Chemiresistive Devices Research Articles

MOF based flexible, low-cost chemiresistive device as a respiration sensor for sleep apnea diagnosis.

The monitoring of respiratory disorders requires breath sensors that are fast, robust, and convenient to use and can function under real time conditions. A MOF based flexible sensor is reported for the first time for breath sensing applications. The properties of a highly porous HKUST-1 MOF and a conducting MoS2 material have been combined to fabricate an electronic sensor on a flexible paper support for studying sleep apnea problems. Extensive breath sensing experiments have been performed and interestingly the fabricated sensor is efficient in detecting various kinds of breaths such as deep, fast, slow and hydrated breath. The MOF breath sensor shows a fast response time of just ∼0.38 s and excellent stability with no decline in its performance even after a month. A plausible mechanism has been proposed and a smartphone based prototype has been prepared to demonstrate the real time applications of the hybrid device. This work demonstrates great potential for the application of MOFs in healthcare with a special focus on breath sensing and sleep apnea diagnosis.

Two-Dimensional Chemiresistive Covalent Organic Framework with High Intrinsic Conductivity.

This paper describes the synthesis of a novel intrinsically conductive two-dimensional (2D) covalent organic framework (COF) through the aromatic annulation of 2,3,9,10,16,17,23,24-octa-aminophthalocyanine nickel(II) and pyrene-4,5,9,10-tetraone. The intrinsic bulk conductivity of the COF material (termed COF-DC-8) reached 2.51 × 10-3 S/m, and increased by 3 orders of magnitude with I2 doping. Electronic calculations revealed an anisotropic band structure, with the possibility for significant contribution from out-of-plane charge-transport to the intrinsic bulk conductivity. Upon integration into chemiresistive devices, this conductive COF showed excellent responses to various reducing and oxidizing gases, including NH3, H2S, NO, and NO2, with parts-per-billion (ppb) limits of detection (for NH3 = 70 ppb, for H2S = 204 ppb, for NO = 5 ppb, and for NO2 = 16 ppb based on 1.5 min exposure). Electron paramagnetic resonance spectroscopy and X-ray photoelectron spectroscopy studies suggested that the chemiresistive response of the COF-DC-8 involves charge transfer interactions between the analyte and nickelphthalocyanine component of the framework.

Hydrogen Sulfide Gas Sensing Capabilities of Solution Processed Vanadium Pentoxide Nanosheets

Vanadium Pentoxide (V2O5) nanosheets, liquid exfoliated in ethanol, were used as sensing material for hydrogen sulfide (H2S) detection. The material properties such as morphology, phase, chemical signature were characterized using Field Emission electron microscopy (FESEM), Transmission electron microscopy (TEM), Atomic force microscopy (AFM), X-ray Diffraction (XRD), Raman Spectroscopy, X-ray photoelectron microscopy (XPS). These nanosheets were further dropcasted on Ti/Pt interdigitated electrode (IDE) to fabricate a chemiresistive gas sensing device. The sensors show excellent response towards H2S gas at an operating temperature of 350 °C, when operated in 500 ppb–4 ppm range. The response in this range was found to be varying linearly from 1.5% (for 500 ppb) to 12.8% (for 4 ppm). Response time and recovery time of 71 seconds and 104 seconds for 1 ppm H2S was observed. The hysteresis error (%) of the device was found to be ±4.21% which suggests it to be a good sensing material for H2S detection. The device was also tested on other parameters like repeatability, stability and reproducibility and it performs well in these tests indicating exfoliated V2O5 nanosheet as a potential sensing material for chemiresistive devices for H2S detection.

Chemical vapor sensing with CVD-grown monolayer MoSe2 using photoluminescence modulation

Monolayer two-dimensional transition metal dichalcogenides (TMDs) such as MoSe2 are promising materials for chemical vapor sensing applications due to their unique monolayer structure, ease of fabrication, low cost, selectivity, sensitivity, and speed of response. To date, most chemical vapor and gas sensors that use TMDs are based on chemiresistive device properties. However, recent studies indicate that the optical properties, in particular the photoluminescence (PL), could be used to sense vapors as well. In this study, we examine the PL of MoSe2 while it is exposed to triethylamine, a strong electron donor and chemically relevant to nerve gas and explosive sensing. We observe a fast and significant decrease in the PL by as much as 75% during exposure. The PL begins to recover as soon as the vapor is switched off, indicating fast adsorption/desorption of the analyte. We analyze the data in terms of possible applications to chemical vapor sensing.

