Micro-electrical impedance-based corrosion sensing and characterization

Abstract

A microfluidic device including an interdigitated electrode (IDE) structure having a plurality of IDE pairs, each of which may include a first electrode and a second electrode. Also, a method including placing a fluid sample and / or cells in contact with an interdigitated electrode (IDE) structure having a plurality of IDE pairs, each of which may include a first electrode and a second electrode. The method may further include measuring electrical impedance between the first electrode and the second electrode over time to analyze the degree of corrosion based on impedance value changes over time as the corrosive electrodes erode over time due to corrosion. The IDE pairs purely composed of non-corrosive metal may provide a baseline impedance value that can be used to calibrate and / or normalize the impedance values of the IDE pairs composed of non-corrosive and corrosive electrode pair.

Description

MICRO-ELECTRICAL IMPEDANCE-BASED CORROSION SENSING AND CHARACTERIZATIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application Serial No. 63 / 606,961 filed on December 6, 2023, and entitled “Micro-Electrical Impedance- Based Corrosion Sensing and Characterization,” which is hereby incorporated herein by reference in its entirety for all purposes.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.TECHNICAL FIELD

[0003] This disclosure relates generally to systems and methods for micro-electrical impedance-based sensing and / or characterization of corrosion.BACKGROUND

[0004] Microbiologically influenced corrosion (referred to herein as “MIC”) is a corrosion process in which microorganisms play a significant role by actively carrying out undesirable electrochemical redox reactions on metal surfaces.

[0005] MIC is a significant problem, for example, in oil- and gas- carrying pipelines and tanks, in water pipelines employed in various chemical-process industries, and on ship hulls. MIC may lead to catastrophic failures, expensive shutdowns, expensive mitigation treatment, as well as safety issues for critical infrastructure, including the oil and gas industry. According to NACE International, the global economic cost of corrosion is estimated to be $2.5 trillion. The devastating impact of corrosion not only affects the environment and economy, but also significantly impacts the U.S. military.

[0006] Conventionally, the early detection of corrosion and characterization of the type of corrosion has been non-trivial, labor-intensive, and time-consuming. Conventional methods include optical and / or microscopic inspections, electrochemical analyses, weight loss analyses, as well as the use of various other analytical techniques. However, none of these methods are ideal. Additionally, with particular respect to MIC, challenges associated with measurement can be even more severe due to the presence of corrosion-causing microorganisms and the biofilm they create.

[0007] Electrical impedance sensing (EIS) generally refers to a technique that may be used to acquire, validate and quantitatively interpret changes in dielectric properties of a substance being evaluated. For example, EIS may be used in the analysis of interfacial properties related to bio-recognition such as antibody-antigen recognition, substrate-enzyme interaction, or whole-cell capturing at the surface of an electrode(s). EIS has also been applied for the analysis of microbial corrosion processes. However, such usages have been in the context of measuring the electrochemical property changes and / or biofilm growth on top of the electrodes, and do not provide highly precise analysis for rapid and easy metal corrosion characterization; likewise, such usages have not involved identifying corrosion of various different metals. Rather, such uses of EIS have mainly been for bulk-level corrosion analyses, for example, global evaluations of corrosion rather than localized evaluations corrosion where localized corrosion is a major issue.

[0008] As such, improved devices, systems, and methods for the detection and characterization of corrosion, more particularly, MIC, are needed.BRIEF SUMMARY OF THE DISCLOSURE

[0009] In some embodiments disclosed herein is a microfluidic device comprising an interdigitated electrode (IDE) structure comprising a plurality of IDE pairs. Each of the plurality of IDE pairs may comprise a first electrode and a second electrode.

[0010] Also, in some embodiments is a method of evaluating a fluid, the method comprising placing a sample of the fluid and / or cells in contact with an interdigitated electrode (IDE) structure comprising a plurality of IDE pairs. Each of the plurality of IDE pairs may comprise a first electrode and a second electrode. The method may further comprise measuring electrical impedance between the first electrode and the second electrode over time to analyze the degree of corrosion based on impedance value changes over time as the corrosive electrodes erode over time due to corrosion. The IDE pairs purely composed of non-corrosive metal may provide a baseline impedance value that can be used to calibrate and / or normalize the impedance values of the IDE pairs composed of non-corrosive and corrosive electrode pair.

