In-channel Amperometric Detection Research Articles

A decoupler-free simple paper microchip capillary electrophoresis device for simultaneous detection of dopamine, epinephrine and serotonin.

This paper demonstrates a new and simplified configuration for capillary electrophoresis-amperometric detection (CE-AD) using a paper microfluidic chip incorporating inexpensive wax printing and screen printing based methods and then used for electrophoretic separation and simultaneous in-channel amperometric detection of three clinically relevant neurochemicals in a single run without using any decouplers. Detection of neurochemicals e.g., dopamine, epinephrine and serotonin is crucial for early prediction of neurological disorders including Parkinson's, Alzheimer's, dementia, as well as progressive neuro-psychiatric conditions such as depression, anxiety, as well as certain cardiovascular diseases. The plasma concentrations of such neurochemicals are as important as those present in cerebrospinal fluid (CSF) and can be useful for rapid and convenient biosensing. However, simultaneous detection of such neurochemicals in a complex mixture such as human serum requires their separation prior to detection. With the developed microchip, separation and detection of the neurochemicals were exhibited within 650 seconds without pre-treatment and the procedure was validated with spiked fetal bovine serum samples. Beside this, the developed paper microfluidic chip has potential to be integrated in point-of-care diagnosis with onsite detection ability. Moreover, the use of a straight channel capillary, a screen-printed carbon electrode without decoupler, in-channel amperometric detection and low sample volume requirements (2 μL) are shown as additional advantages.

Dual-channel Microchip Electrophoresis with Amperometric Detection System for Rapid Analysis of Cefoperazone and Sulbactam.

A dual-channel microchip electrophoresis (ME) with in-channel amperometric detection was developed for cefoperazone and sulbactam determination simultaneously. In this study, a microelectrode detector was made of gold nanoparticles (GNPs) modified indium tin oxide (ITO)-coated poly-ethylene terephthalate (PET) film. The parameters including detection potential applied on working electrode, buffer concentration and pH value were optimized to improve the detection sensitivity and separation efficiency of cefoperazone and sulbactam. Under the optimal conditions, sensitive detection of cefoperazone and sulbactam was obtained with limits of detection (LODs) (S/N = 3) of 0.52 and 0.75 μg/mL, respectively. The plasma sample, which was from a patient with a brain injury taking Sulperazone, was successfully detected with a simple sample pretreatment process by dual-channel ME amperometric detection. This rapid and sensitive method possesses practical potential in clinical applications, and could provide a guidance for clinical rational drug use.

A gold nanoparticle-modified indium tin oxide microelectrode for in-channel amperometric detection in dual-channel microchip electrophoresis

A modified indium tin oxide (ITO) microelectrode detector integrated with a dual-channel polydimethylsiloxane (PDMS) microchip is proposed for in-channel amperometric detection in microchip electrophoresis (ME).

Screen-printed graphene-based electrochemical sensors for a microfluidic device

This work presents a new method for mass fabrication of a new microfluidic device with integrated graphene-based electrochemical electrodes by the screen printing technique for in-channel amperometric detection.

Evaluation of in-channel amperometric detection using a dual-channel microchip electrophoresis device and a two-electrode potentiostat for reverse polarity separations: Microfluidics and Miniaturization

Evaluation of in-channel amperometric detection using a dual-channel microchip electrophoresis device and a two-electrode potentiostat for reverse polarity separations: Microfluidics and Miniaturization

Evaluation of in-channel amperometric detection using a dual-channel microchip electrophoresis device and a two-electrode potentiostat for reverse polarity separations.

In-channel amperometric detection combined with dual-channel microchip electrophoresis is evaluated using a two-electrode isolated potentiostat for reverse polarity separations. The device consists of two separate channels with the working and reference electrodes placed at identical positions relative to the end of the channel, enabling noise subtraction. In previous reports of this configuration, normal polarity and a three-electrode detection system were used. In the two-electrode detection system described here, the electrode in the reference channel acts as both the counter and reference. The effect of electrode placement in the channels on noise and detector response was investigated using nitrite, tyrosine, and hydrogen peroxide as model compounds. The effects of electrode material and size and type of reference electrode on noise and the potential shift of hydrodynamic voltammograms for the model compounds were determined. In addition, the performance of two- and three-electrode configurations using Pt and Ag/AgCl reference electrodes was compared. Although the signal was attenuated with the Pt reference, the noise was also significantly reduced. It was found that lower LOD were obtained for all three compounds with the dual-channel configuration compared to single-channel, in-channel detection. The dual-channel method was then used for the detection of nitrite in a dermal microdialysis sample obtained from a sheep following nitroglycerin administration.

