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We report a chemiresistive cyclohexanone sensor on a flexible substrate based on single-walled carbon nanotubes (SWCNTs) functionalized with thiourea (TU) derivatives. A wrapper polymer containing both 4-vinylpyridine (4VP) groups and azide groups (P(4VP-VBAz)) was employed to obtain a homogeneous SWCNT dispersion via noncovalent functionalization of SWCNTs. The P(4VP-VBAz)-SWCNT composite dispersion was then spray-coated onto an organosilanized flexible poly(ethylene terephthalate) (PET) film to achieve immobilizing quaternization between the pyridyl groups from the polymer and the functional PET substrate, thereby surface anchoring SWCNTs. Subsequent surface functionalization was performed to incorporate a TU selector into the composites, resulting in P(Q4VP-VBTU)-SWCNT, for the detection of cyclohexanone via hydrogen bonding interactions. An increase in conductance was observed as a result of the hydrogen-bonded complex with cyclohexanone resulting in a higher hole density and/or mobility in SWCNTs. As a result, a sensor device fabricated with P(Q4VP-VBTU)-SWCNT composites exhibited chemiresistive responses (ΔG/G0) of 7.9 ± 0.6% in N2 (RH 0.1%) and 4.7 ± 0.4% in air (RH 5%), respectively, upon exposure to 200 ppm cyclohexanone. Selective cyclohexanone detection was achieved with minor responses (ΔG/G0 < 1.4% at 500 ppm) toward interfering volatile organic compounds (VOC). analytes. We demonstrate a robust sensing platform using the polymer-SWCNT composites on a flexible PET substrate for potential application in wearable sensors.

Multivariate analysis is carried out for single-walled carbon nanotubes (SWNTs) functionalized with a cobalt octaethyl porphyrin (CoOEP) chemiresistive sensor device for selective and simultaneous detection of multiple analytes. The chemiresistor was prepared on Si/SiO2 substrate with photolithographically patterned gold microelectrodes having a 3-µm gap. SWNTs were aligned dielectrophoretically and functionalized with CoOEP by drop-casting. The aligned and CoOEP-functionalized SWNTs were characterized with electrical (I–V method), structural, spectroscopic, and morphological techniques, and sensor performance was investigated in a chemiresistive sensing modality. The fabricated sensor shows response towards acetone, dichloromethane, methyl ethyl ketone, ethanol, and methanol, with a lower detection limit of 5 ppm, which is far below the OSHA permissible exposure limit for each analyte, and demonstrates fast response and recovery. The multivariate analysis viz. principal component analysis and linear discrimination analysis reveals high discriminating capability of SWNTs functionalized with the CoOEP chemiresistive sensor towards these analytes, which could be used as an intelligent electronic nose (E-nose). This type of intelligent E-nose can address the crucial need for monitoring environmental pollution in industries, homes, buildings, etc.

Single-walled carbon nanotubes (SWNTs) are incorporated in different device configurations such as chemiresistors and field-effect transistors (FETs) as a sensing element for the fabrication of highly sensitive and specific biochemical sensors. For this purpose, sorting and aligning of semiconducting SWNTs between the electrodes is advantageous. In this work, a silicon shadow mask fabricated using conventional semiconductor processes and silicon bulk micromachining was used to make metal contacts over SWNTs with a minimum feature of 1 μm gap between the electrodes. The developed silicon shadow mask-based metal contact patterning process is cost-effective and free from photoresist (PR) chemical coatings and thermal processing. After a detailed investigation, sodium dodecyl sulfate (SDS), an anionic surfactant, along with ultrasonication process, was found to be effective for the removal of unclamped and metallic SWNTs, resulting in aligned and clamped semiconducting SWNTs between the electrodes. The presence of aligned semiconducting SWNTs was confirmed using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and Raman spectroscopy techniques. The fabricated devices were tested for nitrogen dioxide (NO2) gas sensing as a test case. The sensitivity enhancement of ∼21 to 76% in the 20-80 ppm NO2 concentration range has been observed in the case of aligned semiconducting SWNT devices compared to the random network SWNT-based sensors.

In this paper, an impedance-transduced sensor is developed based on a nanostructured graphene (GN) and poly (methyl methacrylate) (PMMA) sensing film for the detection of individual volatile organic compounds (VOCs) in aqueous media. Benefiting from a porous and high surface area, the nanostructured nanofiber is characterized by scanning electron microscopy (SEM) and optimized by the electrochemical impedance spectroscopy (EIS) technique. The recorded EIS data indicate the selective recognition of four VOCs of interest at a constant pH while there is no redox probe. The non-faradaic responses to each analyte at different concentrations are correlated with a three-element equivalent circuit (resistances of the solution and the film, and a pseudo-capacitance). To analyze the ability of the sensing film in distinguishing between VOCs with similar average boiling points, the values of the individual equivalent circuit elements are used as features and clustered in three-dimensional (3D) plots. Among the features, the two representing the maximum differences between the VOCs are represented in a two-dimensional (2D) plot to show the selectivity of the sensor. The feature extraction analysis demonstrates that the constant phase element (CPE) of the equivalent circuit is a more accurate predictor of VOCs than the interfacial capacitance. These results show high selectivity of the sensorial platform due to the synergistic pairing of nanostructured GN and PMMA.

Ethylene is a dynamic plant hormone, and its temporal monitoring can be used to glean insight into plant health and status. However, the real-time distributed detection of ethylene at trace levels under ambient conditions remains a challenge. We report a single-walled carbon nanotube-based chemiresistor catalyst combination that can detect ppb levels of ethylene in air. Cycling between Pd(II) and Pd(0) via Wacker oxidation with a nitrite cocatalyst imparts response discrimination driven by the chemoselectivity of the chemical transformation. Sensitivity is controlled by a combination of the chemical reaction efficiency and the n-doping strength of the Pd(0) species generated in situ. The covalent functionalization of the carbon nanotube sidewall with pyridyl ligands drastically improves the device sensitivity via enhanced n-doping. The utility of this ethylene sensor is demonstrated in the monitoring of senescence in red carnations and purple lisianthus flowers., Okay, bloomer: Wacker oxidation is used as a signal transduction mechanism for the selective and sensitive detection of ethylene in air via chemiresistive sensing. Using this system, the senescence of lisianthus flowers and carnations is monitored.