[0011] This disclosure describes microfluidic devices featuring an interdigitated electrode (IDE) structure composed of multiple IDE pairs, each comprising one or more types of electrodes or materials. In a given pair, one side of the electrode may be made of a corrosion-susceptible metal such as carbon steel or aluminum, while theother side of the electrode is made of corrosion-resistant metals such as platinum or gold. As the corrosive metal corrodes, this will result in changes in impedance signal, allowing real-time corrosion sensing. As the biofilm is formed and / or cells grow on top of the electrodes, the electrical impedance signal will also change. Since the impedance signal change in the non-corrosive electrode pair will be mainly from biofilm / cell growth, this information can be used to accurately characterize MIC. The IDE corrosion sensor can be applied for corrosion and biofilm sensing. Both electrodes have defined dimensions, with lengths ranging from 50 pm to 5 mm and widths ranging from 1 pm to 500 pm, and thicknesses ranging from 50 nm to 100 pm. The electrodes may overlap partially, entirely, or not at all along their length, and are separated by a space ranging from 1 pm to 500 pm. The IDE structure is fabricated on a substrate, with a chamber built on top so that the IDE structures are integrated within such a structure made of materials like polymers. The device supports precise electrical measurements, including impedance, through the IDE electrodes.

[0012] Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a detailed description of the disclosed embodiments, reference will now be made to the accompanying drawings in which:

[0014] Figure 1 is an illustration of an embodiment of a fluidic chamber with IDE- based corrosion sensor integrated within;

[0015] Figure 2 is a microscope image of the fabricated finger part of the IDE corrosion sensor of Figure 1 ;

[0016] Figure 3 is a microscope image of carbon steel fingers with 20 pm x 450 pm dimension;

[0017] Figure 4 is a microscope image of carbon steel fingers with 20 pm x 375 pm dimension;

[0018] Figure 5 is a microscope image of carbon steel fingers with 20 pm x 250 pm dimension;

[0019] Figure 6 is an array of 10 fluidic chambers each having IDE corrosion sensors integrated within, and interfaced with a printed circuit board-type circuit;

[0020] Figure 7 is an interdigitated electrode pattern fabricated on a glass substrate with a polymer channel placed on top of it;

[0021] Figure 8 is a representation of an embodiment of the microfabrication process of the interdigitated electrode patterns and its integration within a fluidic chamber;

[0022] Figure 9 is an illustration of changes in interdigitated electrode dimensions as corrosion progress over time;

[0023] Figures 10(a)-(b) are demonstrations of metal corrosion in testbed and electrode resistance vs corrosion level;

[0024] Figures 11 (a)-(d) are plots of impedance value change based on the reduction of IDE electrode fingers and overlap length;

[0025] Figures 12(a)-(b) are illustrations of a device image of mimicking fuel tank in testbed;

[0026] Figures 13(a)-(c) are plots of impedance change based on cell growth / biofilm formation in testbed;

[0027] Figures 14(a)-(c) are plots of impedance value decreased as biofilm formation and impedance value increased as metal corroded;

[0028] Figures 15(a)-(d) are impedance measurement plots of tryptic soy broth and three microbiologically influenced corrosion strains cultured in testbed;

[0029] Figures 16(a)-(d) are impedance plots of the frequency value of flat region change vs culture time in testbed;

[0030] Figures 17(a)-(d) are impedance plots of microbiologically influenced corrosion strains Shewanella oneidensis and Kiebsiella aerogenes cultured in testbed;

[0031] Figures 18(a)-(d) are impedance plots of absolute impedance value measured from CS-gold sensor and gold-gold sensor for Shewanella oneidensis and Klebsiella aerogenes measurement; and

[0032] Figures 19(a)-(d) are impedance plots with different stainless steel electrode finger length in microfluidic testbed.DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0033] The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment.

[0034] Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness.

[0035] Unless the context dictates to the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints, and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.

[0036] In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to... Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct engagement between the two devices, or through an indirect connection that is established via other devices, components, nodes, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a particular axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular toa particular axis. For instance, an axial distance refers to a distance measured along or parallel to the axis, and a radial distance means a distance measured perpendicular to the axis. As used herein, the terms “approximately,” “about,” “substantially,” and the like mean within 10% (i.e., plus or minus 10%) of the recited value. Thus, for example, a recited angle of “about 80 degrees” refers to an angle ranging from 72 degrees to 88 degrees.

[0037] Generally, MIC may occur when fluid, gas, and / or solids that carry microorganisms move through and / or are stored in structures, or when any substrate such as, without limitation, a ship hull or other structure is in contact with the fluid, gas, and / or solid for long enough as to act as a substrate to which the microorganisms adhere. As utilized herein, “microorganism” refers to an organism that can be seen only with the aid of a microscope and that can either be unicellular or multicellular. Microorganisms (also referred to herein as “microbes”) can include bacteria, protozoans, and certain algae and fungi. As used herein, the microorganism can refer to and / or include a specific microorganism, for example, Vibrio natriegens, or can refer to and / or include a broader classification, such as bacteria, protozoa, etc. The adherence of microorganisms to the one or more surfaces of a structure may compromise the integrity of those structures. Thus, as will be disclosed herein, there is a need in various industries to be able to study, model, and evaluate the formation and progression of MIC, as well as the efficacy of associated solutions.

