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An amperometric fluorinated xerogei-derived nitric oxide (NO) microelectrode is described. A range of fluorine-modified xerogel polymers were synthesized via the cohydrolysis and condensation of alkylalkoxy--and fluoro-alkoxysilanes. Such polymers were evaluated as NO sensor membranes to identify the optimum composition for maximizing NO permeability while providing sufficient selectivity for NO in the presence of common interfering species. By taking advantage of both the versatility of sol--gel chemistry and the 'poly(tetrafluoroethylene)-like' high NO permselective properties of the xerogels, the performance of the fluorinated xerogel-derived sensors was excellent, surpassing all miniaturized NO sensors reported to date. In contrast to previous electrochemical NO sensor designs, xerogel-based NO microsensors were fabricated using a simple, reliable dip-coating procedure. An optimal permselective membrane was achieved by synthesizing xerogels of methyltrimethoxysilane (MTMOS) and 20% (heptadecafluoro-1,1,2,2-tetrahydrodecyl)tri-methoxysilane (17FrMS, balance MTMOS) under acid-catalyzed conditions. The resulting NO microelectrode had a conical tip of ~20/[micro]m in diameter and ~55 [micro]m in length and exhibited sensitivities of 7.91 pA x [nM.sup.-1] from 0.2 to 3.0 nM ([R.sup.2] = 0.9947) and 7.60 nA x [micro][M.sup.-1] from 0.5 to 4.0 [micro]M ([R.sup.2] = 0.9999), detection limit of 83 pM (S/N= 3), response time ([t.sub.95%]) of

Xerogel sensing films were synthesized via sol--gel chemistry were used to fabricate optical nitroxyl (HNO) sensors. Selective detection of HNO in solution was achieved by monitoring the rates of manganese(III) meso-tetrakis-(4-sulfonatophenyl) porphyrinate ([Mn.sup.III]TPPS) reductive nitrosylation in the anaerobic interior of aminoalkoxysilane-derived xerogel films. Nitroxyl permeability in sensor films deposited in round-bottom 96-well plates was enhanced via incorporation of trimethoxysilyl-terminated poly(amidoamine-organosilicon) dendrimers in the xerogel network. The selectivity of [Mn.sup.III]TPPS for HNO, the overall sensitivity, and the working dynamic range of the resulting sensors were characterized. The HNO-sensing microtiter plates were used to quantify pH-dependent HNO generation by the recently described HNO-donor sodium 1-(isopropylamino)diazene-1-ium-1,2-diolate (IPA/ NO), and compare HNO production efficiency between IPA/NO and Angeli's salt, a traditional HNO-donor.

A xerogel-based optical pH sensor capable of releasing low levels of nitric oxide (NO) and measuring changes in solution pH is reported. Through simple dip-coating procedures, aminoalkoxysilane-based xerogel films modified with N-diazeniumdiolate NO donor precursors and the fluorescent pH indicator seminaphthorhodamine-1 carboxylate (SNARF-1) were sequentially deposited onto optical fibers. The resulting sensors were characterized by fast and linear response to pH throughout the physiological range (pH 7.0-7.8). Real-time chemiluminescence measurements confirmed that the presence of the overlying SNARF-1-containing TMOS layer did not have an inhibitory effect on N-diazeniumdiolate formation or NO release, and the NO-releasing coatings were capable of maintaining NO fluxes >0.4 pmol/[cm.sub.2] s up to 16 h. In vitro blood compatibility studies using porcine platelets confirmed the expected thromboresistivity of the NO-releasing xerogel coatings.

The preparation and characterization of nitric oxide (NO) releasing dendrimer conjugates from primary and secondary amine functionalized dendrimers are reported. It is observed that the total NO released from secondary amine conjugates is significantly greater than from the primary amine parent dendrimers due to the enhanced stability of secondary amine diazeniumdiolates.

The initial phase of fibrin formation, thrombin-catalyzed fibrinopeptide cleavage, from adsorbed fibrinogen is examined using surface plasmon resonance and liquid chromatography-mass spectrometry. Fibrinogen adsorbed on negatively charged surfaces (carboxyl-terminated self-assembled monolayers) released a smaller amount of fibrinopeptides, at a reduced rate relative to those of hydrophobic, hydrophilic, and positively charged surfaces (methyl-, hydroxyl-, and amine-terminated self-assembled monolayers, respectively).

