Chemiresistive Response Research Articles

Chemiresistive Detection of Gaseous Hydrocarbons and Interrogation of Charge Transport in Cu[Ni(2,3-pyrazinedithiolate)2] by Gas Adsorption.

The development of new chemiresistive materials for use in chemical sensors that operate near ambient conditions could potentially reduce the costs of implementation, encouraging their use in new areas. Conductive metal-organic frameworks represent one intriguing class of materials for further investigation in this area, given their vast structural diversity and the specificity of adsorbate interactions afforded by their crystallinity. Here, we re-examine the electronic conductivity of the desolvated and acetonitrile-solvated microporous framework Cu[Ni(pdt)2] (pdt2- = 2,3-pyrazinedithiolate), and find that the conductivity in the pristine material is 200-fold greater than in the solvated state, highlighting the sensitivity of sample conductivity to guest inclusion. Additionally, the desolvated material is demonstrated to selectively adsorb the gaseous hydrocarbons ethane, ethylene, acetylene, propane, propylene, and cis-2-butene at ambient temperature. Investigation of the effect of gas adsorption on conductivity using an in situ measurement cell reveals a chemiresistive response for each adsorbate, and the change in conductivity with adsorbate pressure closely follows an empirical model identical in form to the Langmuir-Freundlich equation. The relative sensitivity of the framework to each adsorbate is, surprisingly, not correlated with binding strength. Instead, the differences in chemiresistive response between adsorbates are found to correlate strongly with gas phase specific heat capacity of the adsorbate. Nanoconfinement effects, manifesting as a relative deviation from the expected chemiresistive response, may influence charge transport in the case of the largest adsorbate considered, cis-2-butene. Time-resolved conductance and adsorption measurements additionally show that the chemiresistive response of the sensor equilibrates on a shorter time scale than gas adsorption, suggesting that interparticle contacts limit conduction through the bulk material and that conductivity at the crystallite surfaces is most responsive to gas adsorption.

Graphene-Based Sensing of Gas-Phase Explosives

Graphene based sensors have shown excellent potential in the trace detection of specific gases which are hazardous to humans or environmentally toxic. Sensor designs incorporating pristine graphene, graphene oxide, and nanopatterned graphene have been the focus of much recent experimental and computational research. The application of graphene based sensors in the trace detection of explosives has seen relatively limited study, due in part to the difficulties of conducting experiments using the nitramine and aromatic explosives of central interest. Computational studies of explosive sensors are not subject to hazardous materials handling constraints, and may be used to complement experimental research on the development of low weight, low power, graphene-based sensors. Ab initio models of five different graphene nanoribbon sensor configurations have been developed, and their chemiresistive response to three widely used explosives and four background gases has been investigated. The results indicate that t...

Welding Metallophthalocyanines into Bimetallic Molecular Meshes for Ultrasensitive, Low-Power Chemiresistive Detection of Gases.

This paper describes the first demonstration of using a series of isoreticular nickel phthalocyanine- and nickel naphthalocyanine-based bimetallic conductive two-dimensional (2D) metal-organic frameworks (MOFs) as active materials in chemiresistive sensing of gases. Devices achieve exceptional sensitivity at sub-part-per-million (ppm) to part-per-billion (ppb) detection limits toward NH3 (0.31-0.33 ppm), H2S (19-32 ppb), and NO (1.0-1.1 ppb) at low driving voltages (0.01-1.0 V) within 1.5 min of exposure. The devices maintain their performance in the presence of humidity (5000 ppm of H2O). The isoreticular analogs enable modular control over selectivity and sensitivity in gas sensing through different combinations of linkers and metal nodes. Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy studies suggest that the chemiresistive response of the MOFs involves charge transfer interactions triggered by the analytes adsorbed on MOFs.

Synthesis of palladium tellurolate complexes derived from hemi-labile tellurolate ligands and studies their reactivity as gas sensing materials

The reaction of [PdCl2(dppf)] with the sodium salt of pyridyl/pyrimidyl tellurolate resulted a mononuclear cis configured complex [Pd(TeAr)2(dppf)] (Ar = C5H4N, C4H3N2). These complexes were characterized by NMR (1H, 31P) spectroscopy and elemental analysis. In addition, the thin film of this complex was fabricated on the glass using solution process and it was found to be sensitive towards detection of H2S gas. The chemi-resistive response of the film was ascribed to the fact that an auxiliary tellurolate ligand attached to palladium metal centre substituted reversibly by thiolate (HS−) species of hydrogen sulphide gas.

Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal–Organic Frameworks

AbstractConductive metal–organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu‐CAT‐1 is described.

Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal-Organic Frameworks.

