Zafer Ziya Öztürk

Recent studies chemical sensors based on phthalocyanines

Phthalocyanines (Pcs) are organic compounds able to act as chemical recognition systems because of the various physical effects induced in them by interaction with a large number of gases. The gas response, stability and other sensing characteristics of the Pc films are affected by many factors, such as film morphology, molecular orientation and so on. The interaction between the Pc coatings and the gas molecules may be classified in terms of irreversible chemical affinity, reversible (usually charge transfer) chemical reaction or sorption. The nature of the interactions between the coating and vapor molecules determines the selectivity, sensitivity, signal kinetics, and the reversibility of the sensor. The magnitude of these interactions may be conveniently described in the frame of the linear sorption energy relationship (LSER) model that has been shown to be very efficient at predicting the behavior of polymer-based sensors. In this paper, the effect of coating parameters on sensing properties and sensing mechanism are reviewed. We have proposed an alternative way to achieve optimal sensor performance: liquid crystalline Pcs forming self-ordered thin films of defined area and thickness simply by heating the sample over the phase transition temperature and synthetized mesomorphic and functionalized phthalocyanines, to develop sensors based on mass-sensitive transducers (quartz crystal microbalance, QCM). Phthalocyanines used are discussed in terms of their physical and chemical properties, as well as their sensing properties: sensitivity, selectivity and reversibility. We showed our results with LSER and the results are in good agreement with this theory.

Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte

A vertically aligned Pd nanowire array was successfully fabricated on an Au/Ti substrate using an anodic aluminum oxide (AAO) template by a direct voltage electrodeposition method at room temperature using diluted neutral electrolyte. The fabrication of Pd nanowires was controlled by analyzing the current–time transient during electrodeposition using potentiostat. The AAO template and the Pd nanowires were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) methods and X-Ray diffraction (XRD). It was observed that the Pd nanowire array was standing freely on an Au-coated Ti substrate after removing the AAO template in a relatively large area of about 5 cm2, approximately 50 nm in diameter and 2.5 μm in length with a high aspect ratio. The nucleation rate and the number of atoms in the critical nucleus were determined from the analysis of current transients. Pd nuclei density was calculated as 3.55 × 108 cm−2. Usage of diluted neutral electrolyte enables slower growing of Pd nanowires owing to increase in the electrodeposition potential and thus obtained Pd nanowires have higher crystallinity with lower dislocations. In fact, this high crystallinity of Pd nanowires provides them positive effect for sensor performances especially.A vertically aligned Pd nanowire array was successfully fabricated on an Au/Ti substrate using an anodic aluminum oxide (AAO) template by a direct voltage electrodeposition method at room temperature using diluted neutral electrolyte. The fabrication of Pd nanowires was controlled by analyzing the current–time transient during electrodeposition using potentiostat. The AAO template and the Pd nanowires were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) methods and X-Ray diffraction (XRD). It was observed that the Pd nanowire array was standing freely on an Au-coated Ti substrate after removing the AAO template in a relatively large area of about 5 cm2, approximately 50 nm in diameter and 2.5 μm in length with a high aspect ratio. The nucleation rate and the number of atoms in the critical nucleus were determined from the analysis of current transients. Pd nuclei density was calculated as 3.55 × 108 cm−2. Usage of diluted neutral electrolyte enables slower growing of Pd nanowires owing to increase in the electrodeposition potential and thus obtained Pd nanowires have higher crystallinity with lower dislocations. In fact, this high crystallinity of Pd nanowires provides them positive effect for sensor performances especially.

Fuzzy Logic and Neural Network Applications on the Gas Sensor Data: Concentration Estimation

In this study, a fuzzy logic based algorithm is presented for the concentration estimation of the CCl4 and CHCl3 gases by using the steady state sensor response and an artificial neural network (ANN) structure is proposed for the concentration estimation of the same gases inside the sensor response time by using the transient sensor response. The Quartz Crystal Microbalance (QCM) type sensors were used as gas sensors. A computer controlled measurement and automation system with IEEE 488 card was used to control the gas concentration values and to collect the sensor responses. Acceptable performance was obtained for the concentration estimation with fuzzy inference. The appropriateness of the artificial neural network for the gas concentration determination inside the sensor response time is observed.

Volatile organic compounds sensing properties of tetrakis(alkylthio)-substituted lutetium(III) bisphthalocyanines thin films.

The effect of volatile organic compounds (VOCs) such as acetone, methanol, ethanol, chloroform, carbon tetrachloride, dichloromethane, and hexane on electrical conductivity of thin films of bis[tetrakis(alkylthio)phthalocyaninato]lutetium(III) double decker complexes [(C(n)H(2n+1)S)(4)Pc](2)Lu(III) was investigated. The [(C(n)H(2n+1)S)(4)Pc](2)Lu(III) molecules substituted with different alkylthia chains (n=6, 8, 10, 12, and 16) were coated on interdigital transducers using a jet spray technique. A change (increase or decrease) in the conductivity of the [(C(n)H(2n+1)S)(4)Pc](2)Lu(III) films was observed depending on the concentration of the VOCs, which was ranging from 500 to 5000 ppm. The decrease in the conductivity of the sensors for the dissolvent of the compounds (chloroform, carbon tetrachloride, dichloromethane and hexane) could be related to swelling of the films. On the other hand, the increase in the conductivity of the sensors for the other VOCs (acetone, methanol and ethanol) could be resulted from that the VOCs act as electron donors and/or acceptors in the films. A linear relationship between the sensor response and concentration of the VOC vapors is obtained. The sensitivities of the [(C(n)H(2n+1)S)(4)Pc](2)Lu(III) films were in the range of 2.10(-4)-3.10(-3)%/ppm.

