Toluene Sensor Research Articles

Highly-selective and temperature-compensated toluene sensor based on MOF-actuated optical WGM microresonator

This paper reports an optical fiber toluene sensor based on whispering gallery mode (WGM) microbottle resonator. The sensor includes a single-mode fiber (SMF)- no-core fiber (NCF)- SMF offset structure, which can be used as not only a coupler to couple light into the microbottle but also a multimode interferometer. The microbottle is formed by self-assembly of polydimethylsiloxane (PDMS) polymer doped with metal-organic framework (MOF) under the action of surface tension and gravity. The high specific surface area, suitable pore size, nitrogen-containing functional groups of MOF-Fe-PD and nonpolar groups on PDMS impart the high sensitivity and specific response of the sensor to toluene. When toluene is captured by the MOF and PDMS, the refractive index and volume of the cavity change, which affects the mode shift of WGM. According to test results, WGM of the sensor shows a linear sensitivity of 12.44pm/ppm with toluene concentration between 0 ppm and 337 ppm at room temperature, but it is affected by temperature crosstalk. While multimode interference dip is only sensitive to temperature, which can compensate for the mode shift of WGM caused by temperature change. Repeatability experiments show that the response and recovery time of the sensor are less than 70s. The method provides a toluene sensor with high selectivity, stable performance and simple preparation, which has potential environmental benefits and good industrial application prospects.

Highly sensitive toluene sensor based on silver Ear-Like F-doped Co3O4 templated from Co(OH)F Guided by SiO2 nanospheres

This study successfully synthesized “silver ear-like” Co(OH)F using 15 nm SiO2 spheres as seeds. Gas sensitivity of Co(OH)F with and without SiO2 spheres to toluene was compared at different annealing temperatures. The results demonstrate that the Co(OH)F-Si-350 sensor exhibits optimal gas sensitivity to toluene, with a response of 35 (Rg/Ra) to 100 ppm of toluene at 220℃, with response and recovery times of 50 s and 80 s, respectively. Notably, the sensor detected toluene concentrations as low as 50 ppb, indicating good sensitivity to low concentrations. These findings suggest that the structural transformation resulting from the introduction of SiO2 nanospheres, forming ultra-thin nanosheet clusters (∼12 nm), provides abundant active sites, effectively promoting substance diffusion and adsorption/desorption processes. Additionally, the incorporation of fluorine enhances the Lewis acidity of the material, facilitating the formation of stable adsorption states for gas molecules on the surface. These results reveal the significant impact of the structural transformation caused by the introduction of SiO2 nanospheres on gas sensitivity, providing a strong theoretical foundation for further optimizing gas sensor design.

Low-temperature and high-selectivity Ag/Co3O4 toluene sensor based on lattice oxygen and d-band and investigation of response behavior shifts induced by Ag nanoparticles

Currently, the sensing mechanism of toluene remains controversial. The sensing action of toluene is often attributed to adsorbed oxygen based on acknowledged Wolkenstein model. However, the role of lattice oxygen often remains neglected. To investigate toluene sensing mechanism, Ag quantum dot-modified Co3O4 were successfully synthesized by the thermal method. X-ray photoelectron spectroscopy (XPS) of Ag-Co3O4 before and after exposure to toluene reveal the role of lattice oxygen, and Gas Chromatography-Mass Spectrometry (GC-MS) and Density Functional Theory (DFT) reveal the catalytic role of Ag particles. Ag particles caused the upshift of Co D-band, more readily hybridizing the s and p orbitals in the toluene and O2 molecules, possibly contributing to the enhanced catalytic and adsorption activity of the materials. Moreover, Ag-induced response behaviors switching from oxidation-reduction transitions were found and explained. Excitingly, the synthesized 16 at% Ag-Co3O4 has good selectivity for toluene at 180 °C. And the response of 16 at% Ag-Co3O4 to 100 ppm toluene reached 2113% with a detection limit 100 ppb. This work provides a novel insight into the toluene sensing mechanism, aiding the design of high-performance toluene sensors.