[0038] Disclosed herein are devices, systems, and methods for the characterization of metal corrosion based upon micro-EIS. Generally, the term “micro-EIS” refers to the use of EIS on a microfluidic scale. Also, generally, the term “microfluidic(s)” refers to the evaluation of fluids in the range of microliters (10-6) to picoliters (10-12).

[0039] In various embodiments, the devices, systems, and methods disclosed herein may be utilized to analyze MIC associated with a fluid(s) disposed within the disclosed devices and / or systems. Generally, the disclosed devices, systems, and methods may utilize electrochemical measurements to determine corrosion. Additionally, in some embodiments, a biofilm can be generated simultaneous with the determination of corrosion which may be subsequently analyzed to determine the offending organisms. Once identified, a corrective action (for example, the delivery of a biocide) may be performed, and one or more subsequent iterations of analysis may be employed to determine the efficacy of the corrective action. As such, the discloseddevices, systems, and methods may thus be utilized to identify the presence of corrosion, to identify the extent of such corrosion, to generate a biofilm to determine the microorganisms present to determine an appropriate corrective action, to analyze an effectiveness of the corrective action executed, or a combination of these. As such, the disclosed micro-EIS devices, systems, and methods may be effective to achieve the goal of fast and highly-precise dynamic monitoring of metal corrosion, including corrosion induced by microorganisms.

[0040] In some embodiments, a microfluidic device, which may be suitably employed in the disclosed systems and methods, generally includes an interdigitated electrode (IDE) structure comprising a plurality of IDE pairs. Each of the plurality of IDE pairs may include a first electrode and a second electrode. In some embodiments, the first electrode may be characterized as a “target,” “working,” or “corrodible” electrode and the second electrode may be characterized as a “counter” or “reference” electrode.

[0041] Referring to Figure 1 , an embodiment of a microfluidic device 100 is illustrated. In the embodiment of Figure 1 , the microfluidic device generally comprises a plurality of target electrodes 110, a plurality of counter electrodes 120, and a body 130. The body 130 generally defines a chamber 135 having a first port 132 disposed at a first end 134 of the body 130 and a second port 136 disposed at a second end 138 of the body 130 in which the plurality of target electrodes 110 and the plurality of counter electrodes 120 so as to form an IED structure 105. The microfluidic device 100 may include any suitable number of target electrodes 110 and / or counter electrodes. For example, in various embodiments, microfluidic device 100 may include about 10, about 20, about 30, about 40, about 50, about 60, about 70, about 80, about 90, about 100, about 120, about 140, about 160, about 180, about 200, about 220, about 240, about 260, about 280, or about 300 the target electrodes 110 and / or counter electrodes 120.

[0042] In various embodiments, the target electrodes 110 are made of and / or comprise a metal that is susceptible (alternatively, relatively not susceptible) to corrosion, examples of which may include but are not limited to carbon steels (e.g., SAE 1018 carbon steel), stainless steels, iron, an iron alloy, aluminum, and an aluminum alloy. For example, the target electrodes 110 may be made from a metal of interest, for example, a metal which is the target of evaluation, Additionally or alternatively, in various embodiments, the counter electrodes 120 are made of and / orcomprise a metal that is not susceptible (alternatively, relatively not susceptible) to corrosion, examples of which may include but are not limited to chromium titanium, platinum, silver, or gold.

[0043] In the embodiment of Figure 1 , the plurality of target electrodes 110 and the plurality of counter electrodes 120 are disposed in an interdigitated pattern. Also, referring to Figure 2, the plurality of target electrodes 110 and the plurality of counter electrodes 120 disposed in the interdigitated pattern of Figure 1 is shown in detail. In the embodiment of Figures 1 and 2, the plurality of the target electrodes 110 and the plurality of counter electrodes 120 are disposed in an alternating arrangement, such that the length of the target electrodes 110 and the plurality of counter electrodes 120 extend parallel to each other from opposite sides of the reservoir. For example, each of the plurality of target electrodes 110 is adjacent to at least one of the plurality of counter electrodes 120 and, likewise, each of the plurality of counter electrodes 120 is adjacent to at least one of the plurality of target electrodes 110. An adjacent target electrode 110 and counter electrode 120 (e.g., an IDE pair) may be disposed apart from each other such that the target electrode 110 and the counter electrode 120 are not in contact with each other.

