Sensitivity Enhancement Factor Research Articles

Enrichment and Separation of Cationic, Neutral, and Chiral Analytes by Micelle to Cyclodextrin Stacking-Micellar Electrokinetic Chromatography.

Analyte focusing by micelle to cyclodextrin stacking (MCDS) in micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS) and fused silica capillaries is demonstrated for neutral, cationic, and chiral analytes. The stacking was at a dynamic boundary formed between the injected charged SDS micelles and neutral γ-cyclodextrin (γ-CD) zones, where the analytes bound inside micelles were released due to the formation of stable SDS-CD inclusion complexes. The complex formation reduced or eliminated the affinity of the analytes to the micellar phase. There was reversal (for charged) or nulling (for neutrals) of the analyte's effective electrophoretic mobility that caused the analytes to accumulate at the boundary. Under the conditions where the SDS micelles velocity is faster than the electroosmotic flow (using acidic buffer), MCDS was conducted by injection of a long plug of sample in a micellar diluent after injection of a CD solution plug into a capillary that was filled with MEKC background solution. By simply extending the length of the CD plug, chiral separations of chlorpheniramine and phenoxyacid herbicides were achieved without optimizing the MEKC conditions. The analytical figures of merit including linearity and repeatability for the tested compounds were found acceptable, and the sensitivity enhancement factors were up to 171. The stacking strategy in MEKC was applied to metabolic stability studies of small molecules with HepG2 cell line, where the samples were only treated with acetonitrile and then diluted with the micellar diluent (demonstrating the reduction of tedious sample preparation requirements for biological samples prior to chemical analysis).

Rapid quantification of quinine by multi-stacking in a portable microchip electrophoresis system.

A new multi-stacking pre-concentration procedure based on field-enhanced sample injection (FESI), field-amplified sample stacking, and transient isotachophoresis was developed and implemented in a compact microchip electrophoresis (MCE) with a double T-junction glass chip, coupled with an on-chip capacitively coupled contactless conductivity detection (C4 D) system. A mixture of the cationic target analyte and the terminating electrolyte (TE) from the two sample reservoirs was injected under FESI conditions within the two sample-loading channels. At the double T-junction, the stacked analyte zones were further concentrated under field-amplified stacking conditions and then subsequently focused by transient-isotachophoresis and separated along the separation channels. The proposed multi-stacking strategy was verified under a Universal Serial Bus (USB) fluorescence microscope employing Rhodamine 6G as the model analyte. This developed approach was subsequently used to monitor the target quinine present in human plasma samples. The total analysis time for quinine was approximately 200s with a sensitivity enhancement factor of approximately 61 when compared to the typical gated injection. The detection and quantification limits of the developed approach for quinine were 3.0μg/mL and 10μg/mL, respectively, with intraday and interday repeatability (%RSDs, n = 5) of 3.6 and 4.4%. Recoveries in spiked human plasma were 98.1-99.8%.

Enhanced sensitivity in THz plasmonic sensors with silver nanowires

We developed hybrid slot antenna structures for microbial sensing in the THz frequency range, where silver nanowires (AgNWs) were employed to increase the sensitivity. In order to fabricate the hybrid devices, we partially etched the AgNW in the slot antenna region, where we can expect the field enhancement effect at the AgNW tip. We measured the resonant-frequency shift observed upon the deposition of a polymer layer, and observed that the sensitivity increased upon the introduction of AgNWs, with an enhancement factor of more than four times (approximately six times in terms of figure-of-merit). The sensitivity increased with the AgNW density until saturation. In addition, we tested devices with PRD1 viruses, and obtained an enhancement factor of 3.4 for a slot antenna width of 3 μm. Furthermore, we performed finite-difference time-domain simulations, which confirmed the experimental results. The sensitivity enhancement factor decreased with the decrease of the slot width, consistent with the experimental findings. Two-dimensional mapping of the electric field confirmed the strong field localization and enhancement at the AgNW tips.

