Amperometric Mode Research Articles

Prussian blue nanofilm-sensitized plasmonic electrochemical microscopy for spatially resolved detection of the localized delivery of hydrogen peroxide

Hydrogen peroxide (H2O2) sensing has been widely investigated using various electrochemical methods, yet the challenge of finding an imaging technique capable of real-time, spatially resolved detection remains. Addressing this, we introduce a Prussian blue (PB) nanofilm-sensitized plasmonic electrochemical microscopy (PEM) technique that successfully visualizes the localized delivery of H2O2. The PB nanofilm was carefully characterized, and its sensing capability towards H2O2 was demonstrated in amperometric mode. Employing a precise micromanipulator system, we controlled a micropipette to create a localized concentration gradient on the sensor surface and monitored the gradient through the PB nanofilm-sensitized PEM. The accuracy of the obtained concentration values was further validated by numerical simulations based on finite-element methods. Our technique ensures dependable localized detection, and we anticipate that advancements in film uniformity will further improve the resolution. The potential applications of this technique are broad and significant, including the opportunity to investigate single-cell exocytosis with neurotransmitters like dopamine, thus offering a promising avenue for future biomedical research.

Zinc stannate oxide perovskite nanomaterial based electrochemical detection of ammonia

Metal oxide perovskites are promising for sensing harmful chemicals at room temperature with high accuracy, sensitivity, selectivity, and ultra-low detection limit. There is a need for material that can have high sensitivity toward hazardous chemicals like ammonia. In this paper, a one-step hydrothermal process has been successfully used for the synthesis of ZnSnO3 nanopowder. With the presence of ample oxygen vacancies and a large surface area, ZnSnO3 nanopowder facilitates excellent electrochemical sensing properties. Here, the electrochemical ammonia sensing was investigated in potentiometric and amperometric modes. At room temperature, ammonia was detected within a linear concentration range from 10 nM to 60 nM, utilizing a low potential of 20 mV. The fabricated ammonia sensor based on ZnSnO3 nanopowder can detect at an ultra-low detection limit of 0.851 pM with a high sensitivity value of 4.548 mAcm−2nM−1. The reproducibility, repeatability, and stability of the ammonia sensor are also reported.

Electrochemical detection of herbicide atrazine using porous MnO2-NiO nanocatalyst

Herein, I report a simple and novel method to the synthesis of MnO2 nanotube decorated with NiO nanoparticles via a simple hydrothermal process, accompanied by a calcination step. The prepared MnO2-NiO nanocomposite was then studied as electrochemical sensing material for the detection of atrazine. I achieved a detection limit of 400 × 10−9 M; the linear range for atrazine was from 0.8 × 10−6 to 120 × 10−6 M in pulse amperometric mode. Moreover, MnO2-NiO modified electrode showed good anti-interference property. In the electrochemical impedance spectroscopic investigation, MnO2-NiO modified electrode exhibited a decrease in the electron transfer resistance in response to increase in the concentration of atrazine indicating improved electron-transfer kinetics for atrazine reduction. Zeta potential study and electrochemical studies further proved that atrazine molecule adsorb onto the MnO2-NiO. The applicability of MnO2-NiO modified electrode was also demonstrated in tap and waste water samples, showing the feasibility of its use for electrochemical sensing application.

Patch Amperometry and Intracellular Patch Electrochemistry.

Both patch amperometry (PA) and intracellular patch electrochemistry (IPE) take advantage of a recording configuration where an electrochemical detector-carbon fiber electrode (CFE)-is housed inside a patch pipette. PA, which is employed in cell-attached or excised inside-out patch clamp configuration, offers high-resolution patch capacitance measurements with simultaneous amperometric detection of catecholamines released during exocytosis. The method provides precise information on single-vesicle size and quantal content, fusion pore conductance, and permeability of the pore for catecholamines. IPE, on the other hand, measures cytosolic catecholamines that diffuse into the patch pipette following membrane rupture to achieve the whole-cell configuration. In amperometric mode, IPE detects total catechols, whereas in cyclic voltammetric mode, it provides more specific information on the nature of the detected molecules and may selectively quantify catecholamines, providing a direct approach to determine cytosolic concentrations of catecholaminergic transmitters and their metabolites. Here, we provide detailed instructions on setting up PA and IPE, performing experiments and analyzing the data.