[0044] The target electrodes 110 and the plurality of counter electrodes 120 may characterized with respect to one or both of a width and a thickness perpendicular to its length. In various embodiments, the target electrodes 110 and / or the plurality of counter electrodes 120 may have a length of at least about 50 micrometers (pm), at least about 100 pm, at least about 200 pm, at least about 225 pm, at least about 250 pm, at least about 275 pm, at least about 300, at least about 325 pm, at least about 350 pm, at least about 375 pm, or at least about 400 pm and, additionally or alternatively, a length of not more than about 5,000 pm. Also, in various embodiments, the target electrodes 110 and / or the plurality of counter electrodes 120 may have a width of at least about 1 pm, at least about 2 pm, at least about 3 pm, at least about 4, at least about 6 pm, at least about 8 pm, at least about 10 pm, at least about 15 pm, at least about 20 pm, or at least about 25 pm and, additionally or alternatively, a width of not more than about 500 pm. Also, in various embodiments, the target electrodes 110 and / or the plurality of counter electrodes 120 may have a thickness of at least about 0.05 pm, at least about 0.1 pm, at least about 0.5 pm, at least about 1 pm, at least about 2 pm, at least about 3 pm, at least about 4, at least about 6 pm, at least about 8pm, at least about 10 pm, at least about 15 pm, at least about 20 pm, or at least about 25 pm and, additionally or alternatively, a width and / or thickness of not more than about 100 pm. In some embodiments, each of the plurality of target electrodes 110 may have a constant length, width, and / or thickness; alternatively, the length, width, and / or thickness of the target electrodes 110 may vary. For example, the length, width, and / or thickness of the target electrodes 110 may increase or decrease over a portion of the distance between the first end 134 and the second end 138. Likewise, in some embodiments, each of the plurality of counter electrodes 120 may have a constant length, width, and / or thickness; alternatively, the length, width, and / or thickness of the counter electrodes 120 may vary. For example, the length, width, and / or thickness of the counter electrodes 120 may increase or decrease over a portion of the distance between the first end 134 and the second end 138.

[0045] Also, in various embodiments, a target electrode 110 and / or a counter electrode 120 may be characterized with respect to portion of its length that is adjacent to or “overlaps” and electrode that is disposed immediately lateral thereto, with respect to the length of the target electrode 110 and / or the counter electrode 120, (referred to as an “immediately lateral” electrode). For example, a target electrode 110 and / or a counter electrode 120 may be adjacent to or overlap with an immediately lateral electrode over about 0% of its length (that is, no overlap), or about 10% of its length, or about 20% of its length, or about 30% of its length, or about 40% of its length, or about 50% of its length, or about 60% of its length, or about 70% of its length, or about 80% of its length, or about 90% of its length, or about 95% of its length, or about 96% of its length, or about 97% of its length, or about 98% of its length, or about 99% of its length. For example, referring to Figures 3, 4, and 5 various embodiments of adjacency and / or overlap between electrodes are illustrated. In Figure 3, immediately lateral electrodes are illustrated as overlapping by about 80%-90% of the length of the electrodes. In Figure 4, immediately lateral electrodes are illustrated as overlapping by about 50%-60% of the length of the electrodes. In Figure 5, immediately lateral electrodes are illustrated as overlapping by about 0% of the length of the electrodes (i.e., as non-overlapping or having no adjacent portion).

[0046] Also, in various embodiments, the spacing between a target electrode 110 and an immediately lateral counter electrode 120 may be at least about 1 pm, at least about 2 pm, at least about 3 pm, at least about 4, at least about 6 pm, at least about 8pm, at least about 10 pm, at least about 15 pm, at least about 20 pm, or at least about 25 pm and, additionally or alternatively, not more than about 500 pm. In some embodiments, the spacing between various immediately lateral target electrode 110 and counter electrode 120 pairs may be constant; alternatively, the spacing between various immediately lateral target electrode 110 and counter electrode 120 pairs may vary. For example, the spacing between various immediately lateral target electrode 110 and counter electrode 120 pairs may increase or decrease over a portion of the distance between the first end 134 and the second end 138.

[0047] Referring again to the embodiment of Figure 1 , the spaces between adjacent and / or immediately lateral and / or target electrodes 110 and counter electrodes 120 (e.g., the void-spaces) define at least a portion of a channel 140. Generally, the channel 140 may be characterized as having a generally serpentine or undulating pattern, for example, as a result of the interdigitated pattern of the plurality of target electrodes 110 and the plurality of counter electrodes 120; the serpentine or undulating pattern is also illustrated in Figures 2, 3, and 4. Generally, the channel may extend and provide a route of fluid communication between the first port 132 and the second port 136. In some embodiments, the channel 140 may be characterized as a microfluidic channel having a width and height or a diameter in cross-section at one or more points that is less than 1000 pm, or less than 500 pm, or less than 250 pm, or less than 200 pm, or less than 150 pm, or less than 100 pm. The channel 140 may have a length that is substantially larger than the width and / or the height thereof, in embodiments, for example, greater than or equal to by a factor of at least about 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or 100 times. For example, in embodiments, the total length of the channel 140 may be greater than or equal to about 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10 mm.

