Sensors response characterisation

McDonagh C., Bowe P., Mongey K., MacCraith B., Characterisation of porosity and sensor response times of sol-gel-derived thin films for oxygen sensor applications, J. Non-Cryst. Solids 2002 306 138-148. 

Center for Healthcare Technologies at Lawrence Livermore National Laboratory in Livermore, potentially capable to measure pH at or near the stroke site29. The probe is the distal end of a 125 pm fibre tapered up to a diameter of 50 pm. A fluorescent pH-indicator, seminaphthorhodamine-1-carboxylate, is embedded inside a silica sol-gel matrix which is fixed to the fibre tip. Excitation of the dye takes place at 533 nm and the emission in correspondence of the acid (580 nm) and basic (640 nm) bands are separately detected. The use of this ratiometric technique obviates worrying about source fluctuations, which have the same effects on the two detected signals. The pH sensor developed was first characterised in the laboratory, where it showed fast response time (of the order of tens of seconds) and an accuracy of 0.05 pH units, well below the limit of detection necessary for this clinical application (0.1 pH units). The pH sensor was also tested in vivo on rats, by placing the pH sensor in the brain of a Spraque-Dawley rat at a depth of approximately 5 mm30. 

Abstract Validation of analytical methods of well-characterised systems, such as are found in the pharmaceutical industry, is based on a series of experimental procedures to establish selectivity, sensitivity, repeatability, reproducibility, linearity of calibration, detection limit and limit of determination, and robustness. It is argued that these headings become more difficult to apply as the complexity of the analysis increases. Analysis of environmental samples is given as an example. Modern methods of analysis that use arrays of sensors challenge validation. The output may be a classification rather than a concentration of analyte, it may have been established by imprecise methods such as the responses of human taste panels, and the state space of possible responses is too large to cover in any experimental-design procedure. Moreover the process of data analysis may be done by non-linear methods such as neural networks. Validation of systems that rely on computer software is well established. 

Characterisation Of Explosives By The Response Of Gas Sensor Array To Modulated Intensity Of The Smell... 

The time constant based characterisation of a smell includes an approximation of the response kinetics by multiexponential decay similar to the description (6). A collection of several pairs of the parameters r, a, is usually obtained for each of the sensors in the array from this approximation. The characteristic parameters, namely the time constants r, and the weigh coefficients a, are used for the composition of a graphical representation of the sensor outputs that might be visually inspected. The graphical representation is build up by an original method. 

The important result of this analysis is that the spatiotemporal information available from a sensor time series can never be less than purely spatial information (such as the mean output over time). By increasing the diversity in the temporal responses the ratio of this information can be very high indeed, leading to large improvements in discrimination performance. The equations here characterise this explicitly in the linear case. 

Dodecyl acrylate microspheres, crosslinked with hexanediol diacrylate, were prepared by emulsion polymerisation and characterised by scanning electron microscopy, particle size measurement, and differential scanning calorimetry. The microspheres were doped with 9-(diethylamino)-5-(octadecanoylimino)-5H-benzo(alpha)phenoxazine (ETH 5294), a chromoionophore whose fluorescence emission spectrum is sensitive to pH. These microspheres adsorb anions selectively according to their lipophilicity, and therefore can be used as anion-selective optical sensors. The responses of the microspheres to chloride, nitrate and perchlorate ions were reported. 27 refs. 

Innocenzi P, Martucd A, GugUelmi M, Bearzotti A, Traversa E (2001) Electrical and structural characterisation of mesoporous sUica thin films as humidity sensors. Sens Actuators B Chem 76 299-303 Innocenzi P, Falcaro P, Bertolo JM, Bearzotti A, Amenitsch H (2005) Electrical responses of silica mesostructured films to changes in environmental humidity and processing conditions. J Non-Cryst Solids 351 1980-1986 Jacobs PA (1977) Carboniogenic activity of zeolites. Elsevier Scientific, New York... 

Casey V, Cleary J, D Arcy G, McMonagle JB (2003) Calorimetric combustible gas sensor based on a planar thermopile array fabrication, characterisation, and gas response. Sens Actuators B 96 114-123 Chadwick B, Tann J, Brungs M, Gal M (1994) A hydrogen sensor based on the optical generation of surface plasmons in a palladium alloy. Sens Actuators B 17 215-220... 

Micro-Electromechanical Systems The measure of the intelligence of this and other systems is both the range and time of response to changes in the monitored equipment or environment. This is most often ensured by micro-electromechanical systems (MEMS), miniature components which measure and process such parameters as acceleration, pressure, distance, temperature, light and the chemical composition of an atmosphere. The heart of MEMS is a processing unit (microprocessor) made in the form of an integrated circuit on a silicon board. The board is then chemically etched and layers of other materials are deposited to make a sensor. Typical features of a MEMS fabricated in this way are shown in Fig. 7.5. Thanks to their small size, sensors in MEMS are characterised by low inertia, which makes it possible to quickly start and stop their functions. Moreover, thanks to their integration with the microprocessor in one substrate, their response to external stimuli is sent to the microprocessor almost immediately. 

Enzyme inhibition sensors are of interest in the environmental context, the most used being those involving acetylcholinesterase inhibited by pesticides e.g. these can involve rather complex architectures, and characterisation of such systems by EIS is becoming more widespread. Complex sensor architectures have been used for endocrine disrupters, with similar characterisation by electrochemical impedance. Recently, EIS was used for the first time to characterise the response of glucose biosensors in the presence of heavy metal ion inhibition. ... 

Fig. 22.4 Typical response ciffve (left) and sensitivity (right) of a generic chemical sensor based on adsorption of target molecules in a sensing layer characterised by a limited amoimt of adsorption sites...

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