Nanoband electrode for high‐performance in‐channel amperometric detection in dual‐channel microchip capillary electrophoresis

A nanoband electrode detector integrated with a dual-channel polydimethylsiloxane microchip is proposed for in-channel amperometric detection in microchip capillary electrophoresis. Gold nanoband electrodes, which were fabricated on SU-8 substrates with a 100-nm-width gold layer, were introduced into the dual-channel microchip to be an electrochemical detector. Due to the nano-sized width of the detector, the noise of the amperometric detection was significantly reduced, and a high separation resolution was achieved for monitoring the analytes. The detection sensitivity of the system was improved by high signal-to-noise ratio, and a low detection limit on microchip was obtained for p-aminophenol (2.09 nM). Because of the high resolution in measuring half-peak width, the plate number that is used to evaluate the separation efficiency was 1.5-fold higher than that using 50-μm-width electrochemical detector. The effect of sample injection time and data acquisition time on separation efficiency was investigated, and an attractive separation efficiency was achieved with a plate number up to 17,500.

Enhanced aminophenols monitoring using in-channel amperometric detection with dual-channel microchip capillary electrophoresis

Improved techniques are needed to monitor toxic aminophenols in industrial wastewater. Microchip capillary electrophoresis (CE)-electrochemical detection (ECD) can be used to develop miniaturized system providing on-site monitoring. Here, a dual-channel microchip CE-ECD has been applied for the monitoring of aminophenols. The effect of conductance and capacitance between a working electrode and a reference electrode has been studied to minimize the noise that was generated in the amperometric detection. A mixture of aminophenols dissolved in a running buffer has been monitored. A separation efficiency with a plate number of 4770 and a high linear concentration dependence from 100 nM to 1 mM have been achieved for p-aminophenol. As a result, the analysis system has been applied for the monitoring of the pollutants with low detection limits of p-aminophenol (14.6 nM), o-aminophenol (10.6 nM) and m-aminophenol (15.3 nM). Here, we show that a wastewater sample from a natural gas refinery can be monitored using the microchip CE-ECD system.

Integrated microfluidic device for the separation and electrochemical detection of catechol estrogen-derived DNA adducts

Catechol estrogen-derived DNA adducts are formed as a result of the reaction of catechol estrogen metabolites (e.g., catechol estrogen quinones) with DNA to form depurinating adducts. Developing a new methodology for the detection of various DNA adducts is essential for medical diagnostics, and to this end, we demonstrate the applicability of on-chip capillary electrophoresis with an integrated electrochemical system for the separation and amperometric detection of various catechol estrogen-derived DNA adducts. A hybrid PDMS/glass microchip with in-channel amperometric detection interfaced with in situ palladium decoupler is utilized and presented. The influence of buffer additives along with the effect of the separation voltage on the resolving power of the microchip is discussed. Calibration plots were constructed in the range 0.4-10 μM with r(2) ≥ 0.999, and detection limits in the attomole range are reported. These results suggest that on-chip analysis is applicable for analyzing various DNA adducts as potential biomarkers for future medical diagnostics.

Deoxyribonucleic acid modified poly(dimethylsiloxane) microfluidic channels for the enhancement of microchip electrophoresis

In this paper, deoxyribonucleic acid (DNA) was employed to construct a functional film on the PDMS microfluidic channel surface and apply to perform electrophoresis coupled with electrochemical detection. The functional film was formed by sequentially immobilizing chitosan and DNA to the PDMS microfluidic channel surface using the layer-by-layer assembly. The polysaccharide backbone of chitosan can be strongly adsorbed onto the hydrophobic PDMS surface through electrostatic interaction in the acidic media, meanwhile, chitosan contains one protonatable functional moiety resulting in a strong electrostatic interactions between the surface amine group of chitosan and the charged phosphate backbone of DNA at low pH, which generates a hydrophilic microchannel surface and reveals perfect resistance to nonspecific adsorption of analytes. Aminophenol isomers ( p-, o-, and m-aminophenol) served as a separation model to evaluate the effect of the functional PDMS microfluidic chips. The results clearly showed that these analytes were efficiently separated within 60 s in a 3.7 cm long separation channel and successfully detected on the modified microchip coupled with in-channel amperometric detection mode at a single carbon fiber electrode. The theoretical plate numbers were 74,021, 92,658 and 60,552 N m −1 at the separation voltage of 900 V with the detection limits of 1.6, 4.7 and 2.5 μM (S/N = 3) for p-, o-, and m-aminophenol, respectively. In addition, this report offered an effective means for preparing hydrophilic and biocompatible PDMS microchannel surface, which would facilitate the use of microfluidic devices for more widespread applications.