Enhancing the sensitivity of a single electron spin sensor by multi-frequency control

The negatively charged nitrogen vacancy (NV) center in diamond is increasingly attractive as a solid-state quantum sensor with high sensitivity and spatial resolution. However, the host non-zero nitrogen nuclear spin of the NV center decreases the signal contrast and sensitivity because of hyperfine coupling. Here, we apply multi-frequency synchronous manipulation to the NV center to recover the signal contrast and enhance the sensitivity. The enhancement effect works over a wide range of bias magnetic fields. Compared to the single-frequency-driven sensing process, a sensitivity enhancement factor of 2.7 is achieved at a low bias magnetic field. Such multi-frequency-controlled sensitivity enhancement works also for sensing temperature, strain, and electric field and can be applied to other spin–spin coupling systems.

Zinc oxide, gold and graphene-based surface plasmon resonance (SPR) biosensor for detection of pseudomonas like bacteria: A comparative study

In the present paper, we have studied the better performance of zinc oxide (ZnO), gold (Au) and graphene-based SPR biosensor for the detection of pseudomonas and pseudomonas like bacteria. The performance of proposed SPR biosensor is based on theoretical analysis of the sensitivity, detection accuracy, quality parameter and electric field intensity enhancement factor (EFIEF) with angular interrogation method. In this biosensor, prism (BK-7 glass) base is coated with ZnO followed by Au, graphene and different affinity layers, water is used as sensing medium. The advantage of the present biosensor is the hybrid structure of graphene, gold and ZnO with enhanced sensitivity in which the molecular recognition sites on graphene bind strongly the pseudomonas like bacteria with the help of affinity layers. ZnO is responsible for the larger shift in resonance angle that leads a significant enhancement in the sensitivity of the present biosensor. On analyzing the results, we have found that the proposed biosensor has a greater sensitivity of 187.43 deg/RIU, detection accuracy of 2.05 deg-1 and quality parameter of 29.33 RIU-1 as compared to the other reported conventional SPR biosensor for the detection of pseudomonas like bacteria.

A study of surface plasmon resonance (SPR) based biosensor with improved sensitivity

In the present study, surface plasmon resonance (SPR) based biosensor with SF-10 glass prism/zinc oxide/gold/MoS2/graphene hybrid structure is reported. The angular interrogation method is used for the reflectance spectra analysis. From the spectral analysis, we study the different performance parameters like sensitivity, detection accuracy, quality parameter and electric field intensity enhancement factor (EFIEF) of the proposed SPR based biosensor. Numerical results show that the base ZnO (zinc oxide) layer which have a large real value of the dielectric constant in combination with gold, MoS2 and graphene, is responsible for enhancing the sensing performance of the proposed SPR based biosensor. The present biosensor can attain a maximum sensitivity (101.58 deg/RIU), detection accuracy (1.81) and quality parameter (15.11 RIU-1) for a large dynamic range of refractive index change from 1.33 to 1.45.

Preconcentration and Determination of Trace Nickel and Cobalt in Milk-Based Samples by Ultrasound-Assisted Cloud Point Extraction Coupled with Flame Atomic Absorption Spectrometry.

In this study, ultrasound-assisted cloud point extraction (UA-CPE) method was developed for the determination of Ni(II) and Co(II) in milk-based products. After extraction and preconcentration, the Ni(II) and Co(II) contents of samples were determined by flame atomic absorption spectrometry (FAAS). After their complexation with hydroxy naphthol blue (HNB) in the presence of cationic surfactant, CTAB at pH 4.0, the Ni(II) and Co(II) were taken within the micellar phase of nonionic surfactant, TX-114. The micellar phase containing the analytes were diluted to a volume of 0.7mL with 1.0-mol/L HNO3 in ethanol to reduce its viscosity and to facilitate sample treatment and then was analyzed by FAAS. The various analytical parameters affecting UA-CPE efficiency were investigated. The analytical features obtained after optimization are as follows: limits of detection are 0.56 and 0.78μg/L; sensitivity enhancement factors are 48.6 and 53.9; the calibration curves were linear 3-180 and 2-160μg/L for Co(II) and Ni(II), respectively, after preconcentration of 50-fold. The precision (as RSD%) between 1.8-3.6% and 2.2-3.8% (25 and 100μg/L, n = 5) for Ni(II) and Co(II), respectively. The accuracy was statistically verified by analysis of two certified reference material samples (CRMs), including recovery studies after spiking. The method was applied to the analysis of milk-based samples with satisfied results.

