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Journal ArticleDOI

A minimally invasive microsensor specially designed for simultaneous dissolved oxygen and pH biofilm profiling

TL;DR: The electrodes spatial resolution, the monitoring sensitivity, and the minimally invasive features exhibited by the proposed microsensor improved biofilm monitoring performance, enabling the quantification of mass transfer resistances and the assessment of biological activity.
Abstract: A novel sensing device for simultaneous dissolved oxygen (DO) and pH monitoring specially designed for biofilm profiling is presented in this work. This device enabled the recording of instantaneous DO and pH dynamic profiles within biofilms, improving the tools available for the study and the characterization of biological systems. The microsensor consisted of two parallel arrays of microelectrodes. Microelectrodes used for DO sensing were bare gold electrodes, while microelectrodes used for pH sensing were platinum-based electrodes modified using electrodeposited iridium oxide. The device was fabricated with a polyimide (Kapton®) film of 127 µm as a substrate for minimizing the damage caused on the biofilm structure during its insertion. The electrodes were covered with a Nafion® layer to increase sensor stability and repeatability and to avoid electrode surface fouling. DO microelectrodes showed a linear response in the range 0-8 mg L-1, a detection limit of 0.05 mg L-1, and a sensitivity of 2.06 nA L mg-1. pH electrodes showed a linear super-Nernstian response (74.2 ± 0.7 mV/pH unit) in a wide pH range (pH 4-9). The multi-analyte sensor array was validated in a flat plate bioreactor where simultaneous and instantaneous pH and DO profiles within a sulfide oxidizing biofilm were recorded. The electrodes spatial resolution, the monitoring sensitivity, and the minimally invasive features exhibited by the proposed microsensor improved biofilm monitoring performance, enabling the quantification of mass transfer resistances and the assessment of biological activity.

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Citations
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Journal ArticleDOI
TL;DR: In this review, the necessary data are compiled to understand the reactions or measurements performed in many of the assays commonly used in various aspects of microbiology.
Abstract: Viability and metabolic assays are commonly used as proxies to assess the overall metabolism of microorganisms. The variety of these assays combined with little information provided by some assay kits or online protocols often leads to mistakes or poor interpretation of the results. In addition, the use of some of these assays is restricted to simple systems (mostly pure cultures), and care must be taken in their application to environmental samples. In this review, the necessary data are compiled to understand the reactions or measurements performed in many of the assays commonly used in various aspects of microbiology. Also, their relationships to each other, as metabolism links many of these assays, resulting in correlations between measured values and parameters, are discussed. Finally, the limitations of these assays are discussed.

70 citations

Journal ArticleDOI
TL;DR: In this paper, a potentiometric sensor based on functionalized reduced graphene oxide was used to monitor the formation and growth of biofilms from three bacterial species (Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus) in liquid and semisolid culture media.
Abstract: Biofilm development on surfaces represents one of the most challenging issues in the medical field. The irreversibility of the biofilm developmental process, and the peculiar characteristics of biofilms (including the low permeability to antibacterial compounds), make biofilm associated infections difficult to treat and prone to relapse. Thanks to the short response time, low-cost, easy fabrication and potential for miniaturization, electrochemical sensors are expected to play an important role in monitoring biofilm formation. Here, we describe the use of a potentiometric sensor based on functionalized reduced graphene oxide for monitoring the formation and growth of biofilms from three bacterial species (Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus) in liquid and semisolid culture media. The Open Circuit Potential (OCP) between an Ag/AgCl pseudo reference electrode and a working electrode, both screen-printed on a flexible polyethylene terephthalate film, was measured during the growth of bacteria. The OCP decreased over time as bacteria grew on the sensor surface exhibiting a negative correlation.

22 citations

Journal ArticleDOI
TL;DR: In this paper, a dual-gate design based on organic electrochemical transistors (OECTs) was proposed to track dissolved oxygen concentration in seawater, a highly challenging matrix owing to its high ionic strength and multitude of chemical interferents.
Abstract: With our marine ecosystems under threat from climate change, there is an urgent need to continuously monitor marine conditions. One key indicator is the dissolved oxygen level, but existing sensors are limited by size and costs that preclude widespread non-intrusive monitoring. This work reports a new dual-gate design based on organic electrochemical transistors (OECTs) to track dissolved oxygen concentration in seawater, a highly challenging matrix owing to its high ionic strength and multitude of chemical interferents. We present the novel operating principle, by deriving the channel conductance with respect to potentials on the two gates. The sensor achieved a detection limit of 0.5 ppm dissolved oxygen concentration in seawater. The device demonstrated reliable operation over five days and was capable of monitoring oxygenation changes arising from the photosynthesis cycles of saltwater macro-algae.

