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Lanqun Mao

Publications and source records attributed to Lanqun Mao.

At least 19 recordsLinked to original sources
PubMed2006

Photomodulation of the electrode potential of a photochromic spiropyran-modified Au electrode in the presence of Zn2+: a new molecular switch based on the electronic transduction of the optical signals.

The electrode potential of a photochromic spiropyran-modified Au electrode could be reversibly modulated by UV/visible light irradiation in the presence of Zn2+, and a new molecular switch and an "AND" logic gate based on this electronic transduction of the optical signals were established.

Benzopyrans↗
PubMed2006

Electrochemical properties of carbon nanotube (CNT) film electrodes prepared by controllable adsorption of CNTs onto an alkanethiol monolayer self-assembled on gold electrodes.

This paper describes electrochemical properties, such as electrode reactivity, electrode dimensions, and interfacial capacitance, of multiwalled carbon nanotube (MWNT) film electrodes prepared by controllable adsorption of the MWNTs onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) deposited onto Au electrodes. The adsorption of the MWNTs onto the SAM-modified Au electrode substantially restores heterogeneous electron transfer between bare Au electrode and redox species in solution phase that is almost totally blocked by the SAM of C18H37SH, and as a result, the prepared MWNT/SAM-modified electrode possesses good electrode reactivity without a remarkable barrier to heterogeneous electron transfer. In addition, the surface coverage of the MWNTs is readily controlled by adjusting the immersion time for the adsorption of the MWNTs onto the SAM of C18H37SH, which essentially endows the prepared MWNT/SAM-modified electrodes with tunable electrode dimensions ranging from a nanoelectrode array to a macro-sized conventional electrode. On the other hand, the MWNT/SAM-modified electrode is found to possess a largely reduced interfacial capacitance, as compared with the MWNT film electrodes prepared with existing methods by directly confining the MWNTs onto electrode surface. This demonstration offers a new approach to fabrication of stable MWNT film electrodes with excellent electrochemical properties that are believed to be very attractive for electrochemical studies and electroanalytical applications.

Journal Article↗
PubMed2006

Online acid barrage stacking anti-salt injection for capillary electrophoresis of 9-fluorenylmethylchloroformate-derivatized amino acids in high ionic strength solutions by UV detection.

An acid barrage stacking (ABS) method has been shown to be feasible for online anti-salt injection in CE of 9-fluorenylmethyl chloroformate (FMOC)-labeled amino acids (AAs) detected by common UV absorption. The operation was performed on normal polar CE by sucking in an extra plug of acid following a sample zone, serving as a selective acid barrage to block the backward migration of weak anionic analytes due to a sudden mobility reduction via acid-base reaction which does not affect strong co-ions such as Cl(-) to penetrate the barrage freely. By CE-UV of FMOC-AAs in various NaCl solutions, the effectiveness of ABS was firmly validated, able to stand up to 500 mM NaCl and to stack analytes by 10(3)-fold calculated from the UV detection limits, that is 0.01 microM for ABS and 10 microM for non-stacking injection. The method was also validated by determining trace Glu and Asp in real samples of rat brain microdialysate, rat serum and human saliva. The intraday RSDs were 0.33-4.9% for migration time and 1.8-9.6% for peak area. The recoveries measured by spiking technique were 82-115% for Glu and 86-116% for Asp. Working equations were obtained by plotting peak height vs. concentration at 0.1-50 microM, with correlation coefficients of >0.999. The contents of Glu and Asp were thus found at 0.26-0.83 microM and 0.24-0.64 microM respectively, in rat brain microdialyste; 37-40 microM and 8.4-10 microM, respectively, in rat serum; and 3.5-5.8 microM and 1.0-4.1 microM, respectively in human saliva. They were consistent with the data from other methods.

Amino Acids↗
PubMed2005

Rational attachment of synthetic triptycene orthoquinone onto carbon nanotubes for electrocatalysis and sensitive detection of thiols.

