the surface of HNTs using a simple chemical precipitation method, subsequent formation of wire-like MnO 2 nanoparticles on the surface of HNTs-Fe 3 O 4 composites by hydrothermal method with potassium permanganate (KMnO 4 ) and ammonium persulfate ((NH 4 ) 2 S 2 O 8 ). The resulting HNTs-Fe 3 O 4 –MnO 2 nanocomposite was suspended in mercury solution and then brought on the surface of a magnetic carbon paste electrode (MCPE). The amount of analyte was detected electrochemically by applying differential pulse voltammetry (DPV). The conditions of extraction and voltammetric determination were studied and optimized. The proposed method exhibited a linear relationship towards Hg(II) concentrations ranging from 0.5 to 150 μg L −1 . The detection limit achieved was 0.2 μg L −1 (3 S b / m ), which is lower than the US Environmental Protection Agency (EPA) standard (2 μg L −1 for drinkable water). The proposed methodology was applied for quantification of Hg(II) in real water samples and good recoveries were obtained from 96.0 to 102.7%.