Sensors

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1864 KiB

Open AccessArticle

Experimental Artifacts for Morphological Tweaking of Chemical Sensor Materials: Studies on ZnO

by Ikram Ul Haq and Abdul-Majeed Azad

Sensors 2012, 12(6), 8259-8277; https://doi.org/10.3390/s120608259 - 13 Jun 2012

Cited by 10 | Viewed by 9042

Abstract

Sensing mechanisms of gases on solid structures are predominantly surface-dominated. Benign surface features in terms of small grain size, high aspect ratio, large surface area and open and connected porosity, are required to realize a successful sensor material. Such morphological artifacts are a [...] Read more.

Sensing mechanisms of gases on solid structures are predominantly surface-dominated. Benign surface features in terms of small grain size, high aspect ratio, large surface area and open and connected porosity, are required to realize a successful sensor material. Such morphological artifacts are a function of the fabrication and processing techniques employed. In this paper, we describe the fabrication of monoshaped and monosized zinc oxide (ZnO) particles by a homogeneous precipitation method, using urea and/or hexmethyltetraamine as the reductant. The effect of operating conditions and experimental variables, such as the relative concentration of the precursors, temperature, and the aging time on the morphology of the resulting particles was studied systematically. These experimental parameters were optimized in order to achieve particles of uniform morphology and of narrow size distribution. Some of these particles were employed for the detection of ammonia gas at room temperature. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1413 KiB

Open AccessArticle

Thermal and Optical Activation Mechanisms of Nanospring-Based Chemiresistors

by Vladimir Dobrokhotov, Landon Oakes, Dewayne Sowell, Alexander Larin, Jessica Hall, Alexander Barzilov, Alex Kengne, Pavel Bakharev, Giancarlo Corti, Timothy Cantrell, Tej Prakash, Joseph Williams, Leah Bergman, Jesse Huso and David McIlroy

Sensors 2012, 12(5), 5608-5622; https://doi.org/10.3390/s120505608 - 2 May 2012

Cited by 18 | Viewed by 8468

Abstract

Chemiresistors (conductometric sensor) were fabricated on the basis of novel nanomaterials—silica nanosprings ALD coated with ZnO. The effects of high temperature and UV illumination on the electronic and gas sensing properties of chemiresistors are reported. For the thermally activated chemiresistors, a discrimination mechanism [...] Read more.

Chemiresistors (conductometric sensor) were fabricated on the basis of novel nanomaterials—silica nanosprings ALD coated with ZnO. The effects of high temperature and UV illumination on the electronic and gas sensing properties of chemiresistors are reported. For the thermally activated chemiresistors, a discrimination mechanism was developed and an integrated sensor-array for simultaneous real-time resistance scans was built. The integrated sensor response was tested using linear discriminant analysis (LDA). The distinguished electronic signatures of various chemical vapors were obtained at ppm level. It was found that the recovery rate at high temperature drastically increases upon UV illumination. The feasibility study of the activation method by UV illumination at room temperature was conducted. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1668 KiB

Open AccessCommunication

Dynamic Sensing of Localized Corrosion at the Metal/Solution Interface

by Wei Li, Boyu Yuan, Chao Wang, Liang Li and Shenhao Chen

Sensors 2012, 12(4), 4962-4973; https://doi.org/10.3390/s120404962 - 18 Apr 2012

Cited by 3 | Viewed by 6620

Abstract

A Mach-Zehnder interferometer is employed to detect localized corrosion at the metal/solution interface in the potentiodynamic sweep of the iron electrode in solutions. During the electrochemical reactions, local variations of the electrolyte’s refractive index, which correlate with the concentration of dissolved species, change [...] Read more.