A MWCNTs-COOH/PSS nanocomposite–modified screen-printed electrode for the determination of synthetic phenolic antioxidants by HPLC with amperometric detection

New sensing platforms based on screen-printed carbon electrodes modified with composites based on polystyrene sulfonate and oxidized multi-walled carbon nanotubes (PSS/MWCNTs-COOH/SPCE) have been used to develop a novel HPLC method with electrochemical detection (ECD) for the determination of the most used synthetic phenolic antioxidants in cosmetics: butylhydroxytoluene (BHT), butylhydroxyanisole (BHA), tert-butylhydroquinone (TBHQ) and propyl gallate (PG). Optimal separation conditions were achieved using methanol: 0.10 mol L−1 acetate solution at pH 6 as mobile phase with a gradient elution program from 60 to 90% of methanol percentage in 15 min. The electrochemical detection was carried out in amperometric mode using the PSS/MWCNTs-COOH/SPCE at + 0.80 V vs. Ag. Under these optimal separation and detection conditions, the limits of detection (LOD) were between 0.11 and 0.25 mg L−1. These LOD values were better, especially for BHT, than those previously published in other HPLC methods. Linear ranges from 0.37 mg L−1, 0.83 mg L−1, 0.69 mg L−1 and 0.56 mg L−1 to 10 mg L−1 were obtained for PG, TBHQ, BHA and BHT, respectively. RSD values equal or lower than 5% and 8% were achieved for repeatability and reproducibility, respectively. The HPLC-ECD method was successfully applied to analyze different cosmetic samples. Recovery values within 83–109% were obtained in the validation studies.Graphical

N-Methylfulleropyrrolidine-Based Multimode Sensor for Determination of Butoconazole Nitrate.

A multimode sensor (a sensor responding simultaneously to more than one mode, e.g., stochastic mode, amperometric mode, voltammetric mode) based on graphite paste modified with N-methylfulleropyrrolidine was proposed for the determination of butoconazole nitrate in its pharmaceutical formulation. The stochastic mode and square wave voltammetry mode were applied for the determinations. Both the stochastic mode and square wave voltammetry mode were applied for a qualitative and quantitative assay of butoconazole nitrate. The sensor can be used between 1.68 × 10-6 and 1.68 × 104 μmol L-1 when the stochastic mode is used and between 0.168 and 16.80 μmol L-1 when the square wave voltammetry mode is used. The multimode sensor was reliably used for the determination of butoconazole nitrate in its pharmaceutical formulation, Gynofort cream, the recorded recoveries being higher than 99.00%, with RSD (%) values of lower than 2.00%.

Hydrogen Sensor with 3D Printed BaCe0.6Zr0.3Y0.1O3-α electrolyte for High-Temperature Applications

Fusion energy is considered a promising source of energy for the near future. The most efficient reaction for that purpose is the fusion of deuterium and tritium, two hydrogen isotopes, to release helium, neutrons and energy. To assure the correct operation of this technology, new online devices able to monitor hydrogen isotopes will be required.Electrochemical sensors based on solid-state proton conductor ceramics can be used for that purpose. These materials have attracted significant interest because of their chemical and physical durability, especially at elevated temperatures. These electrolytes are perovskite-type materials with electrical carriers, positive holes, excess electrons and oxide ion vacancies. In previous work [1], amperometric hydrogen sensors based on BaCe0.6Zr0.3Y0.1O3-α (BCZY) electrolyte have been developed and tested in hydrogen atmospheres obtaining good results. These prototypes were constructed using 13 mm BCZY disks obtained by uniaxial pressure.In the present work, hydrogen sensors based on BCZY were constructed and evaluated in amperometric mode. The BCZY powder was disk-shaped using uniaxial pressure and 3D printing. Sensors were constructed as follows: first, sintered disks were platinized using platinum ink. Then, disks were sealed with a glass binder to alumina tubes. This way, the external face of the disk acted as a working electrode (WE) and the inner part of the sensor as a counter electrode (CE). 3D printed disks were fabricated using a Delta WASP 2040 ceramic 3D printer. For that, the ceramic powder was mixed with PEG400 and water until a viscous paste was obtained. Once green bodies were dried, they were heated for debinding and sintering using an optimized thermal program to reduce porosity. XRD (for crystallographic phases) and SEM (for microstructural defects and sintering) were used for the 3D printed and uniaxial pressed sintered disks characterization. The amperometric response of sensors constructed with both electrolytes (the uniaxially pressed and the 3D printed disks) was compared.[1] A. Hinojo, I. Soriano, J. Abellà, S. Colominas, Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications, Sensors. 20 (2020) 7258. https://doi.org/10.3390/s20247258.

