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A novel mass spectrometric method for probing the flash chemistry of electrogenerated reactive intermediates was developed based on rapid collision mixing of electrosprayed microdroplets by using a theta‐glass capillary. The two individual microchannels of the theta‐glass capillary are asymmetrically or symmetrically fabricated with a carbon bipolar electrode to produce intermediates in situ. Microdroplets containing the newly formed intermediates collide with those of the invoked reactants at sub‐10 microsecond level, making it a powerful tool for exploring their ultrafast initial transformations. As a proof‐of‐concept, we present the identification of the key radical cation intermediate in the oxidative dimerization of 8‐methyl‐1,2,3,4‐tetrahydroquinoline and also the first disclosure of previously hidden nitrenium ion involved reaction pathway in the C−H/N−H cross‐coupling between N,N′‐dimethylaniline and phenothiazine. [ABSTRACT FROM AUTHOR]

A novel electrochemiluminescence resonance energy transfer (ECL-RET) system from Eu 3 + -doped CdS nanocrystals (CdS:Eu NCs) to Ru(bpy) 3 2 + -doped silica nanoparticle (RuSi) was designed for ultrasensitive detection of prostate-specific antigen (PSA). The platform consists of a CdS:Eu NCs film on glassy carbon electrode (GCE) as ECL emitter and a sandwich-type immunocomplex formed by the primary antibody, PSA and RuSi-tagged second antibody. This system showed a maximum of 4.83-fold enhancement of ECL intensity at 620 nm due to the efficient ECL-RET and high Ru(bpy) 3 2 + quantum yields. By the signal amplification of RuSi and the specific antibody–antigen interactions, this ECL-RET system could sensitively respond down to 1.0 fg mL − 1 PSA. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) biosensing with semiconductor quantum dots (QDs) has received great attention because it integrates the advantages of both photo-excitation and electrochemical detection. During the photon-to-electricity conversion in PEC processes, electron-hole (charge) separation competes with electron-hole recombination, and the net effect essentially determines the performance of PEC biosensors. Herein, we propose a new approach for slowing down electron-hole recombination to increase charge separation efficiency for PEC biosensor development. Through doping with Mn2+, a pair of d bands (4T1 and 6A1) is inserted between the conduction and valence bands of CdS QDs, which alters the electron-hole separation and recombination dynamics, allowing the generation of long-lived charge carriers with ms-scale lifetime that decay about 104-105-fold more slowly than in the case of undoped QDs. Photocurrent tests indicated that Mn2+ doping resulted in an approximately 80 % increase in photocurrent generation compared with undoped CdS QDs. For application, the Mn-doped CdS QDs were coated on the surface of a glassy carbon electrode and functionalized with a cell surface carbohydrate-specific ligand (3-aminophenylboronic acid). In this way, a sensitive cytosensor for K562 leukemia cells was constructed. Moreover, the sugar-specific binding property of 3-aminophenylboronic acid allowed the electrode to serve as a switch for the capture and release of cells. This has been further explored with a view to developing a reusable PEC cytosensing platform. [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]

A novel nano-sized copper oxide modified carbon paste electrode has been fabricated to determine the amikacin by cyclic voltammetry and amperometry. The oxidation current of the amikacin on nano-sized copper oxide modified carbon paste electrode was about 40 times higher than that on bulk CuO modified carbon paste electrode. The curve of i vs. concentration was linear in the range of 2–200 µM of the amikacin concentration with a correlation coefficient of 0.998. The detection limit was ca. 1 µM of amikacin with the signal to noise ratio of 3. [ABSTRACT FROM AUTHOR]