High efficiency toluene sensor based on iron-doped nickel oxide triple-shell microspheres with high moisture resistance

This paper provides a simple one-step synthesis of Fe-doped NiO triple-shell layer microsphere structures for toluene gas detection. The 2 at% Fe-doped NiO sensor has excellent sensing ability for toluene gas, with high response (36–100 ppm), low detection limits (100 ppb), fast response and recovery time (2/20 s). Moreover, the sensor demonstrates excellent moisture resistance, with satisfactory response to toluene even in conditions of 99 % relative humidity (34.1–100 ppm). To further investigate the adsorption properties of the sensor, a density functional theory (DFT) approach was employed, and the sensing mechanism of the NiO sensor was discussed detailly. Analysis of the results suggests that Fe-doped NiO triple-shell layer microspheres represent a promising approach for the design of high-performance toluene gas sensors.

Highly sensitive toluene sensor based on porous core-shell-structured In2O3–ZnO nanofibers under UV irradiation at room temperature

Highly sensitive toluene sensor based on porous core-shell-structured In2O3–ZnO nanofibers under UV irradiation at room temperature

Construction of Co3O4/Fe3O4 heterojunctions from metal organic framework derivatives for high performance toluene sensor

A solvothermal method combined with a liquid-based metal organic framework synthesis route was used to synthesize uniform Co3O4/Fe3O4 nanospheres. Different ratio of Co3O4 was used to functionalize Fe3O4, and enhanced toluene sensing performance was achieved. The maximum toluene response value is 87 at 225 °C, which is 20 times of pure Fe3O4 nanospheres based gas sensor. Also, after functionalization with Co3O4, better selectivity and sensitivity were obtained compared with pure Fe3O4 nanospheres. The best performing gas sensor has a response/recovery time of 16/162 s, and the detection limit is decreased to ppb level. In addition, the sensor showed excellent repeatability and long-term stability. The mechanism of the improved sensing performance was detailly analyzed, which were primarily attributed to the construction of p-n heterojunctions at the interface of the p-type Co3O4 and the n-type Fe3O4, and the catalytic influence of Co3O4. This work provides an appropriate way for the sensitization of Fe3O4 in toluene sensing.

Guided-mode resonance sensors: different schemes for different applications

This work performs a quantitative comparison of different dielectric-based guided-mode resonance (D-GMR) sensors. To this end, diverse D-GMR structures are classified into three different classes, and their sensitivity (S) is compared to each other. For one of these classes in various schemes, the sensitivity is investigated for the TE and TM modes. Moreover, grating height effects are studied for different cases in this category, and analytical sensitivity equations are used as benchmarks. Then, the three classes are compared and, based on the numerical results and analytical equations, various applications are proposed for different structures in the refractive index (RI) of interest. Comparing our results to other recent works, we prove that the proposed classification leads to great sensing performances and the predictions are reliable. A comparison has been performed for methane as a gas sample (with RI of 1.0003) and a hemoglobin solution and toluene as two different analytes (with RIs of 1.33 and 1.4778, respectively). The results show a sensitivity of S = 1427.3 n m / r e f r a c t i v e index unit (nm/RIU) for methane with a detection precision of one to a few volume percentages in the air, which can also be calibrated to illuminate the fabrication variation errors. For hemoglobin, a sensitivity of 1073.4 nm/RIU is obtained, with a limit of detection of 116.15 mg/lit for 65-87 g/lit of hemoglobin in water; for the toluene sensor, S = 1019.7 n m / R I U is calculated. As a general result, a high figure of merit/sensitivity can be achieved over a wide range of applications, from gases to high RI analytes, using our proposed classifications.

