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Titanium nitride (TiN) materials have gained an interest over the past years due to their unique characteristics, such as thermal stability, extreme hardness, low production cost, and comparable optical properties to gold. In the present study, TiN nanoparticles were synthesized via a thermal benzene route to obtain black nanoparticles. Scanning electron microscopy (SEM) was carried out to examine the morphology. Further microscopic characterization was done where the final product was drop cast onto double-sided conductive carbon tape and sputter-coated with gold/palladium at a thickness of 4 nm for characterization by field emission scanning electron microscopy (FE-SEM) with energy dispersive X-Ray spectroscopy (EDS) that revealed they are spherical. ImageJ software was used to measure the average size of the particles to be 79 nm in diameter. EDS was used to determine the elements present in the sample and concluded that there were no impurities. Further characterization by Fourier Transform infrared (FTIR) spectroscopy was carried out to identify the characteristic peaks of TiN. X-ray diffraction (XRD) revealed typical peaks of cubic phase titanium nitride, and crystallite size was determined to be 14 nm using the Debye-Scherrer method. Dynamic light scattering (DLS) analysis revealed the size distribution of the TiN nanoparticles, with nanoparticles averaging at 154 nm in diameter. Zeta potential concluded the surface of the TiN nanoparticles is negatively charged.

Electrochemistry offers a wide range of analytical sensing capability and is therefore suited to serve a variety of NASA missions. Advancements in miniaturization and automation in addition to inherent high sensitivity and specificity have made electrochemical sensors especially attractive. Here, we present recent developments for use of electrochemical sensors in planetary exploration and human exploration missions. This article highlights research developments in the area of electrochemical sensors as presented at the Electrochemistry in Space symposium at the 236th ECS Meeting on October 16, 2019 in Atlanta, GA.

Proteases are critical signaling molecules and prognostic biomarkers for many diseases including cancer. There is a strong demand for multiplex bioanalytical techniques that can rapidly detect the activity of extracellular proteases with high sensitivity and specificity. This study demonstrates an activity-based electrochemical biosensor of a 3 × 3 gold microelectrode array for the detection of cathepsin B activity in human serum diluted in a neutral buffer. Proteolysis of ferrocene-labeled peptide substrates functionalized on 200 × 200 μm microelectrodes is measured simultaneously over the nine channels by AC voltammetry. The protease activity is represented by the inverse of the exponential decay time constant (1/τ), which equals to (k(cat)/K(M))[CB] based on the Michaelis–Menten model. An enhanced activity of the recombinant human cathepsin B (rhCB) is observed in a low-ionic-strength phosphate buffer at pH = 7.4, giving a very low limit of detection of 8.49 × 10(−4) s(−1) for activity and 57.1 pM for the active rhCB concentration that is comparable to affinity-based enzyme-linked immunosorbent assay (ELISA). The cathepsin B presented in the human serum sample is validated by ELISA, which mainly detects the inactive proenzyme, while the electrochemical biosensor specifically measures the active cathepsin B and shows significantly higher decay rates when rhCB and human serum are activated. Analyses of the kinetic electrochemical measurements with spiked active cathepsin B in human serum provide further assessment of the protease activity in the complex sample. This study lays the foundation to develop the gold microelectrode array into a multiplex biosensor for rapid detection of the activity of extracellular proteases toward cancer diagnosis and treatment assessment.

The emerging Internet of things (IoT) demands not only new device technologies but also strengthening the security of things in order to prevent tampering and hacking. Humans have unique characteri...

There has been a tremendous growth in the use of MEMS technology for physical sensing, enabled by low cost sensors and resonators for widespread use in smart phones and wearable electronic devices for health and fitness. MEMS technology is now being applied to chemical and biosensing in combination with microfluidic devices. Microfluidic devices provide integrated liquid handling for assays and cell cultures. The detection of volatile organic compounds with micro-gas chromatography is another area where miniaturization can provide lower cost and portable instruments with widespread applications. These topics are areas for technical papers presented at the upcoming IMCS meeting in Montreal in May 2020.

Additive manufacturing technologies are being explored by NASA for the in-space manufacturing of sensors and electronics. Additive manufacturing directly addresses the logistic challenge for long-duration human spaceflight missions while also offering a high degree of customization and tailorability. To ensure the health and safety of crew members during long duration missions, it can be advantageous to develop human health diagnostic tools that can be manufactured during those missions. Here we report the development of a wearable and fully printed electrochemical sensor for the detection of human performance markers in sweat.1 The sensor’s fabrication is complimentary with in-space manufacturing for an on-demand and hands-free fabrication and is comprised of commercial and custom carbon, gold and silver inks on a polyimide substrate to make a flexible, 3-electrode electrochemical sensor, shown in Figure 1. Sensor readout is performed using standard electrochemical procedures via a miniaturized, custom potentiostat. The initial prototyped printed electrochemical sensors demonstrate good electrochemical performance and high mechanical stability while also displaying low batch to batch variability. Our goal is to create a highly adaptable and versatile approach that utilizes fabrication processes consistent with in-space manufacturing, thus enabling the manufacture of point-of-care devices during flight. Reference Brasier, N. & Eckstein, J. Sweat as a Source of Next-Generation Digital Biomarkers. Digit. Biomarkers 3, 155–165 (2019). Figure 1