[0048] In some embodiments, the body 130 may be formed from one or more components. For example, in some embodiments the body 130 comprises a substrate on which the plurality of target electrodes 110 and the plurality of counter electrodes 120 may be disposed. For example, the substrate may be formed from glass. The body 130 may further comprise a structure in contact with the substrate so as to enclose the chamber 135, that is, so as to enclose the plurality of target electrodes 110, the plurality of counter electrodes 120, and the channel 140. Forexample, the structure may be formed from polydimethylsiloxane (PDMS) or poly(methyl methacrylate) (PM MA).

[0049] In some embodiments, two or more microfluidic devices may be incorporated into a single unit. For example, referring to Figure 6, a printed circuit board (PCB) comprising multiple (e.g., ten) microfluidic devices (e.g., testbeds) as disclosed herein is illustrated. In the embodiment of Figure 6, the PCB comprises various routes of electrical connection to more easily enable the operation of each of the testbeds. Similarly, Figure 7 illustrates multiple testbeds incorporated into a single unit.

[0050] In some embodiments, a microfluid device such as the microfluidic device of Figure 1 , may be formed by any suitable methodology. For example, in some embodiments, the microfluidic device may be made by a method that comprises forming a first set of metal electrodes on the substrate (for example, one of the plurality of target electrodes or the plurality of counter electrodes 120) using metal deposition, lithography, and metal etching. When the first set of metal electrodes has been formed on the substrate, the second set of metal electrodes (for example, the other of the plurality of target electrodes or the plurality of counter electrodes 120) may be formed on the substrate using a lift-off process, for example, photolithography followed by metal deposition and removal of a sacrificial photoresist layer. Figure 8 illustrates an example of a process for making a microfluidic device.

[0051] In some embodiments, a fluid to be evaluated, a sample thereof, via the microfluidic device may be disposed, statically, within the chamber 135. Alternatively, in some embodiments, the fluid may be continuation communication through the channels for continuous impedance measurement of corrosion in a smaller area. For example, in some embodiments, the fluid may be communicated via the channel 140 continuously such that a laminar flow is established. In various embodiments, flow rates in the range of from 0.10 mL / h to 2 mL / h, from 0.10 mL / h to 1 mL / h, or from 0.10 mL / h to 2 mL / h or more may be used, depending upon the size of the channel 140 and other factors. As used herein, “laminar” indicates fluid flow of a liquid in which layers glide over one another, e.g., streamline fluid flow in which a fluid flows in parallel layers, with little or no disruption between the layers.

[0052] In operation, as the fluid is disposed within the channel (e.g., either statically or under continuous flow) the electrical impedance between the two electrodes is measured across a broad frequency range, for example, in the range of from sub-Hzto several tens of MHz. Not intending to be bound by theory, as the target metals corrode, this side of the metal electrodes will degrade, including reduction in width / length / thickness of the metal electrodes. For example, referring to Figure 9, the progression of corrosion with respect to a metal of interest (e.g., the target electrodes 110) over time (e.g., to, t1 , and t2). The degradation of the target electrodes 110 over time, as illustrated in Figure 9, will cause changes in the electrical impedance (e.g., the impedance phase, the magnitude of the impedance, or both) between the plurality of target electrodes 110 and the plurality of counter electrodes 120. Also, referring to Figure 10(a), a side-view of a metal that is susceptible to corrosion is shown in various states in comparison to a metal that is not susceptible to corrosion. More particularly, the metal that is susceptible to corrosion is shown with no corrosion, partial corroded, and completely corroded. Referring the Figure 10(b), the resistance corresponding with the different corrosion conditions of Figure 10(a) is shown. Different corrosion levels can be regarded as the different dimensions of the electrode geometry. The relationship between the impedance and the electrode pattern geometry can determine the corrosion characteristics by using electrical impedance sensor (EIS).

[0053] In various embodiments, a microfluidic device like the microfluidic device 100 of Figure 1 can serve of the basis for various configurations of similar microfluidic devices. For example, a microfluidic device may be sized to cover a larger area, for example, for large-area corrosion monitoring. Additionally or alternatively, target electrodes 110 formed of various corrosion-susceptible metals may be employed so that corrosion with respect to various target materials of interest can be measured and characterized. Additionally or alternatively, target electrodes having with varying thicknesses may be employed so that, as corrosion occurs and the thinnest electrodes are completely corroded and disappear, corrosion may continue to be monitored via thicker electrodes which will sustain corrosion over a longer duration. Additionally or alternatively, target electrodes of the same material may be employed to measure the thickness of biofilm growth, for example, in the case of microbiologically induced corrosion.

[0054] Additionally, one or more parameters associated with a microfluidic device as disclosed herein may be altered or manipulated in order to meet various user-defined needs. For example, referring to Figure 11 (a), microscope images of IDEs having differing numbers of electrodes or “fingers” is shown. Figure 11 (b) illustrates theimpedance associated with each of the various numbers of fingers, demonstrating that impedance increases and the flat region shifts to the right as the number of electrodes decrease. Also for example, Figure 1 1 (c) shows microscope images of IDEs with different electrode overlap length between immediately lateral electrodes. Figure 11 (d) illustrates the impedance associated with each of the various overlaps, demonstating that impedance increases and the flat region shifts to the right as the electrode overlap length (e.g., proportion) decreases.

