Sensitive Chemical Sensors Research Articles

A sea-cucumber-like hollow polyaniline spheres electrode-based chemical sensor for the efficient detection of aliphatic alcohols

Sea-cucumber-like hollow polyaniline (PANI) spheres were synthesized by the chemical polymerization of aniline monomers in the presence of salicyclic acid. The synthesized sea-cucumber-like hollow PANI spheres were applied as a working electrode for the fabrication of highly sensitive, reliable and reproducible chemical sensors for detecting ethanol and other alcohols. The sea-cucumber-like hollow PANI spheres were extensively characterized in terms of their morphological, structural, optical, electrical and electrochemical properties. The morphological characterization revealed a sea-cucumber-like hollow morphology with a uniform decoration of nanofibrils covering the shell of the spheres. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) measurements were performed to elucidate the electrochemical behavior of sea-cucumber-like hollow PANI spheres electrode towards the detection of aliphatic alcohols. The sensing performances of the synthesized sea-cucumber-like hollow PANI spheres electrode towards the detection of alcohols were analyzed by the current (I)–voltage (V) characteristics. The sea-cucumber-like hollow PANI spheres electrode based ethanol chemical sensor showed considerably high sensitivity of ∼426.5 μA mM−1 cm−2 and a detection limit of ∼515.7 μM with a correlation coefficient (R) of ∼0.90157 and a short response time (10 s).

Fabrication of Highly Sensitive Phenyl Hydrazine Chemical Sensor based on as-grown ZnO-Fe2O3 Microwires

Fabrication of Highly Sensitive Phenyl Hydrazine Chemical Sensor based on as-grown ZnO-Fe2O3 Microwires

Highly sensitive and stable phenyl hydrazine chemical sensors based on CuO flower shapes and hollow spheres

Chemical sensors are needed to develop efficient sensing systems with high flexibility, and low capital cost for controlled recognition of analytes. Herein, we report a highly sensitive, low cost, simple chemical sensor based on flower shape and hollow sphere CuO. Following the precipitation process, FESEM images revealed that CuO nanosheets are grown in high density and organized in a proper manner to give a flower shape structure; however, following the hydrothermal method in the presence of urea, the cage like micro structures CuO hollow spheres have been discovered. XRD revealed that the grown CuO has a single-crystalline phase of a monoclinic system. The resistivity of CuO hollow spheres (1.93 × 106 Ω m) is ∼100 times higher than flower shape CuO (2.2 × 104 Ω m). The prepared CuO flower shapes and hollow spheres have been evaluated for the detection and quantification of phenyl hydrazine. The findings indicate that CuO hollow spheres and flowers exhibited good sensitivity (0.578 and 7.145 μA cm−2 mM−1) and a lower limit of detection (LOD = 2.4 mM) with a linear dynamic range (LDR) of 5.0 μM to 10.0 mM and rapid assessment of the reaction kinetics (in the order of seconds). The designed flower shape CuO sensing system is 12 times more sensitive than CuO hollow spheres. To the best of our knowledge, the measured sensitivity ∼ 7.145 μA cm−2 mM−1 of CuO flower shapes is found to be among the highest sensitivity values reported for phenyl hydrazine up to now.

In situ synthesized carbon nanotube networks on a microcantilever for sensitive detection of explosive vapors

This paper reports a chemical sensor that consists of a suspended microcantilever and a carbon nanotube (CNT) network that is in situ synthesized on the microcantilever. The in situ synthesis achieves minimized thermal resistance of the interface between the CNTs and the microcantilever, which together with the low thermal mass and the high thermal conductivity allows the sensor to operate in microcalorimeter mode. By heating the CNT networks with an integrated heater, the explosive vapors adsorbed on the CNT surfaces are ignited to deflagration, which releases extra heat to deflect the microcantilever and thus changes the resistance of an integrated piezoresistor. This thermal-mechanical coupling transduction mechanism bridges the heat changes on the CNT networks and the mechanical deflection of the microcantilever. The large surface to volume ratio of CNTs enables fast adsorption of the chemical sensor to explosive vapors and improved equivalent limit of detection (LOD). An equivalent LOD of 2.4 pg is achieved for TNT detection, and run-to-run repeatability and device-to-device reproducibility are better than 4% and 10%. The preliminary results demonstrate the feasibility of development of sensitive CNT chemical sensors using in situ synthesized CNT networks and thermal-mechanical coupling transduction mechanism.