Proteases are a large family of enzymes involved in many important biological processes. Quantitative detection of the activity profile of specific target proteases is in high demand for the diagnosis and treatment monitoring of diseases such as cancers. The overexpression and enhanced activity of proteases were found to correlate well with cancer development. Protease inhibitors are also a class of major anti-cancer drug candidates. However, due to the presence of a large number (over 600) of proteases in human body, their complex interactions with each other, and large influence by the surrounding factors (such as buffer composition, pH value and temperature), it is challenging to accurately detect the activity of specific proteases in complex media. It is even more difficult to measure the activity profiles of a large set of proteases that are relevant to cancers. Here we summarize our studies on the development of a multiplex electrode array biosensor platform toward cancer diagnosis based on rapid profiling of multiple protease activities. Both nano- and micro-electrode arrays have been demonstrated for electrochemical detection of protease activities. The individually addressed 3x3 gold thin-film microelectrode array is particularly attractive for rapid profiling of multiple protease activities. The general sensor scheme involves attaching short peptides with specific sequences of 4 to 8 amino acids on the electrode surface of the electrochemical sensor chip, which serve as the substrates for selective proteolysis by the cognate proteases. The far end is covalently attached with a ferrocene (Fc) group as the redox tag for electrochemical measurements. The quantity of the intact peptides on the electrode surface is measured with an AC voltammetry (ACV) method, which is proportional to the peak current at the specific electrode potential when Fc oxidation is oxidized into ferrocenium (Fc+). As the peptide is cleaved by the cognate protease, the peak current decreases continuously in the continuously repeated ACV curves. The recorded kinetic proteolytic curve can be quantitatively described by the heterogeneous Michaelis-Menten model following an exponential decay. The inverse of exponential decay time constant, i.e., 1/τ, is found to represent the protease activity which equals to [E](kcat /KM), where [E] is the protease concentration and kcat /KM is the specificity constant defined by the kinetic proteolytic reaction constant kcat and the Michaelis equilibrium constant KM. The kcat /KM values have been investigated versus the substrate peptide sequence and length, temperature, and buffer composition to optimize the detection for activity of cathepsin B, a potential cancer biomarker. The limit of detection (LOD) for activated cathepsin B can reach down to 0.57 pM, sufficient to directly detect cathepsin B in diluted human serum. This electrochemical method has been compared and validated with the commonly used affinity assay, i.e., enzyme-linked immunosorbent assay (ELISA). The ELISA measurements were found to be more sensitive to the concentration of proenzyme (zymogen), while the electrochemical method detects the activity of the proteases which reflects the intrinsic biological function. This provides more critical information than the concentration derived from ELISA. Currently, two sets of peptides have been synthesized which are selective for detection of cathepsin B and ADAM-17, respectively. They are functionalized to the 3x3 gold thin-film microelectrode array and used to simultaneously detect these two types of proteases in serum samples from breast cancer patients at different stages. The activity profiles will be correlated to the cancer development. Figure 1

Machine learning (ML) models that classify a sample as non-indicative or indicative of life can play an important role in planning life-detection missions. They are based on clearly defined and con...

Graphene has proven to be useful in biosensing applications. However, one of the main hurdles with printed graphene-based electrodes is achieving repeatable electrochemical performance from one printed electrode to another. We have developed a consistent fabrication process to control the sheet resistance of inkjet-printed graphene electrodes, thereby accomplishing repeatable electrochemical performance. Herein, we investigated the electrochemical properties of multilayered graphene (MLG) electrodes fully inkjet-printed (IJP) on flexible Kapton substrates. The electrodes were fabricated by inkjet printing three materials – (1) a conductive silver ink for electrical contact, (2) an insulating dielectric ink, and (3) MLG ink as the sensing material. The selected materials and fabrication methods provided great control over the ink rheology and material deposition, which enabled stable and repeatable electrochemical response: bending tests revealed the electrochemical behavior of these sensors remained consistent over 1000 bend cycles. Due to the abundance of structural defects (e.g., edge defects) present in the exfoliated graphene platelets, cyclic voltammetry (CV) of the graphene electrodes showed good electron transfer (k = 1.125 × 10−2 cm s−1) with a detection limit (0.01 mM) for the ferric/ferrocyanide redox couple, [Fe(CN)6]−3/−4, which is comparable or superior to modified graphene or graphene oxide-based sensors. Additionally, the potentiometric response of the electrodes displayed good sensitivity over the pH range of 4–10. Moreover, a fully IJP three-electrode device (MLG, platinum, and Ag/AgCl) also showed quasi-reversibility compared to a single IJP MLG electrode device. These findings demonstrate significant promise for scalable fabrication of a flexible, low cost, and fully-IJP wearable sensor system needed for space, military, and commercial biosensing applications.

Complete removal of metal catalyst particles from carbon nanofibers (CNFs) and other carbon nanostructures is extremely difficult, and the envisioned applications may be compromised by the left-over impurities. To circumvent these problems, one should use, wherever possible, such catalyst materials that are meant to remain in the structure and have some application-specific role, making any removal steps unnecessary. Thus, as a proof-of-concept, we present here a nanocarbon-based material platform for electrochemical hydrogen peroxide measurement utilizing a Pt catalyst layer to grow CNFs with intact Pt particles at the tips of the CNFs. Backed by careful scanning transmission electron microscopy analysis, we show that this material can be readily realized with the Pt catalyst layer thickness impacting the resulting structure and also present a growth model to explain the evolution of the different types of structures. In addition, we show by electrochemical analysis that the material exhibits characteristic features of Pt in cyclic voltammetry and it can detect very small amounts of hydrogen peroxide with very fast response times. Thus, the present sensor platform provides an interesting electrode material with potential for biomolecule detection and in fuel cells and batteries. In the wider range, we propose a new approach where the selection of catalytic particles used for carbon nanostructure growth is made so that (i) they do not need to be removed and (ii) they will have essential role in the final application.