[0055] Also for example, referring to Figure 12(a) a side view of electrical impedance sensor is shown. Figure 12(b) demonstrates a configuration or testbed intended for mimicking fuel tank environment, which can help to test the MIC corrosion in fuel tank environment. The device is fuel compatible.

[0056] The following examples demonstrate the utility of the disclosed devices, systems, and methods in the evaluation of corrosion, for example, MIC.

[0057] Referring to Figure 13(a) shows that impedance value decreases and a flat region shifts to the left as Klebsiella aerogenes culture time increased in testbed. Figure 13(b) illustrates normalized impedance value, demonstrating that as culture time increases, the impedance value decreases. Figure 13(c) illustrates bright field and fluorescent images of biofilm on IDEs at various times.

[0058] Referring to Figure 14(a) shows that impedance decreased, and the flat region shifted to left for the first 16 hours, for example, due to cell growth. Figure 14(b) shows that the impedance increased, and the flat region shifted to right after 16 hours, for example, due to metal corrosion. Figure 14(c) illustrates representative microscopic fluorescent images of the testbed after day 3 and day 5, respectively.

[0059] Referring to Figures 15(a)-(d), show the normalized impedance measured for of each testbed with tryptic soy broth (TSB) media and each of three microbes which contributed MIC. As shown, for each of the three microbes, the normalized impedance at 10 Hz decreased and then increased over time, for example, due to the metal corrosion. Generally, the time point at which impedance increases depends upon the corrosion, particularly, MIC, due to the microbes. Figure 15(a) shows impedance of the control with only TSB; Figure 15(b) shows impedance of E. coli BL21 in TSB; Figure 15(c) shows impedance of Klebsiella aerogenes in TSB; and Figure 15(a) shows impedance of Shewanella oneidensis in TSB. Referring to Figures 16(a)-(d), ananalysis of frequency of the end of the flat region for each testbed is shown. For each of these.

[0060] Referring to Figures 17(a)-(d), Shewanella oneidensis and Klebsiella aerogenes were cultured for four (4) days in various microfluidic devices and evaluated. Particularly, Figure 17(a) shows the impedance of Shewanella oneidensis evaluated using a microfluidic device as disclosed herein having both carbon steel and gold electrodes. Figure 17(b) shows the impedance of Klebsiella aerogenes evaluated using a microfluidic device as disclosed herein having both carbon steel and gold electrodes. The impedance slightly decreased up to 8h, and then increased back and the flat region shifted to right side over time. Figure 17(c) show the impedance Shewanella oneidensis evaluated using a microfluidic device as disclosed herein having and first and second set of gold electrodes. Figure 17(d) show the impedance Klebsiella aerogenes evaluated using a microfluidic device as disclosed herein having and a first and second set of gold electrodes. The impedance decreased and then increased back due to the formation of a biofilm.

[0061] Referring to Figure 18(a), shows absolute impedance value at 2 Hz was plotted over time point measured via microfluidic device as disclosed herein having both carbon steel and gold IDEs. Figure 18(b) shows absolute impedance value at 2 Hz was plotted over time measured via microfluidic device as disclosed herein having gold IDEs. Overall, the impedance decreased first, increased back, and continuously increased over time. The turning time points indicate the initiation of metal corrosion and biofilm formation in a testbed. Figure 18(c) and 18(d) illustrate the confirmation of a biofilm in the testbeds, as viewed using fluorescence staining.

[0062] Referring to Figures 19(a)-(d), the evaluation via a microfluidic device as disclosed herein, having both stainless-steel (SS) and gold IDEs, measured in a phosphate-buffered saline (PBS) solution is shown. The SS electrodes had a center length 5.5 mm, 3.5 mm, and 2.5 mm. The microfluidic device comprised 30 pairs of electrodes. The width of each of the electrode fingers was 100 pm. The results with respect to impedance demonstrate that relatively longer SS electrodes yield greater impedance than SS electrodes of medium length, which yield greater impedance than the relatively shorter SS electrodes, which yield greater impedance than the shortest SS electrodes. Phase shift is shown from 1 Hz to 100 Hz. Figure 19(a) shows the impedance result from 1 MHz to 10MHz. Figure 19(b) shows the phase result from1 MHz to 10MHz. Figure 19(c) shows a zoomed-in impedance plot of 1 Hz to 100 Hz. Figure 19(d) shows zoomed-in phase plot of 1 Hz to 100 Hz.

[0063] The following are additional embodiments of the disclosed subject matter.

[0064] A 1stembodiment is a microfluidic device comprising an interdigitated electrode (IDE) structure comprising a plurality of IDE pairs, wherein each of the plurality of IDE pairs comprises a first electrode and a second electrode.

