Response sensors coated with different

Figure 6. Characteristic patterns of response of an array of six sensors coated with different phthalocyanines to various vapor exposures. The maximum concentration was 100 ppm for ammonia, sulfur dioxide, and DMMP and 1000 ppm for water, ethanol, air and benzene. The central metal of each phthalocyanine is shown at the top.

A electronic nose based on an array of eight quartz microbalance-based (QCM) sensors coated with modified MPPs (5,10,15,20-tetraphenylporphyrin) was used for apple aroma measurements [13], The response of each QCM sensor was modeled with Brunauer-Emmett-Teller (BET) adsorption isotherms. By means of multivariate analysis on all sensor responses, the different compounds could be discriminated well and quantified accurately. This calibration protocol can be used to characterize the sensors for the vapors of complex mixtures. 

Traces of VOCs in human breath can be a symptom of diabetes, kidney failure, asthma or breast cancer. VOCs were mainly detected by mass spectroscopy with a ppb detection limit. The most advanced VOC sensor based on SWCNTs for medical application was introduced by Peng et al. (2008a, 2008b). This device is designed as an array of ten SWCNT chemiresistors coated with different non-polymeric organic layers. Since the responses of each chemiresistor are different, a principal component analysis of the measurement allows the direct discrimination between a healthy patient and a patient with cancer or renal diseases. The same authors have also highlighted the dramatic effect of humidity on the sensor response and have proposed coupling the device with a water extractor (Fig. 10.8). 

In Figures 15 and 16 are reported the responses in Hz of QCM sensors coated with cavitands 37-42 to different analytes at the same concentration. In both series the responses increase with increasing the chain length of the substituents at the lower rim, in particular between Ci and Q. 

The key to the successfid use of QCM in liquids is the development of sensitive and stable sensor coatings on the oscillating surface. The material of choice must be insoluble in water with no swelling behaviour. We studied the responses of the QCM sensors coated with cavitands 38-39 and 41-42 toward several different analytes (Figure 18), and compared the resulting sensor signals with their partition coefficients log Poet (octanol/water) as function of their hydrophobicity (Table 3)/... 

The fabrication and characterization of a fiber optic pH sensor based on evanescent wave absorption was presented by Lee63. The unclad portion of a multi-mode optical fibre was coated with the sol-gel doped with pH sensitive dye. The sensitivity of the device increased when the multiple sol-gel coatings were used in the sensing region. The dynamic range and the temporal response of the sensor were investigated for two different dyes -bromocresol purple and bromocresol green. 

As an example of the use of array methodology to study chemical sensor properties let us consider the thirteen molecular structures reported in Figure 5. To investigate the sensing properties of these molecules we studied the behaviour of the response of thickness shear mode resonators (TSMR) sensors, each coated with a molecular film, to different concentration of various volatile compounds (VOC). Analyte compounds were chosen in order to have different expected interaction mechanisms. 

Direct detection of Staphylococcal enterotoxins B (SEB) is illustrated in Fig. 14 which shows binding of SEB to the wavelength-modulated SPR sensor surface coated with respective antibodies for five different SEB concentrations". Figure 15 shows the sensor response to binding after 30-minute SEB incubation and initial binding rate as a function of SEB... 

Conventional humidity sensors of the electric resistance variable type use hydrocarbon polyelectrolyte as a moisture sensing material. Therefore, the sensors usually have insufficient heat resistance, and cannot be used at temperatures of 60°C or more. Another problem is that they deteriorate when in contact with cigarette smoke and oil contained in the air [64,65]. When the fluorinated pitch-deposited coating was breathed upon, the electrical resistance quickly decreased, but electrical resistance quickly recovered when this action was stopped. Then, how to develop a humidity sensor excelling in humidity response sensitivity, heat resistance and durability was attempted [66]. Two kinds of comb-like electrodes with different electrode gaps were made, and a thin film was formed on the surfaces by vacuum deposition of fluorinated pitch. The obtained fluorinated pitch sensors were left at rest in a thermostatic chamber, and electrical resistance was determined under the following conditions. 

Each sensor in an array is designed with a different coating, with each coating selected to respond differently to the members of a set of analytes as described above. The resultant combination of responses should produce a unique finger-... 

Fig. 21.13. QCM responses to coatings polymerised from different porogens (acting as print molecules) with/without embedded calix[6]arene in brackets. The sensor response of 70 nm layers to 500 ppm of xylene isomers is shown. Compared to the layer polymerised in chloroform, the pronounced imprint effect for xylene can be seen. o-Xylene has the lowest volatility of the xylene isomers and therefore is equally detected in all layers.

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