A highly flexible, physically stable, and selective hydrogel-based hydrogen peroxide sensor

Sensitive, rapid, and continuous detection of hydrogen peroxide (H2O2) is of great importance in many systems for quality control, healthcare products, medical diagnostics, food safety, and environmental protection. Yet, the continuous monitoring of H2O2 remains challenging due to the cost, lack of specificity, and bulkiness of current H2O2 sensor technologies. These challenges are exacerbated for applications where the sensor must be fully submerged in a liquid media. In this work, a highly flexible hydrogel-based electrochemical sensor is constructed for reliable and ultrasensitive detection of H2O2 in liquid environments. The hydrogel-based H2O2 sensors are based on poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as the transducer, hydrophilic polyurethane (HPU) as the hydrogel matrix, and horseradish peroxide (HRP) as the H2O2 specific redox enzyme. The sensors have a dual-mode sensing mechanism, namely amperometric and chemiresistive sensing. Benefited from co-redoxing of PEDOT:PSS and HRP, the sensors exhibit high stability, fast response (<6 s), and high selectivity against common interferences, as well as a detection range from 100 µM to 101.6 mM in amperometric mode or 613 nM to 6.13 mM in chemiresistive mode. The hydrogel-based sensors are stable in liquid environments without leaching of PEDOT:PSS after a 2-month storage period in an aqueous media.

Resolution increase of ion-selective electrodes response by using a reversed amperometric setup

Typical ion-selective electrodes (ISEs) used in potentiometric mode suffer from low sensitivity, determined by Nernst (Nikolsky-Eisenman) equation. This limits resolution of potentiometric analysis, ultimately leading to significant problems in determination of relatively small changes of analyte ions concentration. A novel method was proposed using a ‘reversed’ amperometric setup with Ag|AgCl electrode as the working electrode and an ion-selective electrode as the reference one. Advantageously, the proposed approach does not require addition of other chemicals to the sample. A change of primary ions concentration results in change of the potential of the ISE used as the reference electrode and thus in the same change of Ag|AgCl electrode potential in amperometric (potentiostatic) mode. Due to high slope of the current vs. potential dependence for silver / silver chloride electrode small changes of ISE potential will result in significant changes of the recorded current, leading to high amplification of the analytical signal towards primary ions of the ISE. Additional unique advantage of herein proposed approach is a linear dependence of the current on analyte concentration, as tested on model examples of potassium- and calcium-selective ISEs.

Light-Addressable Electrochemical Sensors toward Spatially Resolved Biosensing and Imaging Applications

The light-addressable electrochemical sensor (LAES) is a recently emerged bioanalysis technique combining electrochemistry with the photoelectric effect in a semiconductor. In an LAES, a semiconductor substrate is illuminated locally to generate charge carriers in a well-defined area, thereby confining the electrochemical process to a target site. Benefiting from the unique light addressability, an LAES can not only detect multiple analytes in parallel within a single sensor plate but also act as a bio(chemical) imaging sensor to visualize the two-dimensional distribution of specific analytes. An LAES usually has three working modes: a potentiometric mode using light-addressable potentiometric sensors (LAPS) and an impedance mode using scanning photoinduced impedance microscopy (SPIM), while an amperometric mode refers to light-addressable electrochemistry (LAE) and photoelectrochemical (PEC) sensing. In this review, we describe the detection principles of each mode of LAESs and the concept of light addressability. In addition, we highlight the recent progress and advance of LAESs in spatial resolution, sensor system design, multiplexed detection, and bio(chemical) imaging applications. An outlook on current research challenges and future prospects is also presented.