[0065] A 2ndembodiment is the microfluidic device of the 1stembodiment, wherein the first electrode comprises a metal that is susceptible to corrosion.

[0066] A 3rdembodiment is the microfluidic device of the 2ndembodiment, wherein the metal that it susceptible to corrosion comprises carbon steel, stainless steel, iron, an iron alloy, aluminum, and an aluminum alloy.

[0067] A 4thembodiment is the microfluidic device of one of the 1st— the 3rdembodiments, wherein the second electrode comprises a metal that is not susceptible to corrosion

[0068] A 5thembodiment is the microfluidic device of the 4thembodiment, wherein the metal that is not susceptible to corrosion comprises chromium titanium, platinum, or gold.

[0069] A 6thembodiment is the microfluidic device of one of the 1st— the 5thembodiments, wherein each of the first electrode and the second electrode has a length, a width perpendicular to its length, and a thickness perpendicular to its length.

[0070] A 7thembodiment is the microfluidic device of the 6thembodiment, wherein the length of each of the first electrode and the second electrode is from about 200 micrometers (pm) to about 1 ,000 pm.

[0071] An 8thembodiment is the microfluidic device of one of the 6th— the 7thembodiments, wherein the width and / or the thickness of each of the first electrode and the second electrode is from about 0.1 pm to about 25 pm.

[0072] A 9thembodiment is the microfluidic device of one of the 6th— the 8thembodiments, wherein the first electrode is disposed immediately lateral to the second electrode with respect to its length.

[0073] A 10thembodiment is the microfluidic device of one of the 1st— the 9thembodiments, wherein the first electrode overlaps the second electrode by at least 20% of its length.

[0074] An 11thembodiment is the microfluidic device of one of the 1st— the 10thembodiments , wherein the first electrode does not overlap the second electrode along its length.

[0075] A 12thembodiment is the microfluidic device of one of the 1st— the 11thembodiments, wherein the microfluidic device further comprises a body, wherein the body further comprises a chamber, wherein the IDE structure is disposed within the chamber.

[0076] A 13thembodiment is the microfluidic device of the 12thembodiment, wherein the body comprises a substrate.

[0077] A 14thembodiment is the microfluidic device of the 13thembodiment, wherein the substrate comprises glass.

[0078] A 15thembodiment is the microfluidic device of one of the 12th— the 14thembodiments, wherein the body further comprises a structure enclosing the chamber.

[0079] A 16thembodiment is the microfluidic device of the 15thembodiment, wherein the structure is formed from polydimethylsiloxane (PDMS) or poly(methyl methacrylate) (PM MA).

[0080] A 17thembodiment is the microfluidic device of one of the 1st— the 16thembodiments, wherein a space is disposed between the first electrode and the second electrode.

[0081] A 18thembodiment is the microfluidic device of the 17thembodiment, wherein the space at least partially defines a channel.

[0082] A 19thembodiment is the microfluidic device of the 18thembodiment, wherein the channel has a length and a width, wherein the length is greater than the width by a factor of at least 50.

[0083] A 20thembodiment is a method of evaluating a fluid, the method comprising: placing a sample of the fluid and / or cells in contact with an interdigitated electrode (IDE) structure comprising a plurality of IDE pairs, wherein each of the plurality of IDE pairs comprises a first electrode and a second electrode; and measuring electrical impedance between the first electrode and the second electrode over time to analyze the degree of corrosion based on impedance value changes over time as the corrosive electrodes erode over time due to corrosion; wherein IDE pairs purely composed of non-corrosive metal provides baseline impedance value that can be used to calibrate and / or normalize the impedance values of the IDE pairs composed of non-corrosive and corrosive electrode pair.

[0084] A 21stembodiment is the method of the 20thembodiment, wherein the first electrode comprises a metal that is susceptible to corrosion.

[0085] A 22ndembodiment is the method of the 21stembodiment, wherein the metal that it susceptible to corrosion comprises carbon steel, stainless steel, iron, an iron alloy, aluminum, and an aluminum alloy.

[0086] A 23rdembodiment is the method of one of the 20th— the 22ndembodiments, wherein the second electrode comprises a metal that is not susceptible to corrosion

[0087] A 24thembodiment is the method of the 23rdembodiment, wherein the metal that is not susceptible to corrosion comprises chromium titanium, platinum, or gold.

[0088] A 25thembodiment is the method of one of the 20th— the 24thembodiments, wherein each of the first electrode and the second electrode has a length, a width perpendicular to its length, and a thickness perpendicular to its length.

[0089] A 26thembodiment is the method of the 25thembodiment, wherein the length of each of the first electrode and the second electrode is from about 200 micrometers (pm) to about 1 ,000 pm.

