Extracorporeal life support without systemic anticoagulation: a nitric oxide-based non-thrombogenic circuit for the artificial placenta in an ovine model.

BACKGROUND: Clinical translation of the extracorporeal artificial placenta (AP) is impeded by the high risk for intracranial hemorrhage in extremely premature newborns. The Nitric Oxide Surface Anticoagulation (NOSA) system is a novel non-thrombogenic extracorporeal circuit. This study aims to test the NOSA system in the AP without systemic anticoagulation. METHODS: Ten extremely premature lambs were delivered and connected to the AP. For the NOSA group, the circuit was coated with DBHD-N2O2/argatroban, 100 ppm nitric oxide was blended into the sweep gas, and no systemic anticoagulation was given. For the Heparin control group, a non-coated circuit was used and systemic anticoagulation was administered. RESULTS: Animals survived 6.8 ± 0.6 days with normal hemodynamics and gas exchange. Neither group had any hemorrhagic or thrombotic complications. ACT (194 ± 53 vs. 261 ± 86 s; p < 0.001) and aPTT (39 ± 7 vs. 69 ± 23 s; p < 0.001) were significantly lower in the NOSA group than the Heparin group. Platelet and leukocyte activation did not differ significantly from baseline in the NOSA group. Methemoglobin was 3.2 ± 1.1% in the NOSA group compared to 1.6 ± 0.6% in the Heparin group (p < 0.001). CONCLUSIONS: The AP with the NOSA system successfully supported extremely premature lambs for 7 days without significant bleeding or thrombosis. IMPACT: The Nitric Oxide Surface Anticoagulation (NOSA) system provides effective circuit-based anticoagulation in a fetal sheep model of the extracorporeal artificial placenta (AP) for 7 days. The NOSA system is the first non-thrombogenic circuit to consistently obviate the need for systemic anticoagulation in an extracorporeal circuit for up to 7 days. The NOSA system may allow the AP to be implemented clinically without systemic anticoagulation, thus greatly reducing the intracranial hemorrhage risk for extremely low gestational age newborns. The NOSA system could potentially be applied to any form of extracorporeal life support to reduce or avoid systemic anticoagulation.

Mechanistic analysis of the photolytic decomposition of solid-state S-nitroso-N-acetylpenicillamine.

S-Nitroso-N-acetylpenicillamine (SNAP) is among the most common nitric oxide (NO)-donor molecules and its solid-state photolytic decomposition has potential for inhaled nitric oxide (iNO) therapy. The photochemical NO release kinetics and mechanism were investigated by exposing solid-state SNAP to a narrow-band LED as a function of nominal wavelength and intensity of incident light. The photolytic efficiency, decomposition products, and the photolytic pathways of the SNAP were examined. The maximum light penetration depth through the solid layer of SNAP was determined by an optical microscope and found to be within 100-200 µm, depending on the wavelength of light. The photolysis of solid-state SNAP to generate NO along with the stable thiyl (RS·) radical was confirmed using Electron Spin Resonance (ESR) spectroscopy. The fate of the RS· radical in the solid phase was studied both in the presence and absence of O2 using NMR, IR, ESR, and UPLC-MS. The changes in the morphology of SNAP due to its photolysis were examined using PXRD and SEM. The stable thiyl radical formed from the photolysis of solid SNAP was found to be reactive with another adjacent thiyl radical to form a disulfide (RSSR) or with oxygen to form various sulfonyl and sulfonyl peroxyl radicals {RS(O)xO·, x = 0 to 7}. However, the thiyl radical did not recombine with NO to reform the SNAP. From the PXRD data, it was found that the SNAP loses its crystallinity by generating the NO after photolysis. The initial release of NO during photolysis was increased with increased intensity of light, whereas the maximum light penetration depth was unaffected by light intensity. The knowledge gained about the photochemical reactions of SNAP may provide important insight in designing portable photoinduced NO-releasing devices for iNO therapy.

Controllable release of nitric oxide from an injectable alginate hydrogel.