Probing Electrode-Electrolyte Interfaces Using Nano-Gap Surface-Enhanced Raman Spectroscopy and Imaging

Performance of portable electronic devices and electric vehicles is currently limited by the energy density, lifetime and safety of lithium rechargeable batteries. Overcoming those limitations requires in-depth understanding of the electrode-electrolyte interfaces. Surface-enhanced Raman spectroscopy (SERS) can provide a critical component to this effort as an in situ technique with ultrahigh surface sensitivity that provides quantitative molecular specificity. SERS relies on local electromagnetic field amplification generated by surface plasmon resonance (SPR) at the surface of metal nanoparticles (NPs) with sub-wavelength dimensions. The most significant Raman enhancements have been observed when the local SPRs of multiple NPs interact. This occurs when the NPs are in close proximity (less than 10 nm), which could be achieved in ordered NP monolayers if they could be assembled reproducibly. Methods to assemble gold NPs into large area (cm2) monolayers will be presented. The interparticle gap can be tuned between 1 and 4 nm by using surface ligands of different sizes. The Au NP monolayers exhibit high SERS sensitivity (enhancement factor greater than 107). This allows for the measurement of electrolyte components across a broad range of concentrations. Components include lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), ethylene carbonate (EC) and diethyl carbonate (DEC). The investigation of solutions of LiPF6 in EC + DEC binary solvents using SERS allows for the determination of the solvent coordination numbers, which range from 2 to 5. This result is in sharp contrast to the bulk values calculated from infrared spectroscopy, which range from 3 to 7. Numerical simulations show that the electromagnetic field is concentrated in the nanogap, indicating the information of the aprotic electrolyte solution structures is obtained from the immediately adjacent area of the solid substrate. Our findings facilitate a better understanding of the structure of solvated ions in close proximity to the electrode surface. Acknowledgment This work is funded by Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy. R.L. Sacci is supported by Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. Confocal Raman microscopy experiments were conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Preconcentration and Determination of Trace Vanadium(V) in Beverages by Combination of Ultrasound Assisted-cloud Point Extraction with Spectrophotometry

A novel ultrasound assisted-cloud point extraction method was developed for preconcentration and determination of V(V) in beverage samples. After complexation by pyrogallol in presence of safranin T at pH 6.0, V(V) ions as ternary complex are extracted into the micellar phase of Triton X-114. The complex was monitored at 533 nm by spectrophotometry. The matrix effect on the recovery of V(V) from the spiked samples at 50 μg L-1 was evaluated. In optimized conditions, the limits of detection and quantification of the method, respectively, was 0.58 and 1.93 μg L-1 in linear range of 2-500 μg L-1 with sensitivity enhancement and preconcentration factors of 47.7 and 40 for preconcentration from 15 mL of sample solution. The recoveries from spiked samples were in range of 93.8-103.2% with a relative standard deviation ranging from 2.6% to 4.1% (25, 100 and 250 μg L-1, n: 5). The accuracy was verified by analysis of two certified samples, and the results were in a good agreement with the certified values. The intra-day and inter-day precision were tested by reproducibility (as 3.3-3.4%) and repeatability (as 3.4-4.1%) analysis for five replicate measurements of V(V) in quality control samples spiked with 5, 10 and 15 μg L-1. Trace V(V) contents of the selected beverage samples by the developed method were successfully determined.

Simple and fast spectrophotometric determination of low levels of thiabendazole residues in fruit and vegetables after pre-concentration with ionic liquid phase microextraction