Dual-Channel Method for Interference-Free In-Channel Amperometric Detection in Microchip Capillary Electrophoresis

A novel in-channel amperometric detection method for microchip capillary electrophoresis (CE) has been developed to avoid the interference from applied potential used in the CE separation. Instead of a single separation channel as in conventional CE microchips, we use a dual-channel configuration consisting of two different parallel separation and reference channels. A working electrode (WE) and a reference electrode (RE) are placed equally at a distance 200 microm from its outlet on each channel. Running buffer flows through the reference channel. Our dual-channel CE microchips consist of a poly(dimethylsiloxane) (PDMS) upper plate and a glass lower plate to form a PDMS/glass hybrid chip. Amperometric signals are measured without any potential shift and interference from the applied CE potential, and CE separation maintains its high resolution because this in-channel configuration does not allow additional band broadening that is notorious in end-channel and off-channel configurations. The high performance of this new in-channel electrochemical detection methodology for CE has been demonstrated by analyzing a mixture of electrochemically active biomolecules: dopamine (DA), norepinephrine, and catechol. We have achieved a 0.1 pA detectability from the analysis of DA, which corresponds to a 1.8 nM concentration.

A capillary electrophoresis microsystem for the rapid in-channel amperometric detection of synthetic dyes in food

Abstract An in-channel configuration for amperometric detection has been adopted in capillary electrophoresis performed in photolithographically microfabricated chips. This electrode alignment, compared with the more conventional end-channel configuration, led to a better peak resolution and a higher sensitivity, because it involves no gap between the channel outlet and the working electrode, thus preventing the dispersion of the analyte band leaving the separation channel into the comparatively large detection reservoir. All details concerning the chip fabrication, as well as injection and detection procedures adopted are carefully described. The performance of this approach was first optimized for the experimental parameters affecting both separation and detection steps and then assayed for the separation of two synthetic food dyes, Green S and Patent Blue, concomitantly present in synthetic samples. Under the optimized conditions thus recognized (background electrolyte: 40 mM aqueous carbonate–bicarbonate buffer at pH = 10.5, separation voltage: 1300 V, amperometric detection at controlled potential of 0.9 V vs. Ag / AgCl, Cl ( sat ) - ), a well satisfactory resolution could be achieved within less than 300 s. The recorded peaks were characterized by both a good repeatability (7%) and a linear dependence of their height over a wide concentration range (about 2 orders of magnitude). The detection limit, estimated for a signal-to-noise ratio of three was 10 μM for Patent Blue and 17 μM for Green S. The application of the method to some commercial soft-drinks and candies is also presented.

Proteins modification of poly(dimethylsiloxane) microfluidic channels for the enhanced microchip electrophoresis

This report described proteins modification of poly(dimethylsiloxane) (PDMS) microfluidic chip based on layer-by-layer (LBL) assembly technique for enhancing separation efficiency. Two kinds of protein-coated films were prepared. One was obtained by successively immobilizing the cationic polyelectrolyte (chitosan, Chit), gold nanoparticles (GNPs), and protein (albumin, Albu) to the PDMS microfluidic channels surface. The other was achieved by sequentially coating lysozyme (Lys) and Albu. Neurotransmitters (dopamine, DA; epinephrine, EP) and environmental pollutants ( p-phenylenediamine, p-PDA; 4-aminophenol, 4-AP; hydroquinone, HQ) as two groups of separation models were studied to evaluate the effect of the functional PDMS microfluidic chips. The results clearly showed these analytes were efficiently separated within 140 s in a 3.7 cm long separation channel and successfully detected with in-channel amperometric detection mode. Experimental parameters in two protocols were optimized in detail. The detection limits of DA, EP, p-PDA, 4-AP, and HQ were 2.0, 4.7, 8.1, 12.3, and 14.8 μM (S/N = 3) on the Chit–GNPs–Albu coated PDMS/PDMS microchip, and 1.2, 2.7, 7.2, 9.8, and 12.2 μM (S/N = 3) on the Lys–Albu coated one, respectively. In addition, through modification, the more homogenous channel surface displayed higher reproducibility and better stability.

The use of poly(dimethylsiloxane) surface modification with gold nanoparticles for the microchip electrophoresis

Poly(dimethylsiloxane) (PDMS) microfluidic channels modified by citrate-stabilized gold nanoparticles after coating a layer of linear polyethylenimine (LPEI) were successfully used to separate dopamine and epinephrine, which were difficult to be separated from baseline in native and hybrid PDMS microchannels. In-channel amperometric detection with a single carbon fibre cylindrical electrode was employed. Experimental parameters of separation and detection processes were optimized in detail. The analytes were well separated within 100 s in a 3.7 cm long separation channel at a separation voltage of +800 V using a 30 mM phosphate buffer solution (PBS, pH 7.0). Linear responses of them were obtained both from 25 to 600 μM with detection limits of 2 μM for dopamine and 5 μM for epinephrine, respectively. The modified PDMS channels have a long-term stability and an excellent reproducibility within 2 weeks.