Rapid photocatalytic reduction of graphene oxide indirectly activated by the domino effect of ethanol oxidation on a titanium dioxide film

Deoxygenation of graphene oxide is a low-cost and effective way to yield graphene (i.e., reduced graphene oxide - RGO) for many applications. However, choices of reduction approach and reduction time need consideration due to damaging pre-existing materials on electronic devices. Here, we found a facile and eco-friendly route that was based on the photo-oxidation of ethanol (diluted in water) on a catalytic TiO2 film to rapidly induce the formation of RGO within 15 min under UV (20 mW/cm2) or sun lights (1 sun = 100 mW/cm2). Our reduction route was indirectly activated by chain reactions of ethanol and TiO2 (so-called domino effect) because the GO deoxygenation occurred even when the samples were placed around and not in contact with TiO2 film. To obtain the highest reduction, the samples should stay on the catalytic film to receive lights for activation and acceleration of reactions. Furthermore, effects of exposure time (1–20 min), ethanol concentration (14.3–100%), and light intensity on RGO quality explored with the use of chemiresistive devices. The results of demonstrative sensing measurements towards NO2 and NH3 indicate that our method is promising for electrical applications using solution processable RGO.

Lectin- and Saccharide-Functionalized Nano-Chemiresistor Arrays for Detection and Identification of Pathogenic Bacteria Infection.

Improvement upon, and expansion of, diagnostic tools for clinical infections have been increasing in recent years. The simplicity and rapidity of techniques are imperative for their adoption and widespread usage at point-of-care. The fabrication and evaluation of such a device is reported in this work. The use of a small bioreceptor array (based on lectin-carbohydrate binding) resulted in a unique response profile, which has the potential to be used for pathogen identification, as demonstrated by Principal Component Analysis (PCA). The performance of the chemiresistive device was tested with Escherichia coli K12, Enterococcus faecalis, Streptococcus mutans, and Salmonella typhi. The limits of detection, based on concanavalin A (conA) lectin as the bioreceptor, are 4.7 × 103 cfu/mL, 25 cfu/mL, 7.4 × 104 cfu/mL, and 6.3 × 102 cfu/mL. This shows that the detection of pathogenic bacteria is achieved with clinically relevant concentrations. Importantly, responses measured in spiked artificial saliva showed minimal matrix interference. Furthermore, the exploitation of the distinctive outer composition of the bacteria and selectivity of lectin-carbohydrate interactions allowed for the discrimination of bacterial infections from viral infections, which is a current and urgent need for diagnosing common clinical infections.

Effect of palladium nanoparticle functionalization on the hydrogen gas sensing of graphene based chemi-resistive devices

In this work, we study the effect of palladium nanoparticles (PdNPs) functionalization on the hydrogen sensing performance of devices based on graphene (GR). Microwave irradiation has been used to directly synthetize PdNPs onto GR sheets. PdNPs-GR devices, realized using palladium coverage loads from 0.5mg up to 10mg, have been investigated at Room Temperature (RT). Experiments show that an optimal value of the palladium coverage exists, corresponding to a 5mg loading, that results in a more sensitive and faster device with a gas response of∼30% when exposed to 1% H2. A possible operating mechanism based on the different chemical and physical properties of the α and β phase of palladium hydride layers that grow as a result of reaction between hydrogen and PdNPs-GR, is suggested. The main outcome of this study is to show that it is possible to tune GR sensitivity towards hydrogen suitably adjusting the Pd loading confirming, in turn, that NPs functionalization can be an effective means to tune the graphene physical properties.