Electrochemical synthesis of 2D copper coordination-polymers: Layer-stacking deviation induced by the solvent and its effect on the adsorptive properties

A 2D Cu-based Metal-Organic Framework (MOF), namely copper-terephthalate (Cu(1,4-BDC)), was successfully synthesized by electrochemical method for effective methylene blue (MB) sorption from aqueous solutions. The composition, morphology, and the presence of functional groups in the obtained material were verified by Fourier Transform Infrared spectroscopy (FTIR), Powder X-Ray Diffraction (PXRD), Thermal (TGA), and Elemental (EA) analysis, as well as Scanning Electron Microscopy (SEM). The effect of electrochemical parameters applied in the synthesis protocol (i.e., a potentiometric or amperometric mode) on the resulting product composition was evaluated. The electric current value was determined as a variable controlling the type of crystal structure present in the obtained MOF. A structure with open channels - CuBDC1 was favored under the current higher than 0.35 A conditions. In contrast, for the lower current values and upon the amperometric mode in the material, a CuBDC2 phase with DMF molecules occupying the grids of the layers was also present. The MB sorption studies were analyzed both with kinetic and equilibrium models. The obtained results showed the time evolution could be fitted with a pseudo-second-order model with the rate constant k2 equal to 0.047 g μmol−1 h−1. According to the Langmuir isotherm model, the maximum sorption capacity was determined as 76.63 μmol g−1. After MB sorption, the MOF material could be easily regenerated under mild conditions with good recyclability up to the four cycles (76.77%).

Microfluidic electrochemical magnetoimmunosensor for ultrasensitive detection of interleukin-6 based on hybrid of AuNPs and graphene.

Cytokines are important factors in the early diagnosis of autoimmune diseases and require high sensitivity, high selectivity and quantitative detection. We proposed a miniaturized electrochemical magneto-immunosensor (EC-MIS) on portable interleukin-6 (IL-6) detection based on this requirement. Firstly, a micro-fabricated working electrode is electrochemically modified with a hybrid of reduced graphene oxide (rGO) and gold nanoparticles (AuNPs). Increased surface area and enhanced charge transfer rate improve the performance of this immunosensor on sensitivity. Secondly, magnetic beads attached with the capture antibody (cAb) are employed in sandwich immunoassay. This kind of immunoassay is immobilized on the working electrode surface by an external magnet to enrich the analyte IL-6. Thirdly, the last two features are combined and integrated on a microfluidic device in order to restrict the sample at certain areas and ease the operation of detection. With our prototypic EC-MIS operated in amperometric mode, we have achieved the detection of IL-6 with a linear range from 0.97 to 250pg/mL and a limit of detection (LOD) of 0.42pg/mL. Real serum samples were demonstrated and compared with benchtop equipment's results.

Fabrication of Cu(II) oxide-hydroxide nanostructures onto graphene paper by laser and thermal processes for sensitive nano-electrochemical sensing of glucose

Glucose electrochemical sensors based on nanostructures of CuO/Cu(OH)2 onto graphene paper were prepared by thermal (solid) and nanosecond pulsed laser (molten phase) dewetting of a CuO layer 6 nm thin deposited by sputtering. Dewetted systems, obtained without the use of any binder, act as array of nanoelectrodes. Solid state and molten phase dewetting produce nanostructures of copper oxide-hydroxide with different average size, shape and surface composition. Molten phase dewetting originates particles with size below 100 nm, while solid state dewetting produces particles with average size of about 200 nm. Moreover, molten phase dewetting produce drop-shaped nanostructures, conversely nanostructures derived from solid state dewetting are multifaceted. X-ray photoelectron spectroscopy (XPS) characterization revealed that the surface of nanostructures is formed by a copper(II) species CuO and Cu(OH)2. Shape of anodic branch of the cyclic voltammograms of glucose in alkali solution evidenced a convergent diffusion mechanism. Analytical performances in amperometric mode are as good as or better than other sensors based on copper oxide. Amperometric detection of glucose was done at potential as low as 0.4 V versus saturated calomel electrode by both types of electrodes. Linear range from 50 μM to 10 mM, sensitivity ranging from 7 to 43 μA cm−2 mM−1 and detection limit of 7 μM was obtained. Good analytical performances were obtained by laser dewetted electrodes with a low copper content up to 1.2 by atoms percentage of the surface. Analytical performance of the proposed electrodes is compliant for the determination of glucose both in blood serum, saliva or tear.

