Multimembrane Carbon Fiber Electrodes for Physiological Measurements of Nitric Oxide

Electrochemical Detection of Gasotransmitters: Status and Roadmap

Gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), are a class of gaseous, endogenous signaling molecules that interact with one another in the regulation of critical cardiovascular, immune, and neurological processes. The development of analytical sensing mechanisms for gasotransmitters, especially multianalyte mechanisms, holds vast importance and constitutes a growing area of study. This review provides an overview of electrochemical sensing mechanisms with an emphasis on opportunities in multianalyte sensing. Electrochemical methods demonstrate good sensitivity, adequate selectivity, and the most well-developed potential for the multianalyte detection of gasotransmitters. Future research will likely address challenges with sensor stability and biocompatibility (i.e., sensor lifetime and cytotoxicity), sensor miniaturization, and multianalyte detection in biological settings.

Construction of a thermo-sensitive pRI857 vector for efficient DNA capturing in Escherichia coli

OBJECTIVES

To establish a positive cloning system with a zero background for high-throughput DNA cloning purpose.

RESULTS

The cloning vector, pRI857, and the genomic-library construction vector, pRI857-BAC, were constructed based on the mechanism of expression of the thermo-sensitive cI857 repressor gene that can stringently repress the P_R promoter and kanamycin resistance gene (P_R-kan ^R ) at 30 °C, but have no effect on P_R-kan ^R gene at 37 °C or at higher temperatures. When the pRI857 vectors were transformed into E. coli with or without a target foreign DNA fragment inserted at the BfrBI site of the cI857 gene, only colonies with the foreign DNA fragment survive. We extended this method to construct a pRI857-BAC vector for genomic library cloning which displays an efficiency of ~10⁷ cfu per µg of genomic DNA, with no empty vectors detected.

CONCLUSIONS

Cloning by indirect activation of resistance marker gene represents a novel DNA-capturing system, which can be widely applied for high-throughput DNA cloning.

A review of flux considerations for in vivo neurochemical measurements

The mass transport or flux of neurochemicals in the brain and how this flux affects chemical measurements and their interpretation is reviewed. For all endogenous neurochemicals found in the brain, the flux of each of these neurochemicals exists between sources that produce them and the sites that consume them all within μm distances. Principles of convective-diffusion are reviewed with a significant emphasis on the tortuous paths and discrete point sources and sinks. The fundamentals of the primary methods of detection, microelectrodes and microdialysis sampling of brain neurochemicals are included in the review. Special attention is paid to the change in the natural flux of the neurochemicals caused by implantation and consumption at microelectrodes and uptake by microdialysis. The detection of oxygen, nitric oxide, glucose, lactate, and glutamate, and catecholamines by both methods are examined and where possible the two techniques (electrochemical vs. microdialysis) are compared. Non-invasive imaging methods: magnetic resonance, isotopic fluorine MRI, electron paramagnetic resonance, and positron emission tomography are also used for different measurements of the above-mentioned solutes and these are briefly reviewed. Although more sophisticated, the imaging techniques are unable to track neurochemical flux on short time scales, and lack spatial resolution. Where possible, determinations of flux using imaging are compared to the more classical techniques of microdialysis and microelectrodes.

Electrochemical nitric oxide sensors for physiological measurements

The important biological roles of nitric oxide (NO) have prompted the development of analytical techniques capable of sensitive and selective detection of NO. Electrochemical sensing, more than any other NO detection method, embodies the parameters necessary for quantifying NO in challenging physiological environments such as blood and the brain. In this tutorial review, we provide a broad overview of the field of electrochemical NO sensors, including design, fabrication, and analytical performance characteristics. Both electrochemical sensors and biological applications are detailed.

Nitric oxide sensor based on carbon fiber covered with nickel porphyrin layer deposited using optimized electropolymerization procedure

Electropolymerization regime of meso-tetrakis(3-methoxy-4-hydroxyphenyl) porphyrin is optimized to yield films possessing both electrocatalytical and permselective properties towards nitric oxide oxidation. The sensor composed of electrochemically oxidized carbon fiber, covered solely with nickel porphyrin derivative layer electropolymerized using our method, is characterized by high selectivity towards nitrite (1:600), ascorbate (1:8000) and dopamine (>1:80), determined by constant potential amperometry at 830 mV (vs. Ag/AgCl). Selectivity for ascorbate and dopamine as well as detection limit for NO (1.5 nM at S/N=3) is 5-10 times better than parameters usually reported for Nafion coated porphyrinic sensors. Nafion coating can further enhance selectivity properties as well as aids to the stability of the sensors' responses.