This study demonstrates a novel electrochemical method for sensitive determination of biological thiols including homocysteine, cysteine, and glutathione based on rational functionalization of single-walled carbon nanotubes (SWNTs) with synthetic triptycene orthoquinone (TOQ). Unlike previous strategies used for the functionalization of the carbon nanotubes to fabricate new kind of electrochemically functional nanostructures, the method demonstrated here is essentially based on understanding of the redox properties inherent in the SWNTs themselves. It is demonstrated that the electrochemical oxidation of the thiols at the SWNT-modified electrode is redox-mediated by the quinone-like functional groups at the tube ends and that the low density of such functional groups leads to a follow-up oxidation of the thiols at a more positive potential at the electrode. To mimic the redox properties of the SWNTs and thus to increase the catalytic sites onto the SWNTs, we rationally choose the synthetic TOQ and attach such a compound onto the SWNTs. As a result, it is found that the rational attachment of TOQ onto the SWNTs substantially results in a sufficient electrocatalysis toward the thiols at a low potential of 0.0 V with enhanced sensitivities (i.e., almost by a factor of 10-fold) for the determination of such kind of species in relative to those at the SWNT-modified electrode. The high sensitivity and the good stability as well as the high reproducibility of the TOQ/SWNT-modified electrodes substantially make them very useful for reliable and durable determination of the biological thiols.

Adsorption↗
PubMed2005

Continuous on-line monitoring of extracellular ascorbate depletion in the rat striatum induced by global ischemia with carbon nanotube-modified glassy carbon electrode integrated into a thin-layer radial flow cell.

This study describes a novel analytical system integrating in vivo microdialysis sampling with a radial thin-layer flow cell with a single-walled carbon nanotube (SWNT)-modified glassy carbon electrode as working electrode for continuous and on-line monitoring of ascorbate depletion in the rat striatum induced by global ischemia. The SWNTs, especially those after vacuum heat treatment at 500 degrees C, are found to be able to enhance the electron-transfer kinetics of ascorbate oxidation at a low potential (ca. -50 mV) and possess a strong ability against electrode fouling. These properties essentially make it possible to determine ascorbate with a good stability and high selectivity against catecholamines and their metabolites and other electroactive species of physiological levels. While being integrated with in vivo microdialysis to assemble an on-line analytical system, the electrode is proved useful for continuous and sensitive monitoring of the basal dialysate level of ascorbate and its depletion in the rat striatum induced by global ischemia. The basal dialysate level of ascorbate is determined to be 5.0 +/- 0.5 microM (n = 5) and a 50 +/- 10% (n = 3) depletion is recorded for the basal ascorbate after 4 h of global ischemia.

Animals↗
PubMed2005

Molecular films of water-miscible ionic liquids formed on glassy carbon electrodes: characterization and electrochemical applications.

This letter describes the formation and possible electrochemical applications of molecular films of water-miscible imidazolium-based ionic liquids (ILs) on glassy carbon (GC) electrodes. X-ray photoelectron spectroscopy (XPS) and electrochemical results indicate that the water-miscible ILs used in this study can interact with the GC electrode and form molecular films on the electrode surface. The formed molecular films are found to possess striking electrochemical properties such as electrocatalysis toward ascorbic acid (AA) and the capability to facilitate direct electron transfer of horseradish peroxidase (HRP). This demonstration would pave the way for new electrochemical applications of water-miscible ILs and is envisaged to be useful for the investigation of the electrochemical properties of water-miscible ILs in aqueous media provided the same counteranion is used as the supporting electrolyte.

Journal Article↗
PubMed2005

Bioelectrochemically functional nanohybrids through co-assembling of proteins and surfactants onto carbon nanotubes: facilitated electron transfer of assembled proteins with enhanced faradic response.