Currently, the controlled release of nitric oxide (NO) plays a crucial role in various biomedical applications. However, injectable NO-releasing materials remain an underexplored research field to date. In this study, via the incorporation of S-nitroso-N-acetyl-penicillamine (SNAP) as an NO donor, a family of NO-releasing injectable hydrogels was synthesized through the in situ cross-linking between sodium alginate and calcium ion induced by D-(+)-gluconate δ-lactone as an initiator. Initially, the organic functional groups and the corresponding morphologies of the resulting injectable hydrogels were characterized by IR and SEM spectroscopies, respectively. The NO release times of hydrogels with different SNAP loading amounts could reach up to 36-47 h. Due to the release of NO, the highest antibacterial rates of these injectable hydrogels against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were up to 95 %, respectively. Furthermore, the matrix of these hydrogels demonstrated great water absorption ability, swelling behavior, and degradation performance. Finally, we expect that these NO-releasing injectable hydrogels could have great potential applications various biomedical material fields.

Reducing O2 sensitivity in electrochemical nitric oxide releasing catheters: An O2-tolerant copper(II)-ligand nitrite reduction catalyst and a glucose oxidase catheter coating.

Electrocatalytic nitric oxide (NO) generation from nitrite (NO2-) within a single lumen of a dual-lumen catheter using CuII-ligand (CuII-L) mediators have been successful at demonstrating NO's potent antimicrobial and antithrombotic properties to reduce bacterial counts and mitigate clotting under low oxygen conditions (e.g., venous blood). Under more aerobic conditions, the O2 sensitivity of the Cu(II)-ligand catalysts and the reaction of O2 (highly soluble in the catheter material) with the NO diffusing through the outer walls of the catheters results in a large decreases in NO fluxes from the surfaces of the catheters, reducing the utility of this approach. Herein, we describe a new more O2-tolerant CuII-L catalyst, [Cu(BEPA-EtSO3)(OTf)], as well as a potentially useful immobilized glucose oxidase enzyme-coating approach that greatly reduces the NO reactivity with oxygen as the NO partitions and diffuses through the catheter material. Results from this work demonstrate that very effective NO fluxes (>1*10-10 mol min-1 cm-2) from a single-lumen silicone rubber catheter can be achieved in the presence of up to 10% O2 saturated solutions.

S-Nitrosoglutathione Reduces the Density of Staphylococcus aureus Biofilms Established on Human Airway Epithelial Cells.

Patients with chronic rhinosinusitis (CRS) often show persistent colonization by bacteria in the form of biofilms which are resistant to antibiotic treatment. One of the most commonly isolated bacteria in CRS is Staphylococcus aureus (S. aureus). Nitric oxide (NO) is a potent antimicrobial agent and disperses biofilms efficiently. We hypothesized that S-nitrosoglutathione (GSNO), an endogenous NO carrier/donor, synergizes with gentamicin to disperse and reduce the bacterial biofilm density. We prepared GSNO formulations which are stable up to 12 months at room temperature and show the maximum amount of NO release within 1 h. We examined the effects of this GSNO formulation on the S. aureus biofilm established on the apical surface of the mucociliary-differentiated airway epithelial cell cultures regenerated from airway basal (stem) cells from cystic fibrosis (CF) and CRS patients. We demonstrate that for CF cells, which are defective in producing NO, treatment with GSNO at 100 µM increased the NO levels on the apical surface and reduced the biofilm bacterial density by 2 log units without stimulating pro-inflammatory effects or inducing epithelial cell death. In combination with gentamicin, GSNO further enhanced the killing of biofilm bacteria. Compared to placebo, GSNO significantly increased the ciliary beat frequency (CBF) in both infected and uninfected CF cell cultures. The combination of GSNO and gentamicin also reduced the bacterial density of biofilms grown on sinonasal epithelial cells from CRS patients and improved the CBF. These findings demonstrate that GSNO in combination with gentamicin may effectively reduce the density of biofilm bacteria in CRS patients. GSNO treatment may also enhance the mucociliary clearance by improving the CBF.

Electrochemical Generation of Nitric Oxide for Medical Applications.

Over the past 30 years, the significance of nitric oxide (NO) has become increasingly apparent in mammalian physiology. It is biosynthesized by three isoforms of nitric oxide synthases (NOS): neuronal (nNOS), endothelial (eNOS), and inducible (iNOS). Neuronal and eNOS both produce low levels of NO (nM) as a signaling agent and vasodilator, respectively. Inducible (iNOS) is present in activated macrophages at sites of infection to generate acutely toxic (µM) levels of NO as part of the mammalian immune defense mechanism. These discoveries have led to numerous animal and clinical studies to evaluate the potential therapeutic utility of NO in various medical operations/treatments, primarily using NO gas (via gas-cylinders) as the NO source. In this review, we focus specifically on recent advances in the electrochemical generation of NO (E-NOgen) as an alternative means to generate NO from cheap and inert sources, and the fabrication and testing of biomedical devices that utilize E-NOgen to controllably generate NO for medical applications.