A Mach-Zehnder interferometer is employed to detect localized corrosion at the metal/solution interface in the potentiodynamic sweep of the iron electrode in solutions. During the electrochemical reactions, local variations of the electrolyte’s refractive index, which correlate with the concentration of dissolved species, change the optical path length (OPL) of the object beam when the beam passes through the electrolyte. The distribution of the OPL difference was obtained to present the concentration change of the metal ions visually, which enable direct evidence of corrosion processes. The OPL difference distribution shows localized and general corrosion during the anodic dissolution of the iron electrode in solutions with and without chloride ions, respectively. This method provides an approach for dynamic detection of localized corrosion at the metal/solution interface. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1839 KiB

Open AccessArticle

Nanocharacterization of Soft Biological Samples in Shear Mode with Quartz Tuning Fork Probes

by Jorge Otero, Laura Gonzalez and Manel Puig-Vidal

Sensors 2012, 12(4), 4803-4819; https://doi.org/10.3390/s120404803 - 12 Apr 2012

Cited by 21 | Viewed by 9151

Abstract

Quartz tuning forks are extremely good resonators and their use is growing in scanning probe microscopy. Nevertheless, only a few studies on soft biological samples have been reported using these probes. In this work, we present the methodology to develop and use these [...] Read more.

Quartz tuning forks are extremely good resonators and their use is growing in scanning probe microscopy. Nevertheless, only a few studies on soft biological samples have been reported using these probes. In this work, we present the methodology to develop and use these nanosensors to properly work with biological samples. The working principles, fabrication and experimental setup are presented. The results in the nanocharacterization of different samples in different ambients are presented by using different working modes: amplitude modulation with and without the use of a Phase-Locked Loop (PLL) and frequency modulation. Pseudomonas aeruginosa bacteria are imaged in nitrogen using amplitude modulation. Microcontact printed antibodies are imaged in buffer using amplitude modulation with a PLL. Finally, metastatic cells are imaged in air using frequency modulation. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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631 KiB

Open AccessArticle

Template Free Synthesis of Hollow Ball-Like Nano-Fe₂O₃ and Its Application to the Detection of Dimethyl Methylphosphonate at Room Temperature

by Guokang Fan, You Wang, Meng Hu, Zhiyuan Luo, Kaihuan Zhang and Guang Li

Sensors 2012, 12(4), 4594-4604; https://doi.org/10.3390/s120404594 - 10 Apr 2012

Cited by 15 | Viewed by 6823

Abstract

This paper is focused on the template-free synthesis of nanosized ferric oxide (nano-Fe₂O₃) and its application in quartz crystal microbalance (QCM) resonators to detect dimethyl methylphosphonate (DMMP), a simulant of Sarin. The X-ray diffraction (XRD) patterns confirm that the [...] Read more.

This paper is focused on the template-free synthesis of nanosized ferric oxide (nano-Fe₂O₃) and its application in quartz crystal microbalance (QCM) resonators to detect dimethyl methylphosphonate (DMMP), a simulant of Sarin. The X-ray diffraction (XRD) patterns confirm that the synthesized samples are made of Fe₂O₃ and the scanning electron microscopy (SEM) pictures show that the samples have ball-like shapes. The DMMP sensors with a sensing film of hollow ball-like and solid ball-like Fe₂O₃ are fabricated and their sensing characteristics are compared. The sensitivity of the hollow ball-like Fe₂O₃ sensor is more than 500% higher than the one of the solid ball-like Fe₂O₃ sensor. The hollow ball-like nano-Fe₂O₃ can be synthesized by a novel low temperature hydrothermal method. The sensors with the hollow ball-like Fe₂O₃ film perform well in a range of 1 to 6 ppm, with a sensitivity of 29 Hz/ppm at room temperature, while the appropriate recoverability and selectivity are maintained. In addition, the performance of different thicknesses of the sensing film of the hollow ball-like nano-Fe₂O₃ is investigated and the optimized relative film thickness of the hollow ball-like nano-Fe₂O₃is found to be 20 μg/mm². Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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374 KiB

Open AccessArticle

A CMOS-Compatible Poly-Si Nanowire Device with Hybrid Sensor/Memory Characteristics for System-on-Chip Applications

by Min-Cheng Chen, Hao-Yu Chen, Chia-Yi Lin, Chao-Hsin Chien, Tsung-Fan Hsieh, Jim-Tong Horng, Jian-Tai Qiu, Chien-Chao Huang, Chia-Hua Ho and Fu-Liang Yang

Sensors 2012, 12(4), 3952-3963; https://doi.org/10.3390/s120403952 - 26 Mar 2012

Cited by 27 | Viewed by 8835

Abstract

This paper reports a versatile nano-sensor technology using “top-down” poly-silicon nanowire field-effect transistors (FETs) in the conventional Complementary Metal-Oxide Semiconductor (CMOS)-compatible semiconductor process. The nanowire manufacturing technique reduced nanowire width scaling to 50 nm without use of extra lithography equipment, and exhibited superior [...] Read more.

