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This paper develops an efficient electrochemiluminescence (ECL) enhancement strategy on closed bipolar electrode for the detection of prostate specific antigen (PSA). We first synthesized a cyclometalated iridium(III) complex (pq) 2 Irbza with high ECL efficiency and used as ECL emitter in the anodic cell of BPE. While we introduced a Pt-tipped Au NRs and constructed a sandwich immune structure at the cathodic pole of BPE. Combined the signal amplification strategies of enzyme catalysis and the synergistic catalytic effect of bimetallic structure for the reduction of H 2 O 2 , the attached Pt-tipped Au NRs-GOx-Ab 2 nanocomplex as both recognition probes and signal amplification units could mediate the ECL signals of (pq) 2 Irbza/tripropylamine (TPrA) on the anodes of BPE through faradaic reaction due to the charge neutrality of BPE. Therefore, a highly sensitive BPE-ECL sensor for detection of PSA with a detection limit of 0.72 pg/mL and a linear range from 1.0 pg/mL to 10 ng/mL was obtained. This work is expected to broaden the application of iridium complex and bimetallic nanocatalyst in biological detection and could be utilized to detect many other biological molecules.

In this work, we developed a visual electrochemiluminescence (ECL) sensing platform based on a dual-bipolar electrode (D-BPE) array chip. The chip was composed of two arrays of BPEs and three separated arrays of reservoirs filled with buffer, Ru(bpy)3(2+)-TPrA and luminol solutions, respectively. Both BPEs served as ECL reporting platforms. By applying 6.0 V voltage, an array of orange electrochemiluminescence (ECL) signals belonging to Ru(bpy)3(2+) turned on. After adding DNAzyme and H2O2 in Ru(bpy)3(2+) and luminol reservoirs, the orange Ru(bpy)3(2+) signals decreased until vanished due to the quenching effect; meanwhile, a new array of blue ECL signals turned on because of the luminol-H2O2 ECL reaction. The designed D-BPE owns superior properties compared with the three-electrode system benefiting from the quantitative relation of bipolar systems, which greatly enhanced the ECL detection sensitivity. Meanwhile, the visual color-switch ECL and the ratiometric detecting principle made the results easier to evaluate and more accurate. Quantitative detection of HL-60 cancer cells from 320 cells/mL to 2.5 × 10(5) cells/mL with two linear ranges was achieved. The detection limit was down to 80 cells/mL. Finally, this D-BPE chip could distinguish the tumor cells from normal cells and provide a prospect for cancer diagnosis in a high-throughput, visual way.

This paper describes a novel electrochemiluminescence (ECL) imaging platform for simultaneous detection of cancer biomarkers based on a closed bipolar electrode (BPE) array. It consists of two separated channel arrays: detection channel array and sensing channel array, which are connected by a group of parallel ITO BPEs on a glass substrate. Besides, two parallel ITO strips are fabricated at the two sides of BPE array and employed as driving electrodes. After Au films are electrochemically deposited on the cathodes of the BPE array, nanobioprobes including biorecognition elements (aptamer or antibody) and a novel electrochemical tag, which is synthesized by doping thionine in silica nanoparticles (Th@SiO2 NPs), are introduced into the cathodes by immunoreaction or DNA hybridization. The Th@SiO2 coupled nanobioprobes as both recognition probes and signal amplification indicators could mediate the ECL signals of Ru(bpy)3(2+)/tripropylamine (TPA) on the anodes of BPE array through faradaic reaction due to the charge neutrality of BPE. Thus, multiplex detection of cancer biomarkers (adenosine triphosphate (ATP), prostate-specific antigen (PSA), α-fetoprotein (AFP) and thrombin) is realized by forming specific sensing interfaces onto the cathodic poles of BPEs in different sensing channels and reported by the ECL images of the Ru(bpy)3(2+)/TPA system on the anodic poles of BPEs in detection channels. The results demonstrate that this visual ECL platform enables sensitive detection with excellent reproducibility, which may open a new door toward the development of simple, sensitive, cost-effective, and high throughput detection methods on biochips.

Here we developed a novel hybrid bipolar electrode (BPE)-electrochemiluminescence (ECL) biosensor based on hybrid bipolar electrode (BPE) for the measurement of cancer cell surface protein using ferrocence (Fc) labeled aptamer as signal recognition and amplification probe. According to the electric neutrality of BPE, the cathode of U-shaped ITO BPE was electrochemically deposited by Au nanoparticles (NPs) to enhance its conductivity and surface area, decrease the overpotential of O2 reduction, which would correspondingly increase the oxidation current of Ru(bpy)3(2+)/tripropylamine (TPA) on the anode of BPE and resulting a ∼4-fold enhancement of ECL intensity. Then a signal amplification strategy was designed by introducing Fc modified aptamer on the anode surface of BPE through hybridization for detecting the amount of mucin-1 on MCF-7 cells. The presence of Fc could not only inhibit the oxidation of Ru(bpy)3(2+) because of its lower oxidation potential, its oxidation product Fc(+) could also quench the ECL of Ru(bpy)3(2+)/TPA by efficient energy-transfer from the excited-state Ru(bpy)3(2+)* to Fc(+), making the ECL intensity greatly quenched. On the basis of the cathodic Au NPs induced ECL enhancing coupled with anodic Fc induced signal quenching amplification, the approach allowed detection of mucin-1 aptamer at a concentration down to 0.5 fM and was capable of detecting a minimum of 20 MCF-7 cells. Besides, the amount of mucin-1 on MCF-7 cells was calculated to be 9041 ± 388 molecules/cell. This approach therefore shows great promise in bioanalysis.