S-Nitrosothiol-Impregnated Silicone Catheter for Colorimetric Sensing of Indole and E. coli: Toward On-Body Detection of Urinary Tract Infections.

Although there are many techniques to detect pathogenic bacteria, most of them are only suited for in vitro diagnostics. We report a urinary catheter-based colorimetric sensor for potential on-body detection of E. coli, the most prevalent bacterial species in urinary tract infections associated with the use of urinary catheters. In urine, indole is secreted by E. coli and reacts with a nitrosating agent incorporated in a silicone catheter. A red dimeric product, indoxyl red, is generated within silicone rubber to allow for color-based indole sensing with high sensitivity, linearity, and specificity. This reaction is initiated by the nitrosation reaction of indole at its C-3 position via reagents like sodium nitrite or S-nitroso-N-acetyl-penicillamine under aerobic conditions. The generated 3-nitrosoindole undergoes tautomerization, dimerization, and deoximation to form indoxyl red with high absorbance at 537 nm. In contrast to other indole sensors, the presented method can be applied in real catheters to detect indole and E. coli in biofluids such as urine. The is because (1) S-nitroso-N-acetyl-penicillamine, the nitrosating agent, can be impregnated into silicone elastomers, (2) indole from urine is extracted into silicone due to its hydrophobicity, and (3) the high acidity and oxygen solubility of silicone facilitates the sensing reaction within the silicone matrix. This silicone-based colorimetric sensor clearly differentiates E. coli below and above 105 CFU/mL, which is the threshold concentration of bacteriuria. We expect that early diagnosis of urinary tract infections using the naked eye is possible by functionalizing an exposed section of urinary catheters with the proposed molecular probe.

Characterization of the impact of mixing and droplet volumes on the behavior of microfluidic ion-selective droptodes.

Droplet microfluidic optodes, or "droptodes", have emerged as a powerful technology for rapid detection of small ions in complex matrices. While using segmented aqueous phases provides the benefits of sample isolation, the influence of the liquid nature of the oil carrier phase has not yet been explored. In this paper, we examine the influence of microfluidic parameters on droptode efficiency, using potassium-sensitive droptodes as a model system. We found that while changing flow rates on device does not change droptode performance, both channel geometry and droplet size significantly impact droptode efficiency. Specifically, enhanced mixing of the droplets leads to faster equilibration on device and lowers limits of detection by about one order of magnitude. We also found that increasing the size of the sample droplet, at the expense of the size of the oil carrier/sensing phase, leads to higher sensitivity in the linear region of the droptode. These easily manipulated properties will allow one device to potentially be adapted for several different applications, based upon the type and concentration range of measurement required.

The Effects of the Combined Argatroban/Nitric Oxide-Releasing Polymer on Platelet Microparticle-Induced Thrombogenicity in Coated Extracorporeal Circuits.

Clotting, anticoagulation, platelet consumption, and poor platelet function are major factors in clinical extracorporeal circulation (ECC). We have shown that nitric oxide-releasing (NOReL) coatings prevent thrombosis in a rabbit model of ECC without systemic anticoagulation. Nitric oxide-releasing prevents platelet adhesion and activation, resulting in preserved platelet count and function. Previous work has shown that activated platelets form platelet-derived microparticles (PMPs). These experiments were designed to determine if PMPs can identify platelet function during ECC. The objective of this study is to investigate the effects of NOReL on platelet activation and PMP formation during ECC. Uncoated ECCs, including with and without systemic heparin, and NOReL-coated ECCs, including DBHD/N2O2 and argatroban (AG)/DBHD/N2O2-coated ECCs without systemic heparin, were tested in a 4-hour rabbit thrombogenicity model. Before and after ECC exposure, platelets were stimulated with collagen, and PMPs were measured using flow cytometry. The uncoated ECCs clotted within the first hour, while the NOReL-coated ECCs circulated for 4 hours. During pre-ECC blood exposure, platelets stimulated with collagen produced PMPs. With post-ECC exposure, platelets from uncoated circuits generated less PMPs than baseline (mean ± SDs: 23246 ± 3611 baseline vs. 1300 ± 523 uncoated post circuit, p = 0.018) when stimulated with collagen. However, platelets from the AG/DBHD/N2O2-coated ECCs generated a greater number of PMPs as baseline values (23246 ± 3611 baseline vs. 37040 ± 3263 AG/DBHD/N2O2 post 4 hours circuit, p = 0.023). Blood exposure during ECC results in platelet activation and clotting in uncoated ECCs. The remaining circulating platelets have lost function, as demonstrated by the low PMP formation in response to collagen. AG/DBHD/N2O2-coated ECCs prevented significant platelet activation and clotting, while DBHD/N2O2 trended towards prevention of platelet activation. In addition, function of the circulating platelets was preserved, as demonstrated by PMP formation in response to collagen. These results indicate that PMPs may be an important measure of platelet activation during ECC. Platelet-derived microparticles may provide a simplified way to measure platelet function during clinical ECC.