Toxic and nontoxic volatile organic compound (VOC) gases are emitted into the atmosphere from certain solids and liquids as a consequence of wastage and some common daily activities. Inhalation of toxic VOCs has an adverse effect on human health, so it is necessary to monitor their concentration in the atmosphere. In this work, we report on the fabrication of inorganic nanotube (INT)-tungsten disulfide, paper-based graphene–PEDOT:PSS sheet and WS2 nanotube-modified conductive paper-based chemiresistors for VOC gas sensing. The WS2 nanotubes were fabricated by a two-step reaction, that is oxide reduction and sulfurization, carried out at 900 °C. The synthesized nanotubes were characterized by FE-SEM, EDS, XRD, Raman spectroscopy, and TEM. The synthesized nanotubes were 206–267 nm in diameter. The FE-SEM results show the length of the nanotubes to be 4.5–8 µm. The graphene–PEDOT:PSS hybrid conductive paper sheet was fabricated by a continuous coating process. Then, WS2 nanotubes were drop-cast onto conductive paper for fabrication of the chemiresistors. The feasibility and sensitivity of the WS2 nanotube-modified paper-based chemiresistor were tested in four VOC gases at different concentrations at room temperature (RT). Experimental results show the proposed sensor to be more sensitive to butanol gas when the concentration ranges from 50 to 1000 ppm. The limit of detection (LOD) of this chemiresistor for butanol gas was 44.92 ppm. The WS2 nanotube-modified paper-based chemiresistor exhibits good potential as a VOC sensor with the advantages of flexibility, easy fabrication, and low fabrication cost.

This work describes the design and fabrication of free-standing carbon nanotube-palladium (CNT-Pd) composite sheets for hydrogen gas sensing. The CNT-Pd composites were made by electroplating palladium onto a solvent-densified and oxygen plasma-treated CNT sheet. The latter was prepared using high purity CNTs drawn from a dense, vertically aligned array grown by chemical vapor deposition on silicon substrates. The CNT-Pd sheets were characterized by energy-dispersive spectroscopy, scanning electron microscopy, and X-ray diffraction. The amount of palladium in the composite was 16.5 wt % as measured via thermogravimetric analysis. Thin strips of the CNT-Pd sheets were assembled as chemiresistor sensors and tested for hydrogen gas detection. The sensors demonstrated a limit of detection of 0.1 mol % and displayed signal reversibility without the need for oxygen removal or heat treatment. A decrease in signal reversibility was observed after multiple exposure cycles; however, redensification with ethanol significantly restored the original reversibility. The sensor showed the Freundlich adsorption isotherm behavior when exposed to hydrogen. The material’s potential application toward a wearable, flexible sensor was demonstrated by integrating the chemiresistor onto a fabric material using hot-press processing and testing the composite for hydrogen sensitivity.

Two configurations of single-walled carbon nanotube-based chemi-capacitive gas sensors were fabricated, i.e., horizontal and vertical. Further, their sensing properties for hexane and ammonia (NH3) vapor were characterized and compared with chemi-resistive-type sensing properties. Upon exposure to hexane and NH3 vapor, both capacitance and resistance varied as the analyte concentration increased. The sensing sensitivity measured along the horizontal direction increased with the device resistance. However, the capacitive sensing response along the vertical direction was independent of the number and fraction of semi-conductive single-walled carbon nanotubes. Furthermore, the vertical chemi-capacitive sensing response was dependent on the dipole moment of analytes.

Semiconductor-enriched single-walled carbon nanotubes (s-SWCNTs) have potential for application as a chemiresistor for the detection of breath compounds, including tetrahydrocannabinol (THC), the main psychoactive compound found in the marijuana plant. Herein we show that chemiresistor devices fabricated from s-SWCNT ink using dielectrophoresis can be incorporated into a hand-held breathalyzer with sensitivity toward THC generated from a bubbler containing analytical standard in ethanol and a heated sample evaporator that releases compounds from steel wool. The steel wool was used to capture THC from exhaled marijuana smoke. The generation of the THC from the bubbler and heated breath sample chamber was confirmed using ultraviolet-visible absorption spectroscopy and mass spectrometry, respectively. Enhanced selectivity toward THC over more volatile breath components such as CO2, water, ethanol, methanol, and acetone was achieved by delaying the sensor reading to allow for the desorption of these compounds from the chemiresistor surface. Additionally, machine learning algorithms were utilized to improve the selective detection of THC with better accuracy at increasing quantities of THC delivered to the chemiresistor.

All-carbon fiber-based chemiresistor is fabricated by assembling reduced graphene oxide (RGO) fiber and carbon nanotube (CNT) fiber as reversible NO2 sensing layer and flexible heater, respectively. Both graphene oxide (GO) and CNT fibers were synthesized by wet-spinning technique facilitating lyotropic nematic liquid crystal (LC) property. Randomly entangled CNT fiber-based heater, which is embedded in one surface of colorless polyimide (cPI) film with thickness of ˜200 μm, exhibits high bending stability and heating property up to 100 °C. Single reduced graphene oxide (RGO) fiber obtained after heat treatment at 900 °C in H2/N2 ambient was integrated on the CNT fiber-embedded cPI heater, thereby establishing a new type of all-carbon fiber sensing platform. As a result, accelerated NO2 adsorption and desorption kinetics were achieved with RGO fiber at an elevated temperature. In particular, a 9.22-fold enhancement in desorption kinetic (kdes = 8.85 × 10–3 s–1) was observed at 100 °C compared with the desorption kinetic (kdes = 0.96 × 10–3 s–1) at 50 °C, which was attributed to the effective heating by CNT fiber networks. This work pioneered a research on the use of emerging carbonaceous fibers for potential application in wearable chemical detectors.

The high-performance p-type metal-oxide-semiconductor (MOS)-based gas sensor is an important subject of research in the field of gas-sensing technology. In this work, we demonstrated a p-type MOS-based thin-film transistor (TFT) nitrogen dioxide (NO2) gas sensor that used tin oxide (SnOX) for both the channel and sensing layers. The crystalline status, surface morphology, and atomic-bonding configuration of the thin-film were examined using X-ray diffraction, field emission-scanning electron microscopy, and X-ray photoelectron spectroscopy. The results indicated that the deposited thin-film was mainly composed of polycrystalline SnO with a tetragonal structure. The fabricated p-type SnOX TFT showed a maximum response value of 19.4-10 ppm NO2 at room temperature (RT, 25 °C) when operated in the subthreshold region, which was significantly higher than that of 2.8–10 ppm NO2 obtained from a p-type SnOX thin-film chemiresistor at RT. In addition, the SnOX TFT gas sensor showed significantly higher sensitivity to NO2 gas than to other target gases such as NH3, H2S, CO2, and CO at RT. To the best of our knowledge, this is the first study to a p-type MOS-based field-effect transistor-type gas sensor. Our experimental results demonstrate that the p-type SnOX TFT is a promising gas sensor that can operate at RT with high sensitivity and selectivity to NO2 gas.