With DNA as a rigid spacer, Ag nanoparticles (NPs) were bridged to CdS quantum dots (QDs) for the stimulation of exciton-plasmon interactions (EPI) in a photoelectrochemical (PEC) system. Due to their natural absorption overlap, the exciton of the QDs and the plasmon of Ag NPs could be induced simultaneously. The EPI resonant nature enabled manipulating photoresponse of the QDs via tuning interparticle distances. Specifically, the photocurrent of the QDs could be greatly attenuated and even be completely damped by the generated EPI. The work opens a different horizon for EPI investigation through an engineered PEC nanosystem, and provides a viable mechanism for new DNA sensing protocol.

Herein we demonstrate the protocol of a biocatalytic precipitation (BCP)-based sandwich photoelectrochemical (PEC) horseradish peroxidase (HRP)-linked immunoassay on the basis of their synergy effect for the ultrasensitive detection of mouse IgG (antigen, Ag) as a model protein. The hybrid film consisting of oppositely charged polyelectrolytes and CdS quantum dots (QDs) is developed by the classic layer by layer (LbL) method and then employed as the photoactive antibody (Ab) immobilization matrix for the subsequent sandwich-type Ab-Ag affinity interactions. Improved sensitivity is achieved through using the bioconjugates of HRP-secondary antibodies (Ab(2)). In addition to the much enhanced steric hindrance compared with the original one, the presence of HRP would further stimulate the BCP onto the electrode surface for signal amplification, concomitant to a competitive nonproductive absorption that lowers the photocurrent intensity. As a result of the multisignal amplification in this HRP catalyzed BCP-based PEC immunoassay, it possesses excellent analytical performance. The antigen could be detected from 0.5 pg/mL to 5.0 ng/mL with a detection limit of 0.5 pg/mL.

In this paper, gold nanoparticle-thionine-reduced graphene oxide (GNP-THi-GR) nanocomposites were prepared to design a label-free immunosensor for the sensitive detection of carcinoembryonic antigen (CEA). The nanocomposites with good biocompatibility, excellent redox electrochemical activity and large surface area were coated onto the glassy carbon electrode (GCE) surface and then CEA antibody (anti-CEA) was immobilized on the electrode to construct the immunosensor. The morphologies and electrochemistry of the formed nanocomposites were investigated by using scanning electron microscopy (SEM), ultraviolet-visible (UV-vis) spectrometry, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). CV and differential pulse voltammetry (DPV) studies demonstrated that the formation of antibody-antigen complexes decreased the peak current of THi in the GNP-THi-GR nanocomposites. The decreased currents were proportional to the CEA concentration in the range of 10-500 pg/mL with a detection limit of 4 pg/mL. The proposed method was simple, fast and inexpensive for the determination of CEA at very low levels., (Copyright © 2011 Elsevier B.V. All rights reserved.)

In this paper we report a transparent bipolar electrode based microfluidic chip-electrochemiluminescence (ECL) system for sensitive detection of folate receptors (FR) on cell membranes. This integrated system consists of a poly(dimethylsiloxane) (PDMS) layer containing a microchannel and a glass bottom sheet with indium tin oxide (ITO) strips as bipolar detectors. The ITO strips are fabricated using a PDMS micromold with carbon ink as a protective layer in place of traditional photoresist. The configuration of the bipolar electrode has great influence on the ECL intensity of Ru(bpy)(3)(2+)/tripropylamine(TPA) system. Further studies show that folic acid (FA) can strongly inhibit the ECL of the Ru(bpy)(3)(2+)/TPA system. Based on specific recognition between FA and FR on cell membrane, this microfluidic chip-ECL system is successfully applied for detecting the level of FR on human cervical tumor (HL-60) cells and MEF cells. It is found that the ECL intensity increases with the number of HL-60 cells in the range of 21 to 3.28 × 10(4) cells/mL. The average level of FR on HL-60 cells is calculated to be 8.05 ± 0.75 × 10(-18) mol/cell. While for MEF cells, it shows a much slower ECL increment than HL-60 cells due to the much lower FR level on MEF cells (5.30 ± 0.61 × 10(-19) mol/cell). Moreover, exocytosis of FA after FR mediated endocytosis was observed according to the change of the ECL signal with the incubation time of HL-60 cells in the FA- Ru(bpy)(3)(2+)/TPA system., (This journal is © The Royal Society of Chemistry 2011)

A strategy for label-free oligonucleotide (DNA) analysis has been proposed by measuring the DNA-morpholino hybridization hindered diffusion flux of probe ions Fe(CN)(6)(3-) through nanochannels of a porous anodic alumina (PAA) membrane. The flux of Fe(CN)(6)(3-) passing through the PAA nanochannels is recorded using an Au film electrochemical detector sputtered at the end of the nanochannels. Hybridization of the end-tethered morpholino in the nanochannel with DNA forms a negatively charged DNA-morpholino complex, which hinders the diffusion of Fe(CN)(6)(3-) through the nanochannels and results in a decreased flux. This flux is strongly dependent on ionic strength, nanochannel aperture, and target DNA concentration, which indicates a synergetic effect of steric and electrostatic repulsion effects in the confined nanochannels. Further comparison of the probe flux with different charge passing through the nanochannels confirms that the electrostatic effect between the probe ions and DNA dominates the hindered diffusion process. Under optimal conditions, the present nanochannel array-based DNA biosensor gives a detection limit of 0.1 nM.