Highly sensitive hydrazine chemical sensor fabricated by modified electrode of vertically aligned zinc oxide nanorods

A highly sensitive, reliable and reproducible hydrazine chemical sensor was fabricated using vertically aligned ZnO nanorods (NRs) electrode. The low temperature hydrothermal process was adopted to synthesize the vertically aligned ZnO NRs on fluorine doped tin oxide (FTO) glass. The morphological characterizations revealed the vertical arrangement of highly dense ZnO NRs on FTO substrates. The ultraviolet diffused reflectance spectroscopy (UV-DRS) of aligned ZnO NRs electrode obtained the band gap of ∼3.29eV which was close to that of bulk ZnO nanomaterials. The synthesized aligned ZnO NRs electrode was directly used to elucidate the chemical sensing performance towards the detection of hydrazine by simple current–voltage (I–V) characteristics. The aligned ZnO NRs electrode based hydrazine chemical sensor presented a significantly high sensitivity of ∼4.42446×10−5AmM−1cm−2 and the detection limit of ∼515.7μM with a correlation coefficient (R) of ∼0.73297 and a short response time (10s). The electrochemical analysis of vertically aligned ZnO NRs electrode in the presence of hydrazine showed the increased current with high height of anodic peak which confirmed the involvement of high electron transfer process via high electrocatalytic activity of the electrode.

La0.7Sr0.3MnO3 Nanoparticles Based Ultra-High Sensitive Ammonia Chemical Sensor

A facile, reliable, reproducible and ultra-high sensitive aqueous ammonia chemical sensor has been fabricated based on the utilization of La(0.7)Sr(0.3)MnO3 nanoparticles (LSMO NPs), as efficient electron mediators, and reported in this paper. The LSMO NPs were prepared by hydrothermal protocol followed by the annealing process and characterized in detail in terms of their mophological, structural and compositional properties. The I-V technique based aqueous ammonia sensor exhibits an ultra-high sensitivity of 494.68 +/- 0.01 microA cm(-2)mM(-1) and very low-detection limit of 0.2 microM with a response time less than 10 s. To the best of our knowledge, this is the first report in which LSMO is used as an efficient electron mediator for the fabrication of aqueous ammonia chemical sensor. Moreover, by comparing the literature, it is confirmed that the fabricated sensor exhibits highest sensitivity towards the detection of aqueous ammonia. This LSMO nanomaterial based research broadens the range of efficient electron mediators utilized for the fabrication of ultra-high sensitive chemical sensors.

Hydrazine chemical sensing by modified electrode based on in situ electrochemically synthesized polyaniline/graphene composite thin film

The modified electrode of polyaniline/graphene (PANI/Gr) composites was prepared by in situ electrochemical synthesis of aniline monomer and graphene oxide in hydrochloric acid. The PANI/Gr composites modified electrodes were utilized for fabricating the highly sensitive, reliable and reproducible hydrazine chemical sensor. The PANI/Gr composites modified electrodes were extensively characterized by morphological, structural and the optical properties. The Raman studies revealed that PANI/Gr composite modified electrode possessed both Gr and PANI Raman bands, suggested the π–π* electron interaction between CN+ of PANI and carboxylate group of Gr. The sensing performance of the fabricated chemical sensor toward the detection of hydrazine was measured by a two electrode current–voltage (I–V) technique. A very high sensitivity of ∼32.54 × 10−5 A cm−2 mM−1 and reasonable detection limit of ∼15.38 mM with correlation coefficient (R) of 0.78578 and short response time (10 s) were observed by PANI/Gr composites modified thin film electrode.

