Quantitative Colorimetric Detection of Dissolved Ammonia Using Polydiacetylene Sensors Enabled by Machine Learning Classifiers.

Easy-to-use and on-site detection of dissolved ammonia are essential for managing aquatic ecosystems and aquaculture products since low levels of ammonia can cause serious health risks and harm aquatic life. This work demonstrates quantitative naked eye detection of dissolved ammonia based on polydiacetylene (PDA) sensors with machine learning classifiers. PDA vesicles were assembled from diacetylene monomers through a facile green chemical synthesis which exhibited a blue-to-red color transition upon exposure to dissolved ammonia and was detectable by the naked eye. The quantitative color change was studied by UV-vis spectroscopy, and it was found that the absorption peak at 640 nm gradually decreased, and the absorption peak at 540 nm increased with increasing ammonia concentration. The fabricated PDA sensor exhibited a detection limit of ammonia below 10 ppm with a response time of 20 min. Also, the PDA sensor could be stably operated for up to 60 days by storing in a refrigerator. Furthermore, the quantitative on-site monitoring of dissolved ammonia was investigated using colorimetric images with machine learning classifiers. Using a support vector machine for the machine learning model, the classification of ammonia concentration was possible with a high accuracy of 100 and 95.1% using color RGB images captured by a scanner and a smartphone, respectively. These results indicate that using the developed PDA sensor, a simple naked eye detection for dissolved ammonia is possible with higher accuracy and on-site detection enabled by the smartphone and machine learning processes.

Wash-Durable Conductive Yarn with Ethylene Glycol-Treated PEDOT:PSS for Wearable Electric Heaters.

Recently, wearable electric heaters with high durability and low-power operation have attracted much attention due to their potential to change traditional approaches for personal heating management and thermal therapy systems. Here, we report textile-based wearable heaters based on highly durable conductive yarns, which were transformed from traditional cotton yarns through a facile dyeing process of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) and ethylene glycol (EG). With the EG post-treatment, the conductive yarns exhibited an electrical conductivity of ∼76 S cm-1 and good stability under repeated cycles of washing and drying. The heating elements made from the conductive yarns showed an excellent distribution of temperature and could be heated up to 150 °C at a sufficiently low driving voltage of 5 V. Also, the heating elements showed stable Joule heating performance under repeated bending stress and 2000 cycles of stretching and releasing. To demonstrate its practical use for on-body heating systems, a lightweight and air-breathable thermal wristband was demonstrated by sewing the conductive yarns onto a fabric with a simple circuit structure. From these results, we believe that our strategy to obtain highly conductive and durable yarns can be utilized in various applications, including medical heat therapy and personal heating management systems.

Flexible fabric gas sensors based on reduced graphene-polyaniline nanocomposite for highly sensitive NH3detection at room temperature.

A flexible fabric gas sensor for the detection of sub-ppm-level NH3is reported in this paper. The reduced graphene oxide (rGO)-polyaniline (PANI) nanocomposite was successfully coated on cotton thread via anin situpolymerization technique. The morphology, microstructure and composition were analyzed by field-emission scanning electron microscope, x-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. Furthermore, we have studied the responses of the rGO-PANI nanocomposite-based flexible sensors for the detection of NH3varying from 1-100 ppm, operated at 22 °C. At the optimized concentration of rGO, the response of these sensors increased by 4-5 times in comparison with the pristine rGO and PANI. These flexible sensors exhibited fast response, remarkable long-term stability, good selectivity and a low detection limit. The sensing mechanism for the high sensing performance has been thoroughly discussed and it is mainly due to the distinctive 1D fiber structure, the formation of a p-p heterojunction between the rGO nanosheets and PANI. The rGO-PANI composite-based fabric sensor with low power consumption is a potential flexible electronic device for the detection of NH3.

Highly sensitive polyaniline-coated fiber gas sensors for real-time monitoring of ammonia gas.

