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We successfully demonstrated a Poly (3-hexylthiophene) (P3HT) diode gas sensor with silver nanowires as a gas permeable top electrode. The silver nanowires dispersed in isopropyl alcohol (IPA) were used to form a top electrode by a simple drop-casting method. The meshes between nanowires enable gas molecules pass through the electrode and diffuse into the underlying organic sensing layer to dope or dedope the organic semiconductor. Here, the proposed sensor successfully detects ammonia down to 30 parts-per-billion (ppb), which is sensitive enough in many applications including breath ammonia monitoring as a point-of-care application. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a toxic gas, which is dangerous for human health and causes many respiratory infections, poisoning, and lung damage. In this work, we have successfully grown ZnO nanorod film on annealed ZnO seed layer in different ambient temperatures, and the morphology of the nanorods sensing layer that affects the gas sensing response to nitric oxide (NO) gas were investigated. To acknowledge the effect of annealing treatment, the devices were fabricated with annealed seed layers in air and argon ambient at 300 °C and 500 °C for 1 h. To simulate a vertical device structure, a silver nanowire electrode covered in ZnO nanorod film was placed onto the hydrothermal grown ZnO nanorod film. We found that annealing treatment changes the seed layer's grain size and defect concentration and is responsible for this phenomenon. The I–V and gas sensing characteristics were dependent on the oxygen defects concentration and porosity of nanorods to react with the target gas. The resulting as-deposited ZnO seed layer shows better sensing response than that annealed in an air and argon environment due to the nanorod morphology and variation in oxygen defect concentration. At room temperature, the devices show good sensing response to NO concentration of 10 ppb and up to 100 ppb. Shortly, these results can be beneficial in the NO breath detection for patients with chronic inflammatory airway disease, such as asthma. [ABSTRACT FROM AUTHOR]

In this research work, the gas sensing properties of halogenated chloroaluminum phthalocyanine (ClAlPc) thin films were studied at room temperature. We fabricated an air-stable ClAlPc gas sensor based on a vertical organic diode (VOD) with a porous top electrode by the solution process method. The surface morphology of the solution-processed ClAlPc thin film was examined by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The proposed ClAlPc-based VOD sensor can detect ammonia (NH3) gas at the ppb level (100~1000 ppb) at room temperature. Additionally, the ClAlPc sensor was highly selective towards NH3 gas compared to other interfering gases (NO2, ACE, NO, H2S, and CO). In addition, the device lifetime was tested by storing the device at ambient conditions. The effect of relative humidity (RH) on the ClAlPc NH3 gas sensor was also explored. The aim of this study is to extend these findings on halogenated phthalocyanine-based materials to practical electronic nose applications in the future. [ABSTRACT FROM AUTHOR]

A pentacene-based organic thin-film transistor (OTFT) with a porous active layer is demonstrated for the first time. The porous OTFT exhibits a fast, sensitive, and reversible response to ammonia gas with a detection limit as 500 ppb, whereas the OTFT without porous structure has a slow response and a poor recovery behavior. The sensing mechanism dominated by the dissociation of hydroxyl groups of the polymer dielectric layer is raised and discussed. The proposed device is the first OTFT-based ammonia sensor with reversible response and high sensitivity in low parts-per-million range. It is promising for the development of a diagnostic breath analysis system. [ABSTRACT FROM AUTHOR]

We report a very sensitive gas sensor embedded in a vertical polymer space-charge-limited transistor. The oxidizing and reducing gases act as electron dedoping and electron doping agents on the transistor active layer to change the potential distribution in the vertical channel and hence to change the output current density. With a 30-ppb detection limit to ammonia, the sensor can be used for non-invasive breath monitor in point-of-care applications. The integration of a sensitive gas sensor and a low-operation-voltage transistor in one single device also facilitates the development of low-cost and low-power-consumption sensor array. [ABSTRACT FROM AUTHOR]