Surface-enhanced raman scattering platforms on the basis of assembled gold nanorods

This study investigates the surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) on the surface of gold nanorods (GNRs) assembled on silicon. Two samples of GNRs were synthesized, notably, GNR-670 and GNR-810, with the average (length × thickness) dimensions of 64 × 23 and 45 × 11 nm and with plasmon resonances at 670 and 810 nm, respectively. Three types of substrates were fabricated, namely, a low-density monolayer (S1), a densely packed monolayer with regions of the side-by-side assembly of nanorods (S2), and a fractal film (S3). The extinction spectra of densely packed substrates showed the appearance of new maxima and the broadening and the red-shift of plasmon resonances, as was consistent with the typical behavior of plasmonic particles interacting at an interparticle distance of about 1–3 nm (data of transmission electron microscopy). The intensities of SERS peaks of the rhodamine 6G increased for substrates S1, S2, and S3 as 1: 6: 260, respectively. There was no significant difference in the SERS efficiency of the substrates based on GNR-670 and GNR-810 rods. The average enhancement of the signal over an area of 400 μm was about 105 with a reproducibility error of ±10%, thus making the obtained substrates promising platforms for sensitive SERS chemical and biological sensors.

Preparation of stable core–shell dye adsorbent Ag-coated silica nanospheres as a highly active surfaced-enhanced Raman scattering substrate for detection of Rhodamine 6G

Abstract Silica spheres are used as a template to prepare Ag-coated silica nanospheres through electrostatic interaction, using a technique of homogeneous shaking instead of magnetic stirring. Pre-synthesized spherical Ag nanoparticles are firstly adsorbed onto silica spheres through bifunctional linking molecule, the silane reagent 3-aminopropyltrimethoxysilane, to form thin silver shells. These monodispersed Ag-coated silica nanospheres are assembled onto the glass substrates, which have been functionalized by 3-aminopropyltrimethoxysilane, to form close-packed three-dimensional Ag-coated silica nanosphere arrays by electrostatic interaction. The Ag-coated silica nanospheres were investigated as substrates for surface-enhanced Raman scattering using Rhodamine 6G as a probe molecule, and the enhancement factor of the Raman signal obtained on the Ag-coated silica nanospheres is about 1.74 × 109 for R6G. Compared with pure silver hydrosols, the prepared Ag-coated silica nanospheres have a higher Raman enhancing effect. The hybrid nanosphere substrates can be used as a highly sensitive chemical and biological sensor for Rhodamine 6G dye.

Rationally designed porous silicon as platform for optical biosensors

Optical porous silicon multilayer structures are able to work as sensitive chemical sensors or biosensors based in their optical response. An algorithm to simulate the optical response of these multilayers was developed, considering the optical properties of the individual layers. The algorithm allows designing and customizing the porous silicon structures according to a given application. The results obtained by the simulation were experimentally verified; for this purpose different photonic structures were prepared, such as Bragg reflectors and microcavities. Some of these structures have been derivatized by the introduction of aminosilane groups on the porous silicon surface. The algorithm also permits to simulate the effects produced by a non uniform derivatization of the multilayer.

Selective and sensitive optical chemical sensor for the determination of Hg(II) ions based on tetrathia-12-crown-4 and chromoionophore I

Abstract A reversible optical membrane sensor for detection of Hg(II) was developed based on the colorimetric determination of tetrathia-12-crown-4-Hg(II), incorporating chromoionophore I (ETH5294) as a lipophilic H+-selective indicator, and sodium tetra phenyl borate (NaTPB) as a lipophilic anionic site. A decrease in absorption of the membrane at 664 nm and/or increase at 555 nm could be used as a suitable wavelength for quantitative determination of Hg(II). This membrane is capable of determining mercury(II) ions over a wide linear dynamic range 1.0 × 10−9 to 9.5 × 10−5 mol L−1 Hg(II) at pH 7.0 with detection limits of 8.1 × 10−10 mol L−1 Hg(II) and response time of 100 s. The optode reveals a very good selectivity toward Hg(II) ions over a wide variety of other metal ions in solution and the response to Hg(II) is fully reversible. Performance characteristics of the sensor evaluated as good reversibility, wide dynamic range, long life span, long-term response stability, and high reproducibility. The optode was applied to the determination of mercury(II) in water samples. The accuracy of the results was comparable to those obtained by cold vapor atomic absorption spectrometry.