In this paper, a micro/nanofluidic preconcentration device integrated with an electrochemical detector has been used to study the enrichment of enzymes and homogeneous enzyme reaction kinetics. The enzymes are first concentrated in front of a nanochannel via an exclusion-enrichment effect (EEE) mechanism of the nanochannel integrated in a microfluidics device. If a substrate is electrokinetically transported to the concentrated enzymes, homogeneous enzymatic reaction occurs. The enzymatic reaction product can penetrate through the nanochannel to be detected electrochemically. In this device, the enriched enzymes can be well retained and repeatedly used, thus, the enzymatic reaction occurs in a continuous-flow mode. For demonstration, Glucose oxidase (GOx) was chosen as the model enzyme to study the influence of enzyme concentration on its reaction kinetics. The different concentration of GOx in front of the nanochannel was simply achieved by using different enrichment time. When substrate glucose was introduced electrokinetically, a rapid electrochemical steady-state response could be obtained. It was found that the electrochemical response to a constant glucose concentration increased with the increase of enzyme enrichment time, which is expected for homogeneous enzymatic reactions. Under proper conditions, the electrochemical responds linearly to the glucose concentration ranging from 0 to 15 mM, and the Michaelis constants (K(m)) are relatively low, which indicates a more efficient complex formation between enzyme and substrate. These results suggest that the present micro/nanofluidics device is promising for the study of enzymatic reaction kinetics and other bioassays such as cell assays, drug discovery, and clinical diagnosis.

A novel photoelectrochemical immunosensor based on TiO(2)/CdS hybrid modified electrode was developed. The TiO(2)/CdS hybrid modified electrode was obtained by alternately dipping the TiO(2) modified indium-tin oxide (ITO) electrode into the [Cd(NH(3))(4)](2+) and S(2-) solution repeatedly. Compared with the routine method using Cd(2+) solution for CdS deposition, the as obtained TiO(2)/CdS electrode showed enhanced photocurrent intensity with fewer coating times. After the ITO/TiO(2)/CdS electrode was coated with chitosan (CS), alpha-fetoprotein (AFP) antibodies were covalently conjugated on the surface of the electrode. Thus, a label-free photoelectrochemical immunosensor for the detection of AFP was developed by monitoring the changes in the photocurrent signals of the electrode resulting from the immunoreaction. The immunosensor displayed a linear response to AFP in the ranges from 50pg/mL to 50ng/mL with a relatively low detection limit of 40pg/ml. The photoelectrochemical results for the detection of AFP in five human sera showed acceptable accuracy. The method is simple, sensitive and specific. Moreover, the studied immunosensor possessed acceptable reproducibility and storage stability. The proposed methodology was potentially attractive for clinical immunoassay.

In this paper, we present a novel approach for preparing patterned Au/poly(dimethylsiloxane) (PDMS) substrate. Chemical gold plating instead of conventional metal evaporation or sputtering was introduced to achieve a homogeneous gold layer on native PDMS for the first time, which possesses low-cost and simple operation. An electrochemical oxidation reaction accompanied by the coordination of gold and chloride anion was then exploited to etch gold across the region covered by electrolyte. On the basis of such an electrochemical etching, heterogeneous Au/PDMS substrate which has a gold "island" pattern or PDMS dots pattern was fabricated. Hydrogen bubbles which were generated in the etching process due to water electrolysis were used to produce a safe region under the Pt auxiliary electrode. The safe region would protect gold film from etching and lead to the formation of the gold "island" pattern. In virtue of a PDMS stencil with holes array, gold could be etched from the exposed region and take on the PDMS dots pattern which was selected to for protein and cell patterning. This patterned Au/PDMS substrate is very convenient to construct cytophobic and cytophilic regions. Self-assembled surface modification of (1-mercaptoundec-11-yl)hexa(ethylene glycol) on gold and adsorption of fibronectin on PDMS are suitable for effective protein and cell patterning. This patterned Au/PDMS substrate would be a potentially versatile platform for fabricating biosensing arrays.

Dopamine-coordinated photoactive TiO(2) nanoporous films with a wide excitation range of light in the visible region (up to 580 nm) were prepared and used for sensitive detection of NADH. Colloidal TiO(2) was firstly covered on an indium-tin oxide (ITO) electrode surface and sintered at 450 degrees C to form a nanoporous TiO(2) film, then the electrode was dipped in a dopamine solution to form a dopamine-TiO(2) charge transfer complex via coordinating dopamine with undercoordinated titanium atoms on the electrode surface. This charge transfer complex provided an anodic photocurrent under visible light and the photocurrent could be largely enhanced by NADH. The photocurrent enhancement might be due to the electron transfer between NADH and the holes localized on dopamine. A new photoelectrochemical methodology for sensitive detection of NADH at a relatively low potential was developed. The detection limit of NADH was 1.4x10(-7) M, and the detection range could extend up to 1.2x10(-4) M. The dopamine-TiO(2) modified electrode exhibits its major advantages such as effective electronic transducer, fast response and easy fabrication for photoelectrochemical determination of NADH. This strategy largely reduces the destructive effect of UV light and the photogenerated holes of illuminated TiO(2) to biomolecules and opens a new avenue for the applications of TiO(2) in photoelectrochemical biosensing.