This paper reports a versatile nano-sensor technology using “top-down” poly-silicon nanowire field-effect transistors (FETs) in the conventional Complementary Metal-Oxide Semiconductor (CMOS)-compatible semiconductor process. The nanowire manufacturing technique reduced nanowire width scaling to 50 nm without use of extra lithography equipment, and exhibited superior device uniformity. These n type polysilicon nanowire FETs have positive pH sensitivity (100 mV/pH) and sensitive deoxyribonucleic acid (DNA) detection ability (100 pM) at normal system operation voltages. Specially designed oxide-nitride-oxide buried oxide nanowire realizes an electrically V_th-adjustable sensor to compensate device variation. These nanowire FETs also enable non-volatile memory application for a large and steady V_th adjustment window (>2 V Programming/Erasing window). The CMOS-compatible manufacturing technique of polysilicon nanowire FETs offers a possible solution for commercial System-on-Chip biosensor application, which enables portable physiology monitoring and in situ recording. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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384 KiB

Open AccessArticle

TiO₂ Nanotube Array Sensor for Detecting the SF₆ Decomposition Product SO₂

by Xiaoxing Zhang, Jinbin Zhang, Yichao Jia, Peng Xiao and Ju Tang

Sensors 2012, 12(3), 3302-3313; https://doi.org/10.3390/s120303302 - 7 Mar 2012

Cited by 117 | Viewed by 9666

Abstract

The detection of partial discharge through analysis of SF₆ gas components in gas-insulated switchgear, is significant for the diagnosis and assessment of the operating state of power equipment. The present study proposes the use of a TiO₂ nanotube array sensor for [...] Read more.

The detection of partial discharge through analysis of SF₆ gas components in gas-insulated switchgear, is significant for the diagnosis and assessment of the operating state of power equipment. The present study proposes the use of a TiO₂ nanotube array sensor for detecting the SF₆ decomposition product SO₂, and the application of the anodic oxidation method for the directional growth of highly ordered TiO₂ nanotube arrays. The sensor response of 10–50 ppm SO₂ gas is tested, and the sensitive response mechanism is discussed. The test results show that the TiO₂ nanotube sensor array has good response to SO₂ gas, and by ultraviolet radiation, the sensor can remove attached components very efficiently, shorten recovery time, reduce chemical poisoning, and prolong the life of the components. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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455 KiB

Open AccessArticle

Investigation of the Carbon Monoxide Gas Sensing Characteristics of Tin Oxide Mixed Cerium Oxide Thin Films

by Sardar M. A. Durrani, Mohammad F. Al-Kuhaili, Imran A. Bakhtiari and Muhammad B. Haider

Sensors 2012, 12(3), 2598-2609; https://doi.org/10.3390/s120302598 - 27 Feb 2012

Cited by 56 | Viewed by 8804

Abstract

Thin films of tin oxide mixed cerium oxide were grown on unheated substrates by physical vapor deposition. The films were annealed in air at 500 °C for two hours, and were characterized using X-ray photoelectron spectroscopy, atomic force microscopy and optical spectrophotometry. X-ray [...] Read more.

Thin films of tin oxide mixed cerium oxide were grown on unheated substrates by physical vapor deposition. The films were annealed in air at 500 °C for two hours, and were characterized using X-ray photoelectron spectroscopy, atomic force microscopy and optical spectrophotometry. X-ray photoelectron spectroscopy and atomic force microscopy results reveal that the films were highly porous and porosity of our films was found to be in the range of 11.6–21.7%. The films were investigated for the detection of carbon monoxide, and were found to be highly sensitive. We found that 430 °C was the optimum operating temperature for sensing CO gas at concentrations as low as 5 ppm. Our sensors exhibited fast response and recovery times of 26 s and 30 s, respectively. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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958 KiB

Open AccessArticle

Integrating Metal-Oxide-Decorated CNT Networks with a CMOS Readout in a Gas Sensor

by Hyunjoong Lee, Sanghoon Lee, Dai-Hong Kim, David Perello, Young June Park, Seong-Hyeon Hong, Minhee Yun and Suhwan Kim

Sensors 2012, 12(3), 2582-2597; https://doi.org/10.3390/s120302582 - 27 Feb 2012

Cited by 16 | Viewed by 7861

Abstract

We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. [...] Read more.