A nanoelectrode array of vertically aligned carbon nanofibers was evaluated for the detection of Pb2+ by anodic stripping voltammetry. The achieved detection limit of 1.73 nM is well below the environmental guidelines. The approach provides a safer alternative to the mercury electrodes commonly used for the detection of heavy metals. Keywords: Carbon nanofibers, Lead, Anodic stripping voltammetry

There is a strong demand for bioanalytical techniques to rapidly detect protease activities with high sensitivity and high specificity. This study reports an activity-based electrochemical method toward this goal. Nanoelectrode arrays (NEAs) fabricated with embedded vertically aligned carbon nanofibers (VACNFs) are functionalized with specific peptide substrates containing a ferrocene (Fc) tag. The kinetic proteolysis curves are measured with continuously repeated ac voltammetry, from which the catalytic activity is derived as the inverse of the exponential decay time constant based on a heterogeneous Michaelis–Menten model. Comparison of three peptide substrates with different lengths reveals that the hexapeptide H(2)N─(CH(2))(4)─CO─Pro-Leu-Arg-Phe-Gly-Ala─NH─CH(2)─Fc is the optimal probe for cathepsin B. The activity strongly depends on temperature and is the highest around the body temperature. With the optimized peptide substrate and measuring conditions, the limit of detection of cathepsin B activity and concentration can reach 2.49 × 10(−4) s(−1) and 0.32 nM, respectively. The peptide substrates show high specificity to the cognate proteases, with negligible cross-reactions among three cancer-related proteases cathepsin B, ADAM10, and ADAM17. This electrochemical method can be developed into multiplex chips for rapid profiling of protease activities in cancer diagnosis and treatment monitoring.

Age structure in most developed countries is changing fast as the average lifespan is increasing significantly, calling for solutions to provide improved treatments for age-related neurological diseases and disorders. In order to address these problems, a reliable way of recording information about neurotransmitters from in vitro and in vivo applications is needed to better understand neurological diseases and disorders as well as currently used treatments. Likewise, recent developments in medicine, especially with the opioid crisis, are demanding a swift move to personalized medicine to administer patient needs rather than population-wide averages. In order to enable the so-called personalized medicine, it is necessary to be able to do measurements in vivo and in real time. These actions require sensitive and selective detection of different analytes from very demanding environments. Current state-of-the-art materials are unable to provide sensitive and selective detection of neurotransmitters as well as the required time resolution needed for drug molecules at a reasonable cost. To meet these challenges, we have utilized different metals to grow carbon nanomaterials and applied them for sensing applications showing that there are clear differences in their electrochemical properties based on the selected catalyst metal. Additionally, we have combined atomistic simulations to support optimizing materials for experiments and to gain further understanding of the atomistic level reactions between different analytes and the sensor surface. With carbon nanostructures grown from Ni and Al + Co + Fe hybrid, we can detect dopamine, ascorbic acid, and uric acid simultaneously. On the other hand, nanostructures grown from platinum provide a feasible platform for detection of H2O2 making them suitable candidates for enzymatic biosensors for detection of glutamate, for example. Tetrahedral amorphous carbon electrodes have an ability to detect morphine, paracetamol, tramadol, and O-desmethyltramadol. With carbon nanomaterial-based sensors, it is possible to reach metal-like properties in sensing applications using only a fraction of the metal as seed for the material growth. We have also seen that by using nanodiamonds as growth catalyst for carbon nanofibers, it is not possible to detect dopamine and ascorbic acid simultaneously, although the morphology of the resulting nanofibers is similar to the ones grown using Ni. This further indicates the importance of the metal selection for specific applications. However, Ni as a continuous layer or as separate islands does not provide adequate performance. Thus, it appears that metal nanoparticles combined with fiber-like morphology are needed for optimized sensor performance for neurotransmitter detection. This opens up a new research approach of application-specific nanomaterials, where carefully selected metals are integrated with carbon nanomaterials to match the needs of the sensing application in question.

A 3D-printed microfluidic device coupled with a fluidic processing system was developed to enable autonomous end-to-end sample handling and electrochemical characterization of an Ocean World analogue solution – synthetic seawater (SW). This dual-channel microfluidic cell was populated with 14 electrodes and performed electrochemical measurements similar to those used in the MECA Wet Chemistry Laboratory on board NASA’s Phoenix Lander that landed on Mars in 2008. Biological and metallic redox events were evaluated using cyclic voltammetry with Au, Pt, and glassy carbon electrodes, with the latter displaying superior sensitivity and selectivity. Conductivity and pH were measured using Pt and iridium oxide electrodes respectively, and SW anions such as chloride were quantified using chronopotentiometry with a Ag electrode. The fluidic handling system demonstrated sample transportation to the microfluidic device for electrochemical measurements, and could be readily adapted to accommodate different pre-processing steps. Overall, this study demonstrates the use of electrochemical sensors as part of an autonomous microfluidic handling system that would be functionally analogous to an electrochemical instrument designed for Ocean World exploration.

A vertically aligned carbon nanofiber-based (VACNF) electrode platform was developed for an enzymeless hydrogen peroxide sensor. Vertical nanofibers have heights on the order of 2–3 μm, and diameters that vary from 50 to 100 nm as seen by atomic force microscopy. The VACNF was grown as individual, vertically, and freestanding structures using plasma-enhanced chemical vapor deposition. The electrochemical sensor, for the hydrogen peroxide measurement in solution, showed stability and reproducibility in five consecutive calibration curves with different hydrogen peroxide concentrations over a period of 3 days. The detection limit was 66 μM. The sensitivity for hydrogen peroxide electrochemical detection was 0.0906 mA cm−2 mM−1, respectively. The sensor was also used for the measurement of hydrogen peroxide as the by-product of the reaction of cholesterol with cholesterol oxidase as a biosensor application. The sensor exhibits linear behavior in the range of 50 μM–1 mM in cholesterol concentrations. The surface analysis and electrochemistry characterization is presented.