Flow-Through Electrochemical Biosensor with a Replaceable Enzyme Reactor and Screen-Printed Electrode for the Determination of Uric Acid and Tyrosine

A flow-through biosensor has been developed and manufactured by 3D printing from poly(lactic acid). Uricase or tyrosinase were immobilized on the inner walls of the reactor cell and the concentrations of the reaction products, i.e., hydrogen peroxide in the case of uricase and quinone product of the tyrosine oxidation in the case of tyrosinase, were monitored in the amperometric mode. The screen-printed electrode modified with carbon black, pillar[5]arene and electropolymerized thionine and methylene blue was separated from the enzyme layer by 0.1 mm gap and used as a biosensor transducer. The components of the modifier layer exerted a synergetic effect and increased the cathodic current up to seven times compared to electrodes modified with individual components, increasing the sensitivity of the analysis. In the optimal conditions, biosensor allowed the determination of 1 × 10−7 to 1 × 10−5 M uric acid and 2 × 10−7 to 1 × 10−5 M tyrosine. The biosensors analyzed spiked samples of blood serum and urine and provided recoveries from 95 to 110%. Easy mounting of the flow-through cell and low cost of the replaceable parts make promising future application of the biosensor for routine clinical assays.

Solid‐State Fabrication of Cu2O/CuO Hydroxide Nanoelectrode Array onto Graphene Paper by Thermal Dewetting for High‐Sensitive Detection of Glucose

Nanostructures of Cu2O/CuO hydroxide suitable for the electrochemical determination of glucose are obtained by solid‐state dewetting of CuO layers 6, 8, and 31 nm thin deposited by sputtering onto 240 μm‐thick graphene paper. Solid‐state dewetting in nitrogen produces a partial decomposition of CuO into Cu2O and Cu. X‐ray diffraction patterns reveal the presence of high‐index crystallographic facets, which are reactive and useful toward glucose oxidation to gluconolactone. Typically, morphology studied by scanning electron microscopy reveals faceted nanoparticles with an average size below 200 nm. X‐ray photoelectron spectroscopy shows that the nanostructure surfaces of Cu2O and metallic copper exposed to natural ambient are promptly reoxidized and hydroxidized to a mixture of CuO and Cu(OH)2. Electrochemical characterization in amperometric mode reveals linear response to glucose concentration in the range from 50 to 10 × 10−3 m, sensitivity up to 83 μA cm−2 mm −1, and limit of detection up to 3.6 × 10−6 m. Good combination of low cost and simplicity of preparation with low limit of detection, high sensitivity, and wide linear range makes the proposed electrodes suitable for a variety of applications ranging from health to food and beverage industries.

Simultaneous separation and electroanalysis in a single polydimethylsiloxane-based platform

Channel-based microfluidic devices integrating the separation step and detection system are key factors to expand microanalysis application. However, these devices still depend on macroscale external equipment for pre-treatment of the sample, separation, or detection. The integration of all steps in only one stage is critical to improving feasibility. Herein, we use a low-cost protocol to solve part of the challenge by designing a dual-mode system onto single polydimethylsiloxane (PDMS)-based platform — overall dimensions of 65 mm length × 20 mm width × 14 mm height and the inner diameter of 297±10 μm height × 605±19 μm width — for column-free separation and simultaneous detection. As a proof-of-concept, we used this all-in-one PDMS platform to separate — without the packet-based phase — and determine salicylic acid (SA) and caffeine (CAF) with a detection limit of 0.20 and 0.18 μmol L−1 and quantification limit of 0.70 and 0.60 μmol L−1 for SA and CAF, respectively. We separated the mixture using forced convection into a chemically treated microchannel while detecting the analytes in amperometric mode. Here, we report new insights into how integrating analytes separation and further electroanalysis into a single miniaturized device.