Evaluation of a fast wastewater odour characterisation procedure using a chemical sensor array.

Sewage treatment works are one of the major sources that cause atmospheric odour pollution. The increase in the number of complaints about odour nuisance is due to the increase in environmental concerns. Unfortunately, the legislation on odour nuisance from sewage treatment works is very limited. In order to determine suitable thresholds on which to base legal standards, reliable and efficient odour measurement methods need to be defined. A chemical sensor array was developed for the purpose of measuring wastewater odour. This paper describes the development of the chemical sensor system which is specifically tuned to odours of wastewater origin and which can give an electronic measure of the wastewater odours. Odour emissions from a wastewater treatment facility were detected by using a quartz crystal microbalance (QCM) sensor array. The array consists of nine sensor elements, which were coated with different materials. In this paper, the usage of these novel instruments in the water industry was shown.

Acoustoelectric Effect on the Responses of SAW Sensors Coated with Electrospun ZnO Nanostructured Thin Film

In this study, zinc oxide (ZnO) was a very good candidate for improving the sensitivity of gas sensor technology. The preparation of an electrospun ZnO nanostructured thin film on a 433 MHz Rayleigh wave based Surface Acoustic Wave (SAW) sensor and the investigation of the acoustoelectric effect on the responses of the SAW sensor are reported. We prepared an electrospun ZnO nanostructured thin film on the SAW devices by using an electrospray technique. To investigate the dependency of the sensor response on the structure and the number of the ZnO nanoparticles, SAW sensors were prepared with different coating loads. The coating frequency shifts were adjusted to fall between 100 kHz and 2.4 MHz. The sensor measurements were performed against VOCs such as acetone, trichloroethylene, chloroform, ethanol, n-propanol and methanol vapor. The sensor responses of n-propanol have opposite characteristics to the other VOCs, and we attributed these characteristics to the elastic effect/acoustoelectric effect.

Label Free QCM Immunobiosensor for AFB1 Detection Using Monoclonal IgA Antibody as Recognition Element.

This study introduces the use of an IgA isotype aflatoxin (AF) specific monoclonal antibody for the development of a highly sensitive Quartz Crystal Microbalance (QCM) immunobiosensor for the detection of AF in inhibitory immunoassay format. The higher molecular weight of IgA antibodies proved an advantage over commonly used IgG antibodies in label free immunobiosensor measurements. IgA and IgG antibodies with similar affinity for AF were used in the comparative studies. Sensor surface was prepared by covalent immobilization of AFB1, using self assembled monolayer (SAM) formed on gold coated Quartz Crystal, with 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxy succinimide (EDC/NHS) method using a diamine linker. Nonspecific binding to the surface was decreased by minimizing the duration of EDC/NHS activation. Sensor surface was chemically blocked after AF immobilization without any need for protein blocking. This protein free sensor chip endured harsh solutions with strong ionic detergent at high pH, which is required for the regeneration of the high affinity antibody-antigen interaction. According to the obtained results, the detection range with IgA antibodies was higher than IgG antibodies in QCM immunosensor developed for AFB1.

Liquid crystal porphyrins as chemically sensitive coating materials for chemical sensors

Columnar liquid crystal porphyrin compounds have been deposited onto the gold pads of quartz crystal microbalances (QMBs). The sensitivities of the resulting sensors have been measured with respect to volatile organic compounds (VOCs) and have been found to be of interest for future applications. The results show a strong influence of the length of the side alkyl chains, furthermore the thermal history of the coated film also affects the measured properties. The partition coefficients of the coatings have been calculated from the sensor responses.

A neural network implemented microcontroller system for quantitative classification of hazardous organic gases in the ambient air

In this study, a microcontroller-based gas mixture classification system is proposed to use real-time analyses of the trichloroethylene and acetone binary mixture. A Feed Forward Neural Network (FFNN) structure is performed for quantitative identification of individual gas concentrations (trichloroethylene and acetone) in their gas mixtures. The phthalocyaninecoated Quartz Crystal Microbalance (QCM) type sensors were used as gas sensors. A calibrated Mass Flow Controller (MFC) was used to control the flow rates of carrier gas and trichloroethylene and acetone gas mixtures streams. The components in the binary mixture were quantified by applying the sensor responses from the QCMs sensor array as inputs to the FFNN. The microcontroller-based gas mixture classification system performs Neural Network (NN)-based estimation, the data acquisition and user interface tasks. This system can estimate the gas concentrations of trichloroethylene and acetone with the average errors of 0.08% and 0.97%, respectively.

A Study on Neural Networks with Tapped Time Delays: Gas Concentration Estimation

In this study, an artificial neural network (ANN) structure with tapped time delays is used for the concentration estimation of Toluene gas inside the sensor response time by using the transient sensor response. The Quartz Crystal Microbalance (QCM) type sensors were used as gas sensors. A computer controlled measurement and automation system with IEEE 488 card was used to control the gas concentration values and to collect the sensor responses. The determination of Toluene gas concentrations from the trend of the transient sensor responses achieved with acceptable good performances, and the appropriateness of the artificial neural network for the gas concentration determination inside the sensor response time is observed with these training methods.