Since their discovery [1], carbon nanotubes have been used in everything from lightweight composites to electrical components in sensors and electronics. The development of substrate-grown vertically aligned carbon nanotubes by plasma-enhanced chemical vapor deposition (PECVD ) [2] spurred on exciting new applications in electronics, field emission, and sensors. These materials were later called carbon nanofibers (CN Fs). This article describes the growth, characterization, and electrical properties of CN Fs and their use as stimulating and sensing electrodes in neuromodulation applications.

We present an electrochemical multianalyte or multiplexed immunosensor for simultaneous label free detection of cardiac markers panel, comprising of C-reactive protein, cardiac troponin-I and myoglobin. The multi-electrode biosensor chip contains nine identical but electrically isolated microelectrodes arranged in a 3 × 3 array configuration. Each electrode contains carbon nanofiber nanoelectrodes grown vertically using plasma enhanced chemical vapor deposition. A hydrophobic photoresist layer, lithographically etched on the chip, exposes the electrodes and helps to selectively immobilize the antibody probes for the three target cardiac biomarkers using carbodiimide chemistry. The real-time label free detection of the three cardiac markers from a mixture is demonstrated with high sensitivity and selectivity. Detection in complex protein mixtures in human blood serum does not show any false positives from non-specific protein adsorption. The results show that the present sensor can serve as a miniaturized, low cost lab-on-a-chip system for the detection of various biomarkers in healthcare, environmental monitoring and security applications.

In this letter, we discuss the role of a thin diamond-like carbon (DLC) layer in the growth of carbon nanofibers. We show how the DLC layer acts as an additional carbon source during the pre-annealing stage and changes the nanofiber morphology significantly compared to the case without the DLC layer. Significant amount of carbon is dissolved into the Ni layer during the pre-annealing stage, which leads to supersaturation and subsequent precipitation of carbon out of the Ni particles during the growth stage.

We present a detailed microstructural study comparing conventional carbon nanofibers (CNFs) and novel carbon hybrid CNF materials. The hybrid consists of CNFs grown on top of tetrahedral amorphous carbon (ta-C) thin films on silicon with nickel catalyst and Ti adhesion layers. The conventional CNFs were grown on silicon with nickel catalyst and Cr layers. Even though CNFs can be grown in both systems by tip growth, the micro- and nanoscale features are very different in the two systems. The crystalline structure of the CNF in the hybrid case changes from horizontal alignment to near-vertical alignment from the root to the tip and no bamboo structure is observed. The results show that micro- and nanoscale properties of CNFs grown under the same process conditions can be readily altered by using a sacrificial ta-C layer below the metallic layer to prevent the alloying of Ni with carbide-forming metals used as adhesion promoters and to act as an additional carbon source during the pre-annealing stage. The experimental results are further rationalized with the aid of assessed thermodynamic data and simulations based on density functional theory (DFT) with van der Waals (vdW) corrections.

Understanding the chemical nature of the surface of carbon nanofibers (CNF) is critical in assessing their fundamental properties and tailoring them for the right application. To gain such knowledge, we present here a detailed X-ray adsorption spectroscopy (XAS) study accompanied by high resolution transmission electron microscopy (TEM) micrographs of two morphologically different CNF pairs (tetrahedral amorphous carbon (ta-C) grown “open structured” fibers and traditional bamboo-like “closed structured” fibers), where the surface chemical properties and structural features of the fibers are investigated in depth and the effects of nitric acid treatment on the fibers are revealed. The morphology of the fiber and/or the original seed- and adhesion layers markedly affect the response of the fibers to the acid treatment. Results also show that the nitric acid treatment increases the observed sp2 intensity and modifies the two types of fibers to become more-alike both structurally and with respect to their ox...

Proteases are a large family of enzymes involved in many important biological processes. Quantitative detection of the activity profile of specific target proteases is in high demand for the diagnosis and monitoring of diseases such as cancers. This study demonstrates the fabrication and characterization of an individually addressable 3 × 3 Au microelectrode array for rapid, multiplex detection of cathepsin B activity based on a simple electrochemical method. The nine individual microelectrodes in the array show highly consistent cyclic voltammetric signals in Au surface cleaning experiments and detecting benchmark redox species in solution. The individual Au microelectrodes are further selectively functionalized with specific ferrocene-labeled peptide molecules which serve as the cognate substrates for the target proteases. Consistent proteolytic kinetics are measured by monitoring the decay of the AC voltammetry signal from the ferrocene label as the peptide molecules are cleaved by cathepsin B. Accurate activity of cathepsin B is derived with an improved fitting algorithm. Simultaneous detection of the proteolysis of cathepsin B on the microelectrode array functionalized with three different hexapeptides is demonstrated, showing the potential of this sensor platform for rapid detection of the activity profiles of multiple proteases in various diseases including many forms of cancer.