Preparation and bioelectrochemical properties of functional nanohybrids through co-assembling of hemeproteins (i.e., horseradish peroxidase, hemoglobin, myoglobin and cytochrome c) and surfactants onto carbon nanotubes (CNTs) are described. The prepared protein-surfactant-CNT nanohybrids are found to possess facilitated interfacial electron transfer of the proteins with enhanced faradic responses. The enhancements are ascribed for the first time to the properties of the surfactants for facilitation of protein electrochemistry and the improved portion of electroactive proteins assembled, of which the latter assignment is closely associated with the electrochemical and structural properties of the nanotubes and the three-dimensional architecture of the CNT film confined onto the glassy carbon electrode. It is proposed that the single and/or small bundles of the nanotubes in the CNT film electrode can be rationally functionalized with surfactants to be functional nanoelectrodes capable of facilitating electron transfer of proteins. The three-dimensional confinement of these functional nanowires onto the GC electrode essentially increases the portion of electroactive proteins assembled in the nanohybrids. These properties of the protein-surfactant-CNT nanohybrids, combined with the bioelectrochemical catalytic activity, could make them useful for development of bioelectronic devices and investigation of protein electrochemistry at functional interfaces.

Carbon↗
PubMed2005

Layer-by-layer assembled carbon nanotubes for selective determination of dopamine in the presence of ascorbic acid.

Multilayer films of shortened multi-walled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon (GC) electrodes using layer-by-layer (LBL) method based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged shortened MWNTs. The assembled MWNT multilayer films were studied with respect to the electrocatalytic activity toward ascorbic acid (AA) and dopamine (DA) and were further applied for selective determination of DA in the presence of AA. Scanning electron microscopy (SEM) used for characterization of MWNT films indicates that the assembled MWNTs are almost in a form of small bundles or single nanotubes on the electrodes. Cyclic voltammetric results with assembled MWNT electrode indicate that the strategy based on the LBL method for assembling the MWNT multilayer films on substrate well retains the electrochemical catalytic activity of the MWNTs toward AA and DA, offering some advantages particularly attractive for analytical applications, such as the form of MWNTs assembled on the substrate, i.e., small bundles or single tubes, homogeneity and stability of the as-assembled MWNT films. These features make the assembled MWNTs relatively potential for selective and sensitive determination of DA in the presence of AA.

Ascorbic Acid↗
PubMed2005

A carbon fiber microelectrode-based third-generation biosensor for superoxide anion.

Implantable and miniature carbon fiber microelectrode (CFME)-based third-generation biosensor for superoxide anion (O(2)(-)) was fabricated for the first time. The CFME-based biosensor was constructed by electro-deposition of Au nanoparticles on the CFMEs and then modification of the Au nanoparticles by cysteine followed by immobilization of superoxide dismutase (SOD) on the electrodes. The direct electrochemistry of the SOD immobilized on the CFME-based electrodes was efficiently realized by electron transfer promoter - cysteine molecules confined on the Au nanoparticles deposited on the CFMEs. The CFME-based biosensors were demonstrated to possess striking analytical properties for O(2)(-) determination, such as optional operation potentials, high selectivity and sensitivity as well as good stability. Along with the implantable capacity inherent in the CFMEs, these striking analytical properties of the CFME-based biosensors substantially make them potential for in vivo determination of O(2)(-).

Adsorption↗
PubMed2005

Enzyme-based amperometric biosensors for continuous and on-line monitoring of cerebral extracellular microdialysate.

Analytical systems integrating in vivo microdialysis sampling with enzyme-based electrochemical biosensor detection have been increasingly accepted to be a new technique for continuous and on-line monitoring of biologically important species. Extensive interests in such integrated on-line analytical systems have suggested that these systems are very useful for physiological and pathological investigations. This review mainly focuses on the principle, development and striking applications of the enzyme-based amperometric biosensors integrated with in vivo microdialysis for continuous and on-line monitoring of cerebral extracellular fluid in recent years.

Acetylcholine↗
PubMed2005

Chiral ion-exchange capillary electrochromatography of arylglycine amides with dextran sulfate as a pseudostationary phase.