An electrochemically pretreated glassy carbon electrode (PGCE) was achieved by anodic oxidation at 1.8 V and following potential cycling in the potential range from -0.8 to + 1.0 V. The resulting PGCE gave well-defined redox peaks with E[SUBpa]=-0.073 V, E[SUBpc] = 0.044V. The PGCE showed good activity in improving the electrochemical responses of some water-soluble Vitamins, such as Vitamin (VB[SUB2]), Vitamin (VB[SUB6]) and Vitamin (VC). VB[SUB2], VB[SUB6] could be adsorbed at PGCE and VC proceeded with an electrocatalytic process. The electrochemical behavior of VB[SUB6] at PGCE depended on the potential scanning method and the pretreatment process of the electrode. The PGCE was rather stable and can be used to simultaneously determine these vitamins in multivitamin tablets. [ABSTRACT FROM AUTHOR]

Studies the fabrication and surface morphology of methylene blue (MB)/perfluorosulfonated ionomer (Nafion) modified microcylinder carbon fiber electrode. Stability of the modified electrode; Extraction coefficient K of MB between Nafion film and solution; Significant electrocatalytic activity for the oxidation of hemoglobin.

Abstract: We report a simple approach for the selectively electrochemical sensing of cysteine (CySH) using β-MnO2 nanowires modified glassy carbon (GC) electrode via a direct and facile electrochemical co-deposition process with chitosan hydrogel. The electrode showed excellent electrocatalytic effect toward cysteine oxidation. A possible reaction mechanism related to the formation of surface complexes was proposed: the –SH group is the reacting group in the reaction between cysteine and MnO2, while the –NH2 group acts as an anchor to stabilize the surface complexes. The electrocatalytic behavior is further developed as a sensitive detection scheme for cysteine by amperometric measurement, which shows a large determination range of 0.5–630μM and a low detection limit of 70nM. Other nineteen amino acids in a 20-fold concentration do not interfere in the detection of cysteine. Furthermore, other biological species containing –SH group or Ssuch as glutathione, cystine, and bovine serum albumin (BSA), show no interferences because of steric hindrance and inactive S/ce:simple-para> [Copyright &y& Elsevier]

Abstract: Using chitosan as an effective linker between CMK-3 and glassy carbon electrode surface, {Hb/CMK-3} n multilayer film-modified electrodes were constructed through layer-by-layer assembly. The morphology of thus-formed {Hb/CMK-3} n film was characterized by scanning electron micrographs, and the interaction of hemoglobin (Hb) with CMK-3 was studied by UV–vis spectroscopy and electrochemical methods. Under optimal conditions, {Hb/CMK-3}6 film showed a couple of stable and well-defined redox peaks at about −377 and −296mV in pH 7.0 buffers. Furthermore, the {Hb/CMK-3}6 film displayed excellent electrocatalysis to the reduction of both H2O2 and O2. Based on thus-formed film and its direct electron transfer behavior, a novel biosensor was presented for the determination of H2O2 ranging from 1.2 to 57μM with the detection limit of 0.6μM at S/N=3. CMK-3 provided a desirable matrix for protein immobilization and biosensor preparation. [Copyright &y& Elsevier]

Abstract: Fe3O4 magnetic multilayer films were constructed on several conductive bases (glassy carbon electrode, ITO glass and Al foil) by the firstly electrodeposited chitosan/Fe3O4 nanoparticles thin film and then the layer-by-layer assembly using phytic acid and Fe3O4/chitosan. Scanning electronic microscopy (SEM), UV–vis spectra, electrochemical impedance spectroscopy (EIS) and superconducting quantum interference device (SQUID) measurements were used to characterize the multilayer films. Characteristic superparamagnetic properties of Fe3O4 nanoparticles are well remained in the film and could be controlled simply by changing the assembly layers. Moreover, the multilayer film showed good biocompatibility, the adsorbed hemoglobin (Hb) on the film realized direct electron transfer with the underlying GCE and kept high catalytic activity. This presented system avoid the complex synthesis for protecting Fe3O4 nanoparticles, and supplies a simple, universal way to construct other nanoparticles films on many conductive bases for biosensors’ development. [Copyright &y& Elsevier]