We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 µm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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965 KiB

Open AccessArticle

Optimizing SOI Slot Waveguide Fabrication Tolerances and Strip-Slot Coupling for Very Efficient Optical Sensing

by Vittorio M. N. Passaro and Mario La Notte

Sensors 2012, 12(3), 2436-2455; https://doi.org/10.3390/s120302436 - 23 Feb 2012

Cited by 52 | Viewed by 12116

Abstract

Slot waveguides are becoming more and more attractive optical components, especially for chemical and bio-chemical sensing. In this paper an accurate analysis of slot waveguide fabrication tolerances is carried out, in order to find optimum design criteria for either homogeneous or absorption sensing [...] Read more.

Slot waveguides are becoming more and more attractive optical components, especially for chemical and bio-chemical sensing. In this paper an accurate analysis of slot waveguide fabrication tolerances is carried out, in order to find optimum design criteria for either homogeneous or absorption sensing mechanisms, in cases of low and high aspect ratio slot waveguides. In particular, we have focused on Silicon On Insulator (SOI) technology, representing the most popular technology for this kind of devices, simultaneously achieving high integration capabilities, small dimensions and low cost. An accurate analysis of single mode behavior for high aspect ratio slot waveguide has been also performed, in order to provide geometric limits for waveguide design purposes. Finally, the problem of coupling into a slot waveguide is addressed and a very compact and efficient slot coupler is proposed, whose geometry has been optimized to give a strip-slot-strip coupling efficiency close to 100%. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1248 KiB

Open AccessArticle

Design of Selective Gas Sensors Using Additive-Loaded In₂O₃ Hollow Spheres Prepared by Combinatorial Hydrothermal Reactions

by Sun-Jung Kim, In-Sung Hwang, Yun Chan Kang and Jong-Heun Lee

Sensors 2011, 11(11), 10603-10614; https://doi.org/10.3390/s111110603 - 7 Nov 2011

Cited by 54 | Viewed by 8467

Abstract

A combinatorial hydrothermal reaction has been used to prepare pure and additive (Sb, Cu, Nb, Pd, and Ni)-loaded In₂O₃ hollow spheres for gas sensor applications. The operation of Pd- and Cu-loaded In₂O₃ sensors at 371 °C leads [...] Read more.

A combinatorial hydrothermal reaction has been used to prepare pure and additive (Sb, Cu, Nb, Pd, and Ni)-loaded In₂O₃ hollow spheres for gas sensor applications. The operation of Pd- and Cu-loaded In₂O₃ sensors at 371 °C leads to selective H₂S detection. Selective detection of CO and NH₃ was achieved by the Ni-In₂O₃ sensor at sensing temperatures of 371 and 440 °C, respectively. The gas responses of six different sensors to NH₃, H₂S, H₂, CO and CH₄ produced unique gas sensing patterns that can be used for the artificial recognition of these gases. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1972 KiB

Open AccessArticle

Design of Highly Sensitive C₂H₅OH Sensors Using Self-Assembled ZnO Nanostructures

by Kang-Min Kim, Hae-Ryong Kim, Kwon-Il Choi, Hyo-Joong Kim and Jong-Heun Lee

Sensors 2011, 11(10), 9685-9699; https://doi.org/10.3390/s111009685 - 12 Oct 2011

Cited by 12 | Viewed by 9506

Abstract

Various ZnO nanostructures such as porous nanorods and two hierarchical structures consisting of porous nanosheets or crystalline nanorods were prepared by the reaction of mixtures of oleic-acid-dissolved ethanol solutions and aqueous dissolved Zn-precursor solutions in the presence of NaOH. All three ZnO nanostructures [...] Read more.