Ammonia gas sensor based on flexible polyaniline films for rapid detection of spoilage in protein-rich foods

This work details the fabrication and performance of a sensor for ammonia gas, based on conducting polymer. The fabrication procedure consists following steps; polyaniline synthesis via oxidative polymerization technique, then a sensitive polyaniline film was deposited on a printed circuit board and finally, polyaniline microdevice were assembled on an interdigitated electrode arrays to fabricate the sensor for amomonia gas detection. Response time of this chemiresistive devices and humidity impact were examined for NH3 sensitivity and compared with commercial gas sensors (Taguchi Model 826). Data export from sensor to the computer was carried out via data logger model ADC-24 and analyzed using SPSS software. The sensor was found to have a rapid (t = 40 s) and stable linear response to ammonia gas in the concentration range of interest (50–150 ppm) under room temperature operation condition. It was reviled also reliable results to the variation of environment humidity. Power consumption, sensitivity, dimension, flexibility and fabrication cost were used as most important parameters to compare the new polymer based device with those of other similar works and the results showed that small size, low cost, flexibility, low power consumption and high sensitivity are from the benefits of this innovative device. In real-time application conditions flexible polyaniline based gas sensor with polyimide substrate in thickness 0.25 mm exhibits relatively good performance and accurate evaluation of food spoilage.

Direct Self-Assembly of Conductive Nanorods of Metal–Organic Frameworks into Chemiresistive Devices on Shrinkable Polymer Films

Direct Self-Assembly of Conductive Nanorods of Metal–Organic Frameworks into Chemiresistive Devices on Shrinkable Polymer Films

Two‐Step Solution‐Processed Two‐Component Bilayer Phthalocyaninato Copper‐Based Heterojunctions with Interesting Ambipolar Organic Transiting and Ethanol‐Sensing Properties

The two‐component phthalocyaninato copper‐based heterojunctions fabricated from n‐type CuPc(COOC8H17)8 and p‐type CuPc(OC8H17)8 by a facile two‐step solution‐processing quasi‐Langmuir–Shäfer method with both n/p‐ and p/n‐bilayer structures are revealed to exhibit typical ambipolar air‐stable organic thin‐film transistor (OTFT) performance. The p/n‐bilayer devices constructed by depositing CuPc(COOC8H17)8 film on CuPc(OC8H17)8 sub‐layer show superior OTFT performance with hole and electron mobility of 0.11 and 0.02 cm2 V−1 s−1, respectively, over the ones with n/p‐bilayer heterojunction structure with the hole and electron mobility of 0.03 and 0.016 cm2 V−1 s−1 due mainly to the more intense face‐to‐face π–π interaction in the CuPc(OC8H17)8 sub‐layer than that in CuPc(COOC8H17)8 sub‐layer, revealing the effect of different stacking sequence on tuning the OTFT performance of phthalocyanine‐based bilayer heterojunctions. Furthermore, the chemiresistive devices fabricated from the p/n‐bilayer heterojunction, with both Au and Indium tin oxide (ITO) interdigitated electrodes (IDEs), also display much better sensing properties to ethanol than those with n/p‐bilayer heterojunction in terms of sensitivity and reversibility. Significantly, time‐dependent current plot of the p/n‐bilayer heterojunction with ITO IDEs reveals a detection limit as low as 100 ppm, nearly complete reversibility, and high selectivity to ethanol even at room temperature, rendering this novel two‐component heterojunction device a great application potential in practical detecting ethanol.

Sensitive ammonia gas sensors fabricated using biologically assembled copper sulfide

Copper sulfide-based ammonia (NH3) gas sensors were assembled using a genetically modified viral template. Glutamic acid residues on the filament-shaped bioscaffold surface facilitated the synthesis of nanocrystalline Cu1.8S. Each device comprised a network of biological materials decorated with a nonstoichiometric semiconductor. These chemiresistive devices had high sensitivity to NH3 concentrations from 10 to 80 ppm under room-temperature operation. Response times greater than 15 min were observed. These results demonstrate the potential of biotemplated materials for sensitive gas detection at room temperature.

Pencil-on-paper: electronic devices

Paper based electronics have been rapidly growing in recent years. Drawing with a pencil on paper is perhaps the simplest and easiest way of establishing graphitic circuitry in a solvent-free manner, which in the post-graphene years, has attracted an unusual interest. Here in this focus article, we highlight the recent efforts in the literature employing pencil drawings in various ways including sensors, microfluidics, energy storage and microanalytical devices. Even active devices such as piezo and chemiresistive devices as well as field effect transistors have been realised by utilizing pencil-traces. Pencil-on-paper may offer a viable route for developing lab-on-paper applications through suitable integration of the passive and active roles of the pencil-trace.