A 3D-printed microfluidic device coupled with a fluidic processing system was developed to enable autonomous end-to-end sample handling and electrochemical characterization of an ocean world analogue solution – synthetic seawater (SW). This dual-channel microfluidic cell was populated with 14 electrodes and performed electrochemical measurements similar to those used in the MECA Wet Chemistry Laboratory on board NASA’s Phoenix Lander that landed on Mars in 2008. Biological and metallic redox events were evaluated using cyclic voltammetry with Au, Pt, and glassy carbon electrodes, with the latter displaying superior sensitivity and selectivity. Conductivity and pH were measured using Pt and iridium oxide electrodes respectively, and SW anions such as chloride were quantified using chronopotentiometry with a Ag electrode. The fluidic handling system demonstrated sample transportation to the microfluidic device for electrochemical measurements, and could be readily adapted to accommodate different pre-processing steps. Overall, this study demonstrates the use of electrochemical sensors as part of an autonomous microfluidic handling system that would be functionally analogous to an electrochemical instrument designed for Ocean World exploration.

This paper reports the first known investigation of power dissipation and electrical breakdown in aerosol-jet-printed (AJP) graphene interconnects. The electrical performance of aerosol-jet printed (AJP) graphene was characterized using the Transmission Line Method (TLM). The electrical resistance decreased with increasing printing pass number (n); the lowest sheet resistance measured was 1.5 kΩ/sq. for n = 50. The role of thermal resistance (RTH) in power dissipation was studied using a combination of electrical breakdown thermometry and infrared (IR) imaging. A simple lumped thermal model ($${\boldsymbol{\Delta }}{\bf{T}}={\bf{P}}{\boldsymbol{\times }}{{\bf{R}}}_{{\bf{TH}}}$$ Δ T = P × R TH ) and COMSOL Multiphysics was used to extract the total RTH, including interfaces. The RTH of AJP graphene on Kapton is ~27 times greater than that of AJP graphene on Al2O3 with a corresponding breakdown current density 10 times less on Kapton versus Al2O3.

Space missions have unique requirements for payloads of electronics, sensors, instruments, and other components in terms of mass, footprint, power consumption, and resistance to various types of radiation. Nanomaterials offer the potential for future radiation-hardened or radiation-immune electronics. Gas-sensing needs in planetary exploration and crew-cabin air-quality monitoring are currently being met by bulky instruments. Routine health checkups of astronauts and testing of water in space habitats are being done on a delayed basis by bringing samples back to Earth. Instead, nanomaterials can be used to construct ultrasmall, postage-stamp-sized gas/vapor sensors with selective discrimination and also lab-on-a-chip biosensors for water-quality monitoring and crew health monitoring.

Carbon-based materials, such as diamond-like carbon (DLC), carbon nanofibers (CNFs), and carbon nanotubes (CNTs), are inherently interesting for neurotransmitter detection due to their good biocompatibility, low cost and relatively simple synthesis. In this paper, we report on new carbon-hybrid materials, where either CNTs or CNFs are directly grown on top of tetrahedral amorphous carbon (ta-C). We show that these hybrid materials have electrochemical properties that not only combine the best characteristics of the individual "building blocks" but their synergy makes the electrode performance superior compared to conventional carbon based electrodes. By combining ta-C with CNTs, we were able to realize electrode materials that show wide and stable water window, almost reversible electron transfer properties and high sensitivity and selectivity for detecting dopamine in the presence of ascorbic acid. Furthermore, the sensitivity of ta-C + CNF hybrids towards dopamine as well as glutamate has been found excellent paving the road for actual in vivo measurements. The wide and stable water window of these sensors enables detection of other neurotransmitters besides DA as well as capability of withstanding higher potentials without suffering from oxygen and hydrogen evolution.

Controlled integration of features that enhance the analytical performance of a sensor chip is a challenging task in the development of paper sensors. A critical issue in the fabrication of low-cost biosensor chips is the activation of the device surface in a reliable and controllable manner compatible with large-scale production. Here, we report stable, well-adherent, and repeatable site-selective deposition of bioreactive amine functionalities and biorepellant polyethylene glycol-like (PEG) functionalities on paper sensors by aerosol-assisted, atmospheric-pressure, plasma-enhanced chemical vapor deposition. This approach requires only 20 s of deposition time, compared to previous reports on cellulose functionalization, which takes hours. A detailed analysis of the near-edge X-ray absorption fine structure (NEXAFS) and its sensitivity to the local electronic structure of the carbon and nitrogen functionalities. σ*, π*, and Rydberg transitions in C and N K-edges are presented. Application of the plasma-processed paper sensors in DNA detection is also demonstrated.

Atmospheric pressure plasmas have gained attention in recent years for several environmental applications. This technology could potentially be used to deactivate airborne microorganisms, surface-bound microorganisms, and biofilms. In this work, the authors explore the efficacy of the atmospheric pressure dielectric barrier discharge (DBD) to inactivate airborne Staphylococcus epidermidis and Aspergillus niger that are opportunistic pathogens associated with nosocomial infections. This technology uses air as the source of gas and does not require any process gas such as helium, argon, nitrogen, or hydrogen. The effect of DBD was studied on aerosolized S. epidermidis and aerosolized A. niger spores via scanning electron microscopy (SEM). The morphology observed on the SEM micrographs showed deformations in the cellular structure of both microorganisms. Cell structure damage upon interaction with the DBD suggests leakage of vital cellular materials, which is a key mechanism for microbial inactivation. The chemical structure of the cell surface of S. epidermidis was also analyzed by near edge x-ray absorption fine structure spectroscopy before and after DBD exposure. Results from surface analysis revealed that reactive oxygen species from the DBD discharge contributed to alterations on the chemistry of the cell membrane/cell wall of S. epidermidis.Atmospheric pressure plasmas have gained attention in recent years for several environmental applications. This technology could potentially be used to deactivate airborne microorganisms, surface-bound microorganisms, and biofilms. In this work, the authors explore the efficacy of the atmospheric pressure dielectric barrier discharge (DBD) to inactivate airborne Staphylococcus epidermidis and Aspergillus niger that are opportunistic pathogens associated with nosocomial infections. This technology uses air as the source of gas and does not require any process gas such as helium, argon, nitrogen, or hydrogen. The effect of DBD was studied on aerosolized S. epidermidis and aerosolized A. niger spores via scanning electron microscopy (SEM). The morphology observed on the SEM micrographs showed deformations in the cellular structure of both microorganisms. Cell structure damage upon interaction with the DBD suggests leakage of vital cellular materials, which is a key mechanism for microbial inactivation. The c...

