Sumana Kladsomboon

An optical artificial nose system for odor classifications based on LED arrays

Optical electronic nose (olfactory sensing) technologies have recently become a convenient technique to identify the quality of food and beverage products based on the odor classification. In this paper, we reported an optical-based electronic nose system consisting of thin-film sensing materials, array of light emitting diode (LED), photo-detector and pattern recognition program. The organic mixtures thin film gas sensor was prepared by spin coating of Zinc-2,9,16,23- tetra- tert-butyl-29H,31H-phthalocyanine (ZnTTBPc), Zinc-5,10,15,20-tetra-phenyl-21H,23H-porphyrin (ZnTPP) and manganese(III)-5,10,15,20-tetra-phenyl-21H,23H-porphyrin chloride (MnTPPCl) onto a clean glass substrate. The electronic nose system was developed by using the low-cost LED array as a light source. Then the light intensity that is transmitted through the organic thin film during the experiment was detected by the color light to frequency converter device (photo-detector). The ability of this system was tested by using volatile organic compound (VOCs) vapors such as methanol, ethanol, and isopropanol. Principal component analysis (PCA) has been used as the pattern recognition for this electronic nose system. The result confirms that the sensing layer that composed of the three types of organic compounds described the groups of chemical vapors by using the array of LED.

Alcohol gas sensors based on magnesium tetraphenyl porphyrins

Metallo-porphyrins thin films have been demonstrated as optical gas sensors for detecting various kinds of gases. In this work, magnesium 5,10,15,20-tetraphenyl porphyrin (MgTPP) thin films were prepared by spinning the solution using chloroform as solvent onto clean glass substrates, then subjected to a thermal annealing at 280degC in the argon atmosphere. These MgTPP optical gas sensors have higher responses with methyl alcohol than ethyl alcohol based on dynamic flow of alcohol vapors at 25degC. Quantum mechanical calculation based on density functional theory has found that the interaction energy between MgTPP with methyl alcohol is higher than ethyl alcohol. Principal component analysis (PCA) was used to classify the data from the optical absorbance spectra into three groups of alcohols, which are McOH (100%), EtOH (100%) and a mixture of McOH (50%) and EtOH (50%). From these results, MgTPP thin film can be an efficient sensing material to discriminate alcohols.

An artificial nose based on m-porphyrin (M = Mg, Zn) thin film and optical spectroscopy

Artificial nose has recently become an emerging instrument for quality assurance in the food industry. These paper presents the optical gas sensors based on Magnesium - 5,10,15,20 - tetra phenyl - porphyrin (MgTPP) and Zinc - 5,10,15,20 - tetra phenyl - porphyrin (ZnTPP) thin films and their application as an artificial nose. Based on the measurement of optical absorbance response using a general UV-Vis spectroscopy, this artificial noses was tested to discriminate various volatile organic compounds (VOCs) and Thai beverages. Atomic force microscopy (AFM) and X-rays diffraction were used to confirm the polycrystalline structure of the sensing materials. Density functional theory (DFT) calculations reveal that MgTPP interacts more strongly with the VOCs than ZnTPP, especially with water and methanol. The classification results of VOCs and Thai beverage vapors using the principle component analysis indicate that both MgTPP and ZnTPP-based artificial noses can be an efficient tool for quality assurance of alcoholic beverages.

Optical electronic nose based on porphyrin and phthalocyanine thin films for rice flavour classification

The classification of product quality based on an optical electronic nose is becoming an instrument of much interest in beverage industry. The optical electronic nose is composed of a molecular sensing layer, UV-Vis spectrophotometer and a data analysis unit. The sensing layer was fabricated from 3 types of organic compounds, namely Zinc-2,9,16,23- tetra- tert- butyl- 29H,31H- phthalocyanine (ZnTTBPc), Zinc-5,10,15,20-tetraphenyl- 21H,23H-porphyrin (ZnTPP) and manganese(III)-5,10,15,20-tetraphenyl-21H,23H-porphyrin chloride (MnTPPCl) by using the spin-coating technique. The UV-Vis Spectrophotometer set up was used to detect gases and chemical vapors by measuring changes in the absorption spectrum of the spin-coated thin film upon gas exposure. The sensitivity of the organic film was tested by using volatile organic compounds (VOCs) vapor, for instance, methanol, ethanol, isopropanol, acetone (5% eq.), acetic acid (5% eq.) and methyl benzoate (5% eq.), which are common VOCs in food and beverages. The Principal Components Analysis (PCA) was then applied to the absorption spectral data to classify the type of the tested chemical vapors. The results indicate that this sensing film with the three organic compounds produced a good separation of data groups according to the chemical type.

Investigation of thermal and methanol-vapor treatments for MgTPP as an optical gas sensor

In this paper, we have investigated the sensing properties of magnesium - 5,10,15,20 - tetraphenyl - porphyrin (MgTPP) to various volatile organic compounds (VOCs). The spin-coated MgTPP thin films were subjected to thermal annealing and methanol-vapor exposure to study the effects of pre-treatment on the sensing properties. Atomic force microscopy (AFM) has shown that both pre-treatment techniques have induced re-crystallization of the film, thereby improving the sensitivity over the as-deposited film. The thermally annealed films were found more effective than the methanol-vapor treated ones. The in-house optical sensor setup was applied to discriminate various VOCs and alcoholic beverages. Principal component analysis (PCA) confirms that the thermally annealed MgTPP thin film can distinguish several kinds of VOCs. Computational density functional theory (DFT) indicates that the interaction energy between analyte and sensing molecules can be used to explain comparative sensitivity.

Molecular Interactions Between Alcohols and Metal Phthalocyanine Thin Films for Optical Gas Sensor Applications

Optically active organic gas sensors represent a promising molecular sensing device with low power consumption. We report experimental and computational investigations into the molecular interactions of metal phthalocyanine thin films with alcohol vapor. In the gas-sensing regime, the interactions of zinc phthalocyanine and alcohol molecules were studied by the Density Functional Theory (DFT) calculations, in comparison to the x-ray absorption spectroscopy. The DFT results reveal a reversible charge interaction mechanism between the zinc atom and the oxygen atom in the alcohol OH group, which corresponds to a shift in the x-ray absorption edge of the zinc atom. In the irreversible interaction regime, the effect of saturated alcohol vapor on spin-coated zinc phthalocyanine films was studied by the phase contrast microscopy, the optical absorption spectroscopy, and the transmission electron microscopy. Annealing the spin-coated films in saturated methanol vapor was found to induce an irreversible structural transformation from an amorphous to a crystalline phase, similar to the effect of a thermal annealing process. These crystallization processes of the zinc phthalocyanine films were also found to enhance their stability and alcohol sensing performance.

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.

Optical gas sensor based on MgTPP thin film for the detection of alcohol vapors

Electronic nose devices are of increasing interest for the quality control of beverage and food processing. Optical gas sensors that require low electrical power are in great need for such devices. Magnesium 5, 10, 15, 20-tetraphenylporphyrin thin film sensors have been fabricated by spin coating onto glass substrates for detecting specific alcoholic volatile organic compounds (VOCs). Responses of the films to various alcohols were monitored by UV/Vis spectroscopy using a homemade measurement setup, which employs a LabVIEW program to control the measuring process.