A low-cost tunable chiral ion-exchange capillary electrochromatographic method has been developed for the separation of arylglycine amide racemic mixtures with dextran sulfate (DS) as an anionic and chiral pseudostationary phase and Tris-tartrate as a buffer system. The concentrations of DS and Tris had opposite influences on retention and resolution and could serve as ideal factors to finely tune the running speed and chiral resolution. Tartrate and pH largely impact the separation but pH should be confined within 3.0-5.5, only suitable for coarse tuning, while tartrate was preserved as the key buffering reagent, normally maintained at 40 mmol/L. With a working system composed of 0.1-1.0% DS, 20-60 mmol/L Tris, and 40 mmol/L tartrate at pH 3.50-4.50, the enantioresolution of arylglycine amides was shown to be dependent on their chemical structure: The chiral resolution increased when the hydrogen at the alpha-amino group or at the p-position of phenyl ring was replaced by other larger group(s) but the resolution decreased when the group at the o- or m-site on the phenyl ring was enlarged. Further, the electronegative substitute of -Cl had larger resolution increment than methyl or methoxy at the position p- of phenyl ring but much lower increment at position m-. It is possible to well explain the resolution variation phenomenon by considering the group resistance and the variation of hydrogen-bonds formed inside the amino amides and between the solutes and DS. The amido group was shown irreplaceable to have chiral resolution with DS alone as an ionic and chiral pseudostationary phase.

Buffers↗
PubMed2005

Electrochemistry and electroanalytical applications of carbon nanotubes: a review.

This review addresses recent developments in electrochemistry and electroanalytical chemistry of carbon nanotubes (CNTs). CNTs have been proved to possess unique electronic, chemical and structural features that make them very attractive for electrochemical studies and electrochemical applications. For example, the structural and electronic properties of the CNTs endow them with distinct electrocatalytic activities and capabilities for facilitating direct electrochemistry of proteins and enzymes from other kinds of carbon materials. These striking electrochemical properties of the CNTs pave the way to CNT-based bioelectrochemistry and to bioelectronic nanodevices, such as electrochemical sensors and biosensors. The electrochemistry and bioelectrochemistry of the CNTs are summarized and discussed, along with some common methods for CNT electrode preparation and some recent advances in the rational functionalization of the CNTs for electroanalytical applications.

Journal Article↗
PubMed2004

Sol-gel-derived ceramic-carbon nanotube nanocomposite electrodes: tunable electrode dimension and potential electrochemical applications.

Nanocomposite electrodes made of sol-gel-derived ceramic-carbon nanotube are fabricated by doping mutliwalled carbon nanotubes (MWNTs) into a silicate gel matrix. The electrochemical behavior and potential electrochemical applications of the ceramic-carbon nanotube nanocomposite electrodes (CCNNEs) are also studied. The as-prepared CCNNEs exhibit a tunable dimension ranging from conventional electrode to nanoelectrode ensemble (NEE), depending on the amount of the MWNT dispersed in the silica sol and finally doped within the gel matrix. A high content of the MWNT (i.e., higher than 1.5 mg/mL in the sol) leads to the formation of the CCNNE characteristic of an electrode of conventional dimension, while a low content (typically lower than 0.10 mg/mL) essentially yields the CCNNE like a nanoelectrode ensemble. The NEE is demonstrated to possess good electrocatalytic activity toward the oxidation of ascorbic acid (AA), and the CCNNE of conventional dimension is found to possess remarkable electrocatalytic activity toward the oxidation of glutathione (both reduced and oxidized forms, GSH and GSSG). These properties of the CCNNEs essentially offer a new electrochemical approach for the detection of AA, GSH, and GSSG. The possible essence of the tailor-made dimensions of the CCNNEs is also presented and discussed.

Journal Article↗
PubMed2004

Electrostatic layer-by-layer assembled carbon nanotube multilayer film and its electrocatalytic activity for O2 reduction.

Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions.

Journal Article↗
PubMed2004

Novel electrochemical method for sensitive determination of homocysteine with carbon nanotube-based electrodes.