Enhanced Hemocompatibility and In Vivo Analytical Accuracy of Intravascular Potentiometric Carbon Dioxide Sensors via Nitric Oxide Release.

In this letter, the innate ability of nitric oxide (NO) to inhibit platelet activation/adhesion/thrombus formation is employed to improve the hemocompatibility and in vivo accuracy of an intravascular (IV) potentiometric PCO2 (partial pressure of carbon dioxide) sensor. The catheter-type sensor is fabricated by impregnating a segment of dual lumen silicone tubing with a proton ionophore, plasticizer, and lipophilic cation-exchanger. Subsequent filling of bicarbonate and strong buffer solutions and placement of Ag/AgCl reference electrode wires within each lumen, respectively, enables measurement of the membrane potential difference across the inner wall of the tube, with this potential changing as a function of the logarithm of sample PCO2. The dual lumen device is further encapsulated within a S-nitroso-N-acetyl-DL-penicillamine (SNAP)-doped silicone tube that releases physiological levels of NO. The NO releasing sensor exhibits near-Nernstian sensitivity toward PCO2 (slope = 59.31 ± 0.78 mV/decade) and low drift rates (<2 mV/24 h after initial equilibration). In vivo evaluation of the NO releasing sensors, performed in the arteries and veins of anesthetized pigs for 20 h, shows enhanced accuracy (vs non-NO releasing sensors) when benchmarked to measurements of discrete blood samples made with a commercial blood gas analyzer. The accurate, continuous monitoring of blood PCO2 levels achieved with this new IV NO releasing PCO2 sensor configuration could help better manage hospitalized patients in critical care units.

Nitric Oxide-Releasing Insert for Disinfecting the Hub Region of Tunnel Dialysis Catheters.

The use of tunneled dialysis catheters (TDCs) for patients in need of hemodialysis treatments (HDs) causes a significant number of bloodstream infections (BSIs), with very few viable preventative/treatment methods. Use of antibiotics is relatively ineffective due to the development of multidrug-resistant bacterial strains and the inability to penetrate bacterial biofilms. Nitric oxide (NO) is an endogenous gas molecule that has broad-spectrum antimicrobial/antibiofilm activity. In this study, the potential of creating a NO-releasing insert device that is attached onto the hub region cap of TDCs and locally releases NO within the TDC hub is evaluated for its antimicrobial/antibiofilm effectiveness. The NO-releasing insert contains the natural NO donor S-nitrosoglutathione (GSNO), along with zinc oxide (ZnO) nanoparticles to accelerate NO release from the GSNO, within a short silicone tube that is sealed at both ends and attached to the catheter cap. An in vitro 3-d-long antimicrobial study using catheter hubs yielded >6.6 log reductions of both Pseudomonas aeruginosa and Staphylococcus aureus for the NO-releasing insert device compared to controls. Two 14-d-long sheep studies demonstrated that the NO-releasing insert devices are exceptionally potent at preventing bacteria/biofilm growth on the inner lumen walls of TDCs compared to controls that have no preventative treatment devices as well as implanted TDCs that have commercially available chlorhexidine-treated insert devices placed within the hub regions.

Plasticizer-Free Thin-Film Sodium-Selective Optodes Inkjet-Printed on Transparent Plastic for Sweat Analysis.