An amperometric sol-gel derived nitric oxide microsensor is described. Several silicon-based xerogel membranes are evaluated to identify the optimum composition for maximizing NO permeability while providing sufficient selectivity for NO in the presence of common interfering species. Xerogel permeability and selectivity are further manipulated as a function of reaction/processing conditions. In addition, the effects of incorporating Nation into the xerogel matrix on sensor performance and the stability of the ensuing xerogel/Nafion hybrid film are evaluated. The optimal permselective membrane is achieved by catalyzing polycondensation of the xerogel composed of methyltrimethoxysilane and (aminoethylaminomethyl)-phenethyltrimethoxysilane and Nation with NO gas. The resulting NO microsensor exhibits a sensitivity of 0.17 [+ or -] 0.02 pA/nM (from 25 to 800 nM, r = 0.9991), detection limit of 25 nM (S/N = 3), response time of 9 s ([t.sub.95%], a NO concentration change from 400 to 500 nM), selectivnap ity (log [K.sup.amp.sub.NOj]) of

A potentiometric sol-gel derived (xerogel) pH sensor based on covalently attached amine groups is described. The sensor consists of a Ag/AgCl electrode coated with a hybrid aminosilane/alkylsilane xerogel film. Various combinations of aminosilanes and alkylsilanes are evaluated for their potentiometric response to pH. The optimal sensor design is composed of (aminoethylaminomethyl)phenethyltrimethoxysilane and methyltrimethoxysilane. This sensor exhibits near-Nerstian response (-55 mV x [decade.sup.-1]), responds rapidly ([less than or equal to] 3 s) to changes in pH, and has [H.sup.+] selectivity coefficients (log [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII.]) of -13 and -11 for interfering j cations [Na.sup.+] and [K.sup.+], respectively. In vitro platelet adhesion tests indicate that the xerogel coatings are more blood compatible than conventional poly(vinyl chloride) and poly(urethane) ion-selective electrode coatings.

A hybrid sol--gel/polyurethane glucose biosensor that releases nitric oxide is developed and characterized. The biosensor consists of a platinum electrode coated with four polymeric membranes including the following: (1) sol--gel with immobilized glucose oxidase (GOx); (2) polyurethane to protect the enzyme; (3) NO donor-modified sol--gel particle-doped polyurethane; and (4) polyurethane. This configuration was developed due to the drastic reduction in sensitivity observed for NO donor-modified sol--gel film-based glucose sensors. For the hybrid sol--gel/polyurethane biosensor, sol--gel particles are first modified with the NO donor and then incorporated into a polyurethane layer that is coated onto the preimmobilized GOx electrode. In this manner, the GOx layer is not exposed to the harsh conditions necessary to impart NO release ability to the biosensor, and only a minimal decrease in sensitivity due to the NO release is observed. The glucose response of the NO-releasing glucose biosensor and its NO generation profiles are reported. In addition, the stability of the sol--gel particles in the supporting polyurethane membrane is discussed.

The in vitro analytical performance of fluorescence-based oxygen sensing polymeric films prepared with silicone rubbers that spontaneously release nitric oxide (NO) is examined. The use of NO-release polymers for fabricating functional optical sensors is proposed as a potential solution to lingering biocompatibility and concomitant performance problems encountered with prototype intravascular optical oxygen sensors. Plasticized silicone rubber films formulated with two distinct types of diazeniumdiolate NO donors release NO for more than 24 h. The optical oxygen sensing films prepared by doping these NO release polymeric materials with oxygen indicators (pyrene/ perylene donor/acceptor pair) display different analytical responses, as compared to controls without NO release capability. Nonlinear Stern--Volmer behavior is observed for single-layer NO release oxygen sensors owing to heterogeneous environments for the pyrene/perylene pair and a concomitant quenching of the fluorescence by excess amine sites in such films. In contrast, a dual-layer configuration using an underlying NO-release silicone rubber layer covered with a second polymeric layer containing the fluorescent indicators is shown to yield identical sensitivity and linearity toward oxygen as conventional non-NO-releasing oxygen sensing films, while still providing surface NO fluxes necessary to yield more thromboresistive devices.

The development and in vivo analytical performance of a nitric oxide (NO)-releasing amperometric oxygen sensor with greatly enhanced thromboresistivity are reported. Gas permeable coatings formulated with cross-linked silicone rubber (SR) containing NO-generating compounds (diazeniumdiolates) are shown to release NO for extended periods of time (> 20 h) while reducing platelet adhesion and activation. Oxygen-sensing catheters prepared by dip-coating the NO-releasing films over the outer SR tubes of the implantable devices display similar analytical response properties in vitro (sensitivity, selectivity, response times) when compared to analogous sensors prepared without the NO release coatings. Superior analytical accuracy (relative to blood PO(sub 2) values measured in vitro) and greatly reduced thrombus formation on the outer surface of the sensors are observed in vivo (in canine model) with the NO release PO(sub 2) sensors compared to control sensors (without NO release) implanted simultaneously within the same animals. Based on these preliminary studies, the use of NO release polymers to fabricate catheter-style chemical sensors may be a potential solution to lingering biocompatibility and concomitant performance problems encountered when attempting to employ such devices for continuous intravascular measurements of blood gases and electrolytes.

Research was conducted to examine the air stability of alkanethiol self-assembled monolayers on silver and gold surfaces. Methodologies used were X-ray photoelectron spectroscopy, electrochemistry and surface Raman spectroscopy. Experimental results indicate that ozone is the primary oxidant in ambient laboratory air which generates rapid oxidation of the thiolate moiety.

