Amperometric Detection System Research Articles

Deep eutectic solvents combined with beta-cyclodextrin derivatives for chiral separation of typical adrenergic receptor agonists by capillary electrophoresis with amperometric detection

Enantioseparation has always been one of the research hotspots and difficulties in the field of modern separation science. In this work, a binary chiral electrophoretic separation system was constructed using deep eutectic solvents (DESs) coupled with beta-cyclodextrin derivatives based on capillary electrophoresis with amperometric detection system, and five groups of typical adrenergic receptor agonists (adrenaline, salbutamol, isoproterenol, norepinephrine and terbutaline) were selected as the model enantiomers. The effects of additive types and contents of DESs and cyclodextrins, and the pH value and concentration of the running buffer on the resolution of the selected chiral compounds were investigated in detail. The mechanism of DESs improving separation was explored preliminarily by means of UV spectrophotometry, which was further verified based on the comparison of single and mixed components of choline chlorine-urea DES. Under the optimum conditions, the relative standard deviations for inter-day and intra-day repeatability of the migration time, peak area and resolution for adrenaline and salbutamol were within 8.7%, and the limits of detection reached 0.030 μg mL−1 (S/N = 3). The recovery data were in the range of 96.3–118.7%. The developed methods have been applied for the analyses of (+)-adrenaline hydrochloride injection and (±)-salbutamol aerosol. This binary chiral electrophoretic separation system by CE-AD has high detection sensitivity and low analytical cost, providing an alternative for the separation and analysis of chiral drugs.

Amperometric Detection of NH3 by Aromatic SAM-Modified Graphene

Ammonia (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) is a toxic substance resulting in various acute and chronic effects on individuals. NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> detection, monitoring methods, and detection tools are desperately needed. In this work, we improved the ammonia sensing capabilities of graphene films deposited by chemical vapor deposition (CVD) by modifying aromatic self-assembled monolayer (SAM) molecules such as 5-[(3-methylphenyl) (phenyl) amino] isophthalic acid (MeIPA) and 5-(diphenyl)amino] isophthalic acid (PhIPA) on amperometric detection method. Morphological investigations of the films were carried out by optical and scanning electron microscopy (SEM). Surface potential was characterized with Kelvin Probe Force Microscopy (KPFM), and vibrational properties were characterized with Raman Spectroscopy. MeIPA modification increased NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> uptake by two times compared to unmodified graphene. The results indicated that the SAM modification enhanced NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> molecule adsorption and improved its periodic reversible and reproducible response using the amperometric detection system, indicating that SAM molecules might be a feasible probe for ammonia.

Evaluation of homochiral zeolitic imidazolate framework-8 supported open-tubular column by miniaturized capillary electrochromatography with amperometric detection.

A novel kind of chiral open-tubular (OT) column was established with homochiral zeolitic imidazolate framework-8 nanomaterials using L-histidine as the chiral carbon center (L-His-ZIF-8). The morphologies of L-His-ZIF-8 nanoparticles and chiral OT column were characterized by scanning electron microscopy. The effects of L-His-ZIF-8 concentrations, pH values, and concentrations of the running buffer on the resolution of the selected chiral compounds were investigated based on miniaturized capillary electrochromatography with amperometric detection system (mini-CEC-AD), respectively. The separation performances of the prepared L-His-ZIF-8@OT chiral columns were explored under the optimal conditions, and the RSDs of run-to-run, day-to-day, and column-to-column reproducibility were less than 6.7% using salbutamol raceme as the model enantiomers. The prepared chiral OT columns have been successfully applied to the enantioseparation of one pair of amino acid enantiomers, two pairs of racemic drugs, and three pairs of neurotransmitter enantiomers. Under the optimum conditions, the prepared OT columns were applied to real-world sample analysis of salbutamol aerosol. The limits of detection of salbutamol raceme were 0.90μg·mL-1 (S/N = 3), and the recovery was 80.4-82.7%. The assay results indicated that this kind of chiral OT column modified with homochiral L-His-ZIF-8 possesses good reproducibility and stability. This developed mini-OT-CEC-AD system has some attractive characteristics of sensitivity and low cost, providing a potential way for the separation of chiral compounds.

