This review paper encompasses a detailed study of semiconductor metal oxide (SMO) gas sensors. It provides for a detailed comparison of SMO gas sensors with other gas sensors, especially for ammonia gas sensing. Different parameters which affect the performance (sensitivity, selectivity and stability) of SMO gas sensors are discussed here under. This paper also gives an insight about the dopant or impurity induced variations in the SMO materials used for gas sensing. It is concluded that dopants enhance the properties of SMOs for gas sensing applications by changing their microstructure and morphology, activation energy, electronic structure or band gap of the metal oxides. In some cases, dopants create defects in SMOs by generating oxygen vacancy or by forming solid solutions. These defects enhance the gas sensing properties. Different nanostructures (nanowires, nanotubes, heterojunctions), other than nanopowders have also been studied in this review. At the end, examples of SMOs are given to illustrate the potential use of different SMO materials for gas sensing.

Semiconductor metal oxide gas sensors: A review

Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

Nanostructured Materials for Room-Temperature Gas Sensors

https://cyberleninka.org/article/n/1272461.pdf

Synthesis and characterization of conducting polyaniline nanocomposites containing ZnO nanorods

Epoxy/polyaniline–ZnO nanorods hybrid nanocomposite coatings: Synthesis, characterization and corrosion protection performance of conducting paints

Due to the synergetic or complementary effects between organic and inorganic components, which could result in improved properties or performances, the organic/inorganic hybrid materials have recently gained extensive interest in many fields. Up to date, many reports have been published based on the organic/inorganic hybrid materials for the sensor applications. The paper provided a comprehensive review about recent progress of the organic/inorganic hybrid sensors. The organic/inorganic hybrid sensing materials could be fabricated in several configuration types such as intercalating type, core–shell type, coating type and mixed type. The sensing form of the hybrid sensors could be presented in thin-film, thick-film or pellet form, and the sensing performances could by measured in the flowing or static-state system. The hybrid sensing materials have been applied in gas sensors, humidity sensors, ultraviolet sensors, strain sensors, electrochemical immunosensors and fluorescent chemosensors. Finally, several suggestions related to future development of organic/inorganic hybrid sensing materials were also made.

Organic/inorganic hybrid sensors: A review

Thin films of tin oxide-intercalated polyaniline nanocomposite have been deposited at room temperature, through solution route technique. The as-grown films were studied for some of the useful physicochemical properties, making use of XRD, FTIR, SEM, etc. and optical methods. XRD studies showed peak broadening and the peak positions shift from standard values, indicating presence of tin oxide in nanoparticles form in the polyaniline (PANI) matrix. FTIR study shows presence of the Sn–O–Sn vibrational peak and characteristic vibrational peaks of PANI. Study of SEM micrograph revealed that the composite particles have irregular shape and size with micellar templates of PANI around them. AFM images show topographical features of the nanocomposite similar to SEM images but at higher resolution. Optical absorbance studies show shifting of the characteristics peaks for PANI, which may be due to presence of tin oxide in PANI matrix. On exposure to ammonia gas (100–500 ppm in air) at room temperature, it was found that the PANI film resistance increases, while that of the nanocomposite (PANI + SnO2) film decreases from the respective unexposed value. These changes on removal of ammonia gas are reversible in nature, and the composite films showed good sensitivity with relatively faster response/recovery time. © 2009 Elsevier B.V. All rights reserved.

Studies on tin oxide-intercalated polyaniline nanocomposite for ammonia gas sensing applications

A multifunctional microfluidic cartridge for electrochemical biosensing (μCEB) was developed with a cleanroom-free rapid prototyping technique. A seven-layered μCEB platform including a gold (Au) electrode substrate was fabricated by alternating patterned thin plastic and adhesive films. To provide conformal bonding between layers, pressure sensitive adhesive (PSA) tape was adopted to fabricate a leak-free, porous membranes embedded μCEB platform compatible with relatively high flow rates. In addition, the embedded porous membranes provide multiple functions in the μCEB device, including (1) controlling fluid flow, (2) storing a dried detergent, and (3) trapping liquid waste. To demonstrate the utility of the μCEB, we performed an electrochemical-based immunoassay to detect various concentrations of Creatine Kinase (CK)-Myocardial Band (MB). During the immunoassay, the membranes controlled the flow path to minimize a carryover between the assay steps and released the stored dried-reagent to remove non-specifically bound detection antibodies. With a linear sweep voltammetry (LSV) electrochemical sensing technique, a limit of detection of 0.25 ng mL−1 was achieved. The multilayered prototyping technique enables rapid and low-cost fabrication of multifunctional microfluidic electrochemical devices with single-use sample processing components.