The development of freestanding fiber-type chemiresistors, having high integration ability with various portable electronics including smart clothing systems, is highly demanding for the next-generation wearable sensing platforms. However, critical challenges stemming from the irreversible chemical sensing kinetics and weak reliability of the freestanding fiber-type chemiresistor hinder their practical use. In this work, for the first time, we report on the potential suitability of the freestanding and ultraporous reduced graphene oxide fiber functionalized with WO3 nanorods (porous WO3 NRs-RGO composite fiber) as a sensitive nitrogen dioxide (NO2) detector. By employing a tunicate cellulose nanofiber (TCNF), which is a unique animal-type cellulose, the numerous mesopores are formed on a wet-spun TCNF-GO composite fiber, unlike a bare GO fiber with dense surface structure. More interestingly, due to the superior wettability of TCNF, the aqueous tungsten precursor is uniformly adsorbed on an ultraporous TCNF-GO fiber, and subsequent heat treatment results in the thermal reduction of a TCNF-GO fiber and hierarchical growth of WO3 NRs perpendicular to the porous RGO fiber (porous WO3 NRs-RGO fiber). The freestanding porous WO3 NRs-RGO fiber shows a notable response to 1 ppm NO2. Furthermore, we successfully demonstrate reversible NO2 sensing characteristics of the porous WO3 NRs-RGO fiber, which is integrated on a wrist-type wearable sensing device.

Made available in DSpace on 2022-04-28T19:41:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-06-25 Quality control in the production and processing of raw meat is currently one of the biggest concerns for food industry and would benefit from portable and wireless sensors capable of detecting the onset of spoilage. Raw meat is a natural source of biogenic and volatile amines as byproducts of decarboxylation reactions, and the levels of these compounds can be utilized as quality control parameters. We report herein a hybrid chemiresistor sensor based on inorganic nanofibers of SiO2:ZnO (an n-type material) and single-walled carbon nanotubes functionalized with 3,5-dinitrophenyls (a p-type material) with dosimetric sensitivity ∼40 times higher for amines than for other volatile organic compounds, which also provides excellent selectivity. The hybrid nanomaterial-based chemiresistor sensory material was used to convert radio-frequency identification tags into chemically actuated resonant devices, which constitute wireless sensors that can be potentially employed in packaging to report on the quality of meat. Specifically, the as-developed wireless tags report on cumulative amine exposure inside the meat package, showing a decrease in radio-frequency signals to the point wherein the sensor ceased to be smartphone-readable. These hybrid material-modified wireless tags offer a path to scalable, affordable, portable, and wireless chemical sensor technology for food quality monitoring without the need to open the packaging. Department of Chemistry Institute for Soldier Nanotechnologies Massachusetts Institute of Technology Cambridge, 77 Massachusetts Avenue Department of Materials Science and Engineering Massachusetts Institute of Technology Cambridge, 77 Massachusetts Avenue Nanotechnology National Laboratory for Agriculture (LNNA) Embrapa Instrumentação, São Paulo Institute of Geosciences and Exact Sciences São Paulo State University (UNESP), São Paulo Institute of Geosciences and Exact Sciences São Paulo State University (UNESP), São Paulo

A high-performance chemiresistive gas sensor is described for the detection of hydrogen sulfide (H2S), an acutely toxic and corrosive gas. The chemiresistor operates at room temperature with low power requirements potentially suitable for wearable sensors or for rapid in-field detection of H2S in settings such as pipelines and wastewater treatment plants. Specifically, we report chemiresistors based on single-walled carbon nanotubes (SWCNTs) containing highly oxidizing platinum-polyoxometalate (Pt-POM) selectors. We show that by tuning the vanadium content and thereby the oxidation reactivity of the constituent POMs, an efficient chemiresistive sensor is obtained that is proposed to operate by modulating CNT doping during aerobic H2S oxidation. The sensor shows exceptional sensitivity to trace H2S in air with a ppb-level detection limit, multimonth stability under ambient conditions, and high selectivity for H2S over a wide range of interferants, including thiols, thioethers, and thiophene. Finally, we demonstrate that the robust sensing material can be used to fabricate flexible devices by covalently immobilizing the SWCNT-P4VP network onto a polyimide substrate, further extending the potentially broad utility of the chemiresistors. The strategy presented herein highlights the applicability of concepts in molecular aerobic oxidation catalysis to the development of low-cost analyte detection technologies., ACS Central Science, 7 (9), ISSN:2374-7951

In this work, a TiO2-coated GaN nanowire-based back-gate field-effect transistor (FET) device was designed and implemented to address the well-known cross-sensitive nature of metal oxides. Even though a two-terminal TiO2/GaN chemiresistor is highly sensitive to NO2, it suffers from lack of selectivity toward NO2 and SO2. Here, a Si back gate with C-AlGaN as the gate dielectric was demonstrated as a tunable parameter, which enhances discrimination of these cross-sensitive gases at room temperature (20 °C). Compared to no bias, a back-gate bias resulted in a significant 60% increase in NO2 response, whereas the increase was an insignificant 10% in SO2 response. The differential change in gas response was explained with the help of a band diagram, derived from the energetics of molecular models based on density functional theory (DFT). The device geometries in this work are not optimized and are intended only for proving the concept.