Based on the newly discovered artificial enzyme formed by mixing hemin with supramolecular hydrogels via the self-assembly of amphiphilic oligopeptides, we prepared a novel organic phase artificial enzyme electrode by coating the artificial enzyme on an electrode which was then covered with sodium alginate for protection. Scanning electron micrograph showed that the supramolecular hydrogel kept its nanofibers structure on the electrode surface. Hemin dispersed in the supermolecular hydrogel as monomer greatly promotes its direct electrochemistry behavior in organic solvents. At the same time, this electrode exhibited higher electrocatalytic ability to tert-butyl hydroperoxide (TBHP) than free hemin modified electrode (free hemin mainly present as dimer). As low as 27 microM TBHP could be detected with a linear range from 6.6 x 10(-5) to 1.27 x 10(-2)M via amperometric method. The biosensor can reach 95% of the steady-state current in about 10+/-2s. More importantly, it can be applied in both hydrophilic and hydrophobic solvents without adding extra buffer or mediators to them that cannot be received by most traditional organic phase enzyme electrodes. This unique property greatly promotes the development of the organic phase enzyme electrodes by facilitating the detection of different kinds of substrates of the hemin-based artificial enzyme soluble in hydrophilic and hydrophobic solvents. The artificial enzyme electrode was successfully used to determine organic peroxides in body lotion samples.

Single-walled carbon nanotubes (SWCNTs) selectively wrapped by a water-soluble, environmentally friendly, biocompatible polymer chitosan (CHI) were employed for the construction of a bioelectrochemical platform for the direct electron transfer (DET) of glucose oxidase (GOD) and biosensing purposes. Scanning electron microscopy and Raman spectroscopy were used to investigate the properties of the SWCNT-CHI film. The results show that the preferentially wrapped small-diameter SWCNTs are dispersed within the CHI film and exist on the surface of the electrode as small bundles. The DET between GOD and the electrode surface was observed with a formal potential of about ca. -460 mV vs. SCE in phosphate buffer solution. The heterogeneous electron transfer rate constant and the surface coverage of GOD are estimated to be 3.0 s(-1) and 1.3 x 10(-10)mol/cm(2), respectively. The experimental results demonstrate that the immobilized GOD retains its catalytic activity towards the oxidation of glucose. Such a GOD/SWCNT-CHI film-based biosensor not only exhibits a rapid response time, a wide linear rang and a low detection limits at a detection potential of -400 mV but also shows the effective anti-interference capability. Significantly improved analytical capabilities of the GOD/SWCNT-CHI/GC electrode could be ascribed to the unique properties of the individual SWCNTs and to the biocompatibility of CHI.

We report a simple electrochemical method for the identification of properties of peripheral nerve fibers, based on the detection of a neurotransmitter enzyme, acetylcholinesterase (AChE). A poly(diallydimethylammonium) (PDDA) adulterated poly(dimethylsiloxane) (PDMS) film is spin-coated on the surface of gold electrodes. Gold nanoparticles (AuNPs) are in situ synthesized on the polymer film, which act as "electron antennae" between the film and the electrode surface and also provide a biocompatible interface. This PDMS-PDDA/AuNPs film shows different adsorption sites to choline oxidase (ChO) and AChE; after incubation with ChO, the polymer-gold nanocomposite film also shows excellent adsorption ability to AChE. Moreover the adsorption sites of AChE would not be blocked by bovine serum albumin (BSA) which provides a good platform for the quantitative amperometric determination of AChE via the oxidation of the enzymatically generated H 2O 2 in the bienzyme system in the presence of acetylcholine. The detection limit is down to 1.0 unit/mL. The polymer-gold nanocomposite film shows excellent anti-interference ability to the coexistent electroactive substances such as ascorbic acid. Thus it was applied to determine AChE in peripheral nerve fibers homogenates and identify the motor and sensory fibers for the first time. Compared with histochemical staining methods, the electrochemical technique shows good accurate rate and faster response, which has good potential for a clinical application.

A novel film of chitosan-gold nanoparticles is fabricated by a direct and facile electrochemical deposition method and its application in glucose biosensor is investigated. HAuCl(4) solution is mixed with chitosan and electrochemically reduced to gold nanoparticles, which can be stabilized by chitosan and electrodeposited onto glassy carbon electrode surfaces along with the electrodeposition of chitosan. Then a model enzyme, glucose oxidase (GOD) is immobilized onto the resulting film to construct a glucose biosensor through self-assembly. The resulting modified electrode surfaces are characterized with both AFM and cyclic voltammetry. Effects of chitosan and HAuCl(4) concentration in the mixture together with the deposition time and the applied voltage on the amperometric response of the biosensor are also investigated. The linear range of the glucose biosensor is from 5.0 x 10(-5) approximately 1.30 x 10(-3) M with a Michaelis-Menten constant of 3.5 mM and a detection limit of about 13 microM.