The synthesis and characterization of a new nitric oxide (NO)-releasing scaffold prepared from amine-functionalized silica nanoparticles through a one-pot sol-gel process are described. The results show that advantages of silica-derived NO storage/delivery systems have included the ability to store large qualities of NO, modulate NO release kinetics and readily tune particle size based on the composition of the particle.

The synthesis of ~2 nm NO-releasing gold nanoparticles is an important step toward the development of a NO-delivery system that bridges small-molecule diazeniumdiolates and diazeniumdiolate-modified fumed silica particles. Further functionalization of the nanoparticles with receptor molecules to enable specific antibody-antigen or ligand-receptor interactions may allow for the targeting of specific tissues or cells.

An electrochemical method capable of direct, real-time detection of hydrogen sulfide was developed using triple pulse amperometry (TPA) to mitigate sulfur poisoning and its related passivation of the working electrode surface. Through repeated cycles of discrete potential pulses, the electrooxidation of surface-adsorbed elemental sulfur to water-soluble sulfate ions was exploited to regenerate the glassy carbon electrode surface and maintain consistent sensor performance. Amperometric measurements and X-ray photoelectron spectroscopy surface analysis demonstrated that the TPA sensors provided enhanced analytical performance via decreased sulfur accumulation relative to low-potential (≤+0.7 V) constant potential amperometry. Sensors operated under optimized TPA parameters retained high sensitivity (57.4 ± 13.0 nA/µM), a wide linear dynamic range (150 nM-15 µM), fast response times (<10 s), and a submicromolar detection limit (<100 nM) upon consecutive calibration cycles. The sensitivity and response time achieved were comparable to or better than current electrochemical sensors. Moreover, the simplicity of the method eliminates the need for external redox mediators or semipermeable membranes. [ABSTRACT FROM AUTHOR]

The localized concentration of nitric oxide (NO) between sol-gel micropattern lines is the critical threshold necessary to inhibit platelet adhesion to unmodified regions of the substrate. The ability of micropatterned NO-releasing surfaces to resist platelet adhesion namely surface localized NO release would be an effective strategy for achieving enhanced sensor biocompatibility without modifying an entire surface and potentially compromising analytical sensitivity.

Research into the ability of nitric oxide (NO)-releasing materials to actively reduce Pseudomonas aeruginosa adhesion is presented. It is suggested that sol-gel chemistry may offer a flexible technique for preparing stable and tunable NO-releasing materials.

A 530 nm light emitting diode was coupled to a microfluidic sensor tofacilitate photolysis of nitrosothiols (i.e., S-nitrosoglutathione, S-nitrosocysteine, and S-nitrosoalbumin) and amperometric detection of the resulting nitric oxide (NO). This configuration allowed for maximum sensitivity and versatility, while limiting potential interference from nitrate decomposition caused by ultraviolet light. Compared to similar measurements of total S-nitrosothiol content in bulk solution, use of the microfluidic platform permitted significantly enhanced analytical performance in both phosphate-buffered saline and plasma (6-20× improvement in sensitivity depending on nitrosothiol type). Additionally, the ability to reduce sample volumes from milliliters to microliters provides increased clinical utility. To demonstrate its potential for biological analysis, this device was used to measure basal nitrosothiol levels from the vasculature of a healthy porcine model. [ABSTRACT FROM AUTHOR]

The phytotoxicity of silica nanoparticles (SiNPs) was evaluated as a function of particle size (14, 50, and 200 nm), concentration (250 and 1000 mg L-1), and surface composition toward Arabidopsis thaliana plants grown hydroponically for 3 and 6 weeks. Reduced development and chlorosis were observed for plants exposed to highly negative SiNPs (-20.3 and -31.9 mV for the 50 and 200 nm SiNPs, respectively) regardless of particle concentration when not controlling pH of the hydroponic medium, which resulted in increased alkalinity (pH 8). Particles were no longer toxic to the plants at either concentration upon calcination or removal of surface silanols from the SiNP surface, or adjusting the pH of the growth medium to pH 5.8. The phytotoxic effects observed for the negatively charged 50 and 200 nm SiNPs were attributed to pH effects and the adsorption of macro- and micro-nutrients to the silica surface. Size-dependent uptake of the nanoparticles by the plants was confirmed using transmission electron microscopy (TEM) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) with plant roots containing 32.0, 1.85, and 7.00 × 10-3 mg Si·kg tissue-1/nm3 (normalized for SiNP volume) for the 14, 50, and 200 nm SiNPs respectively, after 6 weeks exposure at 1000 ppm (pH 5.8). This study demonstrates that the silica scaffolds are not phytotoxic up to 1000 ppm despite significant uptake of the SiNPs (14, 50, and 200 nm) into the root system of A. thaliana. [ABSTRACT FROM AUTHOR]