An electrochemical method has been successfully demonstrated for sensitive determination of homocysteine (HcySH) with carbon nanotube (CNT)-modified glassy carbon (GC) electrodes. Cyclic voltammetric results clearly show that carbon nanotubes, especially those pretreated with nitric acid, possess an excellent electrocatalytic activity toward the oxidation of HcySH at a low potential (0.0 V versus Ag/AgCl). The remarkable catalytic property of the acid-pretreated CNTs, which is essentially associated with oxygen-containing moieties introduced on the tube surface, has been further exploited as a sensitive determination scheme for HcySH. Continuous-flow amperometric results suggest that the CNT-based electrodes (p-CNT/Nafion/GC), which were prepared by using Nafion to solubilize and further immobilize CNTs on GC electrodes, show striking analytical properties of good stability and reproducibility and strong ability against electrode fouling. Such analytical properties, along with the low operation potential, substantially enable a reliable and sensitive determination of HcySH with a good dynamic linearity up to 60 microM and a detection limit of 0.06 microM (S/N = 3). The catalytic mechanism and the possible application of the as-prepared p-CNT/Nafion/GC electrodes for the study of the auto-oxidation of HcySH are also demonstrated and discussed.

Biosensing Techniques↗
PubMed2004

Electrochemistry and electrocatalytic activities of superoxide dismutases at gold electrodes modified with a self-assembled monolayer.

In this article, the electrochemical properties and electrocatalytic activity of three kinds of superoxide dismutases (SODs), that is, bovine erythrocyte copper-zinc superoxide dismutase (Cu/Zn-SOD), iron superoxide dismutase from Escherichia coli (Fe-SOD), and manganese superoxide dismutase from E. coli (Mn-SOD), in the SOD family were studied. It was revealed that the direct electron transfer of the three kinds of SODs could be efficiently promoted by a self-assembled monolayer (SAM) of 3-mercaptopropionic acid (MPA) confined on a gold electrode. The electrochemical properties of the SODs at the MPA-SAM electrode vary with the sort of SOD with respect to the formal potential, reversibility of electrode reactions, kinetic parameters, and pH dependence, suggesting different mechanisms for the electrode reactions of the individual SODs. A combination of the facilitated direct electron transfer and the bifunctional enzymatic catalytic activities of the SODs via a redox cycle of their active metals substantially offered a flexible electrochemical route to determination of O(2)(*)(-) where O(2)(*)(-) can be sensed with the SOD-based biosensors in both anodic and cathodic polarizations. Such an intrinsic feature of the SOD-based biosensors successfully enabled a sensitive determination scheme for O(2)(*)(-) free from the interference from some coexisting electroactive species, such as ascorbic acid (AA) and uric acid (UA). Further potential applications for in vivo determination of O(2)(*)(-) is also suggested.

3-Mercaptopropionic Acid↗
PubMed2002

Continuous on-line measurement of cerebral hydrogen peroxide using enzyme-modified ring-disk plastic carbon film electrode.

An amperometric method suitable for the continuous on-line measurement of cerebral hydrogen peroxide from a microdialysate has been successfully performed for the first time by using an enzyme-modified ring-disk plastic carbon film electrode (PCFE) in a thin-layer radial flow cell. PCFE consists of a ring electrode modified with horseradish peroxidase to detect H2O2 at 0.0 V (vs Ag/ AgCl) and a disk electrode coated with ascorbate oxidase (AOx) to preoxidize ascorbic acid (AA) and thus suppress interference via direct oxidation. Analytes in solution (brain dialysates or standards) are mixed on-line with a phosphate-buffered solution containing dissolved oxygen and chelating agent, EDTA. The buffered solution is used to provide the O2 necessary for the AOx catalytic reaction, stabilize the changes in dialysate pH that are associated with the in vivo formation of H2O2, and remove heavy metal ion impurities and thus suppress reactions between AA and H2O2. This procedure enables trace levels of H2O2 to be readily monitored, virtually interference-free from physiological levels of AA, uric acid, electroactive neurotransmitters and their principle metabolites, in a continuous-flow system.

Animals↗