Boron-doped diamond has drawn much attention in electrochemical sensors. However there are few reports on non-doped diamond because of its weak conductivity. Here, we reported a glucose biosensor based on electrochemical pretreatment of non-doped nanocrystalline diamond (N-NCD) modified gold electrode for the selective detection of glucose. N-NCD was coated on gold electrode and glucose oxidase (GOx) was immobilized onto the surfaces of N-NCD by forming amide linkages between enzyme amine residues and carboxylic acid groups on N-NCD. The anodic pretreatment of N-NCD modified electrode not only promoted the electron transfer rate in the N-NCD thin film, but also resulted in a dramatic improvement in the reduction of the dissolved oxygen. This performance could be used to detect glucose at negative potential through monitoring the current change of oxygen reduction. The biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents, such as ascorbic acid (AA), acetaminophen (AP) and uric acid (UA). A wide linear calibration range from 10 microM to 15 mM and a low detection limit of 5 microM were achieved for the detection of glucose.

This paper reports on the study of electroosmotic flow (EOF) in poly(dimethylsiloxane) (PDMS) microchannels on the basis of indirect amperometric detection method. Gradual increase of EOF rate in freshly prepared PDMS microchannels was observed with the running buffer of phosphate buffer solution (PBS). With the same concentration (10 mM) of PBS containing different cations and the same pH value (7.0) and, the time of the stable EOF in PDMS microchannels under the applied separation voltage of 1000 V was 49.8 s (Li+ -PBS), 57.1 s (Na+ -PBS), 91 s (K+ -PBS), respectively. Meanwhile, the different adsorption of cations (Li+, Na+ and K+) on hydrophobic PDMS wall was observed through their separation in PDMS microchannels. Such experimental results demonstrated that the EOF in PDMS microchannels came from the cations and anions adsorbed on PDMS wall. This study would not only help us understand the surface state of PDMS, but also provide a useful guidance for establishing the effective surface modification methods in PDMS microchip CE.

A new strategy for immobilization of horseradish peroxidase (HRP) has been presented by self-assembling gold nanoparticles on chitosan hydrogel modified Au electrode. From a mildly acidic chitosan solution, a chitosan film is electrochemically deposited on Au electrode surface via a negative voltage bias. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the deposited chitosan film with porous structure, which facilitates the assembly of gold nanoparticles and HRP. The resulting substrates were characterized by atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). The immobilized HRP displayed an excellent catalytic property to the reduction of H2O2 in the presence of methylene blue mediator. The resulting biosensor (HRP-modified electrode) showed a wide dynamic range of 8.0 microM-15 mM H2O2, and the linear ranges were 8.0 microM-0.12 mM and 0.50-12 mM, with a detection limit of 2.4 microM estimated at a signal-to-noise ratio of 3. Moreover, the biosensor remained about 85% of its original sensitivity after four weeks' storage.

Field-effect transistor (FET)-based biosensors (BioFETs) have undergone great progress especially in the last decade, since they were first realized in 1980. Recently, BioFETs have become one of the most important branches of biosensors. This paper briefly reviewed the operating principles of BioFETs and summarized the improvement and application of BioFETs, finally, the future prospects of BioFETs were discussed with 126 references.

A novel method was used to prepare the nano-composite by assembling nanogold (NG) particles on the multiwall carbon nanotubes (MWNTs) surface. The nano-composite could be immobilized on a glassy carbon (GC) electrode to get a novel modified electrode. The electrode can easily immobilize the horseradish peroxidase (HRP) molecules to construct a reagentless biosensor. The NG particles in the composite film have a good biological compatibility. And due to the existence of quinone groups on the MWNTs surface, the MWNTs can promote the electron transfer between enzymes and electrode surface. The biosensor shows a good stability and responds to H2O2 in the range from 2.0 microM to 3.5 mM with a detection limit of 1.0 microM.

This paper presents an electrochemical detector for poly(dimethylsiloxane) (PDMS) microchip CE with a three-dimensional adjustor which makes it possible to accurately align a separate working electrode that can be easily fabricated in laboratory to the uncertain PDMS microchannel outlet. The substantial influence of the electrode-PDMS microchannel distance was investigated. The optimal electrode-outlet distance was found to be 10 microm for the PDMS microchannel with the width of 50 microm due to its relatively slow electroosmotic flow. Adrenaline and catechol were well separated, with a linear response range from 20 microM to 1 mM, and a detection limit of 2 microM for catechol, using carbon disk electrode (diameter of 300 microm). Furthermore, arginine and histidine can be well separated and detected directly in the PDMS microchannel using a Cu disk electrode (diameter of 150 microm).