18 citations

Journal ArticleDOI
01 Nov 2021
TL;DR: This review provides a detailed overview of methods that have been used to sense a variety of relevant analytes in biofilms and aims to help readers understand these techniques so that they can be applied to future projects for better understanding of biofilm elements and evolving sensing approaches.
Abstract: Biofilms form complex structures that are ubiquitous in natural environments and can cause chronic infections which are difficult to treat. While much is known about biofilms, many questions remain about how biofilms mature and respond to internal and external stimuli. To understand the phenomena that occur within the biofilm matrix, sensing techniques capable of quantitatively resolving spatial and temporal dynamics of key analytes in the biofilm are needed. Biofilm spatial and temporal heterogeneity provide unique hurdles in fully assessing these intricacies. This review provides a detailed overview of methods that have been used to sense a variety of relevant analytes in biofilms. Electrochemical, optical, and other analytical techniques each possess distinct strengths and weaknesses depending on the application showing that biofilm sensing does not have a “one-size fits all” solution. The analyte being measured, the environment it is analyzed in, and the information that is needed determine whether known approaches may be appropriate or novel methods need to be developed. This review aims to help readers understand these techniques so that they can be applied to future projects for better understanding of biofilm elements and evolving sensing approaches.

16 citations

Journal ArticleDOI
26 Feb 2021-Sensors
TL;DR: In this paper, an all-solid-state, flexible film sensor that allows highly accurate detection of sodium levels in saliva, comparable to those in blood, has been proposed for health monitoring with non-invasive wearable systems.
Abstract: Saliva can be used for health monitoring with non-invasive wearable systems. Such devices, including electrochemical sensors, may provide a safe, fast, and cost-efficient way of detecting target ions. Although salivary ions are known to reflect those in blood, no available clinical device can detect essential ions directly from saliva. Here, we introduce an all-solid-state, flexible film sensor that allows highly accurate detection of sodium levels in saliva, comparable to those in blood. The wireless film sensor system can successfully measure sodium ions from a small volume of infants’ saliva (<400 µL), demonstrating its potential as a continuous health monitor. This study includes the structural characterization and error analysis of a carbon/elastomer-based ion-selective electrode and a reference electrode to confirm the signal reliability. The sensor, composed of a pair of the electrodes, shows good sensitivity (58.9 mV/decade) and selectivity (log K = −2.68 for potassium), along with a broad detection range of 5 × 10−5 ≈ 1 M with a low detection limit of 4.27 × 10−5 M. The simultaneous comparison between the film sensor and a commercial electrochemical sensor demonstrates the accuracy of the flexible sensor and a positive correlation in saliva-to-blood sodium levels. Collectively, the presented study shows the potential of the wireless ion-selective sensor system for a non-invasive, early disease diagnosis with saliva.

14 citations

References
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Book ChapterDOI
TL;DR: There is still a long way to go in understanding of the microbial microenvironments and of the nature of the microorganisms that carry out the measured metabolic activities, and most chemical and radiotracer techniques in use today operate on a centimeter or at best on a millimeter scale and in most cases their results cannot be directly related to the relevant microorganisms.
Abstract: Among the fundamental goals of microbial ecology is the development of methods that will enable the identification and counting of the important microorganisms in nature, the determination of their physical and chemical microenvironment, and the analysis of their metabolic processes and interactions. Due to the small size of the organisms, much effort has been devoted to the development of high-resolution techniques for the observation and understanding of the world of bacteria on a microscale. Scanning and transmission electron microscopy and fluorescent staining, immunofluorescence and other techniques for light microscopy have been the most successful in terms of reaching a high spatial resolution. With respect to our understanding of the microbial microenvironments and of the nature of the microorganisms that carry out the measured metabolic activities, there is still a long way to go. Most chemical and radiotracer techniques in use today operate on a centimeter or at best on a millimeter scale and in most cases their results cannot be directly related to the relevant microorganisms. One notable exception to this is the combined use of autoradiography and fluorescence microscopy on microbial communities.

855 citations


Additional excerpts

  • ...Microsensors based on MEMS technology reduced some of the limitations presented by conventional microsensors, both electrochemical [20] and optical [10]....