A novel strategy to functionalize transparent flexible plastic films with an optical ion-sensing layer using an inkjet-printing technology is described. The hydrophobic sensing chemicals that include a sodium ionophore, a lipophilic proton chromoionophore, and a lipophilic ion-exchanger are co-deposited onto substrates such as transparent polyester film sheets in the absence of any plasticizer and/or hydrophobic polymer matrix. The inkjet-printing process enables the formation of optode films with nanoscale thickness/roughness that readily facilitate interfacing with aqueous samples. Using a smartphone detector, the colorimetric response of the optodes is shown to reach 95% of equilibrium values within 100 s in response to different concentrations of sodium ions, which is more rapid than traditional ion-selective optodes based on plasticized PVC films as the sensing layer. The new optodes also exhibit high selectivity to Na+ over interfering ions including K+, Ca2+, and Mg2+. Chemical leaching experiments show that the highly hydrophobic optode components remain in place on the plastic substrate surface. Hence, excellent sensor stability and fully reversible optical responses are obtained, which is essential for potential continuous monitoring applications. Further testing of the sensors with undiluted human sweat samples is shown to yield accurate values for sodium concentrations. Therefore, the use of plasticizer-free ion-selective optode nanolayers that enable highly selective ion sensing on a clear plastic support is likely to expand the range of available chemical sensors suited for preparing wearable real-time sweat analysis devices.

Studies of combined NO-eluting/CD47-modified polyurethane surfaces for synergistic enhancement of biocompatibility.

The blood compatibility of various intravascular (IV) devices (e.g., catheters, sensors, etc.) is compromised by activation of platelets that can cause thrombus formation and device failure. Such devices also carry a high risk of microbial infection. Recently, nitric oxide (NO) releasing polymers/devices have been proposed to reduce these clinical problems. CD47, a ubiquitously expressed transmembrane protein with proven anti-inflammation/anti-platelet properties when immobilized on polymeric surfaces, is a good candidate to complement NO release in both effectiveness and longevity. In this work, we successfully appended CD47 peptides (pepCD47) to the surface of biomedical grade polyurethane (PU) copolymers. SIRPα binding and THP-1 cell attachment experiments strongly suggested that the pepCD47 retains its biological properties when bound to PU films. In spite of the potentially high reactivity of NO toward various amino acid residues in CD47, the efficacy of surface-immobilized pepCD47 to prevent inflammatory cell attachment was not inhibited after being subjected to a high flux of NO for three days, demonstrating excellent compatibility of the two species. We further constructed a CD47 surface immobilized silicone tubing filled with NO releasing S-nitrosoglutathione/ascorbic acid (GSNO/AA) solution for synergistic biocompatibility evaluation. Via an ex vivo Chandler loop model, we demonstrate for the first time that NO release and CD47 modification could function synergistically at the blood/material interface and produce greatly enhanced anti-inflammatory/anti-platelet effects. This concept should be readily implementable to create a new generation of thromboresistant/antimicrobial implantable devices.

Comparison of Diazeniumdiolated Dialkylhexanediamines as Nitric Oxide Release Agents on Nonthrombogenicity in an Extracorporeal Circulation Model.

When blood from a patient is circulated through extracorporeal circuits (ECCs), such as in cardiopulmonary bypass or extracorporeal life support, platelets in the blood are activated and form a thrombus. This is prevented clinically with a range of different systemic anticoagulation agents (e.g., heparin); however, this increases a patient's risk of hemorrhage. Previous work with nitric oxide (NO) releasing materials using the combined diazeniumdiolated diamine, N-N-di-N'-butyl-1,6-hexanediamine (DBHD), and a polymer-linked thrombin inhibitor, argatroban (AG), showed significant nonthrombogenicity in ECCs using a 4 h rabbit model. Herein, we evaluated if diazeniumdiolated N-N-di-N'-propyl-1,6-hexanediamine (DPHDN2O2), which has a slightly lower degree of lipophilicity compared to DBHDN2O2, would provide similar nonthrombogenicity as the AG/DBHDN2O2-polymer-coated circuits. While DPHDN2O2 releases NO at a higher flux rate than DBHDN2O2 when coated (within CarboSil polymer) on the inner wall of polyvinyl chloride tubing, neither coated circuit significantly affected animal hemodynamics. Both diazeniumdiolated diamines, in combination with immobilized AG or alone, significantly reduced thrombus formation similarly in the 4 h rabbit model (vs uncoated control): AG/DBHDN2O2: 0.12 ± 0.03 cm2; DBHDN2O2: 2.57 ± 0.82 cm2; AG/DPHDN2O2: 0.68 ± 0.22 cm2; DPHDN2O2: 1.87 + 1.26 cm2; uncoated control: 6.95 ± 0.82 cm2. AG/DPHDN2O2 was no different than AG/DBHDN2O in preserving platelet count and function. In addition, AG did not leach into the systemic circulation as the total clotting times were insignificantly different from the baseline values (AG/DPHDN2O2: 12.7 + 0.5 s (n = 3); AG/DBHDN2O2: 12.3 + 0.7 s (n = 3); baseline: 13.9 + 0.3 s (n = 13)). Based on these results, both DPHDN2O2 and DPHDN2O2 are good candidates as NO donor molecules for creating nonthrombogenic polymer coatings for ECCs.