Sensors, capable of detecting trace amounts of gas molecules or volatile organic compounds (VOCs), are in great demand for environmental monitoring, food safety, health diagnostics, and national defense. In the era of the Internet of Things (IoT) and big data, the requirements on gas sensors, in addition to sensitivity and selectivity, have been increasingly placed on sensor simplicity, room temperature operation, ease for integration, and flexibility. The key to meet these requirements is the development of high-performance gas sensing materials. Two-dimensional (2D) atomic crystals, emerged after graphene, have demonstrated a number of attractive properties that are beneficial to gas sensing, such as the versatile and tunable electronic/optoelectronic properties of metal chalcogenides (MCs), the rich surface chemistry and good conductivity of MXenes, and the anisotropic structural and electronic properties of black phosphorus (BP). While most gas sensors based on 2D atomic crystals have been incorporated in the setup of a chemiresistor, field-effect transistor (FET), quartz crystal microbalance (QCM), or optical fiber, their working principles that involve gas adsorption, charge transfer, surface reaction, mass loading, and/or change of the refractive index vary from material to material. Understanding the gas-solid interaction and the subsequent signal transduction pathways is essential not only for improving the performance of existing sensing materials but also for searching new and advanced ones. In this review, we aim to provide an overview of the recent development of gas sensors based on various 2D atomic crystals from both the experimental and theoretical investigations. We will particularly focus on the sensing mechanisms and working principles of the related sensors, as well as approaches to enhance their sensing performances. Finally, we summarize the whole article and provide future perspectives for the development of gas sensors with 2D materials.

The present work shows the synthesis of a graphene-based nanocomposite with titania nanoparticles through a simple one-step, microwave assisted method. The GR/TiO2 nanocomposite was used for the fabrication of a chemiresistor device and characterized towards oxidizing and reducing gases under controlled environment. The results show how the addiction of titania nanoparticles to graphene nanosheets enables the sensing of ethanol at room temperature. A sensitivity curve to ethanol was recorded in the range 15–50 ppm. The interaction with water, the main interferent in ethanol sensing, was also investigated and the findings disclose a weaker interaction respect to ethanol, thus suggesting that steric factors can play a role in the sensing mechanism.

A chemiresistive sensor is described for the detection of methane (CH(4)), a potent greenhouse gas that also poses an explosion hazard in air. The chemiresistor allows for the low-power, low-cost, and distributed sensing of CH(4) at room temperature in air with environmental implications for gas leak detection in homes, production facilities, and pipelines. Specifically, the chemiresistors are based on single-walled carbon nanotubes (SWCNTs) noncovalently functionalized with poly(4-vinylpyridine) (P4VP) that enables the incorporation of a platinum-polyoxometalate (Pt-POM) CH(4) oxidation precatalyst into the sensor by P4VP coordination. The resulting SWCNT-P4VP-Pt-POM composite showed ppm-level sensitivity to CH(4) and good stability to air as well as time, wherein the generation of a high-valent platinum intermediate during CH(4) oxidation is proposed as the origin of the observed chemiresistive response. The chemiresistor was found to exhibit selectivity for CH(4) over heavier hydrocarbons such as n-hexane, benzene, toluene, and o-xylene, as well as gases, including carbon dioxide and hydrogen. The utility of the sensor in detecting CH(4) using a simple handheld multimeter was also demonstrated.

We demonstrated a p-type MOS-based thin-film transistor (TFT) nitrogen dioxide (NO 2 ) gas sensor that uses tin monoxide (SnO) for both the channel and sensing layers. The fabricated SnO TFT showed a maximum response value of 19.4-10 ppm NO 2 at room temperature (RT) when operated in the subthreshold region, which was significantly higher than the maximum response value of 2.8-10 ppm NO 2 obtained with a SnO thin-film chemiresistor at RT. In addition, the SnO TFT gas sensor showed significantly higher sensitivity to NO 2 gas than to other target gases such as NH3, H 2 S, CO 2 , and CO at RT. To our knowledge, this is the first report on a p-type MOS-based field-effect transistor-type gas sensor. Our experimental results demonstrate that the p-type SnO TFT is a promising gas sensor that can operate at RT with high sensitivity and selectivity to NO 2 gas.

We developed an affordable, highly sensitive, and specific paper-based microfluidic platform for fast multiplexed detections of important biomarkers in various body fluids, including urine, saliva, serum, and whole blood. The sensor array consisted of five individual sensing channels with various functionalities that only required a micro liter-sized sample, which was equally split into aliquots by the built-in paper microfluidics. We achieved the individual functionalizations of various bioreceptors by employing the use of wax barriers and 'paper bridges' in an easy and low-cost manner. Pyrene carboxylic acid-modified single-walled carbon nanotubes (PCA/SWNTs) were deposited by quantitative inkjet printing with an optimal 3-dimensional semiconductor density on a paper substrate. Multiple antibodies were immobilized onto the SWNTs surface for highly sensitive and specific field-effect transistor (FET)/chemiresistor (CR) biosensors. We explored the optimal sensing conditions for the paper-based CR biosensor to achieve high sensitivities and specificities towards the target biomarker proteins (human serum albumin (HSA) and human immunoglobulin G (HIgG)) and achieved an ultralow detectable concentration of HSA and HIgG at 1.5 pM. Besides, origami folding was employed to simplify the fabrication process further. The sensing platform described in this work was cost-effective, semi-automated, and user-friendly. It demonstrated the capability of having multiple sensing functions in one paper-based microfluidic sensing platform. It envisioned the potential of a point-of-care device with full-analysis for practical diagnostics in an ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and robust, Equipment-free and Deliverable to end-users) fashion for a quick test of targets of interest.

Porphyrins, with or without metal ions (MPs), have been explored and applied in optical and electrochemical sensor fields owing to their special physicochemical properties. The presence of four nitrogen atoms at the centers of porphyrins means that porphyrins chelate most metal ions, which changes the binding ability of MPs with gas molecules via non-specific binding. In this article, we report hybrid chemiresistor sensor arrays based on single-walled carbon nanotubes (SWNTs) non-covalently functionalized with six different MPs using the solvent casting technique. The characteristics of MP-SWNTs were investigated through various optical and electrochemical methods, including UV spectroscopy, Raman, atomic force microscopy, current-voltage (I-V), and field-effect transistor (FET) measurement. The proposed sensor arrays were employed to monitor the four VOCs (tetradecene, linalool, phenylacetaldehyde, and ethylhexanol) emitted by citrus trees infected with Huanglongbing (HLB), of which the contents changed dramatically at the asymptomatic stage. The sensitivity to VOCs could change significantly, exceeding the lower limits of the SWNT-based sensors. For qualitative and quantitative analysis of the four VOCs, the data collected by the sensor arrays were processed using different regression models including partial least squares (PLS) and an artificial neural network (ANN), which further offered a diagnostic basis for Huanglongbing disease at the asymptomatic stage.