ABSTRACTThere is a great importance of monitoring thiabendazole (TBZ) residues in fruits and vegetables to ensure food safety. Therefore, a new ionic liquid (IL) phase microextraction method using IL, 1-butyl-3-methylimidazoliumhexafluorophosphate [C4mim][PF6], as extracting solvent is proposed for simple and fast determination of low levels of TBZ in fruits and vegetables by spectrophotometry. The method is based on selective complex formation of TBZ with Cu(II) ions in presence of PF6– as counter ion at pH 5.5, and then microextraction of the complex into the fine micro-drops of IL phase. After optimisation of variables affecting microextraction efficiency, the analytical parameters of the method were determined by calibration curves. The method exhibits a linear relationship (0.3–280 μg L−1), low detection limit (0.1 μg L−1), good intra- and inter-day precision (2.4–4.5% as RSDr%, 2.1–5.6% as RSDR%), good recovery (≥95.1–98.2%) and high sensitivity enhancement factor (150) by solvent-based calibration curve. It allows a detection limit of 0.24 μg L−1 and a range of 0.8–250 μg L−1 by the matrix-matched calibration curve. After validation, the method was successfully applied to the determination of TBZ residues with method quantification limits in fruit and vegetables of 2.0 and 2.5 µg kg−1 with and without adding polyvinylpyrrolidone (PVP-15) solution. Recoveries range from 85.5% to 98.2% after spiking (10, 50 and 100 µg kg−1, n: 3).

Cyclodextrin-assisted dispersive liquid-liquid microextraction for the preconcentration of carbamazepine and clobazam with subsequent sweeping micellar electrokinetic chromatography.

A new version of dispersive liquid-liquid microextraction, namely, cyclodextrin-assisted dispersive liquid-liquid microextraction, with subsequent sweeping micellar electrokinetic chromatography has been developed for the preconcentration and sensitive detection of carbamazepine and clobazam. α-Cyclodextrin and chloroform were used as the dispersive agent and extraction solvent, respectively. After the extraction, carbamazepine and clobazam were analyzed using micellar electrokinetic chromatography with ultraviolet detection. The detection sensitivity was further enhanced using the sweeping technique. Under optimal extraction and stacking conditions, the calibration curves of carbamazepine and clobazam were linear over a concentration range of 2.0-200.0ng/mL. The method detection limits at a signal-to-noise ratio of 3 were 0.6 and 0.5ng/mL with sensitivity enhancement factors of 3575 and 4675 for carbamazepine and clobazam, respectively. This developed method demonstrated high sensitivity enhancement factors and was successfully applied to the determination of carbamazepine and clobazam in human urine samples. The precision and accuracy for urine samples were less than 4.2 and 6.9%, respectively.

A new method of UA_CPE coupled with spectrophotometry for the faster and cost-effective detection of proline in fruit juice, honey, and wine

The study developed a new method for proline detection in honey, wine and fruit juice using ultrasound assisted-cloud point extraction (UA-CPE) and spectrophotometry. Initially, a quaternary complex was built, containing proline, histamine, Cu(II), and fluorescein at pH 5.5. Samples were treated with ethanol–water mixture before extraction and preconcentration, using an ultrasonic bath for 10 min at 40 °C (40 kHz, 300 W). After the optimization of variables affecting extraction efficiency, good linearity was obtained between 15 and 600 µg L−1 with sensitivity enhancement factor of 105. The limits of detection and quantification were 5.7 and 19.0 µg L−1, respectively. The recovery percentage and relative standard deviations (RSD %) were between 95.3 and 103.3%, and 2.5 and 4.2%, respectively. The accuracy of the method was verified by the analysis of a standard reference material (SRM 2389a).

Analysis of the performance of strain magnification using uniform rectangular cantilever beam with fiber Bragg gratings

A thorough analysis of the performance of different strain magnification structures with fiber Bragg gratings (FBG) is demonstrated in this paper. Four kinds of cantilever beams with different shapes have been designed by using a laser cutting technique. Simulation results show that the strain magnification structures of the different cantilever beams are different. There is a positive and linear correlation between the displacement of the free end of the cantilever beam and the average strain at the pasting position of the FBG. The correlation is used to calculate the displacement sensitivity and analyze the efficacy of the different strain magnification structures. Sensitivity enhancement factors (compared to a reference beam) of 2.67, 2.14 and 2.57 were measured experimentally for the different beam shapes studied, while the theoretical prediction factors were 2.67, 2.24 and 2.55, respectively. There is a reasonable agreement between simulation and experiment, which shows that the efficacy is related to the increasing rate of the average strain over the FBG length. The proposed method can be used to enhance the sensitivity of the FBG sensor and further improve the sensor structure design.