Screen Printed Carbon Electrodes Sensor for Viral DNA Isothermal Amplification Real-Time Measurement

Recombinase polymerase amplification (RPA) is a gene amplification technology that amplifies template DNA with isothermal(37-42℃) using three core enzymes – a recombinase, a single-stranded DNA-binding protein (SSB) and strand-displacing polymerase. Recently RPA sensors with an electrical analysis function using an electrochemical measurement method have been reported. This RPA technique and electrical measurement method is suitable for low-cost, rapid, miniaturization and POC system development.Amperometric detection is an electrochemical detection method with various advantages that make it suitable biosensors. Amperometric detection system can be easily integrated with the Screen-printed Carbon Electrodes (SPCEs) sensor without the need for complicated additional equipment for optical detection. For this reason, the size of the sensor can be reduced to microchip size, which makes it possible to use point-of-care due to low-cost disposable chips and potable equipment [1]. The optical method which the detection of the fluorescence intensity of the target sample is important. However, amperometric detection omits pretreatment process of the sample such as purification extraction of samples and fluorescent staining for detection [2]. These features allow the device system to be miniaturization and rapid detection for use in lab-on-a-chip or point-of-care applications [3].Modified AuNP SPCEs is proposed for on-chip amperometric detection of RPA isothermal amplification for viral DNA. AuNPs were first electrodeposited on SPCEs. The AuNPs was carried out in 1.0 M NaNO3 solution containing 0.25 mM HAuCl4 using amperometric 0.70V for 10,100 and 500 seconds at the scans of 0.10 V·s−1. After electrodeposition, the AuNPs modified SPCEs were rinsed with water to remove the deposited materials.The surface characterization of this the AuNP-modified SPCEs was shown in Fig. 1(a) using cyclic voltammetry measurement from -0.2V to 0.4V for 3 cycles at the scan rate of 0.10 V·s−1. It was observed that the AuNP was deposited on SPCEs by amplified redox peak.Fig.1. Measurements of the CV of the different printed sensors: (a) Stability of SPCEs; (b) After electrodeposition.

Preparation and evaluation of chiral open-tubular columns supported with zeolite silica nanoparticles and single/dual chiral selectors using capillary electrochromatography with amperometric detection

In this work, novel stationary phase coatings by zeolite SiO2NPs coupled with β-cyclodextrin (β-CD) or β-CD/L-phenylalanine were developed for chiral open-tubular capillary electrochromatography (OT-CEC). The OT columns were prepared taking advantage of the strong adhesion of polydopamine in one-step method. Scanning electron micrography and electroosmotic flow were used to characterize the prepared single/dual-selector OT columns. Chiral separation of four chiral analytes (catechin/epicatechin, ephedrine/pseudoephedrine, ritodrine and salbutamol) was carried out in order to evaluate the performance of the prepared columns in OT-CEC with amperometric detection system. In terms of migration time, peak area, resolution, and selectivity factor of catechin/epicatechin and salbutamol, the run-to-run, day-to-day, and column-to-column repeatability were within 8.9%. Under the optimum conditions, the developed methods were applied for the analyses of Chinese herbal medicine Catechu herbs and salbutamol aerosol samples.

Rapid detection of carbamate pesticide residues using microchip electrophoresis combining amperometric detection

The long-term consumption of food with pesticide residues has harmful effects on human health and the demand for pesticide detection technology tends to be miniaturized and instant. To this end, we demonstrated the first application of indirectly detecting two carbamate pesticides, metolcarb and carbaryl, by gold nanoparticle-modified indium tin oxide electrode in dual-channel microchip electrophoresis and amperometric detection (ME-AD) system. m-Cresol and α-naphthol were obtained after pesticide hydrolysis in alkaline solution, and then separated and detected by ME-AD. Parameters including the detection potential and running buffer concentration and pH were optimized to improve the detection sensitivity and separation efficiency. Under the optimal conditions, the two analytes were completely separated within 80s. m-Cresol and α-naphthol presented a wide linear range from 1 to 100μM, with limits of detection of 0.16μM and 0.34μM, respectively (S/N = 3). Moreover, the reliability of this system was demonstrated by analyzing metolcarb and carbaryl in spiked vegetable samples.