4 figures., Laser-deposited carbon aerogel is a low-density porous network of carbon clusters synthesized using a laser process. A one-step synthesis, involving deposition and annealing, results in the formation of a thin porous conductive film which can be applied as a chemiresistor. This material is sensitive to NO2 compared to ammonia and other volatile organic compounds and is able to detect ultra-low concentrations down to at least 10 parts-per-billion. The sensing mechanism, based on the solubility of NO2 in the water layer adsorbed on the aerogel, increases the usability of the sensor in practically relevant ambient environments. A heating step, achieved in tandem with a microheater, allows the recovery to the baseline, making it operable in real world environments. This, in combination with its low cost and scalable production, makes it promising for Internet-of-Things air quality monitoring., This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement no. 642742. R.A. gratefully acknowledges the support from the Spanish Ministry of Economy and Competitiveness (MINECO) through Project Grant MAT2016-79776-P (AEI/FEDER, UE) and from the European Union H2020 programs “ESTEEM3” (823717), Flagship Graphene (881603), FLAG-ERA - Graphene (MICINN) GATES (PCI2018-093137). WKM and ABM further acknowledge the Gobierno de Aragon (Grupos Reconocidos DGA T03_17R (FEDER, UE) and T03_20R).

High sensitivity, selectivity, and stability are key requirements for carbon nanotube (CNT)-based sensors to realize their full potential in applications ranging from chemical warfare agent detection to disease diagnostics. Herein we demonstrate the sensing of volatile organic compounds (VOCs) relevant to human diseases using an array of chemiresistive carbon nanotube (CNT)-based sensors functionalized with ionic liquids (ILs). The ILs are fluid at ambient temperature and were selected to produce a discriminating sensor array capable of the gas-phase detection of human disease-related VOCs. We find that sensor arrays consisting of imidazolium-based ILs with different substituents and counterions provide selective responses for known biomarkers of infectious diseases of the lungs. Specifically, the sensors discriminate the various volatile biomarkers for tuberculosis based on their polarity, solubility, and chemical affinities. In addition to selectivity, the sensors also show a high level of reversibility and promising long-term stability, which renders them to be suitable candidates for practical applications in breath analysis.

We report a chemiresistive CO2 sensor based on single-walled carbon nanotubes (SWCNTs) noncovalently functionalized with a CO2 switchable copolymer containing amidine pendant groups that transform into amidinium bicarbonates in response to CO2. To fabricate a robust surface-anchored polymer–SWCNT dispersion via spray coating, we first designed and synthesized a precursor copolymer, P(4VP–VBAz), bearing both 4-vinylpyridine (4VP) groups and azide groups. The SWCNT dispersant group, 4VP, is capable of debundling and stabilizing nanotubes to improve their solubility in organic solvents for solution processing. Well-dispersed P(4VP–VBAz)–SWCNT composites are covalently immobilized onto a glass substrate functionalized with alkyl bromides, and then the amidine moieties are subsequently attached to form the resulting CO2-switchable P(Q4VP–VBAm)–SWCNT composites via a copper(I)-catalyzed azide–alkyne cycloaddition click reaction at the film surface. The amidine groups are strong donors that compensate or pin car...

A previously unexplored property of two-dimensional electronic materials is their ability to graft electronic functionality onto colloidal particles to access local hydrodynamics in fluids to impart mobility and enter spaces inaccessible to larger electronic systems. Here, we demonstrate the design and fabrication of fully autonomous state machines built onto SU-8 particles powered by a two-dimensional material-based photodiode. The on-board circuit connects a chemiresistor circuit element and a memristor element, enabling the detection and storage of information after aerosolization, hydrodynamic propulsion to targets over 0.6 m away, and large-area surface sensing of triethylamine, ammonia and aerosolized soot in inaccessible locations. An incorporated retroreflector design allows for facile position location using laser-scanning optical detection. Such state machines may find widespread application as probes in confined environments, such as the human digestive tract, oil and gas conduits, chemical and biosynthetic reactors, and autonomous environmental sensors.

Made available in DSpace on 2018-11-29T12:10:37Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-06-05 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Brazilian Nanotechnology National Laboratory Brazilian Laboratory of Synchrotron Radiation (LNLS) Generalitat Valenciana, Ministerio de Economia y Competitividad Programa de Cooperacion Cientifica con Iberoamerica (Brazil), Ministerio de Educacion This paper consists of an experimental investigation on the effects of annealing temperature on the structural, surface and ozone gas-sensing properties of CuWO4 nanoparticles prepared via a sono-chemical route. X-ray diffraction patterns and X-ray absorption near-edge structure spectroscopy revealed that both long-and short-order structures increase with the annealing temperature. Electrical resistance measurements indicated that CuWO4 samples were sensitive in the range of 15-1400 ppb, exhibiting a good reversibility and repeatability. The enhancement of the ozone gas-sensing properties was attributed to the reduction of hydroxyl species and the improvement of the crystallization degree. This study provides a versatile strategy for obtaining CuWO4 nanoparticles for practical applications as an ozone gas sensor. (C) 2018 Elsevier B.V. All rights reserved. Sao Paulo State Univ, Inst Chem, POB 355, BR-14801907 Araraquara, SP, Brazil Aix Marseille Univ, CNRS UMR 7334 IM2NP, FS St Jerome S152, F-13397 Marseille, France Univ Estadual Piaui, PPGQ CCN, POB 381, BR-64002150 Teresina, PI, Brazil Univ Fed Sao Carlos, Dept Phys, Lab Nanostruct Multifunct Mat, BR-13565905 Sao Carlos, SP, Brazil Jaume I Univ, Dept Chem & Phys, Castellon De La Plana, Spain Sao Paulo State Univ, Inst Chem, POB 355, BR-14801907 Araraquara, SP, Brazil FAPESP: 2013/07296-2 FAPESP: 2017/10313-7 FAPESP: 2017/12437-5 CNPq: 310863/ 2014-7 CNPq: 434266/2016-7 Brazilian Nanotechnology National Laboratory: LMF-18580 Brazilian Laboratory of Synchrotron Radiation (LNLS): D04B-XAFS111883

Fast and efficient alternative methods for wood species identification are needed to combat illegal logging and to control fair trade. One of the possibilities of rapid wood recognition is via chemiresistor gas sensor arrays (“electronic nose”), the application of which is described in the present paper. Carbon nanotube composites (CNTs) of eight insulating polymers were prepared through solution processing and spin casting. The optimum amount of CNTs in the composites was determined by resistance measurement and the CNTs were characterized by scanning electron microscopy. In the case of static headspace analysis, the sensor responses were reproducible and discernible for the wood species. This was demonstrated based on five wood species (Pterocarpus indicus,Acacia auriculiformis,Gmelina arborea,Vitex parvifloraandDiospyros philippinensis). Discrimination of the data was achieved through principal component analysis (PCA) and hierarchical cluster analysis (HCA). PCA score plots and groupings in HCA dendrograms rendered possible the discrimination of these wood species. The potential application of the sensor array approach for wood species identification is high.

