Thara Seesaard

Development of Fabric-Based Chemical Gas Sensors for Use as Wearable Electronic Noses

Novel gas sensors embroidered into fabric substrates based on polymers/ SWNT-COOH nanocomposites were proposed in this paper, aiming for their use as a wearable electronic nose (e-nose). The fabric-based chemical gas sensors were fabricated by two main processes: drop coating and embroidery. Four potential polymers (PVC, cumene-PSMA, PSE and PVP)/functionalized-SWCNT sensing materials were deposited onto interdigitated electrodes previously prepared by embroidering conductive thread on a fabric substrate to make an optimal set of sensors. After preliminary trials of the obtained sensors, it was found that the sensors yielded a electrical resistance in the region of a few kilo-Ohms. The sensors were tested with various volatile compounds such as ammonium hydroxide, ethanol, pyridine, triethylamine, methanol and acetone, which are commonly found in the wastes released from the human body. These sensors were used to detect and discriminate between the body odors of different regions and exist in various forms such as the urine, armpit and exhaled breath odor. Based on a simple pattern recognition technique, we have shown that the proposed fabric-based chemical gas sensors can discriminate the human body odor from two persons.

Portable e-nose based on polymer/CNT sensor array for protein-based detection

Portable electronic nose (e-nose) consisting of polymer/carbon nanotube (CNT) sensor array was developed to detect protein-based foods. Gas sensors were fabricated by spin-coating functionalized CNT/polymer nanocomposite materials onto interdigitated electrodes. The sensors were tested with various types of volatile compounds such as ammonia, amine compounds, acetic acid, water and organic solvents in the range of ppm level. It was found that most sensors yield strong signals to ammonia, amine compounds and acetic acid as well, while they present quite low response to organic solvents and water. To understand the relation of the interaction of amine species related to the sensor response, we have performed molecular modelling based on the density functional theory (DFT) on one polymer structure providing the best response to volatile ammonia. Based on the principal component analysis (PCA), this portable e-nose was successfully applied for the classification of the seafood releasing different amount of amine compounds.

Development of an electronic nose for detection and discrimination of exhaled breath of hepatocellular carcinoma patients

An electronic nose (E-nose) has been designed and fabricated for detection of liver cancer based on measurement of the volatiles in the exhaled breath. This e-nose system is in the form of a briefcase, practical for adoption in both clinical and on field uses. The sensing unit is based on eight commercial metal oxide semiconductor gas sensors that are sensitive to a broad range of volatile chemicals, such as ammonia, sulfides, alcohol and hydrocarbons, sufficient to cover the chemical species contained in the human exhaled breath. Delivery of the odor samples to e-nose can be done easily by collecting the exhaled molecules from face mask worn by patients for several minutes. We have demonstrated the preliminary performance of this portable e-nose by comparing the odor of the breath based on two groups of people, patients diagnosed with hepatocellular carcinoma (HCC) and healthy control. It was found that this e-nose can discriminate the patterns of volatile organic compounds (VOCs) from these two groups, as analyzed by the principal component analysis (PCA). With further validation and development, this e-nose may become very useful for monitoring the exhaled as a screening device for detecting patients with early stage liver cancer. Such a device would help reduce the high mortality associated with this disease.

E-nose based on metallo-tetraphenylporphyrin/ SWNT-COOH for alcohol detection

A handheld electronic nose (e-nose) based on metallo-tetraphenylporphyrin/carboxylic-functionalized single- walled carbon nanotube (MTPP/SWNT-COOH) chemical gas sensors has been demonstrated as a promising instrument for monitoring in food production process. In this work, the gas sensor array was fabricated by dispersing SWNT-COOH in the matrix of different MTPP compounds, namely, MnTPP, FeTPP, ZnTPP, CoTPP and CuTPP. The sensing responses were studied in terms of the changing sensor resistance under the atmosphere of various volatile compounds. The results show that the central metals in tetraphenylporphyrin (TPP) ring play a major role in the selectivity of each gas sensor to each volatile gas. We have investigated the functionality of this handheld e-nose by monitoring the odor of fermented rice during the 5-day fermentation process. Based on the principal component analysis, it was found that the handheld e-nose can track the change of odors generated from the fermentation, in which largest odor change happens on the fifth day.