Conductive metal-organic frameworks are opening new perspectives for the use of these porous materials for applications traditionally limited to more classical inorganic materials, such as their integration into electronic devices. This has enabled the development of chemiresistive sensors capable of transducing the presence of specific guests into an electrical response with good selectivity and sensitivity. By combining experimental data with computational modelling, a possible origin for the underlying mechanism of this phenomenon in ultrathin films (ca. 30 nm) of Cu-CAT-1 is described.

Highly Ammonia Sensing Using Direct In Situ Electro-Deposited Polypyrrole-Dodecylbenzene Sulfonic Acid Film on ITO Coated Flexible Substrates

Air quality monitoring is of major concern as it is directly linked to public health. It requires the development of high sensitive devices with fast response towards hazardous gas and volatile compounds. Such performances depend on the nature and quality of deposition of the sensing layer. Herein, adherent polypyrrole-dodecylbenzene sulfonic acid (PPy–DBSA) films were deposited on a N-(3-trimethoxysilylpropyl) pyrrole modified ITO coated polyethylene teraphtalate (PET) flexible substrate by facile direct electrochemical oxidation of pyrrole in an aqueous solution of sulfonic acid. The obtained PPy-DBSA films were subjected to various characterization techniques such as, FTIR, Raman, SEM and conductivity measurements. Chemiresistive gas sensing tests have demonstrated selectivity and sensitivity of films toward ammonia vapors over the other vapors (nitrogen dioxide, carbon dioxide, hydrogen sulfide, acetone, methanol and ethanol) with higher response at 20 ppm, reasonably fast response time of 3 min and reaching detection limit of 3ppm. The response of the sensor can reasonably be related to the strong electrostatic interactions between vapor molecules and the dopant agents within PPy films. In comparison PPy-DBSA films prepared on pristine ITO/PET has exhibited lower response at 20 ppm of ammonia exposure, which highlights the role of surface modification and the contribution from the dopant agent nature for ammonia sensing. Moreover, chemiresistive response performances have been tested in the presence of humidity, under varied temperatures, and finally their behaviors were featured by an impedance spectroscopy in both presence and absence of gas. This work conclusively shows that the sensing performances are not only driven by the molecular interactions between the sensor and the analyte but also by the quality of deposition and adhesion of the former to the transducer. The latter feature can be controlled by appropriate chemical surface modification.

A study of the structural features and sensor properties of zinc 2,9,16,23-tetra-tert-butylphthalocyanine films

A comparative study of the structural features of zinc 2,9,16,23-tetra-tert-butylphthalocyanine films (ZnPc( t Bu)4) obtained by vacuum thermal deposition and spin coating techniques is performed. By powder X-ray diffraction, 2D GIXD, and optical absorption spectroscopy it is shown that ZnPc( t Bu)4 films obtained by the spin coating technique consist of a disordered α-phase with small crystallites. After annealing at 200 °C for 3 h the films transform into the β-phase, with crystallite sizes increasing, however, they remain disordered relative to the substrate surface. On heating under the same conditions, the ZnPc( t Bu)4 films obtained by thermal vacuum sublimation transform from the weakly oriented low-temperature α-phase into the oriented β-phase. Dependences of a chemiresistive sensor response of the ZnPc( t Bu)4 films to ammonia (10-50 ppm) are investigated depending on the preparation and annealing methods of the films.

Electron beam modified zinc phthalocyanine thin films for radiation dosimeter application

Present study deals with the effect of electron beam irradiation on electrical and gas sensing properties of zinc phthalocyanine (ZnPc) thin film prepared on flexible Biaxially Oriented Polyethylene Terephthalate (BOPET) sheet. The electron beam irradiation of ZnPc films were carried out using a 10MeV RF Linear accelerator, under different radiation dose levels from 1kGy to 30kGy. The pristine and irradiated films were characterized by using X-ray photoelectron spectroscopy, Atomic Force microscopy, UV–vis spectroscopy and X-ray diffraction. Samples irradiated in the dose range of 1–18kGy exhibit linear enhancement of electrical conductance due to increasing content of adsorbed oxygen. Beyond 18kGy the sample exhibit saturation in the content of adsorbed oxygen as well as in electrical conductance. The pristine ZnPc films exhibit excellent chemi-resistive response towards H2S gas in 1–20ppm range at room temperature. The response of the irradiated films decreases monotonically with increasing electron beam dose due to the strong binding of oxygen at the Zn sites. A plausible mechanism of electron beam induced modification of ZnPc films and its implication on charge transport as well as chemi-resistive gas sensing behavior are discussed. This work highlight the utilization of ZnPc thin films as potential radiation dosimeter based upon linear rise in electrical conductance.