The surface properties of the electrode materials play a crucial role in determining the performance and efficiency of energy storage devices. Graphene oxide and nanostructures of 3d transition metal oxides were synthesized for construction of electrodes in supercapacitors, and the electronic structure and oxidation states were probed using near-edge X-ray absorption fine structure. Understanding the chemistry of graphene oxide would provide valuable insight into its reactivity and properties as the graphene oxide transformation to reduced-graphene oxide is a key step in the synthesis of the electrode materials. Polarized behavior of the synchrotron X-rays and the angular dependency of the near-edge X-ray absorption fine structures (NEXAFS) have been utilized to study the orientation of the σ and π bonds of the graphene oxide and graphene oxide–metal oxide nanocomposites. The core-level transitions of individual metal oxides and that of the graphene oxide nanocomposite showed that the interaction of graphene oxide with the metal oxide nanostructures has not altered the electronic structure of either of them. As the restoration of the π network is important for good electrical conductivity, the C K edge NEXAFS spectra of reduced graphene oxide nanocomposites confirms the same through increased intensity of the sp2-derived unoccupied states π* band. A pronounced angular dependency of the reduced sample and the formation of excitonic peaks confirmed the formation of extended conjugated network.

In this paper we describe a method for three-dimensional wax patterning of microfluidic paper-based analytical devices (μPADs). The method is rooted in the fundamental details of wax transport in paper and provides a simple way to fabricate complex channel architectures such as hemichannels and fully enclosed channels. We show that three-dimensional μPADs can be fabricated with half as much paper by using hemichannels rather than ordinary open channels. We also provide evidence that fully enclosed channels are efficiently isolated from the exterior environment, decreasing contamination risks, simplifying the handling of the device, and slowing evaporation of solvents.

Biological redox is a promising indicator of life for NASA’s future exploration missions of Ocean Worlds. Electrochemical sensors are valuable tools for detecting these biological redox signatures on Earth; however their application to planetary exploration has been limited. All forms of life on Earth contain cellular machinery that can transform and regulate chemical energy through electron transfer pathways performed by key classes of naturally-occurring biological redox molecules including flavins, nicotinamides, porphyrins, and quinones. In this study, we use electrochemical techniques to measure these redox molecules in a synthetic seawater solution. This study also appropriates an electrochemical immunoassay technique for alkaline phosphatase detection, where comparison of the unique redox signatures of enzyme substrates and products reflect enzymatic activity. Naturally-occurring redox molecules exhibit unique redox signatures with anodic peak locations indicative of their respective molecular class. In this work, we report measured limits of detection as low as 10 nM and 3.13 aM for naturally-occurring redox molecules and alkaline phosphatase respectively. Overall, the findings of this study demonstrate that electrochemical sensors are effective tools for life detection applications for future Ocean Worlds missions.

The impact of space environment in human physiology is one of the biggest hurdles for the success of long duration manned missions.1 Traditionally, the impact of space environment is assessed by comparing different physiological parameters before and after deployment. For long duration missions (i.e Moon or Mars), sample return for a ground base analysis will be impractical and in-flight, portable analytical devices will be required. Additionally, the further crew travel from earth, the less feasible it is to rely on resupply of these portable analytical devices. One solution is to develop methodologies for manufacturing analytical devices on-demand and in an in-space environment. Electrochemical biosensors can serve as point-of-care (POC) analytical devices as they can be easily fabricated onto cheap, disposable substrates by printing nanomaterial-based electronic inks. Inkjet printing is a suitable deposition technique as it provides contactless deposition of material droplets (ink) in very precise coordinates (high spatial resolution), allowing the fabrication of complex features.2 This offers a highly tailorable manufacturing process as the printed features are based on a easily adjustable/editable digital file. Also, this manufacture approach is amenable for an in-space environment fabrication due to its low dependence on an operator, fast manufacturing time with low waste generation, easily scalable, highly/easily tunable, ability to print a variety of electronic inks (conductors and insulators) with minimal chance of cross contamination between materials and different types of sensors can be manufactured using the same printer.3,4 Inkjet printing has the added advantage of allowing POC devices to be manufacture on a demand basis, optimizing resource use. Here we present the first steps of the development of a print-on-demand 3-electrode electrochemical biosensor for the detection of cortisol, a stress biomarker.5 For these devices, 3 types of inks were use: multi walled carbon nanotubes (MWCNT), silver nanoparticles (AgNP) and SU-8. First, AgNP ink was printed onto a kapton substrate to define the reference electrode (RE), electrical contact pads and electrical connections. Second, MWCNT ink was printed to generate the working electrode (WE) and the counter electrode (CE). Third, the SU-8 ink is used to encapsulate and insulate the AgNP electrical connectors. Lastly, the surface of the WE was modified with an antibody anti-cortisol using EDC/NHS coupling chemistry. The surface modification and detection of cortisol is identified through a measurable electrical change such as current and impedance, etc.6 (1) Demontis, G. C.; Germani, M. M.; Caiani, E. G.; Barravecchia, I.; Passino, C.; Angeloni, D. Human Pathophysiological Adaptations to the Space Environment. Front. Physiol. 2017, 8, 1–17. (2) Raut, N. C.; Al-Shamery, K. Inkjet Printing Metals on Flexible Materials for Plastic and Paper Electronics. J. Mater. Chem. C 2018, 6 (7), 1618–1641. (3) Li, J.; Rossignol, F.; Macdonald, J. Inkjet Printing for Biosensor Fabrication: Combining Chemistry and Technology for Advanced Manufacturing. Lab Chip 2015, 15 (12), 2538–2558. (4) Khan, S.; Ali, S.; Bermak, A. Recent Developments in Printing Flexible and Wearable Sensing Electronics for Healthcare Applications. Sensors (Basel). 2019, 19 (5). (5) Hellhammer, D. H.; Wüst, S.; Kudielka, B. M. Salivary Cortisol as a Biomarker in Stress Research. Psychoneuroendocrinology 2009, 34 (2), 163–171. (6) Kimmel, D. W.; LeBlanc, G.; Meschievitz, M. E.; Cliffel, D. E. Electrochemical Sensors and Biosensors. Anal. Chem. 2012, 84, 685–707.