Rapid preparation and evaluation of chiral open-tubular columns supported with bovine serum album and zeolite imidazolate framework-8 for mini-capillary electrochromatography

In this work, a class of novel and eco-friendly open-tubular (OT) chiral column was presented for the first time by one step preparation with zeolite imidazolate framework-8 (ZIF-8) and bovine serum album (BSA) based on electrostatic adsorption and adsorption affinity. This stationary phase materials combined the features of large surface areas and adsorption affinity of ZIF-8, and also the multiple chiral binding sites of BSA, which contributes to the π-interaction and hydrophobic interaction with the analytes. The separation performance of BSA@ZIF-8-OT chiral columns was evaluated with a miniaturized capillary electrochromatography and amperometric detection (mini-CEC-AD) system; in particular, nine groups of model molecules, including homologues, structural isomers, and chiral compounds, were baseline separated under the certain optimum conditions. The RSDs of run-to-run, day-to-day, column-to-column, and batch-to-batch reproducibility were less than 13.8 %. Furthermore, the prepared OT columns were successfully applied to fast analysis of ephedrine isomers in Chinese herb ephedra, and the LODs achieved 1.5-2.0 ng mL−1 (S/N=3) by an electrophoretic stacking technique of moving chemical reaction boundary. This mini-CEC-AD system with BSA@ZIF-8-OT chiral columns provides a promising potential in pharmaceutical analysis due to its fast, sensitive, enantioselective, and low-cost characteristics.

Graphene Oxide Modified Electrode for DNA Amperometric Detection Using Microfluidic Electrophoresis Chip

The amperometric technique of capillary electrophoresis (CE) is an electrochemical detection method with various advantages that is suitable for biosensors. The amperometric detection system can be easily integrated with the CE system without the need for complicated additional equipment for optical detection. For this reason, the size of the sensor can be reduced to micro-scale, also reducing the cost of the fabrication process, enabling this system to be used in point-of-care applications [1]. The optical method depends on the detection of the fluorescence intensity of the target sample. However, amperometric detection omits the pretreatment process of the sample, such as purification extraction of samples and fluorescent staining for detection [2]. These features allow the device system to be miniaturized and having a rapid response for applications like lab-on-a-chip [3]. Modified Au electrodes integrated with PDMS based microfluidic channels were proposed as an on-chip amperometric detection of CE for DNA sensors. The graphene oxide (GO)-modified Au electrodes were fabricated via photolithography process and drop-casting deposition. First, the deposited Au electrodes were patterned with positive photoresist (PR) using the photolithography method. Next, the graphene oxide was deposited 5 layers on the bare Au using drop-casting technique. Finally, the PR was dissolved by acetone and the unwanted GO was lifted-off. The surface characterization of this the GO-modified Au electrodes is shown in Fig. 1(a) by microscopy image. It was observed that the GO was deposited on Au electrodes following the desired pattern. This treatment amplifies the current signal of amperometric detection of the CE microchip. The performance of the CE amperometric detection device has been demonstrated by sensing an amplicon lambda phage DNA. Then, 1 µL of amplified lambda phage DNA (1 ng/µL) using the conventional polymerase chain reaction (PCR) with a 30-cycle reaction was used as target sample. Figure 1(b) shows the current peak of amperometric detection before (1.9 µA) and after (6.6 µA) GO-modified on the Au electrodes which amplified the sensitivity more than 3.5 times before electrode modification. The emphasized detection of lambda phage DNA using modified electrodes gives a further possibility of biomedical applications through our developed microchip.

Salt-effect enhanced hollow-fiber liquid-phase microextraction of glutathione in human saliva followed by miniaturized capillary electrophoresis with amperometric detection.

