Evaluation of a wearable fabric-based sensor for accurate sodium determination in sweat during exercise.

INTRODUCTION: Newly developed wearable fabric sensors (WFS) can increase the ease and accuracy of sweat sodium measurements by performing simultaneous sampling and analysis on the body during exercise. PURPOSE: Determine the accuracy of a WFS for measurement of sodium concentration in sweat. METHODS: Subjects wore a WFS prototype and sweat collectors on their forearm during cycle ergometry. Subjects exercised at a moderate intensity (~ 65% heart rate reserve) for 30-60 min. Sweat samples were collected and analyzed using a commercial sweat sodium analyzer (SSA) every 10-15 min. WFS were adhered with an armband and connected to custom built electronics. Accuracy was determined by comparing predicted WFS concentration to the actual concentration from the commercial SSA and analyzed statistically using ANOVA and Bland-Altman plots. RESULTS: A total of 19 subjects completed the study. The average sweat sodium concentration was 59 mM ± 22 mM from a SSA compared with 54 mM ± 22 mM from the WFS. Overall, the average accuracy of the WFS was 88% in comparison to the SSA with p = 0.45. A line of best fit comparing predicted versus actual sweat sodium concentration had a slope of 0.99, intercept of - 4.46, and an r2 of 0.90. Bland-Altman analysis showed the average concentration difference between the WFS and the SSA was 5.35 mM, with 99% of data points between ± 1.96 times the standard deviation. CONCLUSION: The WFS accurately predicted sweat sodium concentration during moderate intensity cycle ergometry. With the need for precise assessment of sodium loss, especially during long duration exercise, this novel analysis method can benefit athletes and coaches. Further research involving longer duration and more intense exercise is warranted.

Uniform and Pitting Corrosion of Carbon Steel by Shewanella oneidensis MR-1 under Nitrate-Reducing Conditions.

Despite observations of steel corrosion in nitrate-reducing environments, processes of nitrate-dependent microbially influenced corrosion (MIC) remain poorly understood and difficult to identify. We evaluated carbon steel corrosion by Shewanella oneidensis MR-1 under nitrate-reducing conditions using a split-chamber/zero-resistance ammetry (ZRA) technique. This approach entails the deployment of two metal (carbon steel 1018 in this case) electrodes into separate chambers of an electrochemical split-chamber unit, where the microbiology or chemistry of the chambers can be manipulated. This approach mimics the conditions of heterogeneous metal coverage that can lead to uniform and pitting corrosion. The current between working electrode 1 (WE1) and WE2 can be used to determine rates, mechanisms, and, we now show, extents of corrosion. When S. oneidensis was incubated in the WE1 chamber with lactate under nitrate-reducing conditions, nitrite transiently accumulated, and electron transfer from WE2 to WE1 occurred as long as nitrite was present. Nitrite in the WE1 chamber (without S. oneidensis) induced electron transfer in the same direction, indicating that nitrite cathodically protected WE1 and accelerated the corrosion of WE2. When S. oneidensis was incubated in the WE1 chamber without an electron donor, nitrate reduction proceeded, and electron transfer from WE2 to WE1 also occurred, indicating that the microorganism could use the carbon steel electrode as an electron donor for nitrate reduction. Our results indicate that under nitrate-reducing conditions, uniform and pitting carbon steel corrosion can occur due to nitrite accumulation and the use of steel-Fe(0) as an electron donor, but conditions of sustained nitrite accumulation can lead to more-aggressive corrosive conditions.IMPORTANCE Microbially influenced corrosion (MIC) causes damage to metals and metal alloys that is estimated to cost over $100 million/year in the United States for prevention, mitigation, and repair. While MIC occurs in a variety of settings and by a variety of organisms, the mechanisms by which microorganisms cause this damage remain unclear. Steel pipe and equipment may be exposed to nitrate, especially in oil and gas production, where this compound is used for corrosion and "souring" control. In this paper, we show uniform and pitting MIC under nitrate-reducing conditions and that a major mechanism by which it occurs is via the heterogeneous cathodic protection of metal surfaces by nitrite as well as by the microbial oxidation of steel-Fe(0).

Use of an Electrochemical Split Cell Technique to Evaluate the Influence of Shewanella oneidensis Activities on Corrosion of Carbon Steel.

Microbially induced corrosion (MIC) is a complex problem that affects various industries. Several techniques have been developed to monitor corrosion and elucidate corrosion mechanisms, including microbiological processes that induce metal deterioration. We used zero resistance ammetry (ZRA) in a split chamber configuration to evaluate the effects of the facultatively anaerobic Fe(III) reducing bacterium Shewanella oneidensis MR-1 on the corrosion of UNS G10180 carbon steel. We show that activities of S. oneidensis inhibit corrosion of steel with which that organism has direct contact. However, when a carbon steel coupon in contact with S. oneidensis was electrically connected to a second coupon that was free of biofilm (in separate chambers of the split chamber assembly), ZRA-based measurements indicated that current moved from the S. oneidensis-containing chamber to the cell-free chamber. This electron transfer enhanced the O2 reduction reaction on the coupon deployed in the cell free chamber, and consequently, enhanced oxidation and corrosion of that electrode. Our results illustrate a novel mechanism for MIC in cases where metal surfaces are heterogeneously covered by biofilms.