Flow injection amperometry as an alternative to potentiometry for solid contact ion-selective membrane-based electrodes.

In this work we propose a flow injection amperometry at constant potential as a perspective alternative to classical potentiometry for solid contact ion-selective electrodes (SC-ISEs). The amperometric readout mode eliminates the problem of background drift and potential instability – common limitations of potentiometry for SC-ISEs. The selectivity in flowinjection and constant flow amperometric modes is similar to the potentiometric one. Moreover, flow injection amperometry in comparison to potentiometry for ion-selective electrodes provides a shorter response time, within 15–30 s, by two orders of magnitude decreased detection limit and 5-6 fold increased signal-to-noise ratio. The proposed approach is an attractive readout mode that opens new horizons for the improvement of performance characteristics of solid contact ISEs.

Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications

In many industrial fields, there is a need to design and characterize on-line and on-board hydrogen monitoring tools able to operate under extreme conditions. One of these applications is in future nuclear fusion reactors, which will use hydrogen isotopes as a plasma fuel. In this context, the measurement of the concentration of these hydrogen isotopes will be of interest to ensure the correct operating conditions for such reactors. Hydrogen sensors based on solid-state electrolytes will be the first step in the development of new analytical tools able to quantify deuterium and tritium in aggressive environments. In the present work, amperometric hydrogen sensors were constructed and evaluated using two solid-state electrolytes, BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α. Prototype sensors were built in order to study their sensitivity in on-line measurements. The experiments were performed in a reactor with a hydrogen-controlled environment. The sensors were evaluated at 500 and 600 °C in amperometric mode by applying 2 and 4 V voltages between electrodes. Both sensors showed increases in sensitivity when the temperature or voltage were increased.

Potentiometric Vs. Amperometric Modes for High Temperature Hydrogen BaCe0.6Zr0.3Y0.1O3-Α Sensor

Fusion energy is considered a source of energy for the near future, due to its no contribution to the greenhouse effect. In a fusion reactor, deuterium and tritium collide and fuse, releasing helium, neutrons and energy. Deuterium can be obtained from water, however tritium must be in situ generated [1]. ITER (International Thermonuclear Experimental Reactor) is being constructed for testing the technology, materials and R&D concepts in order to evaluate its energy gain. One of its goals is to verify the tritium self-sufficiency by breeding systems [2], including the molten Pb-15.7Li eutectic alloy.In this frame, the chemically aggressive and reducing environment creates the necessity to design new devices for tritium concentration monitoring in the lithium-lead eutectic [3]. For this purpose, electrochemical sensors based on proton-conducting solid-state electrolytes have been proved to be able to operate at high temperatures, with high physical and chemical stabilities. These electrolytes are perovskite phase materials, in which the electrical carriers are positive holes, excess electrons, oxide ion vacancies and interstitial protons, which interact with oxide ions.Different proton-conducting solid-state electrolytes have been studied previously in the Electrochemical Methods Laboratory at Institut Quimic de Sarria (IQS). These solid electrolytes have been employed in the construction of electrochemical probes that can work on potentiometric and amperometric modes [4]. In the present work, the response of potentiometric and amperometric hydrogen sensors, constructed with BaCe0.6Zr0.3Y0.1O3-α ceramic electrolyte, was compared. The sensors consisted on an open alumina tube with a sealed proton conducting ceramic pellet in one side. Both sides of the pellet were platinized and connected to platinum wires. The wires ends were the positive and the negative poles of the sensor.Both operating modes were tested at different hydrogen and argon mixtures at the working compartment. In the potentiometric mode, the potential difference between both electrodes was measured and it was compared with the theoretical value calculated from the Nernst equation. In the reference electrode, the hydrogen partial pressure was kept constant during all the experiments. Moreover, the amperometric sensor measured the current through both electrodes when a voltage was applied, obtaining a calibration curve.