A single-yarn-based gas sensor has been made from conductive polyaniline coated on commercial yarns. This can detect ammonia gas concentration in an environment or a working area. Cotton, rayon and polyester are utilized as substrates using a dip-coating process. The conductive yarns show ohmic behavior with an electrical resistance of 15-31 kΩ cm-1. The conductive polyester yarn exhibits higher mechanical strength even after intensive chemical treatment. It also has the highest gas response of 57% of 50 ppm ammonia gas, the concentration at which health problems will occur. A linear gas response of the yarn sensor appears in a range of 5-25 ppm ammonia concentration. The polyester yarn sensor can be reused without any change in its sensing response. It can monitor gas levels continuously giving real-time results. By using a microcontroller as part of the circuitry, the gas detection results are transferred and updated wirelessly to a computer or to a smartphone. The textile-based gas sensor can be sewn directly onto the fabrics since it is made with the same fabric. This single-yarn-based gas sensor is suitable for mass production and is appropriate for sophisticated applications.

Highly Sensitive Textile Strain Sensors and Wireless User-Interface Devices Using All-Polymeric Conducting Fibers.

Emulation of diverse electronic devices on textile platform is considered as a promising approach for implementing wearable smart electronics. Of particular, the development of multifunctional polymeric fibers and their integration in common fabrics have been extensively researched for human friendly wearable platforms. Here we report a successful emulation of multifunctional body-motion sensors and user-interface (UI) devices in textile platform by using in situ polymerized poly(3,4-ethylenedioxythiophene) (PEDOT)-coated fibers. With the integration of PEDOT fibers in a fabric, via an optimization of the fiber pattern design, multifunctional textile sensors such as highly sensitive and reliable strain sensors (with maximum gauge factor of ∼1), body-motion monitoring sensors, touch sensors, and multilevel strain recognition UI devices were successfully emulated. We demonstrate the facile utilization of the textile-based multifunctional sensors and UI devices by implementing in a wireless system that is capable of expressing American Sign Language through predefined hand gestures.

Ultrasensitive Room-Temperature Operable Gas Sensors Using p-Type Na:ZnO Nanoflowers for Diabetes Detection.

Ultrasensitive room-temperature operable gas sensors utilizing the photocatalytic activity of Na-doped p-type ZnO (Na:ZnO) nanoflowers (NFs) are demonstrated as a promising candidate for diabetes detection. The flowerlike Na:ZnO nanoparticles possessing ultrathin hierarchical nanosheets were synthesized by a facile solution route at a low processing temperature of 40 °C. It was found that the Na element acting as a p-type dopant was successfully incorporated in the ZnO lattice. On the basis of the synthesized p-type Na:ZnO NFs, room-temperature operable chemiresistive-type gas sensors were realized, activated by ultraviolet (UV) illumination. The Na:ZnO NF gas sensors exhibited high gas response (S of 3.35) and fast response time (∼18 s) and recovery time (∼63 s) to acetone gas (100 ppm, UV intensity of 5 mW cm-2), and furthermore, subppm level (0.2 ppm) detection was achieved at room temperature, which enables the diagnosis of various diseases including diabetes from exhaled breath.

Low-Temperature Photochemically Activated Amorphous Indium-Gallium-Zinc Oxide for Highly Stable Room-Temperature Gas Sensors.

We report on highly stable amorphous indium-gallium-zinc oxide (IGZO) gas sensors for ultraviolet (UV)-activated room-temperature detection of volatile organic compounds (VOCs). The IGZO sensors fabricated by a low-temperature photochemical activation process and exhibiting two orders higher photocurrent compared to conventional zinc oxide sensors, allowed high gas sensitivity against various VOCs even at room temperature. From a systematic analysis, it was found that by increasing the UV intensity, the gas sensitivity, response time, and recovery behavior of an IGZO sensor were strongly enhanced. In particular, under an UV intensity of 30 mW cm(-2), the IGZO sensor exhibited gas sensitivity, response time and recovery time of 37%, 37 and 53 s, respectively, against 750 ppm concentration of acetone gas. Moreover, the IGZO gas sensor had an excellent long-term stability showing around 6% variation in gas sensitivity over 70 days. These results strongly support a conclusion that a low-temperature solution-processed amorphous IGZO film can serve as a good candidate for room-temperature VOCs sensors for emerging wearable electronics.