MOF-derived Au-NiO/In2O3 for selective and fast detection of toluene at ppb-level in high humid environments

Development of highly sensitive toluene gas sensor is desirable but challenging for both indoor air quality monitoring and medical diagnosis. Herein, we proposed to design Au nanoparticles (NPs) decorated MOF-derived NiO/In2O3 hollow microspheres as efficient sensing materials for toluene detection. Benefiting from the structural merits and synergetic effects, the Au0.6Ni4In-based toluene sensor exhibited a high response, fast response and recovery speed, good linearity, low detection limitation (~5.1 ppb) with excellent selectivity and good stability in both relatively dry (11% RH) and ultra humid (95% RH) atmospheres. The improved toluene detection performance might be attributed to the synergistic effects of several points including the formation of p-n junction between NiO and In2O3, the sensitization effect of Au NPs, high affinity of NiO to water vapor as well as the loose structure. The obtained sensing performances unambiguously indicated that the Au0.6Ni4In-based sensor can quantitatively detect toluene at ppb-level in a complex environment.

An ultra-sensitive room temperature toluene sensor based on molten-salts modified carbon nitride

In this work, two-dimensional crystalline C3N4 (CCN) was obtained by promoting the self-condensation reaction of dicyandiamide in an air atmosphere via the molten salt method. Studies show that compared with polymer-C3N4 (PCN) ((9.8 m2/g)), CCN has a larger specific surface area (77.1 m2/g)) and better crystallinity. Additionally, the resistance of CCN in the air is 40 MΩ, 1250 times lower than that of polymer-C3N4 (PCN) (∼50000 MΩ). Secondly, when 50 ppm toluene gas analysis flows into the CCN based gas sensor at room temperature, the gas response value is 350. The CCN based gas sensor works for 60 days, or after 25 cycles continuously, the gas response value remains at about 350 (Rg/Ra), which is due to the excellent crystallinity, optimized π conjugate system, and enhanced interlayer van der Waals of CCN. Additionally, the critical effect of crystallinity on the gas sensitivity of carbon nitride is also discussed in detail.

Unexpected and enhanced electrostatic adsorption capacity of oxygen vacancy-rich cobalt-doped In2O3 for high-sensitive MEMS toluene sensor

Benefiting from the enhanced electrostatic adsorption derived from surface oxygen vacancy, the reported MEMS based hollow-porous Co-In 2 O 3 gas sensor exhibits excellent selectivity and response, and toluene detection limits as low as 100 ppb at the lowest temperature so far. • The hollow-porous Co-doped In 2 O 3 microspheres with abundant electrostatic adsorption sites were synthesized by ultrasonic spray pyrolysis. • The MEMS toluene sensor reported in this work with the characteristic of low power consumption. • The Co-In 2 O 3 gas sensor exhibits high sensitivity and superior selectivity to ppb level of toluene at relatively lower temperature. • Demonstrating the impact of electrostatic adsorption on charge carrier transport and toluene sensing performance by DFT calculation. Semiconductor metal oxide (SMO) gas sensor has been widely researched in artificial olfactory for monitoring gases and odor. However, realizing the characteristics of low detection limit, immunity from interference capacity and low operating temperature still remains challenge. Herein, the synthesis of hollow-porous cobalt-doped In 2 O 3 sensing material with abundant surface oxygen vacancy (SOV) via one-pot and in-situ doping approach is reported. With their rich active sites, the Co-In 2 O 3 exhibits unexpected and high electrostatic adsorption of toluene at 175 °C, which obviously inducing the charge carrier transport. Accordingly, the final Microelectro Mechanical Systems (MEMS) based Co-In 2 O 3 gas sensor exhibits excellent selectivity and response, and toluene detection limits as low as 100 ppb at the lowest temperature so far. Density functional theory (DFT) calculations elucidated that the enhanced electrostatic adsorption is ascribed to the toluene preferentially bound to O 3c atom site (bridging oxygen atom near SOV) on Co-In_b-D 4 (110) surface, which will induce charge carrier accumulation layer and cause temperature-dependent abnormal pseudo p-type response. This work points out that the electrostatic adsorption derived from SOV could obviously modulate SMO sensing properties, and further supplements the defect engineering.