Highly sensitive formaldehyde chemical sensor based on hydrothermally prepared spinel ZnFe2O4 nanorods

A considerable effort has been made for the growth and development of face-centered-cubic spinel zinc ferrite (ZnFe2O4) nanorods using hydrothermal method at room conditions. The structural, optical and chemical properties of ZnFe2O4 nanorods were characterized using various methods such as UV/visible, Fourier transform infrared spectroscopy, Raman spectroscopy, powder X-ray diffraction, and field-emission scanning electron microscopy etc. Spinel ZnFe2O4 is an attractive nanorods for potential application in chemical sensing by easy and reliable I–V method, where formaldehyde is considered as a model compound. The chemical sensor performances are exhibited the higher sensitivity, good stability, and repeatability of the sensor enhanced significantly using spinel ZnFe2O4 nanorods of thin-film with conducting binders on silver electrodes (AgE). The calibration plot is linear over the large dynamic range, where the sensitivity (∼4.10 ± 0.05 μA cm−2 mM−1) and detection limit (∼0.0089 μM) were calculated based on signal/noise ratio (∼3N/S) in short response time. Finally, it is concluded that the structural and optical characteristics could be encompassed to a broad-scale in spinel ZnFe2O4 nanorods and efficient chemical sensor applications for environmental and healthcare fields.

Distinguishing octane grades in gasoline using terahertz metamaterials

Distinguishing octane numbers of commercial gasoline is experimentally demonstrated by use of single split-ring resonator metamaterials functioning at terahertz frequencies. The differences in frequency-dependent absorption coefficients and refractive indices of various grades of gasoline lead to a modification in the surrounding dielectric environment and consequently the resonance properties of the planar metamaterials. This consequently enables a distinct frequency shift in the inductive-capacitive electric dipolar resonances. This paper reveals that such metamaterial arrays, as highly sensitive chemical sensors, have promising potential in petroleum industrial applications.

Highly sensitive methanol chemical sensor based on undoped silver oxide nanoparticles prepared by a solution method

We have prepared silver oxide nanoparticles (NPs) by a simple solution method using reducing agents in alkaline medium. The resulting NPs were characterized by UV–vis and FT-IR spectroscopy, X-ray powder diffraction, and field-emission scanning electron microscopy. They were deposited on a glassy carbon electrode to give a sensor with a fast response towards methanol in liquid phase. The sensor also displays good sensitivity and long-term stability, and enhanced electrochemical response. The calibration plot is linear (r2 = 0.8294) over the 0.12 mM to 0.12 M methanol concentration range. The sensitivity is ~2.65 μAcm−2 mM−1, and the detection limit is 36.0 μM (at a SNR of 3). We also discuss possible future prospective uses of this metal oxide semiconductor nanomaterial in terms of chemical sensing.

Extreme chemical sensitivity of nonlinear conductivity in charge-ordered LuFe2O4

Nonlinear transport behaviors are crucial for applications in electronic technology. At the nonlinear critical turning point, the nonequilibrium states cause rich physics responses to environment. The corresponding study in this field is crucial for physics and industry application. Here nonlinear conductivity in charge-ordered (CO) LuFe2O4 has been demonstrated. Remarkable resistivity switching behavior was observed and the gas-sensing property can be reversibly tuned by a small alternation of partial pressure and/or chemical components of the environment. These facts allow us to use LuFe2O4 materials as a sensitive chemical gas sensor in technological applications. Careful analysis of the gas sensing process in LuFe2O4 suggests a novel sensing mechanism in sharp contrast with that discussed for the conventional gas sensors which depend fundamentally on surface chemical reactions.

Effect of molecular vibrations on the selectivity character of pyridino-18-crown-6 derivatives towards potassium ion

The complex formation of ‘flexible’ dimethyl-pyridino-18-crown-6 (M2P18C6) or ‘rigid’ dimethyl-diketo-pyridino-18-crown-6 (M2K2P18C6) host molecules with potassium ions in methanol were investigated by UV spectroscopy. Results show same stability of flexible or rigid crown ether complexes with potassium ion. However, negative entropy change has been detected when M2P18C6 forms complexes with potassium ions while entropy increasing was obtained when M2K2P18C6 associates with potassium ions. Theoretical calculations suggest that among other possible effects characteristic vibrations of crown rings could be identified as background of this unexpected complexation phenomena. This finding may contribute to the development of design of sensitive and selective chemical sensors.