Electrochemical Sensing Platforms for Tuberculosis-Associated VOCs from Patient Breath

In this presentation two point-of-care electrochemical sensing platforms (gas and liquid phase) to detect volatile organic compounds (VOCs) present in the breath of tuberculosis (TB) patients will be discussed. Rapid screening using patient breath is significantly faster, less expensive and more convenient than traditional sputum-based tests, and up to one third of adults and the majority of young children with TB are unable to produce sufficient sputum for traditional culture testing, making the development of non-sputum-based tests a priority in TB screening and diagnostics. Methyl nicotinate (MN) and methyl p-anisate (MPA) have been identified as specific biomarkers for TB in patient breath and culture by GC-MS [1], and are not found in readily in ambient air or the breath of healthy patients, making them good candidates for TB screening. Previous modelling studies [2] suggest that these biomarkers complex with certain transition metals (such as cobalt and copper) given a particular bias voltage and oxidation state of the metal. This known interaction was used as the basis for the sensing platforms described.A solid-state titanium dioxide nanotube array-based sensor is used to directly detect TB biomarkers in the gas phase, utilizing a divalent cobalt-functionalized surface (Co-TNA) to specifically bind MN and MPA [3]. The original sensor design consisted of a simple two-electrode setup and chronoamperometry at binding voltages specific to the VOCs of interest was used to selectively sense these biomarkers. However, the lack of a separate reference electrode in this system can cause a high level of variability in the sensors, limiting sensitivity and specificity. In order to improve reproducibility and specificity, a solid-state, electron-conductive polymer “electrolyte” of known resistance is used to create a gas-phase three-electrode system, utilizing silver screen-printed references and counter electrodes. This new configuration ensures more consistent interactions with the analyte of interest between sensors in the amperometric mode, and allows the sensor to be operated using more complex scanning techniques traditionally used in liquid systems. Scanning potential methods such as cyclic voltammetry (CV) have shown promise in detecting these VOCs more specifically than chronoamperometry alone. For example, the CV of a Co-TNA sensor shows a reduction peak at about -0.5 V vs the silver quasi-reference electrode when exposed to methyl nicotinate vapor which is not present when exposed to simple humid air (figure 1). In preliminary field studies, CVs of the Co-TNA sensor in response to the breath of sick patients show artifacts not present in healthy controls. Results comparing suspected TB patients (Xpert positive and negative) as well as healthy controls will be presented.Because the VOCs associated with Tuberculosis are only semi-volatile and readily dissolve in water at significantly high concentrations (mM range), collection of these compounds from breath and condensate into an aqueous solution can provide a simple concentration method when very low levels of VOC are present. In addition, breath condensate can be frozen and saved for later analysis when immediate testing is not available. Therefore, we have developed a liquid-phase sensing platform utilizing engineered electroactive solutions (EASs) containing a functional metal ion which can be customized to the analyte of interest without the need for a more expensive, highly specific working electrode as used in the gas-phase platform. Rather than observing interactions of the biomarker at the specific electrode surface, a functional metal solution of known electrochemical activity is used to detect the VOC of interest by observing the change electrochemically when it is added to the EAS. In this application, copper is preferred over cobalt because of its highly reversible redox reactions and the ability to observe multiple redox peaks within a relatively small potential window. Testing of this platform with a divalent copper EAS has shown that the cyclic voltammogram of a copper redox pair changes significantly when as little as 1 mM methyl nicotinate (MN) is added to the solution. The variation of peak oxidation voltage with MN concentration can be seen in figure 2. In order to further understand the reactions taking place and specifically identify the biomarkers, square wave voltammetry (SWV) is employed to show which oxidation states of the functionalized metal are complexing with the biomarker of interest. The SWV for the copper EAS alone shows three distinct peaks for each of the redox reaction couples present in the voltage window (less than ±1 V). When a small amount of MN is added, the size, shape and in some cases peak-voltage of each distinct peak is affected differently, implying a difference in reaction to specific valence states of copper (figure 3). When methyl p-anisate (MPA) was added at the same concentration, different interactions were observed. In this way, a “fingerprint” method can be used to identify biomarkers once their known interaction is established.