Switchable p-n gas response for 3D-hierarchical NiFe2O4 porous microspheres for highly selective and sensitive toluene gas sensors

Rationally designed gas sensing materials have become essential for modern efficient gas sensor with enhanced performance. This study designed and prepared ordered porous, three-dimensional hierarchical NiFe2O4 (NFO) nanoarchitectures for highly selective and sensitive toluene sensors. Two hierarchical NFO nanostructures including nanospheres and microsphere were fabricated by facile hydrothermal (NFO-Hy) and temperature-programmed calcination (NFO-550), respectively. Physicochemical characterization confirmed structure, composition, and morphology for the as-prepared materials. Nitrogen adsorption-desorption revealed improved surface area and porous properties for NFO-550 compared with NFO-Hy sensing materials, and the NFO-550 sensor achieved the maximum response 5.65 higher than NFO-Hy at optimal operating temperature. Primary analyses for carcinogenic analyte detection suggest NFO as a gas-sensitive material to be potential applicants for real-world toluene gas sensing applications.

Nanostructured Indium Oxide Thin Films as a Room Temperature Toluene Sensor.

Toluene gas is the most toxic and affects the respiratory system of humans, and thereby, its detection at lower levels is an important task. Herein, we report a room temperature-operatable indium oxide-based chemiresistive gas sensor, which detects 50 ppm toluene vapors. Nanocrystalline indium oxide (In2O3) films were sprayed on a pre-cleaned glass substrate using a cost-effective spray pyrolysis method at different substrate temperatures in the range of 350–500 °C. The X-ray diffraction studies confirmed that the sprayed thin films, which were deposited at different substrate temperatures, exhibit a cubic structure. The preferred orientation was aligned along the (222) orientation. Average crystallite size calculation based on the Scherrer formula indicates that the crystallite size increases with the enhancement of substrate temperature. FESEM analysis showed that the indium oxide thin films possess uniform grain distribution, which persists over the entire substrate. As the substrate temperature is increased, a partial agglomeration in the film morphology was observed. The deposited film’s nanostructured nature was confirmed by transmission electron microscopy, and the polycrystalline nature was confirmed from the selected area electron diffraction pattern. Root mean square roughness of the samples was determined from the atomic force microscopy studies. From the Raman spectra, characteristic vibrational modes appeared at 558.61, 802.85, and 1097.18 cm–1 in all the samples, which confirms the cubic structure of indium oxide thin films. Photoluminescence emission spectra have been recorded with an excitation wavelength of 280 nm. The optical band gap was measured using the Tauc plot. The band gap was found to decrease with an increase in the substrate temperature. The gas-sensing performance of indium oxide films sprayed at various substrate temperatures has demonstrated a better response toward 50 ppm toluene gas at room temperature with good stability, and the response and recovery times were determined using a transient response curve.

Field Tests of Smart Mos Gas Sensor Systems for Selective Quantification of VOCs

Field Tests of Smart Mos Gas Sensor Systems for Selective Quantification of VOCs

Hybridization of silicon nanowires with TeO2 branch structures and Pt nanoparticles for highly sensitive and selective toluene sensing

In this study, based on Si NW-TeO2 composites sensitized with Pt nanoparticles (NPs), a novel toluene sensor was fabricated. Dense TeO2 branches formed on the stem of Si NWs, and isolated Pt NPs were dispersed uniformly on the composite surfaces. Several different gases present in exhaled breath (NO2, CO, C6H6, and C7H8) at different concentrations were tested at the optimal working temperature (200 °C). To study the role of Pt sensitization on the gas sensing characteristics of the composites, both Si NW-TeO2 and Si NW-TeO2/Pt composites were tested. Pt-loaded composite was more sensitive to toluene than Pt-deficient one. A sensing mechanism was proposed. Our results indicate that the inexpensive, fast, and easy-to-use sensor described here has the potential to be employed as a medical diagnostics tool, as well as an environmental monitoring tool.