Various ZnO nanostructures such as porous nanorods and two hierarchical structures consisting of porous nanosheets or crystalline nanorods were prepared by the reaction of mixtures of oleic-acid-dissolved ethanol solutions and aqueous dissolved Zn-precursor solutions in the presence of NaOH. All three ZnO nanostructures showed sensitive and selective detection of C₂H₅OH. In particular, ultra-high responses (R_a/R_g = ~1,200, R_a: resistance in air, R_g: resistance in gas) to 100 ppm C₂H₅OH was attained using porous nanorods and hierarchical structures assembled from porous nanosheets, which is one of the highest values reported in the literature. The gas response and linearity of gas sensors were discussed in relation to the size, surface area, and porosity of the nanostructures. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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Review

Jump to: Research

1384 KiB

Open AccessReview

Gas Sensors Based on One Dimensional Nanostructured Metal-Oxides: A Review

by M. M. Arafat, B. Dinan, Sheikh A. Akbar and A. S. M. A. Haseeb

Sensors 2012, 12(6), 7207-7258; https://doi.org/10.3390/s120607207 - 30 May 2012

Cited by 527 | Viewed by 27348

Abstract

Recently one dimensional (1-D) nanostructured metal-oxides have attracted much attention because of their potential applications in gas sensors. 1-D nanostructured metal-oxides provide high surface to volume ratio, while maintaining good chemical and thermal stabilities with minimal power consumption and low weight. In recent [...] Read more.

Recently one dimensional (1-D) nanostructured metal-oxides have attracted much attention because of their potential applications in gas sensors. 1-D nanostructured metal-oxides provide high surface to volume ratio, while maintaining good chemical and thermal stabilities with minimal power consumption and low weight. In recent years, various processing routes have been developed for the synthesis of 1-D nanostructured metal-oxides such as hydrothermal, ultrasonic irradiation, electrospinning, anodization, sol-gel, molten-salt, carbothermal reduction, solid-state chemical reaction, thermal evaporation, vapor-phase transport, aerosol, RF sputtering, molecular beam epitaxy, chemical vapor deposition, gas-phase assisted nanocarving, UV lithography and dry plasma etching. A variety of sensor fabrication processing routes have also been developed. Depending on the materials, morphology and fabrication process the performance of the sensor towards a specific gas shows a varying degree of success. This article reviews and evaluates the performance of 1-D nanostructured metal-oxide gas sensors based on ZnO, SnO₂, TiO₂, In₂O₃, WO_x, AgVO₃, CdO, MoO₃, CuO, TeO₂ and Fe₂O₃. Advantages and disadvantages of each sensor are summarized, along with the associated sensing mechanism. Finally, the article concludes with some future directions of research. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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802 KiB

Open AccessReview

A Critical Review of Glucose Biosensors Based on Carbon Nanomaterials: Carbon Nanotubes and Graphene

by Zhigang Zhu, Luis Garcia-Gancedo, Andrew J. Flewitt, Huaqing Xie, Francis Moussy and William I. Milne

Sensors 2012, 12(5), 5996-6022; https://doi.org/10.3390/s120505996 - 10 May 2012

Cited by 480 | Viewed by 28739

Abstract

There has been an explosion of research into the physical and chemical properties of carbon-based nanomaterials, since the discovery of carbon nanotubes (CNTs) by Iijima in 1991. Carbon nanomaterials offer unique advantages in several areas, like high surface-volume ratio, high electrical conductivity, chemical [...] Read more.

There has been an explosion of research into the physical and chemical properties of carbon-based nanomaterials, since the discovery of carbon nanotubes (CNTs) by Iijima in 1991. Carbon nanomaterials offer unique advantages in several areas, like high surface-volume ratio, high electrical conductivity, chemical stability and strong mechanical strength, and are thus frequently being incorporated into sensing elements. Carbon nanomaterial-based sensors generally have higher sensitivities and a lower detection limit than conventional ones. In this review, a brief history of glucose biosensors is firstly presented. The carbon nanotube and grapheme-based biosensors, are introduced in Sections 3 and 4, respectively, which cover synthesis methods, up-to-date sensing approaches and nonenzymatic hybrid sensors. Finally, we briefly outline the current status and future direction for carbon nanomaterials to be used in the sensing area. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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Graphical abstract

2602 KiB

Open AccessReview

Time-Domain Fluorescence Lifetime Imaging Techniques Suitable for Solid-State Imaging Sensor Arrays

by David Day-Uei Li, Simon Ameer-Beg, Jochen Arlt, David Tyndall, Richard Walker, Daniel R. Matthews, Viput Visitkul, Justin Richardson and Robert K. Henderson

Sensors 2012, 12(5), 5650-5669; https://doi.org/10.3390/s120505650 - 2 May 2012

Cited by 53 | Viewed by 10344

Abstract

We have successfully demonstrated video-rate CMOS single-photon avalanche diode (SPAD)-based cameras for fluorescence lifetime imaging microscopy (FLIM) by applying innovative FLIM algorithms. We also review and compare several time-domain techniques and solid-state FLIM systems, and adapt the proposed algorithms for massive CMOS SPAD-based [...] Read more.