The effect of thermal treatments, on the benzene vapor sensitivity of polyethylene (co-)vinylacetate (PEVA)/graphene nanocomposite threads, used as chemiresistive sensors, was investigated using DC resistance measurements, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). These flexible threads are being developed as low-cost, easy-to-measure chemical sensors that could be incorporated into smart clothing or disposable sensing patches. Chemiresistive threads were solution-cast or extruded from PEVA and

A highly sensitive and selective carbon nanotube-based vapor sensor was developed toward the detection of methamphetamine vapor, one of the most widespread, harmful and addictive illegal drugs in the world. Poly[3-(6-carboxyhexyl)thiophene-2,5-diyl)] (P3CT) was chosen to non-covalently functionalize carbon nanotubes, which can facilitate the suspension of carbon nanotubes in the solvents as well as introduce a carboxylic acid functional group. The carboxylic acid group in the polymer acts as a binder of organic amines via acid-base interaction. The P3CT-functionalized carbon nanotube sensors show sensitivity to n -methylphenethylamine (NMPEA), a detection simulant of methamphetamine, as low as 4 ppb. The sensors were able to distinguish NMPEA from two other amine compounds, various volatile chemical compounds (VOCs), and water vapor by observing the recoverability of the sensor’s signal after exposure. The sensor showed higher sensitivity to amine vapors even when the vapor concentrations of amines were several orders of magnitude lower than those of the VOCs. Our research gives a simple but effective method for detecting trace amounts of methamphetamine in ambient air. Meanwhile, the sensor developed in this study can be used as one component in a next generation portable, intelligent, and low-cost chemical sensor array system for more complex real-life applications.

With the emergence of non-invasive disease diagnosis, the development of a specific volatile organic compounds (VOCs) gas sensors in exhaled breath is on-going. Described herein is a flexible and lightweight chemiresistor made of a thin film based on WO 3 /reduced graphene oxide (GO) nanosheets decorated with Pt nanoparticles, which were printed onto a flexible polyamide substrate by using gravure technique. In order to study the effect of graphene size on the performance of gas sensing, graphene with two sized such as large-sized reduced GO microsheets (GMs) and small-sized reduced GO nanosheets (GNs) were synthesized and used as modified materials incorporated into WO 3 -based system. The printed WO 3 /Pt-GNs sensor exhibits a good selectivity, a high response of 12.2 to 10 ppm acetone as well as a fast gas response/recovery time (14.1/16.8 s) at the operating temperature of 200 °C. The sensing performance is attributed to the exposed (002) facets of WO 3 which were not wrapped into GNs, the massive p - n junction active sites at the WO 3 /GNs interface, as well as catalytic Pt nanoparticles. The printed WO 3 /Pt-GNs sensor is a promising candidate for selective, fast and sensitive detection of acetone at relatively low operating temperature.

We present a novel gas phase detection prototype based on assembling core-shell nanospheres made of a silver core and coated with a molecularly imprinted polymer (MIP) adsorbed onto an interdigitated array (IDA) electrode chemiresistor (CR). The core-shell nanospheres, AgNP@MIPs, were imprinted with linalool, a volatile terpene alcohol, as a model system. The thickness of the MIP layer was tuned to a few nanometers to enable the facile ingress and egress of the linalool, as well as to enhance the electrical transduction through the Ag core. The AgNP@MIPs were spread onto the IDA-CR modified with various positively charged polymers, by drop casting and dip-coating. The AgNP@MIPs were characterized by various techniques such as extra high-resolution scanning and tunnelling electron microscopy and X-ray diffraction. The MIP recognition event was transduced into a measurable increase in the resistance. The response to linalool exposure and removal was fast and the device was fully recovered and could be reused. Finally, the difference in the resistance change between imprinted and non-imprinted nanospheres was substantial.

This study reports the design and development of a novel chemiresistor (CR) sensor using ion imprinted polymer (IIP)-functionalized reduced graphene oxide (rGO) [IIP/rGO-CR] for cadmium ions (Cd(II)) determination in water. The sensor consisted of a CR transducer made of rGO channel bridging source and drain electrodes prepared by self-assembly and thermal reduction of graphene oxide (GO) on Au interdigitated electrodes chip fabricated on Si/SiO2 substrate. The IIP was then grafted on rGO using surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization with polyethylenimine (PEI) and methylacrylic acid (MAA) as dual functional monomers and Cd(II) ions as template through UV light-initiated copolymerization. The IIP functionalized on rGO acted as an effective recognition element that modulated the resistance of rGO-CR upon binding of Cd(II), enabling Cd(II) detection at ppb level in aqueous solutions. The prepared IIP/rGO-CR sensor worked effectively in the linear range of 2～200 ppb and achieved a limit of detection (LOD) of 0.83 ppb, which is lower than the World Health Organization guidelines of 3 ppb for drinking water quality. The developed sensor of IIP/rGO-CR showed a high selectivity against a variety of trace and heavy metal ions found in water and good stability for up to 60 days when stored at room temperature for Cd(II) determination in water. Further, the sensor was successfully applied to analyzing Cd(II) spiked in tap, lake and river waters with a 94.5%–113.5% recovery, demonstrating a high degree of accuracy even in complex water samples. Our results illustrated that the CR sensor of IIP functionalized rGO provides a potential platform for sensitive, robust and low-cost environmental analysis of Cd(II) in water.

In this study, a biosensor to detect a stress biomarker of cortisol using cortisol monoclonal antibody (c-Mab) covalently immobilized on reduced graphene oxide (rGO) channel as electrical sensing element was demonstrated. Highly specific immune-recognition between the c-Mab and the cortisol was identified and characterized on a basis of resistance change at the rGO channel based chemiresistor sensor achieving the limit of detection of 10pg/mL (27.6 pM). In addition, cortisol concentrations of real human salivary sample and buffer solution of rat adrenal gland acute slices, which could secret the cortisol induced by adrenocorticotropic hormone (ACTH), were directly measured by the chemiresistor corresponding to the specific sensing of the cortisol. The rGO chemiresistor could selectively measure the cortisol levels in spite of diverse neuroendocrine's existence. The potential perspective of this study can be a protocol of new cortisol sensor development, which will be applicable to point-of-care testing (POCT) targeted for salivary cortisol, in vitro psychobiological study on cortisol induction, and implantable sensor chip in the future.