Nitric oxide in brain: diffusion, targets and concentration dynamics in hippocampal subregions

Nitric oxide (NO(*)) is a diffusible regulatory molecule involved in a wide range of physiological and pathological events. At the tissue level, a local and temporary increase in NO(*) concentration is translated into a cellular signal. From our current knowledge of biological synthesis and decay, the kinetics and mechanisms that determine NO(*) concentration dynamics in tissues are poorly understood. Generally, NO(*) mediates its effects by stimulating (e.g., guanylate cyclase) or inhibiting (e.g., cytochrome oxidase) transition metal-containing proteins and by post-translational modification of proteins (e.g., formation of nitrosothiol adducts). The borderline between the physiological and pathological activities of NO(*) is a matter of controversy, but tissue redox environment, supramolecular organization and compartmentalisation of NO(*) targets are important features in determining NO(*) actions. In brain, NO(*) synthesis in the dependency of glutamate NMDA receptor is a paradigmatic example; the NMDA-subtype glutamate receptor triggers intracellular signalling pathways that govern neuronal plasticity, development, senescence and disease, suggesting a role for NO(*) in these processes. Measurements of NO(*) in the different subregions of hippocampus, in a glutamate NMDA receptor-dependent fashion, by means of electrochemical selective microsensors illustrate the concentration dynamics of NO(*) in the sub-regions of this brain area. The analysis of NO(*) concentration-time profiles in the hippocampus requires consideration of at least two interrelated issues, also addressed in this review. NO(*) diffusion in a biological medium and regulation of NO(*) activity.

Nitric oxide and Fenton/Haber-Weiss chemistry: nitric oxide is a potent antioxidant at physiological concentrations

We have examined the action of nitric oxide (NO) on the ability of Fenton's reagent (ferrous iron and hydrogen peroxide), to oxidize a number of organic optical probes. We found that NO is able to arrest the oxidation of organic compounds at concentrations of NO found in brain, in vivo. We present evidence that Fenton's reagent proceeds via a ferryl intermediate ([Fe[double bond]O]2+), before the generation of hydroxyl radical *OH. NO reacts rapidly with this ferryl, blocking the production of *OH. We propose that NO has an important role in protecting biological tissues, and the brain in particular, from Fenton chemistry.

Detection of ATP-induced nitric oxide in a biomimetic circulatory vessel containing an immobilized endothelium

Conditions for the adhesion of bovine pulmonary artery endothelial cells (bPAECs) in microbore tubing of 250-microm i.d. are described. When immobilized to the lumen of microbore tubing, these cells represent a mimic of a circulatory vessel's endothelium. The microbore tubing is coated with 100 microg mL(-1) fibronectin in order to promote bPAEC adhesion to the lumen of the tubing. A series of micrographs of the cells inside of the tubing indicates that approximately 3.5 h is necessary for cell adhesion. In this study, adenosine triphosphate (ATP) is used to induce the release of nitric oxide from the endothelium mimic. The endothelium-derived NO is detected amperometrically at a parallel flow cell containing a glassy carbon working electrode modified with Nafion. Results indicate that detectable amounts of NO are only produced by the endothelium mimic when ATP is present in the buffer. The typical concentration of NO produced by the endothelium mimic upon the introduction of 100 microM ATP is approximately 0.80 microM. Based on the injection volume of ATP and the estimated number of cells on the tubing lumen, this value corresponds to approximately 1 amol of NO/cell. Moreover, shear stress alone does not provide the agonistic effect required for NO production in the submicromolar range.

