Narrow Results

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.

Octa-substituted metallophthalocyanines [M = Ni(II), Zn(II), Co(II), and Cu(II)] carrying 3,4-dialkoxyphenyl tosylamino groups at the peripheral positions have been synthesized from 1,2-dicyano-4,5-bis[(3,4-dialkoxyphenyl-tosylamino)methyl]benzene in the presence of the corresponding anhydrous metal salt. Next to the metal ion center, the length of the alkyl chains in the dialkoxyphenyl moiety ($n=4$, 5, 6, and 12) was varied. In total, sixteen soluble phthalocyanines have been characterized by elemental analysis, FT-IR and ${}^{\mathrm{\text{1}}}$H-NMR spectroscopy as well as mass spectrometry. Furthermore, the gas sensing properties of these new compounds have been studied using quartz crystal microbalance transducers. The sensing properties are described on the basis of sensor responses to nine different test analytes comprising volatile organic compounds, toxic gases, and chemical warfare agent simulants. The influence of the metal ion center and substituents on sensor selectivity and sensitivity is discussed. The compounds show good performance in the gas-sensing experiments with diverse responses to the analytes. Phthalocyanine species with pronounced selectivity for polar analytes, hydrocarbons or amines have been identified among the set of sensors with the help of multivariate data exploration methods. The results reveal that quite a high diversity in terms of selectivity is introduced through the minute variations to the phthalocyanine structure.

The interaction of different amino acids and vacuum evaporated tetraphenyl porphyrin films was investigated by using kinetic isotherms, UV-vis spectroscopy, quartz crystal microbalance and density functional theory techniques. The adsorption process was analyzed by using pseudo-first-order and pseudo-second-order models. From these results, the adsorption order changed depending on the chemical characteristics of the porphyrin film, although most of the interactions were classified as pseudo-second-order at the films interface. From absorbance measurements, red shifts on the Soret peak positions were observed for all amino acids interacting with the metal free and the ZnTPP systems, while the position of the Soret peak barely change for the CuTPP surface, except for a slight bathocromic shift for arginine. On the other hand, the broadening of the Soret peak was more important for the ZnTPP and H₂TPP surfaces, but the interaction with the CuTPP interfaces decreased the width of the peaks in all cases. In addition, a quartz crystal microbalance analysis was employed to investigate the film sensing performance during amino acid exposure. From these results, positively charged amino acids were more easily adsorbed on the films in contrast with the polar (serine) molecule. DFT calculations exhibited important deformations for H₂TPP, the out-of-plane displacement of the Zn atom for ZnTPP, and hydrogen bond interactions with the CuTPP molecule. DFT also showed high binding energies for the positively charged amino acids but low binding energies for serine in agreement with experimental data. From these results, porphyrin films could be used as selective detectors for various L-amino acid molecules.

Electrical impedance analysis and energy dissipation methods are the two main methods to evaluate the damping behaviour of the quartz crystal. The motional resistance of the quartz crystal, which can reflect the quality factor (Q), is monitored in the electrical impedance analysis and the dissipation factor (D), which is inversely proportional to the Q, is measured in the energy dissipation methods. A comparison of the Q from electrical impedance analysis, termed as "electrical Q" and from the energy dissipation methods, termed as "mechanical Q" is presented in this work. The damping behavior of 5 MHz QCMs subjected to polymer caotings are studied by both methods. The resonant frequency, f, and Q before and after polymer coatings are measured using the network analyzer and a QCM-energy dissipation (QCM-D) instrument. The frequency shifts from both methods are quite comparable and the changes of the dissipation factor and the Q factor are also similar. Possible factors accounting for the Q change such as mass loading effect, evenness of the polymer coating, surface roughness of the crystal, are analyzed. The thickness range of the coating over the QCM can be used as a platform for bio sensing is also discussed.

Chemical sensor layers for environmental applications require optimal selectivity, sensitivity, and long term stability, which can be achieved in artificial matrices. For detecting thiols in air, reversible affinity interactions can be optimized by varying the stoichiometry of molybdenum disulphide nanoparticles to achieve sulphur deficiencies. Generating MoS_1.9 increases the quartz crystal microbalance (QCM) sensor responses towards butane thiol by a factor of three. Artificial recognition sites are accessible by molecular imprinting: acrylate copolymers can be tuned in polarity to interact selectively with atrazine in water leading to detection limits below one ppb with QCM sensors. Finally, sensor arrays coated with six different molecularly imprinted polymers (MIP) correctly reproduce the ethyl acetate concentration of a composter over a period of two weeks validated by GC-MS measurements.

Thiol-functionalized three-dimensional (3D) mesoporous silica FDU-12 and SBA-15 with ordered pore were prepared. All the obtained materials were characterized by small angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Mesoporous silica FDU-12 (Fm3m) materials with various unit cell sizes, multifaceted pore were convenient for the interaction of subject and object; the 2D SBA-15 mesoporous silica materials with short and order pore channel were better than the traditional SBA-15 mesoporous silica, in which the pore channel can be used fully. 3D mesoporous silica FDU-12 is used as a sensing material to reconstruct QCM sensors to enhance the stability and this material is an ideal material to deal with heavy metal ions in water.

ZnO is known as a promising material for surface acoustic wave (SAW) sensor devices because of its piezoelectric property. Recently, quartz crystal microbalances (QCMs) have been promising as a sensor platform due to their high sensitivity and ease of measurement. In particular, the alignment of ZnO nanosheets (NSs) into ordered nanoarrays is expected to improve the device sensitivity and stability due to large specific surface area, which allows the captured significant quantities of gas molecules. In this study, we fabricated a quartz crystal microbalance sensor with ZnO NSs structures using polyvinylidene fluoride as a receptor for nerve agent detection. We synthesized two-dimensional NSs by chemical bath deposition (CBD) via the potassium hydroxide etching method. CBD is an excellent method that can easily form uniform structures at low cost. We fabricated ZnO NSs modified with polyvinylidene fluoride and used it for detection of dimethyl methylphosphonate (DMMP) gas. The NSs structure indicated that, when a similar functional group material is coated, the specific surface area increased compared to the nanorods (NRs) structure. As a result, the sensitivity of the quartz crystal microbalance sensor to DMMP gas was improved.

Micro-nanomachining technologies based on extended microfabrication for integrated circuit have been applied for minimal invasive medical tools such as catheter and for highly sensitive sensors and actuators. Hydraulic suction type active catheters were developed. Micromachined quartz crystal microbalances designed especially for use in solution were fabricated to detect absorbed molecules gravimetrically. Micro fluidic channel made of quartz glass was fabricated for the purpose of electrophoresis. Thin cantilever resonators have potentials of extremely sensitive magnetic sensors for micro magnetic resonance imaging. Not only fabrication but also the noise reduction of the cantilever resonating sensor have been studied. Electrostatically actuated bow-tie antenna probe was developed for the purpose of high resolution near-field scanning optical microscope.