Chelsea N. Monty

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.

Ion Sensor for the Quantification of Sodium in Sweat Samples

We present the conception of an electrochemical sodium ion sensor for point-of-care sweat analysis. This flexible amperometric sensor was developed to quantify the amount of sodium ions in sweat (in real-time), alleviating the wait time, large sample size, possible contamination, and expensive analytical equipment associated with current diagnostic procedures requiring sweat analysis. This sensor is composed of a multiwall carbon nanotube (MWNT) functionalized nylon-6 mat, for a flexible yet conductive sensor. The MWNTs are then functionalized with a cyclo-oligomeric calixarene, which is shown to selectively form a supramolecular complex with sodium ions. Upon complex formation, the charge carriers are drawn away from the carbon layer, hence the current is impeded, and the sodium ion detection is prevalent at appropriate physiological ranges for healthy and ailing humans. In this paper, the optimization of MWNT and calixarene functionalization, as well as the selectivity and sensitivity of the sensor will be discussed.

Fabric Nanocomposite Resistance Temperature Detector

This paper illustrates the characterization of a fabric resistance temperature (RTD) detector made from electrospun nylon-6 functionalized with multiwalled carbon nanotubes (MWCNTs) and polypyrrole (PPy) for use in supracutaneous applications like smart clothing, prosthetic sockets, and other medical devices where a temperature detecting fabric is better suited than a rigid detector. The nanocomposite material acts like a RTD, because the conductivity increases linearly with temperature. The empirically determined temperature coefficient of resistance (TCR) is reported for this material, and is -0.204 ± 0.008%/C. Development of a simple and scalable process for constructing the detector utilized electrospinning nylon-6 as a membrane style substrate, vacuum filtration of MWCNTs onto the nylon scaffold, and vapor phase polymerization of pyrrole to PPy onto the MWCNT functionalized nylon nanofibers. The optimal loading of MWCNTs is 6.6 wt%. The conductivity of the device follows a percolative behavior and TCR values indicate this is a viable option for temperature detection. Resistance decreases with increasing temperature, which indicates this is a negative TCR material.

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.

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.

Electrochemical Multiphase Microreactor as Fast, Selective, and Portable Chemical Sensor of Trace Toxic Vapors

A novel type of gas chemical sensor is fabricated by combining microfabrication techniques and electrochemical transducer. The microchannel sensor we built is composed of liquid/gas microchannels separated by a nanoporous membrane. When oxime chemistry is adapted into it, the microchannel sensor gives response of hundreds of mV to trace vapor (10 ppb) of acetylcholine simulant within s. Double microchannel design further reduces potential drift and simplifies the sensor setup.

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.

Enzyme-Based Electrochemical Multiphase Microreactor for Detection of Trace Toxic Vapors

A dual microchannel device with a gas-liquid interface was developed for use as an amperometric biosensor for the detection of organophosphate chemicals based on acetylcholinesterase inhibition. Electric eel acetylcholinesterase was immobilized on the liquid microchannel by creating a cross-linked gel with glutaraldehyde. The system was tested with malathion, an organophosphorus pesticide. The detection limit of the sensor is in the parts-per-trillion range and the detection is rapid, sensitive, and selective to only phosphonates. Incorporation of existing acetylcholinesterase biochemistry into a microscale sensor improves the sensitivity of the device by about an order of magnitude and the reaction speed by two orders of magnitude. Also, a microscale sensor allows the device to be easily portable.

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

ABSTRACT 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

Detection of halogenated organics by their inhibitory action in a catalytic reaction between dimethyl acetylenedicarboxylate and 2-methyl-4-nitroaniline

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).