[0090] A 27thembodiment is the method of one of the 25th— the 26thembodiments, wherein the width and / or the thickness of each of the first electrode and the second electrode is from about 0.1 pm to about 25 pm.

[0091] A 28thembodiment is the method of one of the 25th— the 27thembodiments, wherein the first electrode is disposed immediately lateral to the second electrode with respect to its length.

[0092] A 29thembodiment is the method of one of the 20th— the 28thembodiments, wherein the first electrode overlaps the second electrode by at least 20% of its length.

[0093] A 30thembodiment is the method of one of the 20th— the 29thembodiments , wherein the first electrode does not overlap the second electrode along its length.

[0094] A 31stembodiment is the method of one of the 20th— the 30thembodiments, wherein the microfluidic device further comprises a body, wherein the body further comprises a chamber, wherein the IDE structure is disposed within the chamber.

[0095] A 32ndembodiment is the microfluidic device of the 31stembodiment, wherein the body comprises a substrate.

[0096] A 33rdembodiment is the method of the 32ndembodiment, wherein the substrate comprises glass.

[0097] A 34thembodiment is the method of one of the 31st— the 33rdembodiments,wherein the body further comprises a structure enclosing the chamber.

[0098] A 35thembodiment is the microfluidic device of the 34thembodiment, wherein the structure is formed from polydimethylsiloxane (PDMS) or poly(methyl methacrylate) (PM MA).

[0099] A 36thembodiment is the method of one of the 20th— the 35thembodiments, wherein a space is disposed between the first electrode and the second electrode.

[0100] A 37thembodiment is the method of the 36thembodiment, wherein the space at least partially defines a channel.

[0101] A 38thembodiment is the method of the 37thembodiment, wherein the channel has a length and a width, wherein the length is greater than the width by a factor of at least 50.

[0102] While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the disclosure. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1 ), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.

Claims

CLAIMSWhat is claimed is:1 . A microfluidic device comprising: an interdigitated electrode (IDE) structure comprising a plurality of IDE pairs, wherein each of the plurality of IDE pairs comprises a first electrode and a second electrode.

2. The microfluidic device of claim 1 , wherein the first electrode comprises a metal that is susceptible to corrosion.

3. The microfluidic device of claim 2, wherein the metal that it susceptible to corrosion comprises carbon steel, stainless steel, iron, an iron alloy, aluminum, and an aluminum alloy.

4. The microfluidic device of claim 1 , wherein the second electrode comprises a metal that is not susceptible to corrosion5. The microfluidic device of claim 4, wherein the metal that is not susceptible to corrosion comprises chromium titanium, platinum, or gold.

6. The microfluidic device of claim 1 , wherein each of the first electrode and the second electrode has a length, a width perpendicular to its length, and a thickness perpendicular to its length.

7. The microfluidic device of claim 6, wherein the length of each of the first electrode and the second electrode is from about 200 micrometers (pm) to about 1 ,000 pm.

8. The microfluidic device of claim 6, wherein the width and / or the thickness of each of the first electrode and the second electrode is from about 0.1 pm to about 25 pm.

9. The microfluidic device of claim 6, wherein the first electrode is disposed immediately lateral to the second electrode with respect to its length.

10. The microfluidic device of claim 1 , wherein the first electrode overlaps the second electrode by at least 20% of its length.

11. The microfluidic device of claim 1 , wherein the first electrode does not overlap the second electrode along its length.

12. The microfluidic device of claim 1 , wherein the microfluidic device further comprises a body, wherein the body further comprises a chamber, wherein the IDE structure is disposed within the chamber.

13. The microfluidic device of claim 12, wherein the body comprises a substrate.

14. The microfluidic device of claim 13, wherein the substrate comprises glass.

15. The microfluidic device of claim 12, wherein the body further comprises a structure enclosing the chamber.

16. The microfluidic device of claim 15, wherein the structure is formed from polydimethylsiloxane (PDMS) or poly(methyl methacrylate) (PMMA).

17. The microfluidic device of claim 1 , wherein a space is disposed between the first electrode and the second electrode.

18. The microfluidic device of claim 17, wherein the space at least partially defines a channel.

19. The microfluidic device of claim 18, wherein the channel has a length and a width, wherein the length is greater than the width by a factor of at least 50.

20. A method of evaluating a fluid, the method comprising: placing a sample of the fluid and / or cells in contact with an interdigitated electrode (IDE) structure comprising a plurality of IDE pairs, wherein each of the plurality of IDE pairs comprises a first electrode and a second electrode; and measuring electrical impedance between the first electrode and the second electrode over time to analyze the degree of corrosion based on impedance value changes over time as the corrosive electrodes erode over time due to corrosion; wherein IDE pairs purely composed of non-corrosive metal provides baseline impedance value that can be used to calibrate and / or normalize the impedance values of the IDE pairs composed of non-corrosive and corrosive electrode pair.

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