A hollow-fiber liquid-phase microextraction (HF-LPME) method was established for purification and enrichment of glutathione (GSH) in human saliva followed by a miniaturized capillary electrophoresis with amperometric detection system (mini-CE-AD). Based on regulating isoelectric point and increasing salt effect to modify donor phase, HF-LPME could provide high enrichment efficiency for GSH up to 471 times, and the extract was directly injected for mini-CE-AD analysis. The salt-effect enhanced HF-LPME/mini-CE-AD method has been successfully applied to saliva analysis, and acceptable LOD (0.46ng/mL, S/N = 3) and recoveries (92.7-101.3%) could be obtained in saliva matrix. The sample pretreatment of this developed method was simple and required no derivatization, providing a potential alternative for non-invasive fluid analysis using portable instrument.

Clearing up the oxygen dip in HPAEC–PAD sugar analysis: Sodium sulfite as an oxygen scavenger

A baseline dip caused by the reduction of dissolved oxygen in samples has been a source of trouble in the analysis of major monosaccharides (galactose, glucose, mannose, and fructose) in the high-performance anion-exchange chromatography with pulsed amperometric detection system. This study attempted three different methods to remove the baseline dip from the resulting chromatograms, and among the approaches, sodium sulfite was found to act as the best oxygen scavenger. Clean chromatograms were obtained by adding at least 3 mg/mL sodium sulfite to samples, which removed the baseline dip and improved the accuracy of sugar analysis. Although sodium sulfite does not influence analytical sensitivity, it can cause a reduction of sugar retention; however, retention time can be recovered by washing with 200 mM sodium hydroxide solution. Results demonstrated that sodium sulfite is an effective means either to remove the baseline dip for low concentration analysis under 1 mg/L, or to separate the target sugar from the baseline dip by retention time rearrangement.

Fast Determination of Main Bioamines and Precursor Amino Acids in Beer by Miniaturized Electrophoresis Using Gold Nanoparticle Composite Electrode

A gold nanoparticle/reduced graphene oxide composite electrode (AuNP/rGO) was fabricated for the determination of the main bioamines and their precursor amino acids in beer based on a miniaturized capillary electrophoresis with amperometric detection system (mini-CE-AD). The surface morphology and structure of the synthetic AuNP/rGO material were observed by scanning electron microscope, energy dispersive X-ray spectroscope, X-ray diffraction, and Fourier transform infrared spectroscopy. The analytical performance of the composite electrode was verified by cyclic voltammetry and mini-CE-AD approaches. Four target analytes were separated within 7 min in 50 mM Na2B4O7-NaOH buffer (pH 9.35) at a separation voltage of 3 kV. This developed method has been applied to the beer samples, and acceptable recovery could be obtained ranging from 84.5 to 108%. The assay results indicated that this AuNP/rGO composite electrode has the advantages of simple preparation, low working potential (+ 0.65 V vs. SCE), good sensitivity (0.13~0.87 μM), and satisfactory reproducibility. This proposed method provides an alternative for rapid analysis of food safety.

Low pressure ion pair chromatography with amperometric detection for the determination of trigonelline in coffee samples

In this work, the use of ion pair chromatography strategy in low pressure chromatographic flow systems is explored for the first time. The straightforward flow manifold encompassed a peristaltic pump, an injection valve and a 1 cm-length C18 monolithic column. The amperometric detection system relied on a boron-doped diamond electrode, used as working electrode. The determination of trigonelline in coffee samples was the case-study selected. This alkaloid is an important quality marker for this commodity and is usually determined using HPLC-UV methodologies. The proposed methodology, based on ion-pair chromatography with amperometric detection, enabled the quantitative resolution of the studied analyte from the matrix compounds by adding to the mobile phase the ion pair reagent, 1-tetradecanosulfonate sodium. The present work, following the recent developments of the low pressure chromatography approach, demonstrates the potentialities of coupling monolithic columns to traditional flow analysis systems for separation and quantification of ionic or ionisable compounds.