A simple and reliable method based on adsorptive stripping at an electrochemically pretreated glassy carbon electrode (GCE) was proposed for simultaneous or individual determination of guanine and adenine in DNA. The detection sensitivity of guanine and adenine was improved greatly by activating the GCE electrochemically. After accumulation on pretreated GCE at open circuit for 5 min or at the potential of +0.3 V for 120 s, guanine and adenine produced well-defined oxidation peaks at about +0.8 and +1.1 V, respectively in pH 5 phosphate buffer. The detection limit for individual measurement of guanine and adenine was 4.5 ng ml−1 (3×10−8 mol l−1) and 4 ng ml−1 (3×10−8 mol l−1), respectively. Acid-denatured DNA showed two oxidation peaks corresponding to guanine and adenine residues in the same buffer. The proposed method can be used to estimate the guanine and adenine contents in DNA with good selectivity in a linear range of 0.25–5 μg ml−1. [Copyright &y& Elsevier]

Abstract: This work demonstrates an aptasensor for ultrasensitive electrochemiluminescence (ECL) detection of thrombin based on an “off–on–off” approach. The system is composed of an Eu3+-doped CdS nanocrystals (CdS:Eu NCs) film on glassy carbon electrode (GCE) as ECL emitter. Then gold nanoparticles (AuNPs) labeled hairpin-DNA probe (ssDNA1) containing thrombin-binding aptamer (TBA) sequence was linked on the NCs film, which led to ECL quenching (off) as a result of Förster-resonance energy transfer (FRET) between the CdS:Eu NC film and the proximal AuNPs. Upon the occurrence of hybridization with its complementary DNA (ssDNA2), an ECL enhancement (on) occurred owing to the interactions of the excited CdS:Eu NCs with ECL-induced surface plasmon resonance (SPR) in AuNPs at large separation. Thrombin could induce ssDNA1 forming a G-quadruplex and cause the AuNPs to be close to CdS:Eu NCs film again, which resulted in an enhanced ECL quenching (off). This “off–on–off” system showed a maximum 7.4-fold change of ECL intensity due to the configuration transformation of ssDNA1 and provides great sensitivity for detection of thrombin in a wide detection range from 50aM to 1pM. [Copyright &y& Elsevier]

Abstract: Potassium (K) doping plays a critical role in adjusting the electronic properties of carbon materials. In this work, K-doped graphene, as a new electrode material, was used to modify glassy carbon electrode (GCE) for the simultaneous determination of nitrite (NO2 −) and sulfite (SO3 2−) under neutral conditions. The advantages of K-doped graphene/GCE are illustrated from comparison with the graphene/GCE, K-doped multi-walled carbon nanotubes (MWNTs)/GCE, MWNTs/GCE, graphite/GCE and bare/GCE for electrocatalytic and sensing applications. It exhibited a linear response over the concentration range from 0.5μM to 3.9mM, with a detection limit of 0.2μM (S/N=3) for NO2 − and a corresponding linear range of 2.5μM to 10.3mM, with a detection limit of 1.0μM (S/N=3) for SO3 2−. The proposed sensor could be successfully applied in the simultaneous detection of residual NO2 − and SO3 2− in polluted water accurately and precisely. [Copyright &y& Elsevier]

Abstract: Herein, we demonstrated a facile strategy for preparing high-loading Au nanoparticles using thionine functionalized graphene oxide as the supporting material. Glassy carbon electrodes modified with the as-obtained nanocomposites showed remarkably electrocatalytic activity towards the oxidation of glucose, leading to an enzymeless glucose sensor with a wide linear range and a lower detection limit of 0.05μmol/L. [Copyright &y& Elsevier]

Abstract: 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 10–500pg/mL with a detection limit of 4pg/mL. The proposed method was simple, fast and inexpensive for the determination of CEA at very low levels. [Copyright &y& Elsevier]