Determination of tetracyclines in human urine samples by capillary electrophoresis in combination with field amplified sample injection.

A sensitive method using CZE-UV detection has been developed for the determination of five tetracycline antibiotics in human urine samples. To improve the sensitivity of the method, an on-line preconcentration strategy, named field-amplified sample injection, has been developed, based on the electrokinetic injection of the sample, which requires only a 1:100 dilution with sample solvent before injection. Under optimum conditions, sensitivity enhancement factors ranged from 450 to 800 for the studied compounds. The applicability of the proposed method was demonstrated by the determination of these antibiotics in spiked urine samples. The limits of quantification were lower than 0.8mg/L and the precision (intra- and inter-day), expressed as %RSD was below 14%. Recoveries ranged from 92.1 to 96.7%. Thus, the proposed procedure is a simple, fast and efficient strategy which could be used as therapeutic drug monitoring in human urine samples.

Simple and Rapid Dual-Dispersive Liquid-Liquid Microextraction as an Innovative Extraction Method for Uranium in Real Water Samples Prior to the Determination of Uranium by a Spectrophotometric Technique.

An innovative, rapid, and simple dual-dispersive liquid-liquid microextraction (DDLL-ME) approach was used to extract uranium from real samples for the first time. The main objective of this study was to disperse extraction solvent by using an air-agitated syringe system to overcome matrix effects and avoid dispersion of hazardous dispersive organic solvents by using heat. The DDLL-ME method consisted of two dispersive liquid-liquid extraction steps with chloroform as the extracting solvent. Uranium formed complexes with 4-(2-thiazolylazo) resorcinol in the aqueous phase and was extracted in extracting solvent (chloroform) after the first dispersive liquid-liquid process. Uranium was then back-extracted in the acidic aqueous phase in a second dispersive liquid-liquid process. Finally, uranium was determined by a spectrophotometric detection technique. The variables that played a key role in the proposed method were studied and optimized. The LOD and sensitivity enhancement factor for uranium were found to be 0.60 µg/L and 45, respectively, under optimized conditions. Calibration graphs were found to be linear in the range of 5.0-600 µg/L. The RSD was 2.5%. Reliability of the proposed method was verified by analyzing certified reference material TM-28.3.

Extraction and reliable determination of acrylamide from thermally processed foods using ionic liquid-based ultrasound-assisted selective microextraction combined with spectrophotometry

ABSTRACTAcrylamide (AAm) is a carcinogenic chemical that can form in thermally processed foods by the Maillard reaction of glucose with asparagine. AAm can easily be formed especially in frequently consumed chips and cereal-based foods depending on processing conditions. Considering these properties of AAm, a new, simple and green method is proposed for the extraction of AAm from thermally processed food samples. In this study, an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim][BF4]) as extractant was used in the presence of a cationic phenazine group dye, 3,7-diamino-5-phenylphenazinium chloride (PSH+, phenosafranine) at pH 7.5 for the extraction of AAm as an ion-pair complex from selected samples. Under optimum conditions, the analytical features obtained for the proposed method were as follows; linear working range, the limits of detection (LOD, 3Sb/m) and quantification (LOQ, 10Sb/m), preconcentration factor, sensitivity enhancement factor, sample volume and recovery% were 2.2–350 µg kg−1, 0.7 µg kg−1, 2.3 µg kg−1, 120, 95, 60 mL and 94.1–102.7%, respectively. The validity of the method was tested by analysis of two certified reference materials (CRMs) and intra-day and inter-day precision studies. Finally, the method was successfully applied to the determination of AAm levels in thermally processed foods using the standard addition method.