A new type of sol-gel/organic hybrid composite material based on the cross-linking of natural polymer chitosan with (3-aoryloxypropyl) dimethoxymethylsilane was developed for the fabrication of an amperometric H(2)O(2) biosensor. The composite film was used to immobilize horseradish peroxidase (HRP) on a gold disk electrode. The properties of sol-gel/chitosan and sol-gel/chitosan-HRP films have been carefully characterized by atomic force microscopy and Fourier transform infrared. By using fluorescent label, a protein density on sol-gel/chitosan has been calculated to be 3.14 x 10(12) moleculescm(-2). With the aid of catechol mediator, the biosensor had a fast response of less than 2 s with linear range of 5.0 x 10(-9)-1.0 x 10(-7) mol l(-1) and a detection limit of 2 x 10(-9) mol l(-1). Its current response shows a typical Michaelis-Menten mechanism. The apparent Michaelis-Menten constant K(M)(app) is found to be 1.30 micromol l(-1). The activation energy for enzymatic reaction is calculated to be 8.22 kJ mol(-1). The biosensor retained approximately 75% of its original activity after about 60 days of storage in a phosphate buffer at 4 degrees C., (Copyright 2002 Elsevier Science B.V.)

Single‐cell epigenetics is envisioned to decipher manifold epigenetic phenomena and to contribute to our accurate knowledge about basic epigenetic mechanisms. Engineered nanopipette technology has gained momentum in single‐cell studies; however, solutions to epigenetic questions remain unachieved. This study addresses the challenge by exploring N6‐methyladenine (m6A)‐bearing deoxyribozyme (DNAzyme) confined within a nanopipette for profiling a representative m6A‐modifying enzyme, fat mass and obesity‐associated protein (FTO). Electroosmotic intracellular extraction of FTO could remove the m6A and cause DNAzyme cleavage, leading to the altered ionic current signal. Because the cleavage can release a DNA sequence, we simultaneously program it as an antisense strand against FTO‐mRNA, intracellular injection of which has been shown to induce early stage apoptosis. This nanotool thus features the dual functions of studying single‐cell epigenetics and programmable gene regulation. [ABSTRACT FROM AUTHOR]

Single‐cell protein therapeutics is expected to promote our in‐depth understanding of how a specific protein with a therapeutic dosage treats the cell without population averaging. However, it has not yet been tackled by current single‐cell nanotools. We address this challenge by the use of a double‐barrel nanopipette, in which one lumen was used for electroosmotic cytosolic protein delivery and the other was customized for ionic evaluation of the consequence. Upon injection of protein DJ‐1 through the delivery lumen, upregulation of the antioxidant protein could protect neural PC‐12 cells against oxidative stress from phorbol myristate acetate exposure, as deduced by targeting of the cytosolic hydrogen peroxide by the detecting lumen. The nanotool developed in this study for single‐cell protein therapeutics provides a perspective for future single‐cell therapeutics involving different therapeutic modalities, such as peptides, enzymes and nucleic acids. [ABSTRACT FROM AUTHOR]

Herein, we report the rapid mass spectrometric identification of the short-lived intermediates generated under AC electrolysis via combining bipolar electrochemistry with nanoelectrospray ionization in a hybrid ultramicroelectrode/ion emitter. The key reactive intermediates involved in the C–O/O–H cross-metathesis between 4-alkoxy anilines and alcohols were successfully captured and identified for the first time, providing direct evidence for the previously proposed mechanism. [ABSTRACT FROM AUTHOR]

New tools for single‐cell interrogation enable deeper understanding of cellular heterogeneity and associated cellular behaviors and functions. Information of RNA expression in single cell could contribute to our knowledge of the genetic regulatory circuits and molecular mechanism of disease development. Although significant progresses have been made for intracellular RNA analysis, existing methods have a trade‐off between operational complexity and practical feasibility. We address this challenge by combining the ionic current rectification property of nanopipette reactor with duplex‐specific nuclease‐assisted hybridization chain reaction for signal amplification to realize a simple and practical intracellular nanosensor with minimal invasiveness, which enables single‐cell collection and electrochemical detection of intracellular RNA with cell‐context preservation. Systematic studies on differentiation of oncogenic miR‐10b expression levels in non‐malignant breast cells, metastatic breast cancer cells as well as non‐metastatic breast cancer cells were then realized by this nanotool accompanied by assessment of different drugs effects. This work has unveiled the ability of electrochemistry to probe intracellular RNA and opened new opportunities to study the gene expression and heterogeneous complexity under physiological conditions down to single‐cell level. [ABSTRACT FROM AUTHOR]

Electrochemical surface stress is important in nanomaterials because of their large surface-to-volume ratios, which lead to unique mechanical and electrocatalytic properties, but directly measuring this quantity has been challenging. Here we report on experimental determination of the surface stress, and associated electrochemical processes of a single gold nanowire with an optical imaging technique. We show that surface stress changes linearly and reversibly with the potential between 0 and 0.8 V versus Ag/AgCl, but abruptly with large hysteresis, associated with the oxidation and reduction of the nanowire, between 0.8 and 1.5 V. The potential derivative of the surface stress closely resembles the cyclic voltammograms. We described the observations in terms of anion adsorption and surface oxidation/reduction. This work demonstrates a new approach to study electrochemical processes and the associated surface stress changes of nanomaterials. [ABSTRACT FROM AUTHOR]