Volatile urine biomarkers detection in type II diabetes towards use as smart healthcare application

In this work, we fabricated six chemiresistive sensors, employed in a portable e-nose and performed tests with urine samples from two groups of population, namely type II diabetes and healthy subjects. To identify sensitivity and selectivity of chemiresistive gas sensors, the first test was performed towards five volatile organic compounds (VOCs) which are particularly found in human urine profiles and the second test with real urine samples from the volunteers. Principal component analysis (PCA) and cluster analysis (CA) applied to validate the obtained sensing response successfully spilt urinary volatile odors into two separate groups of diabetes and healthy status. A hypothesis testing (p-value approach) demonstrated that S3 and S4 (p˂0.05) responded specifically to the urine odors from diabetic patients and healthy subjects. Our findings suggest the possibility of using chemiresistive gas sensors in e-nose as an alternative diagnostic tool for diabetes detection through analysis of volatile urine odors.

Development of Organic-Inorganic Hybrid Optical Gas Sensors for the Non-Invasive Monitoring of Pathogenic Bacteria

Hybrid optical gas sensors, based on different organic and inorganic materials, are proposed in this paper, with the aim of using them as optical artificial nose systems. Three types of organic and inorganic dyes, namely zinc-porphyrin, manganese-porphyrin, and zinc-phthalocyanine, were used as gas sensing materials to fabricate a thin-film coating on glass substrates. The performance of the gas sensor was enhanced by a thermal treatment process. The optical absorption spectra and morphological structure of the sensing films were confirmed by UV-Vis spectrophotometer and atomic force microscope, respectively. The optical gas sensors were tested with various volatile compounds, such as acetic acid, acetone, ammonia, ethanol, ethyl acetate, and formaldehyde, which are commonly found to be released during the growth of bacteria. These sensors were used to detect and discriminate between the bacterial odors of three pathogenic species (Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) grown in Luria-Bertani medium. Based on a pattern recognition (PARC) technique, we showed that the proposed hybrid optical gas sensors can discriminate among the three pathogenic bacterial odors and that the volatile organic compound (VOC) odor pattern of each bacterium was dependent on the phase of bacterial growth.

Indoor air quality monitoring system based on polymer/functionalized-SWNT gas sensors

Recently, people pay more attention to healthy living conditions. Such changing lifestyle leads to demand for wearable health monitoring, new medical technology, healthy food and clean air. Thus, indoor air monitoring and control will be an emerging industry with a huge market size. In this paper, we have developed an indoor air monitoring system with ability to observe volatile contaminants, especially related to household origin. This system consists of an array of chemical gas sensor based on polymer/functionalized single-walled carbon nanotubes (SWNT) with ability to detect different gases. A microcontroller was used for data processing and alarming when the concentration of a target gas becomes danger. This system was developed based on consumer-friendly having a compact size and using low-cost technologies. From the experiment, it was demonstrated that such indoor air monitoring device provides an ability to detect contaminated gases in ambient air. The results imply a possibility appropriate for indoor air monitoring in general home and even in factory as well.

Intelligent smelling shirt based on fabric sensors for health status monitoring

In this work, we have implemented a wearable device for detecting the body odor of wearer. The sensing unit of this device consists of four fabric based gas sensors based on nanocomposite between polymers and carboxylic-functionalized single-walled carbon nanotubes (SWNT-COOH) simply fabricated by embroidering on textile. The communication between smelling shirt and computer is based on a serial communication using ZigBee wireless network. We have tested the performance of these sensors with eight types of volatile organic gases. Based on principal component analysis (PCA), it was found that this device is able to track change in the human body odor, thereby showing a potential for application in real-time health status monitoring.

Healthcare shoe system for gait monitoring and foot odor detections

Recently, we are living in an era filled with unprecedentedly growing senior population. Nowadays, smart technologies for healthcare have been increasingly interested by general consumers due to their numerous advantages such as affordability, user-friendliness, point-of-care usability and social-ability. In this paper, we have developed a smart shoe system with ability to observe human gait patterns and foot odor. The motion pattern and foot odor measurement systems were installed inside the shoes using force sensitive resistors (FRSs), bending sensors and chemical gas sensors. Thereby the FRSs and bending-sensor were installed beneath the foot while chemical gas sensor array was installed inside the tongue of the shoes. In addition, zigbee technology was used as data communication between all sensors with a receiver USB-connected to a computer. This system was developed to be consumer-friendly having a compact size and using low-cost technologies. It was demonstrated that this wearable device could classify different types of human gait patterns and foot odors during the duration of wearing time.