An ultralow cost vapor sensor platform is developed, incorporating a chemiresistor-based sensor that enables targeted sensing through surface functionalization. Humidity, ammonia, and acetone sensing are demonstrated by PEDOTPSS, DPP-CN, and graphene surface modification, respectively. The integrated USB connector, use of a standard HMI interface, and microcontroller interface allows us installation-free data collection on any device with a USB port.

We developed chemiresistor-type biosensors based on carbon nanotubes for highly efficient and fast detection of avian influenza virus (AIV) subtype H5N1 DNA sequences. Semiconducting single-walled carbon nanotubes (sc-SWCNTs) or nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were used as two alternative active sensing elements, and their sensitivity to different concentrations of DNA target were compared. In these sensors long nanotubes (>5 μm) were placed between interdigitated metal electrodes so that individual nanotubes connect the electrodes. The nanotubes were functionalized with DNA probe sequences non-covalently attached to the sidewalls. Such functionalized-nanotube sensors could reliably detect complementary DNA target sequences of the AIV H5N1 with concentration ranging from 2 pM to 2 nM in 15 min and at room temperature. Our nanotube-based biosensors are small, flexible, disposable and easy-to-fabricate that makes them promising for point-of-care applications and clinical diagnostics.

In general, alkane vapors are difficult to detect due to their non-reactive nature at room temperature. Here, we show chemiresistive sensors made of carbon nanotubes (CNTs) noncovalently functionalized with three kinds of poly(3-alkylthiophene) (P3AT), namely, poly(3-butylthiophene) (P3BT), poly(3-octylthiophene-2,5-diyl) (P3OT) and poly(3-dodecylthiophene-2,5-diyl) (P3DT). We compared the responses of sensors composed of these materials to four linear alkanes, hexane, octane, decane and dodecane. The results show that sensors with CNTs functionalized with P3ATs that have alkyl side chains with length similar to the length of the analyte alkane produced a bigger response than the case in which the lengths are different. Based on this response trend, a sensor array was made, which can distinguish different sizes of linear alkane vapors. This work facilitates the future design of CNT-based sensor arrays for distinguishing analytes with similar physical and chemical properties.

Detection of highly toxic Cr(VI) is greatly desired. In the present study, a highly sensitive method for Cr(VI) detection by reduced graphene oxide (rGO) chemiresistor and 1,4-dithiothreitol (DTT) functionalized Au nanoparticles (AuNPs) is reported. The detection strategy is based on the selective binding between DTT functionalized AuNPs1 located in rGO conductive channels and DTT functionalized AuNPs2 in solution through the formation of disulfides induced by Cr(VI) at acidic condition, which results in aggregation of DTT functionalized AuNPs2 on the rGO channels producing a readily measurable resistance change. The response of the chemiresistor is rapid and allows real-time monitoring of Cr(VI). Using this method, as low as 0.9 nM of Cr(VI) in water was detected with good selectivity. The proposed method has great potentials for monitoring of trace Cr(VI) in drinking water.

In this work, the uniform and vertically aligned single wall carbon nanotubes (SWCNTs) have been grown on Iron (Fe) deposited Silicon (Si) substrate by plasma enhanced chemical vapor deposition (PECVD) technique at very low temperature of 550 °C. The as-grown samples of SWCNTS were characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM) and Raman spectrometer. SWCNT based chemiresistor gas sensing device was fabricated by making the proper gold contacts on the as-grown SWCNTs. The electrical conductance and sensor response of grown SWCNTs have been investigated. The fabricated SWCNT sensor was exposed to ammonia (NH3) gas at 200 ppm in a self assembled apparatus. The sensor response was measured at room temperature which was discussed in terms of adsorption of NH3 gas molecules on the surface of SWCNTs. The achieved results are used to develope a miniaturized gas sensor device for monitoring and control of environment pollutants.

Interparticle spatial properties influence the electrical and functional properties of nanoparticle-structured assemblies. This report describes the nanoscale curvature-induced change in chemiresistive properties of molecularly-linked assemblies of gold nanoparticles on multiwalled carbon nanotubes, which are exploited for sensitive detection of volatile organic compounds. In addition to using linking/capping molecules to define interparticle spatial distances, the nanoscale curvature radius of the carbon nanotubes provides intriguing tunability of the interparticle spatial properties to influence electrical properties, which contrast with those observed for nanoparticle thin films assembled directly on chemiresistor devices. The electrical characteristics of the nanoparticle-nanotube composite give positive response profiles for the vapor molecules that are distinctively different to those observed for conventional nanoparticle thin-film assemblies. The dominant effect of electron coupling on overall chemiresistive properties is shown in relation to that of nanoscale curvature radius on the nanoparticle thin-film sensing properties. Sensing data are also further assessed in correlation with the solubility parameters of the vapor molecule. These findings have significant implications for the design of sensitive interfaces with nanocomposite-structured sensing materials and microfabricated chemiresistor devices.

Hydrogen peroxide is an intermediate molecule that can be used to detect numerous other analytes using peroxidase assays. Methods for detection of hydrogen peroxide can be broadly classified into colorimetric or electrochemical. Colorimetric methods require reagents while electrochemical methods require reference electrodes, both of which make sensing complicated. As an alternative, in this paper, we demonstrate a reliable, simple, reagent free solid state chemiresistive sensor for hydrogen peroxide detection. The chemiresistor is composed of a drop casted carbon nanotube film with two parallel carbon ink contact electrodes. Carbon nanotube electrode is functionalized with phenyl capped aniline tetramer (PCAT). This sensor was able to sense over a wide range of concentrations from 3ppm to 1200 ppm. Further, we also demonstrate that this sensor can be employed in a peroxidase assay to detect biomolecules such as glucose by adding the appropriate enzyme.