Microextraction and preconcentration of Mn and Cd from vegetables, grains and nuts prior to their determination by flame atomic absorption spectrometry using room temperature ionic liquid

In this paper, a new and eco-friendly vortex-assisted dispersive liquid–liquid microextraction (VA-DLLME) procedure based on application of the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium chloride, [C4mim][Cl], followed by flame atomic absorption spectrometry (FAAS) was introduced for preconcentration and determination of trace amounts of Mn and Cd from vegetables, grains and nuts samples. The Mn(II) and Cd(II) ions were complexed with 1,3-dihydroxybenzene (Resorcinol) in presence of methanol containing the RTIL acting as both an extractant and auxiliary ligand at pH4.0 separately, and then extracted by IL at room temperature using a vortex mixer. Some important parameters affecting performance of the microextraction including pH, amount of IL and chelating ligand, volume of dispersive solvent, vortex time and rate, as well as effects of interfering species were optimized by univariate analysis. At optimized conditions, the limits of detection (defined as 3Sb/m) and sensitivity enhancement factors for Mn and Cd were determined as 0.15μgL−1, 0.25μgL−1, 150 and 110, respectively, with relative standard deviations (RSDs) <2.5%. The accuracy and precision were controlled and confirmed by analysis of certified reference materials (CRMs) using standard addition method. Lastly, the method was successfully applied to the determination of Mn and Cd in acid digested samples.

Transient NOE enhancement in solid-state MAS NMR of mobile systems

It has been known that the heteronuclear cross-relaxation affects the dilute S spin magnetization along the longitudinal direction, causing an overshoot phenomenon for those mobile systems in spin-lattice relaxation rate measurements. Here, we analyze the Solomon equations for an I-S system and derive the transient cross relaxation effect as to when an overshoot phenomenon would take place and what the maximum enhancement could be at the time of the overshoot. In order to utilize such a transient nuclear Overhauser effect (NOE), we first time apply it to dynamic solid samples by inverting the 1H magnetization prior to the excitation of the S spin. It is found that the overshoot depends on the ratio of the I and S spin-lattice relaxation rates, i.e. RSS/RII. When RSS/RII≫1, the maximum enhancement factor for transient NOE could be larger than that obtained in steady-state NOE experiments. Furthermore, transient NOE appears to be more efficient in terms of sensitivity enhancement of dilute spins in solid-state NMR of mobile systems than the traditional cross polarization scheme whose efficiency is greatly compromised by molecular mobility. A sample of natural abundance l-isoleucine amino acid, in which the spin-lattice relaxation rates for the four methyl carbons are different, has been used to demonstrate sensitivity enhancement factors under various experimental schemes.

Graphene Based Nano Bio-sensor: Sensitivity Improvement

n this paper we attempt to present a multilayered structure biosensor. A graphene-based surface plasmon resonance (SPR) biosensor is considered as a structure which offers the enhancement of sensitivity in comparison with the conventional biosensors. The sensitivity improvement caused by the presence of graphene is discussed through monitoring of the biomolecular interactions and following that the refractive index (RI) changes. For this purpose, a RI change which is increased during the course of biomolecular interactions is considered from 1.462 to 1.52. Our numerical results show that the proposed SPR biosensor with a graphene layer can provide a better sensitivity due to the field distribution at the binding region. This paper investigates the sensitivity enhancement factor (SEF) according to the S-parameters and the effects of design parameters such as the thicknesses of gold and graphene layers and the refractive index change during the course of DNA hybridization in this biosensor.

Ionic liquid based ion-pairing microextraction combined with spectrophotometry for preconcentration and quantitation of melamine in milk and milk-based products

A simple, rapid and economical ultrasound-assisted microextraction (UA-ME) procedure was developed for extraction and determination of trace amounts of melamine in milk products, followed at 310 nm by UV-Visible spectrophotometry. In the study, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C6mim][Tf2N] as ionic liquid (IL) was used in presence of sodium dodecyl sulfate (SDS) as an oppositely charged auxiliary ligand at pH 4.0 for extraction of melamine, and methanol was selected as a disperser solvent. Under the optimal conditions, the analytical features of method were established by calibration curves prepared from both solvent based calibration and matrix-matched calibration solutions. The method exhibits a linear relationship (from 5 to 250 μg L−1), low detection limit (1.6 μg L−1), good recovery (93.5–97.8%), and high sensitivity enhancement factor (125) by solvent based calibration curve while it allows a detection limit of 2.1 μg L−1 in range of 5–210 μg L−1 by the matrix-matched calibration curve. The method accuracy (trueness and precision) was checked by applying matrix-matched calibration strategy to all the spiked samples including quality control samples as well as comparison with an independent micellar LC method, and then it was successfully applied to the determination of melamine in milk based products.