We demonstrate a (poly[(4,8-bis(2-ethylhexyloxy)-benzo-(1,2-b:4,5-b)dithiophene)− 2,6-diyl-alt-(4-(2-ethylhexyl)− 3-fluorothieno[3,4- b ]thiophene-)− 2-carboxylate-2,6-diyl)]) (PTB7) based ammonia gas sensor with high operational current up to 10 − 4 A. Using (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) (F4-TCNQ) as a p-type dopant for PTB7, the operation current under driving voltage of 5 V was effectively increased to 1.5 × 10 − 4 A, while that of a standard device was only 3 × 10 − 6 A. According to the study of space-charge-limited current and ultraviolet photoemission spectroscopy (UPS), the enhanced operational current can be attributed both to the higher mobility and lower carrier injection barrier of the F4-TCNQ doped PTB7. Detailed comparative analysis between the F4-TCNQ doped sensor and the non-doped sensor was also studied. The increased operational current and the current drop during sensing of the F4-TCNQ doped sensors are both beneficial to the realization of low-cost circuitry sensing system, which demonstrates the potential of the strategy of utilizing p-type doping in organic gas sensors for the developing of affordable point-to-care (POC) devices. [Display omitted] • P-type dopant, F4-TCNQ, was used to effectively enhance the current of the ammonia gas sensor up to 10−4 A. • The reason of the current enhancement can be attributed by increased mobility and reduced energy level mismatch. • The increased operational current and the current drop during sensing are beneficial for low-cost circuitry sensing system. • The breath ammonia detection region shown in this work is 300–2000 ppb. [ABSTRACT FROM AUTHOR]

Acetone and ammonia are the gases in human breath with relatively high concentrations of 1–200 ppm and 0.5–2 ppm respectively. Gas sensors with vertical current channels covered with organic polymer semiconductors have been proved to have high sensitivity and reliability in breath ammonia detection. But the polymers have a large current drift in air and poor sensitivity to acetone. Here, the polymer is replaced by the iridium metal complex tris[2-(p -tolyl)pyridine]iridium(III), (Ir(mppy) 3), a common emitter in organic light-emitting diode (OLED). The vertical gas sensor now has good sensitivity to acetone in the important range of 0.5–100 ppm. The current of Ir(mppy) 3 sensor has a smaller drift in air during the measurement. In 800 s, the current drift of Ir(mppy) 3 device is only 3.2% percent, whereas the drift of PTB7 polymer device is 35% and P3HT polymer device is 29%. The good resolution of 0.5 ppm acetone is related to the stability of the current of Ir(mppy) 3 device. [Display omitted] • OLED light emitter Ir(mppy) 3 is used as gas sensing material. • Vertical-channel gas sensor with Ir(mppy) 3 can resolve acetone down to 0.5 ppm. • The acetone sensor with Ir(mppy) 3 can be applied in medical diagnosis using breath. [ABSTRACT FROM AUTHOR]

In this work, we proposed a rapid and easy check of the drinking water pollution level due to bacteria growth by semiconductor gas sensor. Highly sensitive vertical channel organic ammonia gas sensor was used to detect the gases emitted from the polluted water, and then determined effective ammonia concentration according to its response. Residues from meat of fish, shrimp, and fruits were mashed and added to the clean water. The water samples were stored at 35 °C for natural decay. Initially the bacteria concentration was below 100 colony forming unit per ml (cfu/ml), then it increased to103 cfu/ml in 2 h and 105 cfu/ml in 4 h, which was beyond the drinking safety standard, 500 cfu/ml. At this gas level no bad odor can be sensed by human yet, however, the effective ammonia concentration of those samples rises to 300–500 ppb in 2 h. The amine gas sensor can therefore be used as a rapid check if the bacteria level inside the water is far over the safety standard. [Display omitted] • Bacteria concentration in meat-polluted water can be detected by the gas emission. • Amine gas is detected by vertical organic gas sensor when the bacteria is over 500 CFU/ml(drinking safety standard). • The gas senor provides a rapid way to check the water quality without 24 h of bacteria incubation. • This method can be applied in areas with poor sanitary infrastructure and high drinking water risk. [ABSTRACT FROM AUTHOR]

• Human skin gas sensing by sensitive organic semiconductor gas sensor. • The highest signal from palms detected by healthy people,4 men and 4 women. • Using three organic material sensors to analyze human skin gas, the dominant component from the palm has different pattern from ammonia. • Gas chromatography study suggests aldehydes in the palm gas. [Display omitted] The gas emitted from the human skin is collected and measured by the highly sensitive room-temperature organic semiconductor gas sensor with vertical electrical channel. Among various positions, palms give the highest signal and heads follow. The signals are collected from 4 healthy men and 4 healthy women. The response is defined as the percent of electric current change at 5 V in 30 s after the measurement. By comparing the responses from sensors made by three different organic materials, the dominant component from the palm has different pattern from ammonia. Gas chromatography study suggests aldehydes in the palm gas. Different people show consistent results but slightly depending on sex. The body skin measurement can be extended to patients in order to establish the connection between skin gas and the diseases situations. [ABSTRACT FROM AUTHOR]