Bipolar electrochemistry is based on the gradient distribution of free-electron density along an electrically isolated electrode, which causes a positive electrode potential at one end and a negative potential at the other, allowing for wide applications in analytical chemistry and materials science. To take full advantage of its wireless and high-throughput features, various types of optical probes, such as pH indicators and fluorescence and electrochemiluminescence reagents, have often been used to indirectly monitor the interfacial electron transfer through chromogenic or fluorogenic reactions. Herein, we report the first probe-free imaging approach that can directly visualize the distribution of the interfacial potential in bipolar electrodes, providing essential information for the validation and development of the theory and applications of bipolar electrochemistry. This approach is based on the sensitive dependence of surface plasmon resonance imaging on the local electron density in the electrode, which enables the direct mapping of potential with a spatial resolution close to the optical diffraction limit, a temporal resolution of 50 ms, and a sensitivity of 10 mV. In addition, in contrast to previous optical readouts that relied on faradaic reactions, the present work achieved the impedance-based measurements under non-faradaic conditions. It is anticipated that this technique will greatly expand the application of bipolar electrochemistry as a platform for chemical and biosensing. [ABSTRACT FROM AUTHOR]

We have developed a novel nitric oxide (NO) cellular biosensor based upon the immobilization of red blood cells (RBCs) onto nanometer‐size colloidal gold that is attached to an electrochemically pretreated glassy carbon electrode via the bridging of an ethylenediamine monolayer. The biosensor has been characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and electrochemistry. The immobilized RBCs display an excellent electrocatalytic response to nitric oxide. The electrocatalytic currents are proportional to the NO concentration in the range from 1.0×10–8 to 1.0×10–6 M and the detection limit is as low as 5.0×10–9 M (S/N=3). Furthermore, the biosensor is very stable and relatively free of potential interference. [ABSTRACT FROM AUTHOR]

An electrochemical immunosensor has been constructed by the self-assemble technique and studied by the AC impedance and potential method respectively. The change of the surface impedance shows that the antibody can be assembled on the electrode surface and recognize the antigen. The gold nanoparticles are not only used to immobilize the CRP antibody, but also can amplify the potential response. The immunosensor responds to antigen in the linear range from 5 to 25 µg/mL and can meet the needs of clinical assay. [ABSTRACT FROM AUTHOR]

A platinum electrode modified with lanthanum hexacyanoferrate (LaHCF) was prepared by electrochemical scanning and characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and voltammetry. The results show that the deposit on the platinum substrate is composed of lanthanum potassium hexacyanoferrate (II) tetrahydrate. The electrochemical behavior of the LaHCF modified electrode was investigated preliminarily by voltammetry, and the experiments showed that hydrogen ion has a considerable effect on the electrochemical behavior of the modified electrode. [Copyright &y& Elsevier]

Electrochemistry, Hybridization Chain Reaction, Nanopipette, RNA, Single Cell Analysis Keywords: Electrochemistry; Hybridization Chain Reaction; Nanopipette; RNA; Single Cell Analysis EN Electrochemistry Hybridization Chain Reaction Nanopipette RNA Single Cell Analysis 1 1 1 06/05/21 20210607 NES 210607 B Einzelzellanalyse b Eine auf einer duplexspezifischen Nuklease basierende Nanopipette wurde im Forschungsartikel auf S. 13352 von Wei-Wei Zhao, Jing-Juan Xu et al. hergestellt und zur Analyse der wirkstoffinduzierten Schwankung des miR-10b-Spiegels auf Einzelzellniveau verwendet. [Extracted from the article]

A dual-functional electrochemical biosensor for adenosines and hydrogen peroxide from cancer cells was developed based on a traditional switchable electrochemical sensing format and ATP improved G-quadruplex DNAzyme as a biolabel. [ABSTRACT FROM AUTHOR]

A novel switch-cytosensing strategy has been designed, which is based on the changes of electron transfer efficiency between ferrocene at the end of DNA and the electrode surface before and after cell transfection. This strategy provided a general and convenient method to fabricate efficient electrochemical cell sensors. [ABSTRACT FROM AUTHOR]

This work firstly reports an opto–magnetic interaction–induced enhancement of electrochemiluminescence (ECL) from CdS : Mn nanocrystals (NCs) film by superparamagnetic Fe3O4nanoparticles and its application to sensitive immunosensing. [ABSTRACT FROM AUTHOR]

Abstract: An ultrathin platinum film is fabricated on a nanoporous gold (NPG) scaffold through a catalytic chemical deposition method. The morphology and active surface area of the deposited Pt film, which will greatly influence the electro-catalytic properties of the catalyst, can be controlled by adjusting the deposition condition. Compared with bare NPG and high Pt loaded NPG, the performances of methanol electro-oxidation on the low-Pt-content bimetallic film are greatly improved, both in its catalytic current enhancement and signal stability. The best condition for methanol oxidation can be achieved when the area ratio of deposited Pt and uncovered Au was 3:1. [Copyright &y& Elsevier]