We have successfully demonstrated video-rate CMOS single-photon avalanche diode (SPAD)-based cameras for fluorescence lifetime imaging microscopy (FLIM) by applying innovative FLIM algorithms. We also review and compare several time-domain techniques and solid-state FLIM systems, and adapt the proposed algorithms for massive CMOS SPAD-based arrays and hardware implementations. The theoretical error equations are derived and their performances are demonstrated on the data obtained from 0.13 μm CMOS SPAD arrays and the multiple-decay data obtained from scanning PMT systems. In vivo two photon fluorescence lifetime imaging data of FITC-albumin labeled vasculature of a P22 rat carcinosarcoma (BD9 rat window chamber) are used to test how different algorithms perform on bi-decay data. The proposed techniques are capable of producing lifetime images with enough contrast. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1395 KiB

Open AccessReview

Hydrogen Gas Sensors Based on Semiconductor Oxide Nanostructures

by Haoshuang Gu, Zhao Wang and Yongming Hu

Sensors 2012, 12(5), 5517-5550; https://doi.org/10.3390/s120505517 - 30 Apr 2012

Cited by 385 | Viewed by 25053

Abstract

Recently, the hydrogen gas sensing properties of semiconductor oxide (SMO) nanostructures have been widely investigated. In this article, we provide a comprehensive review of the research progress in the last five years concerning hydrogen gas sensors based on SMO thin film and one-dimensional [...] Read more.

Recently, the hydrogen gas sensing properties of semiconductor oxide (SMO) nanostructures have been widely investigated. In this article, we provide a comprehensive review of the research progress in the last five years concerning hydrogen gas sensors based on SMO thin film and one-dimensional (1D) nanostructures. The hydrogen sensing mechanism of SMO nanostructures and some critical issues are discussed. Doping, noble metal-decoration, heterojunctions and size reduction have been investigated and proved to be effective methods for improving the sensing performance of SMO thin films and 1D nanostructures. The effect on the hydrogen response of SMO thin films and 1D nanostructures of grain boundary and crystal orientation, as well as the sensor architecture, including electrode size and nanojunctions have also been studied. Finally, we also discuss some challenges for the future applications of SMO nanostructured hydrogen sensors. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1457 KiB

Open AccessReview

Exploitation of Unique Properties of Zeolites in the Development of Gas Sensors

by Yangong Zheng, Xiaogan Li and Prabir K. Dutta

Sensors 2012, 12(4), 5170-5194; https://doi.org/10.3390/s120405170 - 20 Apr 2012

Cited by 87 | Viewed by 14983

Abstract

The unique properties of microporous zeolites, including ion-exchange properties, adsorption, molecular sieving, catalysis, conductivity have been exploited in improving the performance of gas sensors. Zeolites have been employed as physical and chemical filters to improve the sensitivity and selectivity of gas sensors. In [...] Read more.

The unique properties of microporous zeolites, including ion-exchange properties, adsorption, molecular sieving, catalysis, conductivity have been exploited in improving the performance of gas sensors. Zeolites have been employed as physical and chemical filters to improve the sensitivity and selectivity of gas sensors. In addition, direct interaction of gas molecules with the extraframework cations in the nanoconfined space of zeolites has been explored as a basis for developing new impedance-type gas/vapor sensors. In this review, we summarize how these properties of zeolites have been used to develop new sensing paradigms. There is a considerable breadth of transduction processes that have been used for zeolite incorporated sensors, including frequency measurements, optical and the entire gamut of electrochemical measurements. It is clear from the published literature that zeolites provide a route to enhance sensor performance, and it is expected that commercial manifestation of some of the approaches discussed here will take place. The future of zeolite-based sensors will continue to exploit its unique properties and use of other microporous frameworks, including metal organic frameworks. Zeolite composites with electronic materials, including metals will lead to new paradigms in sensing. Use of nano-sized zeolite crystals and zeolite membranes will enhance sensor properties and make possible new routes of miniaturized sensors. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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588 KiB