An alternative electrochemical approach for toluene detection with ZnO/MgO/Cr2O3 nanofibers on a glassy carbon electrode for environmental monitoring.

In situ fabrication of a sensitive electrochemical sensor using a wet-chemically prepared ternary ZnO/MgO/Cr2O3 nanofiber (NF)-decorated glassy carbon electrode (GCE) with Nafion adhesive was the approach of this study. The resultant NFs were characterized by various tools, such as powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area analysis, and ultraviolet–visible spectroscopy (UV/Vis). The analytical parameters of the proposed toluene sensor were characterized as follows: good sensitivity (23.89 μA μM−1 cm−2), a lower limit of detection (LOD; 95.59 ± 1.5 pM), a limit of quantification (LOQ; 318.63 ± 2.0 pM), efficient response time (18 s), and the dynamic range (LDR) for toluene detection of 0.1 nM–0.01 mM. The real-time application of the sensor is to protect the environmental ecosystem, as well as the public health from the harmful effects of toluene. In an environmental application, the toluene sensor exhibited good reproducibility, robustness, LOD, LOQ, and good reliability, which are discussed in detail and compared to the literature.

Influence of different carbon allotrope filler on the VOC sensitivity of polymer composite

In this work, both, pristine and hybrid polyisoprene as well as ethylene vinyl acetate copolymer nanocomposites with carbon nanoparticles and carbon nanotubes were developed and studied for their application in toluene sensors. The response to toluene was determined for pristine and hybrid composite samples. Hybrid samples were compared to pristine composite samples and the composite with highest sensing effect is obtained.

Ultraselective Toluene-Gas Sensor: Nanosized Gold Loaded on Zinc Oxide Nanoparticles.

Selectivity is an important parameter of resistive-type gas sensors that use metal oxides. In this study, a highly selective toluene sensor is prepared using highly dispersed gold-nanoparticle-loaded zinc oxide nanoparticles (Au-ZnO NPs). Au-ZnO NPs are synthesized by coprecipitation and calcination at 400 °C with Au loadings of 0.15, 0.5, and 1.5 mol %. The Au NPs on ZnO are about 2-4 nm in size, and exist in a metallic state. Porous gas-sensing layers are fabricated by screen printing. The responses of the sensor to 200 ppm hydrogen, 200 ppm carbon monoxide, 100 ppm ethanol, 100 ppm acetaldehyde, 100 ppm acetone, and 100 ppm toluene are evaluated at 377 °C in a dry atmosphere. The sensor response of 0.15 mol % Au-ZnO NPs to toluene is about 92, whereas its sensor responses to other combustible gases are less than 7. Such selective toluene detection is probably caused by the utilization efficiency of the gas-sensing layer. Gas diffusivity into the sensing layer of Au-ZnO NPs is lowered by the catalytic oxidation of combustible gases during their diffusion through the layer. The present approach is an effective way to improve the selectivity of resistive-type gas sensors.

Development of engineered sensor perceiving gaseous toluene signal in the cyanobacterium Synechocystis sp. PCC 6803

Microalgae have been used to produce useful compounds. In many cases in which target compounds are produced from CO2 via photosynthesis, there is a trade-off between the proliferation of cells and the production of the target compounds. This is due to carbon partitioning between the synthesis of cellular components and the target compounds, and/or the toxicity of the target products. Therefore, there is a requirement to develop a gene switch that can modulate the metabolism from the growth phase of cells to the production phase of the target molecules. In this study, we attempted to develop an artificial sensory protein that can respond to insoluble gaseous compounds and regulate gene expression in the model cyanobacterium Synechocystis sp. PCC 6803. We constructed a chimeric histidine kinase by fusing the signal input domain of TodS, a toluene sensor from Pseudomonas putida, and the kinase domain of SphS, a phosphate-deficient sensor from Synechocystis. Because TodS contains two kinase domains, we substituted either of the kinase domains of TodS with the kinase domain of SphS to obtain TodSS_SphS and TodSL_SphS. We introduced a gene for the chimeric sensor to Synechocystis cells and evaluated their response to toluene by measuring alkaline phosphatase (AP) activity and phoA mRNA expression. Although the cells harboring TodSL_SphS did not exhibit AP activity, both in the presence or absence of toluene, the cells harboring TodSS_SphS accumulated the transcript of the phoA gene after 5-h exposure to toluene, and only exhibited AP activity after exposure to toluene.