    [...]

Journal ArticleDOI
TL;DR: Oxygen profiles in marine sediments obtained from measurements with microoptrodes show good correlation to profiles measured with oxygen microelectrodes, and show excellent long-term stability and storage stability.
Abstract: A new fiber-optic oxygen microsensor (microoptrode) based on dynamic fluorescence quenching has been developed to measure oxygen gradients in marine sediments and microbial mats. The microoptrodes are fabricated by immobilizing an oxygen-quenchable fluorophore at the tapered tip of an optical fiber. A special optoelectronic system has been designed to measure oxygen with these microoptrodes. It is based on small and cheap optical components and can easily be miniaturized for field applications. In contrast to oxygen microelectrodes, the new oxygen microoptrodes are easy to make, do not consume oxygen, and show no stirring dependence of the signal. In addition, they show excellent long-term stability and storage stability. Hydrogen sulfide, carbon dioxide, and other relevant chemical parameters do not interfere with the measurement. Oxygen profiles in marine sediments obtained from measurements with microoptrodes show good correlation to profiles measured with oxygen microelectrodes.

380 citations


"A minimally invasive microsensor sp..." refers background in this paper

  • ...Microsensors based on MEMS technology reduced some of the limitations presented by conventional microsensors, both electrochemical [20] and optical [10]....

    [...]

  • ...The technical limitations for the study of biofilms by in situ measurements (due to their reduced thickness ranging from hundreds of microns to a few millimeters) have been partially solved by the development of several microsensors, both electrochemical [8,9] and optical [10,11]....

    [...]

Journal ArticleDOI
TL;DR: A more detailed review of biofiltration is proposed, presenting the most recent and latest developments achieved in the field of bioprocessing.
Abstract: In this paper we present a review of the existing air pollution control technologies (APCT), when used essentially for the elimination of volatile organic compounds (VOC). The biotechnologies referred to, bioscrubbers, biotrickling filters and biofilters, are also described. A more detailed review of biofiltration is proposed, presenting the most recent and latest developments achieved in the field of bioprocessing. In particular, the influence of the filter bed, the polluted air flowrates, the pollutants, the pressure drop, bed moisture content, temperature, nutrients, pH and the microorganisms are reviewed. Models of biofiltration are also presented.

358 citations


"A minimally invasive microsensor sp..." refers background in this paper

  • ...Air pollution control has become an essential issue to ensure the health and the welfare of future societies as well as to limit and reduce the degradation of the environment [1]....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the peak-current potential-differences obtained from cyclic voltammetry and charge transfer resistance obtained from electrochemical impedance spectroscopy were used to characterize surface cleanliness.

279 citations


"A minimally invasive microsensor sp..." refers methods in this paper

  • ...To this aim, several metal-cleaning methods were investigated [33]....

    [...]

Journal ArticleDOI
TL;DR: The electrodes showed very low sensitivities for different species, such as Na+, K+, Li+, NH4+, Ca2+, Mg2+, dissolved oxygen, lactate, ascorbate, and urate, which are important for physiological applications.
Abstract: In the present paper, fabrication, characterization, and physiological applications of a solid-state pH electrode are described. The pH sensing layer was based on an anodic electrodeposited iridium oxide film (AEIROF). Sputtered platinum electrodes (1 mm diameter) fabricated on flexible Kapton films or platinum wires were used as planar or cylindrical supports. Each electrode site was coated with Nafion to attenuate the interference of anionic redox species and to protect the electrode surface during in vivo measurements. Performance of the AEIROF was evaluated, for the first time, as a pH electrode and proved to have a slightly super-Nernstian response with slope of -63.5 +/- 2.2 mV/pH unit for both wire and planar sputtered platinum electrodes. Linear pH responses were obtained in the pH range 2-10. The electrodes have a working lifetime of at least 1 month with accuracy of about 0.02 pH unit and fast response time. The electrodes showed very low sensitivities for different species, such as Na+, K+, Li+, NH4+, Ca2+, Mg2+, dissolved oxygen, lactate, ascorbate, and urate, which are important for physiological applications. The electrodes were applied in extracellular pH measurements during brief regional ischemia in a swine heart and no-flow ischemia in an isolated rabbit papillary muscle. A first report on extracellular pH, K+, and lactate simultaneous measurements during no-flow ischemia using the AEIROF pH electrode and the previously described K+ and lactate electrodes is presented as well.

206 citations