Rapid prototyping of multifunctional microfluidic cartridges for electrochemical biosensing platforms

A sample analysis cartridge and a sample cartridge reader are provided. In measuring a particular component included in a sample flowing in a microfluidic channel, a numerical value of hematocrit is reflected to thus improve the accuracy of measurement of the particular component.

Sample analysis cartridge and sample analysis cartridge reader

We present dual-mode, on-demand droplet routing in a multiple-outlet microfluidic device using an oil-based magnetic fluid. Magnetite (Fe3O4) nanoparticle-contained oleic acid (MNOA) was used as a carrier phase for droplet generation and manipulation. The water-in-MNOA droplets were selectively distributed in a curved microchannel with three branches by utilizing both a hydrodynamic laminar flow pattern and an external magnetic field. Without the applied magnetic field, the droplets travelled along a hydrodynamic centerline that was displaced at each bifurcating junction. However, in the presence of a permanent magnet, they were repelled from the centerline and diverted into the desired channel when the repelled distance exceeded the minimum offset allocated to the channel. The repelled distance, which is proportional to the magnetic field gradient, was manipulated by controlling the magnet's distance from the device. To evaluate routing performance, three different sizes of droplets with diameters of 63, 88, and 102 μm were directed into designated outlets with the magnet positioned at varying distances. The result demonstrated that the 102-μm droplets were sorted with an accuracy of ∼93%. Our technique enables on-demand droplet routing in multiple outlet channels by simply manipulating magnet positions (active mode) as well as size-based droplet separation with a fixed magnet position (passive mode).

/pdf/dual-mode-on-demand-droplet-routing-in-multiple-49afnm5ddo.pdf

Dual-mode on-demand droplet routing in multiple microchannels using a magnetic fluid as carrier phase.

This study aims to establish an improved solid phase DNA amplification technique for the detection of DNA biomarkers in the point of care (POC) based molecular diagnostic fields of human diseases including cancer. To date, a complex of DNA biomarkers is known to be associated with human diseases. In particular, many known biomarkers are associated with human cancers, and these need to be simultaneously tested for early detection and prognosis of cancer. In this study, we developed a DNA amplification technique with signal enhancement that combines with solid phase bridge PCR and fluorescence resonance energy transfer (FRET), which can be improved the multiple targets detection simultaneously without obtaining false-positives that caused by the primers binding to each other when multiple targets are amplifying on a solid surface. Here, we showed that the fluorescence signals are 2.5 times enhanced on the Au surface with the KRAS gene (target DNA), which is a common DNA biomarker of human cancers, compared to on the Au surface with non-target DNA by using the present technique. Furthermore, we confirmed the storage conditions of the Au sensor with the immobilized primers for the commercialization as a molecular diagnostic device in the field of POC (point of care)-based cancer applications. Therefore, the present technique will be useful not only for the detection of multiple targets simultaneously without any false-positive signal generated by primers, but also enable integration with a microfluidic system in order to minimize the platform for the genetic analysis of DNA biomarkers in the field of diagnostic applications for disease treatment.

Jitae Kim

Papers

Studies on tin oxide-intercalated polyaniline nanocomposite for ammonia gas sensing applications

Rapid prototyping of multifunctional microfluidic cartridges for electrochemical biosensing platforms

Sample analysis cartridge and sample analysis cartridge reader

Dual-mode on-demand droplet routing in multiple microchannels using a magnetic fluid as carrier phase.

A solid phase-bridge based DNA amplification technique with fluorescence signal enhancement for detection of cancer biomarkers