It is well known that the over-expression, increased activity and altered localization of many proteases are associated with tumor progression. Many clinical diagnoses target proteases as biomarkers. However, the quantitative analyses of the activity of tumor-related protease are challenging, because of the network interaction among the large set of proteases. Hence, there is a strong demand to develop a bioanalytical technique that can rapidly detect protease activities with high sensitivity and specificity. In this presentation, I will report an efficient electrochemical quantitative analyses method for detecting the cathepsin B activity by using a peptide-functionalized nanoelectrode array. The nanoelectrode array (NEA) was fabricated with vertically aligned carbon nanofibers (VACNFs), which serves as a unique electrochemical platform to enhance the protease detection. VACNFs of ~100-150 nm in diameter and ~5 mm in length are grown on chromium coated silicon wafer in uniform vertical alignment and are fully separated from each other to form a brush-like structure. With further processes to encapsulate the VACNFs in SiO2 by chemical vapor deposition (CVD) followed by mechanical polishing and reactive ion etching (RIE), ~100 nm long VACNF tips can be exposed above the SiO2 matrix, forming a stable NEA. By covalently attaching the exposed tip with proper peptide probes containing a ferrocene (Fc) redox tag at the distal, the VACNF NEA can be used to detect proteolysis with AC voltammetry. Such NEAs showed improved temporal resolution and reduced steric hindrance. As a result, reliable real-time proteolytic kinetics are recorded, from which the protease activity is quantitatively derived based on the heterogeneous Michalis-Menten model. In this work, we systematically investigated the cathepsin B activity with peptides of different length (including tetrapeptide, hexapeptide, and octapeptide) and at different temperatures (at 19.3, 29.5, 38.6, and 44.2 °C) to reveal their effects on the kinetic proteolysis rate by cathepsin B. The hexapeptide gave the highest proteolysis rate over tetrapeptide and octapeptide, as reflected by the smallest exponential decay time constant t. Meanwhile, 38.6 °C gave the highest proteolysis rate over the other 3 temperatures. At 38.6 °C, the optimized temperature, the limit of detection of cathepsin B activity and concentration has been determined to be 2.49 X 10-4 s-1 and 0.32 nM, respectively. Furthermore, the Fc-hexapeptide functionalized VACNF NEA shows very high selectivity, with essentially no measurable cross-reaction with 6.0 nM of other two cancer-related proteases, ADAM10 and ADAM17. This study demonstrates the potential to develop this method into a multiplex electronic chip for rapidly profiling the activity of up to 9 proteases simultaneously, which would facilitate accurate diagnoses of cancers and fast careening effective protease inhibitors as drug candidates. It would be a useful tool toward developing precision medicine.

The ability to rapidly detect neurotransmitter release has broad implications in the study of a variety of neurodegenerative diseases. Electrochemical detection methods using carbon nanofiber nanoelectrodes integrated into the Wireless Instantaneous Neurotransmitter Concentration Sensing System (WINCS) offer many important advantages including biocompatibility, selectivity, sensitivity, and rapid adsorption kinetics. Carbon nanofiber nanoelectrodes exhibit greater selectivity and sensitivity in the electrochemical detection of neurotransmitters compared to macroelectrodes and are able to resolve a ternary mixture of dopamine (DA), serotonin (5-HT), and ascorbic acid as well as to detect individual neurotransmitters in concentrations as low as 50 nM for DA and 100 nM for 5-HT using differential pulse voltammetry. Adsorption kinetics studies and isopropyl alcohol treatments modeled on previous studies on carbon fiber microelectrodes were conducted to investigate the analogous properties on carbon nanofiber electrodes using fast-scan cyclic voltammetry with WINCS and showed analogous results in carbon nanofiber electrodes compared with carbon fiber microelectrodes.