A Hydrogen Peroxide Biosensor Based on the Immobilization of the Highly Stable Royal Palm Tree Peroxidase (Roystonea regia) with Chitosan and Glutaraldehyde on Screen-printed Graphene Electrodes

This paper present the fabrication and electrochemical stud-ies of a screen-printed graphene electrode (SPGE) modified with Roy-al palm tree peroxidase (RPTP) in combination with chitosan (CS) and cross-linking of glutaraldehyde (GA) for detection of hydrogen perox-ide. Cyclic voltammograms in the presence of potassium ferrocyanide ([Fe(CN)6]3-/4-) as a redox species demonstrated an increasing of 50mA evidenced by the electron transfer process of SPGE modified with CS-GA-RPTP. The graphene modified electrode exhibits excellent electrocatalytic activity to the reduction of H2O2, with a linear response in the 100 mM to 5 mM concentration range and a detection limit of 87 mM. The new sensor based on the modification of graphene electrode with the high stable RPTP will provide a potential amperometric detection system for determination of H2O2 in real samples with some biomedical or environmental importance.

Electroanalytical thread-device for estriol determination using screen-printed carbon electrodes modified with carbon nanotubes

Microflow systems are powerful analytical tools that explore similar principles of typical flow injection analysis driven to in a microfluidic device. Generally, microfluidic devices can promote a low consumption of reagents and samples, high speed of analysis and possibility of portability. Several advances have been reached applying a simple and low cost device based on cotton thread as microfluidic channel where the transportation of solutions is based on capillary force helped by gravity. In the present work, we have demonstrated the versatility of thread-based electroanalytical devices (μTED) constructed using a cotton thread as the solution channel and screen-printed electrodes (SPE) surface modified with carbon nanotubes (CNT) as electrochemical detectors for the amperometric determination of estriol hormone in pharmaceutical samples. The parameters involved in the amperometric detection and microflow system were studied and optimized, using the best experimental conditions (flow rate of 0.50μLs−1, 10mm of analytical path, 2.0μL of volume of injection and potential of detection of 0.75V) a linear response was observed for concentration range (LDR) of 1.0 to 1000μmolL−1 with limits of detection (LOD) and quantification (LOQ) of 0.53μmolL−1 and 1.77μmolL−1, respectively, and frequency of injection of 32 per hour. The proposed methodology was applied for determination of estriol in commercial samples and results were compared with those provided by spectrophotometric method (official methodology). The obtained results are in agreement at a 95% of confidence level.

Wiring Bacterial Electron Flow for Sensitive Whole-Cell Amperometric Detection of Riboflavin

A whole-cell bioelectrochemical biosensing system for amperometric detection of riboflavin was developed. A "bioelectrochemical wire" (BW) consisting of riboflavin and cytochrome C between Shewanella oneidensis MR-1 and electrode was characterized. Typically, a strong electrochemical response was observed when riboflavin (VB2) was added to reinforce this BW. Impressively, the electrochemical response of riboflavin with this BW was over 200 times higher than that without bacteria. Uniquely, this electron rewiring process enabled the development of a biosensing system for amperometric detection of riboflavin. Remarkably, this amperometric method showed high sensitivity (LOD = 2.2 nM, S/N = 3), wide linear range (5 nM ∼ 10 μM, 3 orders of magnitude), good selectivity, and high resistance to interferences. Additionally, the developed amperometric method featured good stability and reusability. It was further applied for accurate and reliable determination of riboflavin in real conditions including food, pharmaceutical, and clinical samples without pretreatment. Both the cost-effectiveness and robustness make this whole-cell amperometric system ideal for practical applications. This work demonstrated the power of bioelectrochemical signal amplification with exoelectrogen and also provided a new idea for development of versatile whole-cell amperometric biosensors.

Partial Characterization of exopolysaccharides produced from novel isolates of Weissella Spp.

Current work was aimed to determine the monosaccharide composition and relative molecular weight of the biopolymer produced by fermented food isolates of W. cibaria using high-performance anion-exchange chromatography pulse amperometric detection (HPAEC) system and size exclusion chromatography (SEC), respectively. Both W. cibaria isolates found to produce homopolysaccharide of glucose and having a molecular mass higher than 220 000 Da.