Hydrogen sulfide (H2S) is a corrosive, flammable, and extremely toxic chemical compound which is typically formed under septic conditions in wastewater collection systems, and the root cause of odor from and corrosion of liquid waste service infrastructure. To control and mitigate H2S buildup in sewer pipelines, it is necessary to detect low concentrations of dissolved H2S. In this paper, a chemiresistive sensor, based on graphene and polymethyl methacrylate (PMMA) is developed, which is able to electrochemically measure various concentrations of H2S in aqueous media. Several tests using electrochemical impedance spectroscopy (EIS) have been conducted to characterize the sensor. The synergetic properties of graphene as the conductive component and PMMA as the linker depicted excellent performance of the thin film sensor to H2S in the range of 10-2 %v/v. The results demonstrated the potential of the sensor for detection of H2S in aqueous media with high selectivity and sensitivity.

Graphene is a good candidate for filling the market requirements for cheap, high sensitivity, robust towards contamination, low noise, and low power consumption gas sensors, thanks to its unique properties, i.e., large surface, high mobility, and long-term stability. Inkjet printing is a cheap additive manufacturing method allowing fast, relatively precise and contactless deposition of a wide range of materials, it can be considered therefore the ideal technique for fast deposition of graphene films on thin substrates. In this paper, the sensitivity of graphene-based chemiresistor gas sensors, fabricated through inkjet printing, is investigated using different concentrations of graphene in the inks. Samples have been produced and characterized in terms of response towards humidity, nitrogen dioxide, and ammonia. The presented results highlight the importance of tuning the layer thickness and achieving good film homogeneity in order to maximize the sensitivity of the sensor.

Citrus greening, or Huanglongbing (HLB), is currently the most devasting disease of citrus, creating unprecedented crisis for the multibillion-dollar global citrus industry. To-date, there is no effective cure and disease management relies on early detection and removal of infected trees. Thus, it is imperative that accurate, timely, and robust disease detection and diagnosis technologies are available to minimize the spread of disease. This study reports a sensitive and selective label-free biosensor that combines the physical and chemical advantages of carbon nanomaterials like single-walled carbon nanotubes (SWNTs) in a field-effect transistor (FET)/chemiresistor architecture with selective antibodies against Sec-delivered effector 1 (SDE1), a secreted protein biomarker, for the detection of HLB. The biosensor detected SDE1 biomarkers for citrus greening in plant tissue extracts with the dynamic range over three orders of magnitude in the low nanomolar to micromolar concentration range and limit of detection of 5 nM. The study also demonstrated the use of the standard additions assay method with the biosensor to attain a 90-percent signal recovery in concentrated plant tissue extract, allowing for quantitative detection without an external calibration. Adopting the novel detection strategy targeting the secreted protein biomarker, SDE1, addresses some of the challenges faced by current methods of nucleic acid-based assays and symptom-based diagnosis, which have been found prone to false negatives and misdiagnoses, respectively.

Paper-based sensors fabricated using the pencil-on-paper method are expected to find wide usage in many fields owing to their low cost and high reproducibility. Here, hydrogen (H2) detection was realized by applying palladium (Pd) nanoparticles (NPs) to electronic circuits printed on paper using a metal mask and a pencil. We confirmed that multilayered graphene was produced by the pencil, and then characterized Pd NPs were added to the pencil marks. To evaluate the gas-sensing ability of the sensor, its sensitivities and reaction rates in the presence and absence of H2 were measured. In addition, sensing tests performed over a wide range of H2 concentrations confirmed that the sensor had a detection limit as low as 1 ppm. Furthermore, the sensor reacted within approximately 50 s at all H2 concentrations tested. The recovery time of the sensor was 32 s at 1 ppm and 78 s at 1000 ppm. Sensing tests were also performed using Pd NPs of different sizes to elucidate the relationship between the sensing rate and catalyst size. The experimental results confirmed the possibility of fabricating paper-based gas sensors with a superior sensing capability and response rate.

The objective of this work is the application of laser-induced forward transfer (LIFT) for the fabrication of chemiresistor sensors. The receiver substrate is an array with metal electrodes and the active materials placed by LIFT are single-walled carbon nanotubes (SWCNT). The functionality of such sensors depends on the geometry of the active material onto the metallic electrodes. First the best geometry for the sensing materials and electrodes was determined, including the optimization of the process parameters for printing uniform pixels of SWCNT onto the sensor electrodes. The sensors were characterized in terms of their sensing characteristics, i.e., upon exposure to ammonia, proving the feasibility of LIFT., Applied Physics A, 117 (1), ISSN:0947-8396, ISSN:1432-0630, ISSN:0340-3793

Nowadays, sensitive biosensors with high selectivity, lower costs and short response time are required for detection of DNA. The most preferred materials in DNA sensor designing are nanomaterials such as carbon and Au nanoparticles, because of their very high surface area and biocompatibility which lead to performance and sensitivity improvements in DNA sensors. Carbon nanomaterials such as carbon nanotubes (CNTs) can be considered as a suitable DNA sensor platform due to their high surface-to-volume ratio, favourable electronic properties and fast electron transfer rate. Therefore, in this study, the CNTs which are synthesised by pulsed AC arc discharge method on a high-density polyethylene substrate are used as conducting channels in a chemiresistor for the electrochemical detection of double stranded DNA. Moreover, the response of the proposed sensor is investigated experimentally and analytically in different temperatures, which confirm good agreement between the presented model and experimental data.

Here, we report the engineering of a solid-state micro pH sensor based on polyaniline-functionalized, electrochemically reduced graphene oxide (ERGO-PA). Electrochemically reduced graphene oxide acts as the conducting layer and polyaniline acts as a pH-sensitive layer. The pH-dependent conductivity of polyaniline occurs by doping of holes during protonation and by the dedoping of holes during deprotonation. We found that an ERGO-PA solid-state electrode was not functional as such in fermentation processes. The electrochemically active species that the bacteria produce during the fermentation process interfere with the electrode response. We successfully applied Nafion as a proton-conducting layer over ERGO-PA. The Nafion-coated electrodes (ERGO-PA-NA) show a good sensitivity of 1.71 Omega/pH (pH 4 - 9) for chemiresistive sensor measurements. We tested the ERGO-PA-NA electrode in real-time in the fermentation of Lactococcus lactis. During the growth of L. lactis, the pH of the medium changed from pH 7.2 to pH 4.8 and the resistance of the ERGO-PA-NA solid-state electrode changed from 294.5 Omega to 288.6 Omega (5.9 Omega per 2.4 pH unit). The pH response of the ERGO-PA-NA electrode compared with the response of a conventional glass-based pH electrode shows that reference-less solid-state microsensor arrays operate successfully in a microbiological fermentation.