Open AccessReview

New Trends in Impedimetric Biosensors for the Detection of Foodborne Pathogenic Bacteria

by Yixian Wang, Zunzhong Ye and Yibin Ying

Sensors 2012, 12(3), 3449-3471; https://doi.org/10.3390/s120303449 - 12 Mar 2012

Cited by 228 | Viewed by 17612

Abstract

The development of a rapid, sensitive, specific method for the foodborne pathogenic bacteria detection is of great importance to ensure food safety and security. In recent years impedimetric biosensors which integrate biological recognition technology and impedance have gained widespread application in the field [...] Read more.

The development of a rapid, sensitive, specific method for the foodborne pathogenic bacteria detection is of great importance to ensure food safety and security. In recent years impedimetric biosensors which integrate biological recognition technology and impedance have gained widespread application in the field of bacteria detection. This paper presents an overview on the progress and application of impedimetric biosensors for detection of foodborne pathogenic bacteria, particularly the new trends in the past few years, including the new specific bio-recognition elements such as bacteriophage and lectin, the use of nanomaterials and microfluidics techniques. The applications of these new materials or techniques have provided unprecedented opportunities for the development of high-performance impedance bacteria biosensors. The significant developments of impedimetric biosensors for bacteria detection in the last five years have been reviewed according to the classification of with or without specific bio-recognition element. In addition, some microfluidics systems, which were used in the construction of impedimetric biosensors to improve analytical performance, are introduced in this review. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1138 KiB

Open AccessReview

Size Matters: Problems and Advantages Associated with Highly Miniaturized Sensors

by Andreas B. Dahlin

Sensors 2012, 12(3), 3018-3036; https://doi.org/10.3390/s120303018 - 6 Mar 2012

Cited by 80 | Viewed by 9994

Abstract

There is no doubt that the recent advances in nanotechnology have made it possible to realize a great variety of new sensors with signal transduction mechanisms utilizing physical phenomena at the nanoscale. Some examples are conductivity measurements in nanowires, deflection of cantilevers and [...] Read more.

There is no doubt that the recent advances in nanotechnology have made it possible to realize a great variety of new sensors with signal transduction mechanisms utilizing physical phenomena at the nanoscale. Some examples are conductivity measurements in nanowires, deflection of cantilevers and spectroscopy of plasmonic nanoparticles. The fact that these techniques are based on the special properties of nanostructural entities provides for extreme sensor miniaturization since a single structural unit often can be used as transducer. This review discusses the advantages and problems with such small sensors, with focus on biosensing applications and label-free real-time analysis of liquid samples. Many aspects of sensor design are considered, such as thermodynamic and diffusion aspects on binding kinetics as well as multiplexing and noise issues. Still, all issues discussed are generic in the sense that the conclusions apply to practically all types of surface sensitive techniques. As a counterweight to the current research trend, it is argued that in many real world applications, better performance is achieved if the active sensor is larger than that in typical nanosensors. Although there are certain specific sensing applications where nanoscale transducers are necessary, it is argued herein that this represents a relatively rare situation. Instead, it is suggested that sensing on the microscale often offers a good compromise between utilizing some possible advantages of miniaturization while avoiding the complications. This means that ensemble measurements on multiple nanoscale sensors are preferable instead of utilizing a single transducer entity. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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1637 KiB

Open AccessReview

Metal Oxide Nanostructures and Their Gas Sensing Properties: A Review

by Yu-Feng Sun, Shao-Bo Liu, Fan-Li Meng, Jin-Yun Liu, Zhen Jin, Ling-Tao Kong and Jin-Huai Liu

Sensors 2012, 12(3), 2610-2631; https://doi.org/10.3390/s120302610 - 27 Feb 2012

Cited by 995 | Viewed by 37157

Abstract

Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure [...] Read more.

Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called “small size effect”, yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them. In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion. Besides, doping is also an effective method to decrease particle size and improve gas sensing properties. Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article. The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given. Full article

(This article belongs to the Special Issue Sensing at the Nano-Scale: Chemical and Bio-Sensing)

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