A cross-functional nanostructured platform based on carbon nanotube-Si hybrid junctions: where photon harvesting meets gas sensing

A combination of the functionalities of carbon nanotube (CNT)-Si hybrid heterojunctions is presented as a novel method to steer the efficiency of the photovoltaic (PV) cell based on these junctions, and to increase the selectivity and sensitivity of the chemiresistor gas sensor operated with the p-doped CNT layer. The electrical characteristics of the junctions have been tracked by exposing the devices to oxidizing (NO2) and reducing (NH3) molecules. It is shown that when used as PV cells, the cell efficiency can be reversibly steered by gas adsorption, providing a tool to selectively dope the p-type layer through molecular adsorption. Tracking of the current-voltage curve upon gas exposure also allowed to use these cells as gas sensors with an enhanced sensitivity as compared to that provided by a readout of the electrical signal from the CNT layer alone. In turn, the chemiresistive response was improved, both in terms of selectivity and sensitivity, by operating the system under illumination, as the photo-induced charges at the junction increase the p-doping of CNTs making them more sensitive to NH3 and less to NO2.

Chemi-resistive response of rutile titania nano-particles towards isopropanol and formaldehyde: a correlation with the volatility and chemical reactivity of vapors

The performance of phase pure rutile titania nano-particles for gas/vapor sensing is not well explored in open literature, mostly because of their moderate chemical activity. However, the high thermal stability of rutile titania could be beneficial towards making a stable chemi-resistive sensor, operable generally at higher temperature. Herein, we have investigated the chemi-resistive response characteristics of rutile phase titania nano-particles for the detection of isopropanol and formaldehyde vapors. Titania nano-particles are synthesized through a hydrothermal route and characterized in terms of their phase formation behavior and micro-structural features. The sensing characteristics of the particles are measured by varying the operating temperature (275 °C–350 °C) of the sensor and concentrations (20–200 ppm) of the vapors, using a static flow gas sensing measurement set-up. The rutile titania particles are found more responsive towards isopropanol than formaldehyde. An attempt is made here to correlate the sensing performance of titania sensors with the volatility and chemical reactivity of studied vapors. The higher response of the sensor towards isopropanol is predicted, due to its comparatively lower volatility and more suitable chemical structure for oxidation on the sensor surface.

Chemiresistor Arrays Prepared by Simple and Fast Vapor‐Phase Thiol Place‐Exchange Functionalization of Gold Monolayer‐Protected Cluster Films

AbstractWe describe a simple, versatile, and relatively fast method to alter the sensor selectivity of chemiresistors based on films of Au monolayer‐protected clusters (MPCs) by varying their functionalization via vapor‐phase thiol place‐exchange reactions. Drop‐cast deposited films of hexanethiolate (C6S)‐coated Au MPCs are exposed to volatile thiol liquids, such as mercaptoethanol (HOC2S), mercaptopropionic acid (HOOCC2S), and mercaptopropyltrimethoxysilane (H3COSiC3S), which leads to thiol place‐exchange and new functionalities in the film. Generally, the film is about 10–20 % exchanged during the first 4 to 5 h and 80–90 % exchanged after 24 h. The extent and the rate of exchange decreases as the thickness of the film of C6S Au MPCs increases, leading to irreproducibility issues if film thickness is not carefully controlled. Importantly, the chemiresistive sensing response ratio of 2‐propanol relative to toluene vapor increased significantly from about 0.3 prior to exchange to 2.0 after 24 to 48 h of exchange with HOC2S, showing that the selectivity of the sensor could be significantly altered by this method, which is simpler, faster, and more amenable to a wide variety of ligands compared to solution‐based functionalization methods. The chemiresistive response of an unexchanged C6S Au MPC films and those exchanged with HOC2S, HOOCC2S, and H3COSiC3S demonstrates potential electronic nose applications.

Gold nanoparticle superlattices: correlating chemiresistive responses with analyte sorption and swelling

In this study the chemiresistive responses of gold nanoparticle superlattices are investigated by GISAXS and microgravimetry.

Hierarchical zinc oxide nano-tips and micro-rods: hydrothermal synthesis and improved chemi-resistive response towards ethanol

In the present work, a novel hierarchical architecture of zinc oxide has been synthesized through a spherical carbon template assisted two step hydrothermal process.

Fast Response and High Sensitivity of ZnO Nanowires-Cobalt Phthalocyanine Heterojunction Based H2S Sensor.