Indirect measurement of nitric oxide production by monitoring nitrate and nitrite using microchip electrophoresis with electrochemical detection

An indirect method for monitoring nitric oxide (NO) by determining nitrate and nitrite using microchip capillary electrophoresis (CE) with electrochemical (EC) detection has been developed. This method combines determination of nitrite by direct amperometric detection following a microchip-based CE separation and conversion of nitrate to nitrite by chemical reduction using Cu-coated Cd granules. The amount of nitrate is quantified by calculating the difference in the amount of nitrite in the sample before and after the reduction of nitrate. Optimization of the separation, injection, detection, and reduction reaction conditions, as well as studies involving integration of the reduction reaction onto the microchip, are described. It was found that nitrite can be separated and detected in approximately 45 s by microchip CEEC. The reduction reaction was successfully integrated on-chip and carried out in approximately 1 min following activation of the Cd granules. The usefulness of this device was demonstrated by monitoring the amount of nitrate and nitrite produced from 3-morpholinosydnonimine, a NO-releasing compound.

Recent developments in amperometric detection for microchip capillary electrophoresis

The interest in microfluidic devices has increased considerably over the past decade due to the numerous advantages of working within a miniature, microfabricated format. This review focuses on recent advances in coupling amperometric detection with microchip capillary electrophoresis (CE). Advances in electrochemical cell design, isolation of the detector from the separation field, and integration of both pre- and postseparation reaction chambers are discussed. The use of microchip CE with amperometric detection for enzyme/immunoassays, clinical and environmental assays, and the determination of neurotransmitters is described.

Activity-dependent nitric oxide concentration dynamics in the laterodorsal tegmental nucleus in vitro

The behavioral-state related firing of mesopontine cholinergic neurons of the laterodorsal tegmental nucleus appears pivotal for generating both arousal and rapid-eye-movement sleep. Since these neurons express high levels of nitric oxide synthase, we investigated whether their firing increases local extracellular nitric oxide levels. We measured nitric oxide in the laterodorsal tegmental nucleus with a selective electrochemical microprobe (35 microm diam) in brain slices. Local electrical stimulation at 10 or 100 Hz produced electrochemical responses that were attributable to nitric oxide. Stimulus trains (100 Hz; 1 s) produced biphasic increases in nitric oxide that reached a mean peak concentration of 33 +/- 2 (SE) nM at 4.8 +/- 0.4 s after train onset and decayed to a plateau concentration of 8 +/- 1 nM that lasted an average of 157 +/- 23.4 s (n = 14). These responses were inhibited by N(G)-nitro-L-arginine-methyl-ester (1 mM; 92% reduction of peak; n = 3) and depended on extracellular Ca(2+). Chemically reduced hemoglobin attenuated both the electrically evoked responses and those produced by authentic nitric oxide. Application of the precursor, L-arginine (5 mM) augmented the duration of the electrically evoked response, while tetrodotoxin (1 microM) abolished it. Analysis of the stimulus-evoked field potentials indicated that electrically evoked nitric oxide production resulted from a direct, rather than synaptic, activation of laterodorsal tegmental neurons because neither nitric oxide production nor the field potentials were blocked by ionotropic glutamate receptor inhibitors. Nevertheless, application of N-methyl-D-aspartate also increased local nitric oxide concentration by 39 +/- 14 nM (n = 8). Collectively, these data demonstrate that laterodorsal tegmental neuron activity elevates extracellular nitric oxide concentration probably via somatodendritic nitric oxide production. These data support the hypothesis that nitric oxide can function as a local paracrine signal during the states of arousal and rapid-eye-movement sleep when the firing of mesopontine cholinergic neurons are highest.

Pharmacological evidence for the selectivity of in vivo signals obtained with enzyme-based electrochemical sensors

Carbon fiber microelectrodes that support enzyme-containing redox polymer gels permit the amperometric detection of glutamate, choline, and glucose. These devices are of interest for in vivo neurochemical monitoring because their small dimensions may permit highly localized measurements within small brain nuclei. In vitro calibration procedures confirm that the sensors respond in a selective fashion towards their respective target analyte. In the current work, the selectivity of the in vivo response of the microsensors during pharmacological manipulations is considered. The response of choline and glucose microsensors during the local infusion of tetrodotoxin and neostigmine in rat striatum is reported. The results of this study support the conclusion that these microsensors respond selectively to their respective targets under in vivo conditions.