On-line focusing of 5-hydroxy-tryptamine type 3 receptor antagonists via the combination of field-enhanced sample injection and dynamic pH junction in capillary electrophoresis with amperometric detection

In the present work, an on-line dual focusing technique based on field-enhance sample injection (FASI) and dynamic pH junction (DypH) was developed for the analysis of two 5-hydroxy-tryptamine type 3 receptor (5-HT3) antagonists ondansetron (Ond) and tropisetron (Tro) by capillary electrophoresis with amperometric detection (CE-AD) system. By preparing the sample in a lower conductivity (FASI condition) and lower pH value (DypH condition) matrix relative to the background electrolyte (BGE) solution, a simple and effective dual focusing approach, FASI–DypH was achieved. In this stacking mode, a large amount of analytes could be electrokinetically injected into the capillary and stacked at the boundary of the sample and the BGE zone as a result of deprotonation and decrease in the electric field. Effects of separation, detection and FASI–DypH focusing conditions were investigated in detail. Under the optimum conditions, good separation for Ond and Tro was achieved within 8min. In comparison with the conventional CE-AD analysis method, the present dual focusing technique enabled the enhancement factors in terms of peak heights to reach 357-fold and 345-fold for Ond and Tro, respectively. The limits of detection (LODs) (S/N=3) for Ond and Tro were 2nM and 5nM, respectively. The intraday and interday repeatabilities (RSDs) were less than 4.5% and 2.9% for peak height and migration time, respectively. The proposed method was successfully applied for the analysis of Ond and Tro in human urine sample.

Simultaneous determination of monoamines in rat brain with Pt/MWCNTs@Pdop hybrid nanocomposite using capillary electrophoresis— amperometric detection

In this article, polydopamine (Pdop) functionalized multiwalled carbon nanotubes (MWCNTs@Pdop) were firstly synthesized and employed as the template for the dispersion of Pt nanoparticles to form Pt/MWCNTs@Pdop hybrid nanocomposite. The characterizations of the Pt/MWCNTs@Pdop were investigated by SEM, transmission electron microscopy, x-ray diffraction, and voltammetry. Based upon the Pt/MWCNTs@Pdop nanocomposite, a modified carbon disk electrode was fabricated and successfully applied to the simultaneous detection of four important monoamines, including dopamine, epinephrine, norepinephrine, and serotonin, using capillary electrophoresis--amperometric detection system. Compared with the bare electrode, the four analytes at the Pt/MWCNTs@Pdop electrode exhibited higher sensitivity, broad linear responses from 0.5 to 1.0 × 10(2) nmol/L. The detection limits (S/N = 3) were lower than 9.2 × 10(-10) mol/L. More importantly, the effect of noise exposure on monoamines (MAs) in hippocampus and hypothalamus was investigated for the first time. Compared with the control group, the levels of the MAs all varied to different extents after rats receiving the same noise stimulation. The results showed that the proposed method could be applied to the determination of low levels of MAs in biological samples and screening the target molecules for the diagnosis and treatment of various related diseases.

Chromatographic System for Detecting Biomarkers of Dangerous Human Diseases

A chromatographic system for amperometric detection of biomarkers (homocysteine, catecholamines, and their precursors and metabolites) of dangerous diseases in human biological fluids (blood serum, urine) is suggested.

Simultaneous determination of three β-blockers at a carbon nanofiber paste electrode by capillary electrophoresis coupled with amperometric detection

In the paper, a novel carbon nanofiber paste electrode (CFPE) was fabricated and firstly used as a sensitive amperometric detector in capillary electrophoresis (CE) for the simultaneous determination of three β-blockers: sotalol, alprenolol and atenolol. Compared with the bare carbon paste electrode, the CFPE exhibited enhanced oxidation peak current responses to the analytes due to its excellent electrocatalytic activities, high conductivity and large effective surface area. Subsequently, effects of several important factors such as detection potential, pH and concentration of running buffer, separation voltage and injection time on the analysis were investigated. Under the optimum conditions, the three analytes could be separated and detected in a phosphate buffer (pH 8.5) within 11min. The linear ranges were 0.1–100μM for sotalol, 0.2–150μM for alprenolol and 0.1–50μM for atenolol and the detection limits were as low as 10−8M magnitude (S/N=3). Moreover, the CFPE exhibited good repeatability and long-time stability. The proposed method was applied to determine the three β-blockers in spiked urine samples with satisfactory assay results. The good performance, low cost and straightforward preparation method of CFPE demonstrated that it could be used as a detector for CE–amperometric detection system for drug analysis.