Feedback-controlled photolytic gas phase nitric oxide delivery from S-nitrosothiol-doped silicone rubber films.

Constant therapeutic gas phase nitric oxide (NO) delivery is achieved from S-nitrosothiol (RSNO) type NO donor doped silicone rubber films using feedback-controlled photolysis. For photo-release of the NO gas, the intensity of the LED light source is controlled via a PID (proportional-integral-derivative) controller implemented on a microcontroller. The NO concentration within the emitted gas phase is monitored continuously with a commercial amperometric NO gas sensor. NO release was accurately adjustable up to 10 ppm across a broad range of setpoints with response times of roughly 1 min or less. When NO is generated into an air recipient stream, lower NO yields and a comparable level of toxic nitrogen dioxide (NO2) formation is observed. However, NO gas generated into an N2 recipient gas stream can be blended into pure O2 with very low NO2 formation. Following scale-up, this technology could be used for point-of-care gas phase NO generation as an alternative for currently used gas cylinder technology for treatment of health conditions where inhaled NO is beneficial, such as pulmonary hypertension, hypoxemia, and cystic fibrosis.

Nitric Oxide Generation On Demand for Biomedical Applications via Electrocatalytic Nitrite Reduction by Copper BMPA- and BEPA-Carboxylate Complexes.

Intravascular (IV) catheters are essential devices in the hospital that are used to monitor a patient's blood and for administering drugs or nutrients. However, IV catheters are also prone to blood clotting at the point of insertion and infection by formation of robust bacterial biofilms on their surface. Nitric oxide (NO) is ideally suited to counteract both of these problems, due to its antimicrobial properties and its ability to inhibit platelet activation/aggregation. One way to equip catheters with NO releasing properties is by electrocatalytic nitrite reduction to NO by copper complexes in a multi-lumen configuration. In this work, we systematically investigate six closely related Cu(II) BMPA- and BEPA-carboxylate complexes (BMPA = bis-(2-methylpyridyl)amine); BEPA = bis-(2-ethylpyridyl)amine), using carboxylate groups of different chain lengths. The corresponding Cu(II) complexes were characterized using UV-Vis, EPR spectroscopy, and X-ray crystallography. Using detailed cyclic voltammetry (CV) and bulk electrocatalyic studies (with real-time NO quantification), in aqueous buffer, pH 7.4, we are able to derive clear reactivity relations between the ligand structures of the complexes, their Faradaic efficiencies for NO generation, their turnover frequencies (TOFs), and their redox potentials. Our results show that the complex [Cu(BEPA-Bu)](OAc) is the best catalyst with a high Faradaic efficiency over large nitrite concentration ranges and the expected best tolerance to oxygen levels. For this species, the more positive redox potential suppresses NO disproportionation, which is a major Achilles heel of the (faster) catalysts with the more negative reduction potentials.

Comparison of electrochemical nitric oxide detection methods with chemiluminescence for measuring nitrite concentration in food samples.

Nitrite is a naturally occurring species present in various food samples and also present in our bodies as a product of nitric oxide (NO) oxidation. Considering the ubiquity of nitrite, its determination is of great importance in both biological and food samples. Herein, a very facile indirect method of nitrite determination in meat samples via selective reduction to nitric oxide (NO) is presented. The resulting gaseous product is quantified via portable and cost-effective electrochemical sensors. Both a novel laboratory prepared Pt-Nafion based NO sensor and a commercially available amperometric NO sensor are compared. Excellent correlations between the nitrite amount found in tested samples using both of the electrochemical sensors and a reference chemiluminescence method are demonstrated (r = 0.997 and r = 0.999 for Pt-Nafion based and commercially available NO-B4 electrochemical sensors, respectively, n = 12). Moreover, the slope of the linear regression curves are very close to unity for the comparison of the three systems tested. The amperometric sensors compared within this work exhibit good precision and accuracy and are shown to be an attractive alternative to the costly chemiluminescence detection method for accurately determining nitrite levels in food samples.