Amplifying the Signal of Metal Oxide Gas Sensors for Low Concentration Gas Detection

Nowadays, detection of trace concentration gases is still challenging for portable sensors, especially for the low-cost and easily operated metal-oxide-semiconductor (MOX) gas sensors. In this paper, a widely applicable amplification circuit is designed and fabricated to evidently enhance the signal of the MOX sensors by adding a field effect transistor (FET) into the conventional circuits. By optimizing the FET parameters and the loading resistance, this amplification circuit enables the commercial Figaro TGS2602 toluene sensors response effectively to the highest permissive limit (0.26 ppm) of toluene in indoor air of cars, with the detection limit of ~0.1 ppm. Furthermore, this circuit can also make the commercial Hanwei MP502 acetone sensors and MQ3 ethanol sensors response to the 1-2-ppm acetone in breath of diabetes and 2-ppm ethanol for fast and effectively drinker driver screening. The mechanism is investigated to be the gate voltage induced resistance change of the FET, with the highest theoretically estimated and experimentally measured magnification factor of 5-6. This FET amplifier can effectively enable the ppm level commercial MOX sensors response to sub-ppm level gases, promising for MOX gas sensor integration and also for other kind of resistive sensors.

Using Synthetic Biology methods to construct a rapid and efficient estrogen biosensor

Synthetic Biology demonstrates the integral relationship between biology, chemistry, mathematics and computer science. The field provides innovative approaches to a wide range of applications, such as bioremediation, sustainable energy production and biomedical therapies. Synthetic biology involves construction of genetic circuits when DNA sequences are modified to include standard restriction enzyme sites making the DNA sequences interchangeable and allowing for construction of a variety of circuits. New tools and devices are constantly needed to enhance the already extensive list of BioBricks housed at the Registry of Standard Biological Parts. As proof of concept we constructed a new BioBricks based on the toluene sensor built by Stiner and Haverson (AEM, 2002) in Pseudomonas. Toluene is an environmental contaminant that is the byproduct of oil contamination. Biosensors generated from BioBrick parts yield more affordable, transportable, and faster methods of pollutant detection. The tbuT cassette from Stiner and Haverson's work was digested with XbaI and SpeI sites then ligated with the GFP reporter gene and cloned into iGEM BioBrick vectors in order to create a biosensor in Escherichia coli. These BioBricks can be readily used with a variety of reporter genes to create new versions of the biosensor. We expanded our biosensor construction to create a dual functional estrogen sensitive BioBrick. The presence of estrogenic compounds (endocrine‐disruptors, EDCs) in the water supply raises concerns about human and aquatic health. Current methods for detecting estrogen contamination require expensive, time‐consuming techniques such as liquid chromatography‐mass spectrometry and high performance liquid chromatography. Previously reported estrogen biosensors required multiple cloning and transformation steps for successful detection in bacteria. Our estrogen responsive plasmid contains parts that allow for both the constitutive expression of the estrogen receptor followed by an estrogen response element toggled to a reporter gene in a single vector. When the estrogen response element is activated the reporter gene, red fluorescent protein, will produce a color change in E.coli. We will present data demonstrating the efficiency of this dual‐functional biosensor and it effectiveness for estrogenic compounds in contaminated water.Support or Funding InformationNSF grant #NSF‐GPG‐1444406, GPG: Research Collaboration: REU Pilot: Synthetic Biology Boot camp