Ultra-high sensitive hydrazine chemical sensor based on low-temperature grown ZnO nanoparticles

Using well-crystalline ZnO nanoparticles (NPs), an ultra high sensitive hydrazine amperometric sensor has been fabricated and reported in this paper. The ZnO NPs have been synthesized by very simple aqueous solution process at 90°C and characterized in detail in terms of their morphological, compositional, structural and optical properties. The detailed investigations reveal that the synthesized products are well-crystalline NPs, possessing wurtzite hexagonal phase and exhibit good optical properties. The fabricated amperometric hydrazine sensor exhibits ultra-high sensitivity of ∼97.133μAcm−2μM−1 and very low-detection limit of 147.54nM. To the best of our knowledge, this is the first report in which an ultra-high sensitivity and low-detection limit have been obtained for the hydrazine chemical sensor based on ZnO nanostructures.

Growth and properties of Ag-doped ZnO nanoflowers for highly sensitive phenyl hydrazine chemical sensor application

We report here the fabrication of a robust, highly sensitive, reliable and reproducible phenyl hydrazine chemical sensor using Ag-doped ZnO nanoflowers as efficient electron mediators. The Ag-doped ZnO nanoflowers were synthesized by facile hydrothermal process at low-temperature and characterized in detail in terms of their morphological, structural, compositional and optical properties. The detailed morphological and structural characterizations revealed that the synthesized nanostructures were flower-shaped, grown in very high-density, and possessed well-crystalline structure. The chemical composition confirmed the presence of Ag into the lattices of Ag-doped ZnO nanoflowers. High sensitivity of ∼557.108±0.012mAcm−2(molL−1)−1 and detection limit of ∼5×10−9molL−1 with correlation coefficient (R) of 0.97712 and short response time (10.0s) were observed for the fabricated chemical sensor towards the detection of phenyl hydrazine by using a simple current–voltage (I–V) technique. Due to high sensitivity and low-detection limit, it can be concluded that Ag-doped ZnO nanoflowers could be an effective candidate for the fabrication of phenyl hydrazine chemical sensors.

Optical fibre long period grating with a nanoporous coating formed from silica nanoparticles for ammonia sensing in water

A fibre optic long period grating (LPG) with an nano-assembled mesoporous coating of alternate layers of poly(diallyldimethylammonium chloride) (PDDA) and SiO2 nanospheres was used for the development of a highly sensitive fibre-optic chemical sensor. Sensor fabrication involves a 2-stage process: firstly, the deposition of the base mesoporous thin film (PDDA/SiO2) over an LPG written in the optical fibre using a layer-by layer technique, followed by the infusion of a functional material into the porous film. The refractive index of the base mesoporous coating, determined at a wavelength of 633nm using ellipsometry, was found to be 1.2. The infusion of the functional material into the coating resulted in a significant change in the RI of the coating, producing a dramatic change in the transmission spectrum of the LPG. The sensing mechanism exploited is based upon chemically induced desorption of the functional material from the mesoporous coating. The sensing of ammonia in aqueous solution was chosen as an example to demonstrate the sensing principle of the LPG sensor. The operation of the sensor was characterized using two functional materials, tetrakis-(4-sulfophenyl)porphine (TSPP) and polyacrylic acid (PAA). The device showed high sensitivity to ammonia with a response time less than 100s and a limit of detection of 140ppb when the TSPP infused (PDDA/SiO2) film was employed as a sensitive element.

The relationship of selective surrounding response and the nanophotonic structures of Morpho butterfly scales

This paper investigates the sensitivity of micro/nano structures in Morpho butterfly scales to surrounding media. The theory of multilayer-thin-film interference is introduced to explain the mechanism of sensitivity. Two-dimensional optical models with three different geometrical designs and similar size were constructed to authenticate the theory. The rigorous coupled-wave analysis (RCWA) technique was employed for theoretical calculation of vector diffraction. By comparing the modeling results from RCWA with the experimental results, we identified the key to sensitivity, multilayer-thin-film interference occurred over a structure composed of alternating films with high and low refractive indexes. Further, we identified the main characteristics of the scales that were relevant to sensitivity. These characteristics should be applied to designing and fabricating artificial nanostructures for highly sensitive and selective bio-inspired chemical sensors.