The brain operates through complex interactions in the flow of information and signal processing within neural networks. The 'wiring' of such networks, being neuronal or glial, can physically and/or functionally go rogue in various pathological states. Neuromodulation, as a multidisciplinary venture, attempts to correct such faulty nets. In this review, selected approaches and challenges in neuromodulation are discussed. The use of water-dispersible carbon nanotubes has been proven effective in the modulation of neurite outgrowth in culture and in aiding regeneration after spinal cord injury in vivo. Studying neural circuits using computational biology and analytical engineering approaches brings to light geometrical mapping of dynamics within neural networks, much needed information for stimulation interventions in medical practice. Indeed, sophisticated desynchronization approaches used for brain stimulation have been successful in coaxing 'misfiring' neuronal circuits to resume productive firing patterns in various human disorders. Devices have been developed for the real-time measurement of various neurotransmitters as well as electrical activity in the human brain during electrical deep brain stimulation. Such devices can establish the dynamics of electrochemical changes in the brain during stimulation. With increasing application of nanomaterials in devices for electrical and chemical recording and stimulating in the brain, the era of cellular, and even intracellular, precision neuromodulation will soon be upon us.

While the mechanism of Deep Brain Stimulation (DBS) remains poorly understood, previous studies have shown that it evokes release of neurochemicals and induces activation of functional magnetic resonance imaging (fMRI) blood oxygen level-dependent signal in distinct areas of the brain. Therefore, the main purpose of this paper is to demonstrate the capabilities of the Wireless Instantaneous Neurotransmitter Concentration Sensor system (WINCS) in conjunction with a carbon nanofiber (CNF) multiplexed array electrode as a powerful tool for elucidating the mechanism of DBS through the simultaneous detection of multiple bioactive-molecules.Patterned CNF nanoelectrode arrays were prepared on a 4-inch silicon wafer where each device consists of 3 × 3 electrode pads, 200 μm square, that contain CNFs spaced at 1μm intervals. The multiplexed carbon nanofiber CNF electrodes were integrated with WINCS to detect mixtures of dopamine (DA) and oxygen (OFirst, simultaneous detection of OMultiplexed CNF nanoelectrode arrays for electrochemical detection of neurotransmitters show promise for the detection of multiple analytes with the application of time independent decoupled waveforms. Electrochemistry on CNF electrodes may be helpful in elucidating the mechanism of DBS, and may also provide the precision and sensitivity required for future applications in feedback modulated DBS neural control systems.

Single wall carbon nanotubes due to their unique structural and electronic characteristics have revolutionized the field of nanotechnology and are widely used the field of transistors, drug delivery, and nanocomposities. For improved efficiency of these applications, the utilized tubes must of preeminent purity. Here, we report key parameters that are optimized to achieve their highest purity upto 98 wt%, and yield as high as 50 wt% by thermal and chemical oxidation. The as-produced SWCNT were heated in air at 470 °C, for 90 min, and later subjected to chemical oxidation. The chemical oxidation involved the treatment of thermally treated SWCNT with different concentrations of HCl (4N, 6N, 8N) and 30% H₂O₂, for different time periods (4 hr, 6 hr). This method does not cause damage to the walls of the tubes, observing no loss of nanotubes. The sheet resistance of as-produced and purified tubes was measured and the conductivity was calculated.

This study presents the morphological and chemical modification of the cell structure of aerosolized Escherichia coli treated with a dielectric barrier discharge (DBD). Exposure to DBD results in severe oxidation of the bacteria, leading to the formation of hydroxyl groups and carbonyl groups and a significant reduction in amine functionalities and phosphate groups. Near edge x-ray absorption fine structure (NEXAFS) measurements confirm the presence of additional oxide bonds upon DBD treatment, suggesting oxidation of the outer layer of the cell wall. Electron microscopy images show that the bacteria undergo physical distortion to varying degrees, resulting in deformation of the bacterial structure. The electromagnetic field around the DBD coil causes severe damage to the cell structure, possibly resulting in leakage of vital cellular materials. The oxidation and chemical modification of the bacterial components are evident from the Fourier transform infrared spectroscopy and NEXAFS results. The bacterial reculture experiments confirm inactivation of airborne E. coli upon treating with DBD.

We report ricin detection using antibody and aptamer probes immobilized on a nanoelectrode array (NEA) consisting of vertically aligned carbon nanofibers (VACNFs). These biosensor chips are fabricated on a wafer scale using steps common in integrated circuit manufacturing. Electrochemical impedance spectroscopy is used to characterize the detection event and the results indicate that the electron transfer resistance changes significantly after the ricin protein binds to the probe. Further confirmation is obtained from evaluation of the electrode surface by atomic force microscopy which clearly shows a change in height from the bare electrode to the surface bound by the probe-protein.

2018 marks the 10-year anniversary of the landing of the NASA Phoenix spacecraft on the ice-rich northern plains of Mars. The Phoenix Lander carried the Wet Chemistry Laboratory (WCL), a component instrument of the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) and was used to perform a comprehensive electrochemical characterization of martian soil in an aqueous solution. Designed to characterize the habitability of the martian surface, WCL contained an array of ion selective electrodes, a conductivity cell, a platinum electrode to measure redox potential, electrodes to perform perform cyclic voltammetry, chronopotentiometry and anodic stripping voltammetry, as well as a set of chemical reagents used to perform a sulfate titration and sample acidification. The measurements made with WCL resulted in a number of major discoveries, including the detection of percent levels of perchlorate on the martian surface, and represent the first, and to date, the only time electrochemical methods have been used for planetary exploration beyond Earth. NASA is now embarking on a new era of astrobiology exploration as plans are being formulated for missions to Ocean Worlds of the outer solar system, including Europa, an ice covered Jovian moon. Based on lessons learned during the development of WCL and its operation on the surface of Mars, we will discuss new design approaches and strategies that will enable the implementation of autonomous microfluidic electrochemical sensor arrays during upcoming missions to these yet to be explored solar system environments.