Abstract: The cationic luminescence probe, tris(2,2′-bipyridyl)ruthenium(II) complex ([Ru(bpy)3]2+), was incorporated into laponite-modified glassy carbon electrode (GCE) via two strategies, namely, the adsorption and intercalation methods. These two incorporation methods resulted in different microenvironment for the immobilized [Ru(bpy)3]2+ within laponite as well as the different host–guest and guest–guest interactions. Herein, cyclic voltammetry and electrochemiluminescence (ECL) were innovatively performed to monitor the interactions. Tripropylamine (TPA) was used as coreactant in the electrochemical and ECL system. [Copyright &y& Elsevier]

Abstract: Direct electrochemistry of hemoglobin (Hb) was observed at glassy carbon electrode (GCE) modified with undoped nanocrystalline diamond (UND) and Hb multilayer films via layer-by-layer assembly. UV–VIS absorbance spectroscopy, electrochemical impedance spectroscopy and cyclic voltammograms were employed to characterize the film. The results showed that the UND had the effect of enhancing the electron transfer between Hb and the electrode surface. Hb in the multilayer films maintained its bioactivity and structure. It also exhibited a good catalytic activity towards the reduction of H2O2. The reciprocal of catalytic current showed a linear dependence on the reciprocal of H2O2 concentration ranging from 0.5 μM to 0.25 mM with a detection limit of 0.4 μM. The apparent Michaelis–Menten constant was estimated to be 0.019 mM. [Copyright &y& Elsevier]

Abstract: 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. HAuCl4 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 HAuCl4 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 5.0×10−5 ∼1.30×10−3 M with a Michaelis–Menten constant of 3.5 mM and a detection limit of about 13 μM. [Copyright &y& Elsevier]

Abstract: Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)3 2+)–Zirconia–Nafion composite modified glassy carbon disk electrode as a solid-state electrochemiluminescence (ECL) detector is successfully applied to an electrophoretic microchip system with a wall-jet configuration. Pharmaceuticals such as tramadol, lidocaine and ofloxacin were selected to characterize the performance of this microchip capillary electrophoresis (CE)–ECL detection system. Voltammetric and ECL behaviors of immobilized Ru(bpy)3 2+ were investigated in lidocaine system. Influences of the separation electric field to cyclic voltammograms (CVs) of the immobilized Ru(bpy)3 2+ were also investigated. Tramadol, lidocaine and ofloxacin can be baseline separated without any additives. The detection limits (S/N=3) were 2.5×10−5 molL−1 for tramadol, 5.0×10−6 molL−1 for lidocaine, 1.0×10−5 molL−1 for ofloxacin under the sample injection of picoliters, and the linear ranges were from 5.0×10−5 to 2.5×10−3 molL−1 for tramadol, 1.0×10−5 to 1.0×10−3 molL−1 for lidocaine, and 1.0×10−5 to 2.5×10−3 molL−1 for ofloxacin, respectively. [Copyright &y& Elsevier]

Abstract: A novel solid-contact potentiometric sensor for ascorbic acid based on cobalt phthalocyanine nanoparticles (NanoCoPc) as ionophore was fabricated without any need of auxiliary materials (such as membrane matrix, plasticizer, and other additives). The electrode was prepared by simple drop-coating NanoCoPc colloid on the surface of a glassy carbon electrode. A smooth, bright and blue thin film was strongly attached on the surface of the glassy carbon electrode. The electrode showed high selectivity for ascorbic acid, as compared with many common anions. The influences of the amount of NanoCoPc at the electrode surface and pH on the response characteristics of the electrode were investigated. To overcome the instability of the formal potential of the coated wire electrode, a novel electrochemical pretreatment method was proposed for the potentiometric sensor based on redox mechanism. This resulting sensor demonstrates potentiometric response over a wide linear range of ascorbic acid concentration (5.5×10−7 to 5.5×10−2 M) with a fast response (<15s), lower detection limit (ca. 1.0×10−7 M), and a long-term stability. Furthermore, microsensors based on different conductors (carbon fiber and Cu wire) were also successfully fabricated for the determination of practical samples. [Copyright &y& Elsevier]