Nitric oxide releasing two-part creams containing S-nitrosoglutathione and zinc oxide for potential topical antimicrobial applications.

Currently, most antimicrobial topical treatments utilize antibiotics to prevent or treat infection at a wound site. However, with the ongoing evolution of multi-drug resistant bacterial strains, there is a high demand for alternative antimicrobial treatments. Nitric oxide (NO) is an endogenous gas molecule with potent antimicrobial activity, which is effective against a wide variety of bacterial strains. In this study, the potential for creating NO releasing creams containing the naturally occurring NO carrier, S-nitrosoglutathione (GSNO), are characterized and evaluated. GSNO is shown to have prolonged stability (>300 days) when mixed and stored within Vaseline at 24 °C. Further, enhanced proliferation of NO from GSNO using zinc oxide nanoparticles (ZnO) is demonstrated. Triggering NO release from the GSNO/Vaseline mixture using a commercial zinc oxide-containing cream exhibits first-order NO release kinetics with the highest %NO release over the first 6 h. Significant killing effects against S. aureus, S. epidermidis, and P. aeruginosa are demonstrated for the GSNO/Vaseline/ZnO cream mixtures in a proportional manner dependent upon the concentration of GSNO in the final mixture.

Ionophore-Based Biphasic Chemical Sensing in Droplet Microfluidics.

Droplet microfluidics is an enabling platform for high-throughput screens, single-cell studies, low-volume chemical diagnostics, and microscale material syntheses. Analytical methods for real-time and in situ detection of chemicals in the droplets will benefit these applications, but they remain limited. Reported herein is a novel heterogeneous chemical sensing strategy based on functionalization of the oil phase with rationally combined sensing reagents. Sub-nanoliter oil segments containing pH-sensitive fluorophores, ionophores, and ion-exchangers enable highly selective and rapid fluorescence detection of physiologically important electrolytes (K+ , Na+ , and Cl- ) and polyions (protamine) in sub-nanoliter aqueous droplets. Electrolyte analysis in whole blood is demonstrated without suffering from optical interference from the sample matrix. Moreover, an oil phase doped with an aza-BODIPY dye allows indication of H2 O2 in the aqueous droplets, exemplifying sensing of targets beyond ionic species.

Nitric oxide releasing poly(vinylidene fluoride-co-hexafluoropropylene) films using a fluorinated nitric oxide donor to greatly decrease chemical leaching.

Nitric oxide (NO) releasing polymers have been widely applied as biomaterials for a variety of biomedical implants and devices. However, the chemical leaching of NO donors and their byproduct species is almost always observed during the application of polymers doped with NO donors, unless the donor is covalently linked to the polymer. Herein, we report the first NO releasing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fluorinated copolymer prepared by incorporating a fluorinated S-nitrosothiol as the NO donor. Under physiological conditions, the resulting polymeric films can release NO for 16 days. Importantly, due to both fluorine-fluorine and electrostatic charge interactions between the fluorinated NO donor and the PVDF-HFP copolymer, the total chemical leaching of the fluorinated NO donor and its disulfide product after 9 day was only 0.6% (mol%) of the initial amount of NO donor loaded into the film. These new NO release PVDF-HFP films exhibit antimicrobial and anti-biofilm activities against both Gram positive S. aureus and Gram negative P. aeruginosa strains. The NO-releasing PVDF-HFP polymer can also be coated on Teflon tubing to release NO under physiological conditions for extended time periods. This NO-releasing PVDF-HFP copolymer with greatly reduced chemical leaching could help enhance the biocompatibility and antimicrobial activity of various biomedical devices. STATEMENT OF SIGNIFICANCE: Fluoropolymers have been widely used in creating various biomedical implants and devices. However, nitric oxide (NO) release fluoropolymers have not been well studied to date. Additionally, in the application of biomaterials doped with NO donors, a significant amount of NO donors and their byproducts almost always leach into aqueous environment. We now report an NO releasing poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) fluoropolymer by incorporating a new fluorinated S-nitrosothiol. The NO release can last for 16 days under physiological conditions. The total chemical leaching was determined to be only 0.6 mol% of the initial S-nitrosothiol loaded. As expected, significant antimicrobial/anti-biofilm activities of the NO release PVDF-HFP film were observed against Gram positive S. aureus and Gram negative P. aeruginosa bacterial strains.