Nanochannels have brought new opportunities for biosensor development. Herein, we present the novel concept of a nanochannels photoelectrochemical (PEC) biosensor based on the integration of a unique CuxO-nanopyramid-islands (NPIs) photocathode, an anodic aluminum oxide (AAO) membrane, and alkaline phosphatase (ALP) catalytic chemistry. The CuxO-NPIs photocathode possesses good performance, and further assembly with AAO yields a designed architecture composed of vertically aligned, highly ordered nanoarrays on top of the CuxO-NPIs film. After biocatalytic precipitation (BCP) was stimulated within the channels, the biosensor was used for the successful detection of ALP activity. This study has not only provided a novel paradigm for an unconventional nanochannels PEC biosensor, which can be used for general bioanalytical purposes, but also indicated that the new concept of nanochannel -- semiconductor heterostructures is a step toward innovative biomedical applications. [ABSTRACT FROM AUTHOR]

Here we report the studies on the electrochemical behaviors at a closed bipolar cell which is composed of two separated reaction cells containing a closed bipolar electrode (c-BPE) and its driving electrodes. The influence factors such as the concentration of the reagents, the size and material of the electrodes are studied experimentally and theoretically. And the experimental results fit with the theoretic calculation very well. Significantly, unlike the previous studies focusing on the coupling of the two c-BPE poles, this work also considers the effect of the reaction on the driving electrode on the electrochemical behavior. We believe that this research could deepen our understanding of bipolar chemistry and be useful for the future c-BPE-based applications. [ABSTRACT FROM AUTHOR]

Herein, a facile and sensitive dual mode sensing strategy for amantadine (AMD) level evaluation by coupling the plasmonic Au nanorod (NR) and supramolecular SH-cyclodextrin (CD) through strong Au-S bond is proposed. Methylene blue (MB) molecules can be inserted into the cavity of CD molecules through the hydrophobic interaction, which would cause the plasmon resonance energy transfer (PRET) process as well as electrochemical signal response due to the spectrum overlap between Au NR and MB molecules and the electrochemical conversion activity of MB molecules. Subsequently, AMD would induce the replacement of MB molecules because of the stronger interaction with CD, resulting the recovery of scattering intensity of Au NR and decrease of the electrooxidation current of MB. On one hand, the increase of Au NR scattering intensity is linearly proportional to AMD with the concentration from 0.4 to 3.0 μM, and reaches a limit of detection (LOD) of 0.28 μM. On the other hand, electrochemical measurement method enlarged the detection range of AMD. The variation of electrochemical oxidation peak current of MB is linearly proportional to the logarithm value of AMD concentration from 2.5 to 375.0 μM, with LOD of 1.9 μM. Subsequently, the proposed dual mode response sensing strategy was successfully employed for the detection of AMD in human serum samples with great selectivity and sensitivity, with a recovery percentage ranged from 92.6 to 112.0%. Overall, this Au NR@SH-CD-MB nanoparticle based single particle plasmonic and electrochemical dual mode sensing method provides great potential in the field of clinical drug detection or metabolic process investigation in the future. Au NR@SH-CD-MB NPs for dual mode AMD detection. [Display omitted] • The CD molecules were introduced for simpler and more effective construction of PRET based plasmonic sensors. • Au NR@SH-CD-MB NPs could produce scattering and electrochemical dual signals for AMD detection. • The prepared Au NR@SH-CD-MB NPs have a good sensitivity and selectivity toward AMD. • The dual signal responsive detection method could achieve a lower LOD and broader dynamic range in biosensing. [ABSTRACT FROM AUTHOR]

Abstract: Here we report a novel approach for the detection of adenosine in cancer cells by electrochemiluminescence (ECL) on a wireless indium tin oxide bipolar electrode (BPE). In this approach, ferrocene (Fc) which is labeled on adenosine aptamer is enriched on one pole of the BPE by hybridization with its complementary DNA (ssDNA) and oxidized to Fc+ under an external voltage of 5.0V at the two ends of BPE. Then, a reversed external voltage was added on the BPE, making Fc+ enriched pole as cathode. The presence of Fc+ promotes the oxidation reaction on the anodic pole of the BPE, resulting in a significant increase of ECL intensity using Ru(bpy)3 2+/tripropylamine (TPA) system as test solution. The presence of target adenosine was reflected by the ECL signal decrease on the anodic pole caused by the target-induced removal of ferrocene-aptamer on the cathodic pole. The decrease of ECL signal was logarithmically linear with the concentration of ATP in a wide range from 1.0fM to 0.10μM. This ECL biosensing system could accurately detect the level of adenosine released from cancer cells. [Copyright &y& Elsevier]

Abstract: Quinones are a group of potent antineoplastic agents. Here we described effective and facile routes to synthesize a series of ubiquinone analogues (UQAs). These unique compounds have been investigated by electrochemistry and in situ UV–vis spectroelectrochemistry to explore their electron-transfer processes and radical properties in aprotic media. The structure–activities relationships of inhibiting cancer cell proliferation of UQAs were examined in murine melanoma B16F10 cells using a 72 h continuous exposure MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Our results revealed that UQAs had improved antiproliferative activity and displayed better inhibitory effects than natural ubiquinone 10. The cytotoxic activities of UQAs were correlated to the semiubiquinone radicals, which were confirmed by in situ electron spin resonance (ESR). In the cytotoxicity test, 6-vinylubiquinone 5 and 6-(4′-fluorophenyl) ubiquinone 7 that possess half maximal inhibitory concentration value (IC50) of 6.1 μM and 6.2 μM. This would make them as valuable candidates for future pharmacological studies. [Copyright &y& Elsevier]