Nanotechnology for implantable sensors: carbon nanotubes and graphene in medicine.

Implantable sensors utilizing nanotechnology are at the forefront of diagnostic, medical monitoring, and biological technologies. These sensors are often equipped with nanostructured carbon allotropes, such as graphene or carbon nanotubes (CNTs), because of their unique and often enhanced properties over forms of bulk carbon, such as diamond or graphite. Because of these properties, the fundamental and applied research of these carbon nanomaterials have become some of the most cited topics in scientific literature in the past decades. The age of carbon nanomaterials is simply budding, however, and is expected to have a major impact in many areas. These areas include electronics, photonics, plasmonics, energy capture (including batteries, fuel cells, and photovoltaics), and--the emphasis of this review--biosensors and sensor technologies. The following review will discuss future prospects of the two most commonly used carbon allotropes in implantable sensors for nanomedicine and nanobiotechnology, CNTs and graphene. Sufficient further reading and resources have been provided for more in-depth and specific reading that is outside the scope of this general review.

An acetylcholinesterase-inspired biomimetic toxicity sensor.

This work demonstrates the ability of an acetylcholinesterase-inspired biomimetic sensor to accurately predict the toxicity of acetylcholinesterase (AChE) inhibitors. In surface waters used for municipal drinking water supplies, numerous pesticides and other anthropogenic chemicals have been found that inhibit AChE; however, there is currently no portable toxicity assay capable of determining the potential neurotoxicity of water samples and complex mixtures. Biological assays have been developed to determine the toxicity of unknown samples, but the short shelf-life of cells and other biological materials often make them undesirable for use in portable assays. Chemical methods and structure-activity-relationships, on the other hand, require prior knowledge on the compounds of interest that is often unavailable when analyzing environmental samples. In the toxicity assay presented here, the acetylcholinesterase enzyme has been replaced with 1-phenyl-1,2,3-butanetrione 2-oxime (PBO) a biomimetic compound that is structurally similar to the AChE active site. Using a biomimetic compound in place of the native enzyme allows for a longer shelf-life while maintaining the selective and kinetic ability of the enzyme itself. Previous work has shown the success of oxime-based sensors in the selective detection of AChE inhibitors and this work highlights the ability of an AChE-inspired biomimetic sensor to accurately predict the toxicity (LD50 and LC50) for a range of AChE inhibitors. The biomimetic assay shows strong linear correlations to LD50 (oral, rat) and LC50 (fish) values. Using a test set of eight AChE inhibitors, the biomimetic assay accurately predicted the LC50 value for 75% of the inhibitors within one order of magnitude.

Non-biological inhibition-based sensing (NIBS) demonstrated for the detection of toxic arsenic compounds.

This work demonstrates the success of a recently developed technique in chemical amplification, non-biological inhibition-based sensing (NIBS), for the detection of toxic arsenic compounds. Screening for toxic arsenic compounds is especially important due to their prevalence in wastewater and water sources. The detection method presented in this work amplifies the chemical response of toxic arsenic compounds by developing a sensor chemistry where the analyte inhibits, rather than enhances, the rate of a catalytic reaction. This technique mimics the work done with enzyme inhibition; however, using non-biological molecules allows for selective detection without the shelf-life issue associated with biological molecules. Using NIBS we find that we can enhance the sensitivity of the system by two orders of magnitude with no apparent loss in selectivity. This work demonstrates the versatility of NIBS, showing that the technique can be of general use for the detection of toxic compounds.

Nonbiological inhibition-based sensing (NIBS) demonstrated for the detection of toxic sulfides.

The purpose of this paper is to report on a new technique in chemical detection: nonbiological inhibition-based sensing (NIBS). This method uses a new approach to chemical amplification, where the analyte inhibits rather than enhances the rate of catalytic reaction. Although there are many possible catalysts for this technique, such as enzymes, this paper focuses on using the selective binding found in colorimetric detection. Colorimetric methods are selective; however, they are not particularly sensitive. Using nonbiological-based molecules allows for selective detection without the shelf-life issues that are associated with enzymes. In practice, we can use the active substances in Draeger tubes and related systems as catalysts. Analytes of interest inhibit the catalysts that leads to a large signal. The work presented here focuses on the detection of toxic sulfide compounds. Using NIBS, we observe that we can enhance the sensitivity of the system by 2 orders of magnitude with no apparent loss in selectivity. We can also decrease the detection time from 5 h to 10 min. So far, we have demonstrated the technique for sulfide detection; however, we believe that the technique can have general use in the detection of toxic compounds.