The room temperature chemiresistive response of n-type ZnO nanowire (ZnO NWs) films modified with different thicknesses of p-type cobalt phthalocyanine (CoPc) has been studied. With increasing thickness of CoPc (>15 nm), heterojunction films exhibit a transition from n- to p-type conduction due to uniform coating of CoPc on ZnO. The heterojunction films prepared with a 25 nm thick CoPc layer exhibit the highest response (268% at 10 ppm of H2S) and the fastest response (26 s) among all samples. The X-ray photoelectron spectroscopy and work function measurements reveal that electron transfer takes place from ZnO to CoPc, resulting in formation of a p-n junction with a barrier height of 0.4 eV and a depletion layer width of ∼8.9 nm. The detailed XPS analysis suggests that these heterojunction films with 25 nm thick CoPc exhibit the least content of chemisorbed oxygen, enabling the direct interaction of H2S with the CoPc molecule, and therefore exhibit the fastest response. The improved response is attributed to the high susceptibility of the p-n junctions to the H2S gas, which manipulates the depletion layer width and controls the charge transport.

Hematite iron oxide nano-particles: facile synthesis and their chemi-resistive response towards hydrogen

In the present work, hematite iron oxide nano-particles are synthesized through a facile wet chemical precipitation route. The phase formation behavior and microstructure evolution of the synthesized nano-particles are studied using infrared spectroscopy in conjunction with x-ray diffraction analyses and electron microscopy. Chemi-resistive type hydrogen sensing characteristics (e.g. response %, response time, recovery time) of hematite iron oxide nano-particulate sensing element are evaluated using an automated, dynamic flow gas sensing measurement set-up. The sensing characteristics are measured by varying the operating temperature (275–350 °C) of the sensor and concentration of hydrogen (250–1660 ppm). From the operating temperature dependence of response and recovery times, we have estimated the respective activation energies for response and recovery processes.

Single-walled carbon nanotube/metalloporphyrin composites for the chemiresistive detection of amines and meat spoilage.

Chemiresistive detectors for amine vapors were made from single-walled carbon nanotubes by noncovalent modification with cobalt meso-arylporphyrin complexes. We show that through changes in the oxidation state of the metal, the electron-withdrawing character of the porphyrinato ligand, and the counteranion, the magnitude of the chemiresistive response to ammonia could be improved. The devices exhibited sub-ppm sensitivity and high selectivity toward amines as well as good stability to air, moisture, and time. The application of these chemiresistors in the detection of various biogenic amines (i.e. putrescine, cadaverine) and in the monitoring of spoilage in raw meat and fish samples (chicken, pork, salmon, cod) over several days was also demonstrated.

Single‐Walled Carbon Nanotube/Metalloporphyrin Composites for the Chemiresistive Detection of Amines and Meat Spoilage

AbstractChemiresistive detectors for amine vapors were made from single‐walled carbon nanotubes by noncovalent modification with cobalt meso‐arylporphyrin complexes. We show that through changes in the oxidation state of the metal, the electron‐withdrawing character of the porphyrinato ligand, and the counteranion, the magnitude of the chemiresistive response to ammonia could be improved. The devices exhibited sub‐ppm sensitivity and high selectivity toward amines as well as good stability to air, moisture, and time. The application of these chemiresistors in the detection of various biogenic amines (i.e. putrescine, cadaverine) and in the monitoring of spoilage in raw meat and fish samples (chicken, pork, salmon, cod) over several days was also demonstrated.

Multi-analyte detection of chemical species using a conducting polymer nanowire-based sensor array platform

This paper proposes a novel sensing platform for a conducting polymer nanowire-based chemiresistive sensor array for multi-analyte detection capability. In order to create a cross-reactive sensor array with each individual sensor having partial selectivity, distinct catalytic nanoparticles are incorporated into each sensing element resulting in a unique response from each sensor when exposed to a specific analyte. Based on the chemiresistive signal responses from the sensor array, a pattern recognition algorithm is applied to simultaneously differentiate one chemical species from another within a sample containing a mixture of analyte species. As a demonstration of the concept, the proposed sensor array was tested for the simultaneous classification and quantification of three chemical species: ascorbic acid, dopamine, and hydrogen peroxide. A highly conductive polyaniline nanowire network was used as a generic chemiresistive sensing platform for the device. Each sensor in the array responded distinctly with partial selectivity to each analyte, and hence provided a unique “fingerprint” response for the given composition of the sample solution. The results suggest that this technique can be applied either as an electronic nose or as an electronic tongue for the simultaneous classification and quantification of individual species within a mixture of a large number of chemical analyte.

Vertically ordered hematite nanotube array as an ultrasensitive and rapid response acetone sensor.

Vertically ordered nanotube array is a desirable configuration to improve gas sensing properties of the hematite which is the most abundant and cheapest metal oxide semiconductor on earth but has low and sluggish chemiresistive responses. We have synthesized a vertically aligned, highly ordered hematite nanotube array directly on a patterned SiO2/Si substrate and then it used as a gas sensor without additional processing. The nanotube array sensor shows unprecedentedly ultrahigh and selective responses to acetone with detection limits down to a few parts per billion and response time shorter than 3 s.