Sensor performance

Applicability of Semiconductor Gas Sensors Research into the applications of this type of sensor has mainly been concerned with measuring carbon monoxide concentration in flue gases. Tests show that sensors follow the concentration of carbon monoxide in the flue gas. Improvement in sensor performance has resulted with the introduction of a catalytic additive (palladium or... 

The immobilization procedure may alter the behavior of the enzyme (compared to its behavior in homogeneous solution). For example, the apparent parameters of an enzyme-catalyzed reaction (optimum temperature or pH, maximum velocity, etc.) may all be changed when an enzyme is immobilized. Improved stability may also accrue from the minimization of enzyme unfolding associated with the immobilization step. Overall, careful engineering of the enzyme microenvironment (on the surface) can be used to greatly enhance the sensor performance. More information on enzyme immobilization schemes can be found in several reviews (7,8). 

Three different ways in which a zeolite membrane can contribute to a better sensor performance can be distinguished (i) the add-on selective adsorption or molecular sieving layer to the sensor improves selectivity and sensitivity, (ii) the zeolite layer acts as active sensing material and adds the selective adsorption and molecular sieving properties to this, and (iii) the zeohte membrane adds a catalytically active layer to the sensor, improving the selectivity by specific reactions. 

The calibration curve obtained for hydrogen peroxide exhibited a detection limit of 30 pmol and ranged over three decades at least. These performances compared well with those previously obtained in non-micellar media54. The presence of surfactant compounds in the ECL measurement buffer appeared thus to have little effect on the H2O2 ECL sensor performances. In optimized conditions, the determination of free cholesterol could be performed with a detection limit of 0.6 nmol and a calibration curve ranging over two decades at least. 

Often given for commercial polymers, but usually neglected when sensor performance is discussed. 

The one-substrate mechanism is frequently operative in enzyme-based sensors. However, when several substrates or two or more (coupled enzymatic reactions) are required for sensor performance, the derived equations are more complex and usually require simplification for solving35. 

For the OFRR-based vapor sensor, the ring resonator wall thickness has a significant impact on the sensor performance. Since the polymer layer is treated as the extension of the ring resonator, the relative thickness between the wall and the polymer determines the radial intensity distribution of the WGMs. As a result,... 

The need for improved sensor performance has led to the emergence of micro and nanofluidics. These fields seek to develop miniaturized analysis systems that combine the desired attributes in a compact and cost-effective setting. These platforms are commonly labeled as labs-on-chip or micro total analysis systems (pTAS)2, often using optical methods to realize a desired functionality. The preeminent role that optics play has recently led to the notion of optofluidics as an independent field that deals with devices and methods in which optics and fluidics enable each other3. Most of the initial lab-on-chip advances, however, occurred in the area of fluidics, while the optical components continued to consist largely of bulk components such as polarizers, filters, lenses, and objectives. 

In recent years, rapid advancements in photonic technologies have significantly enhanced the photonic bio/chemical sensor performance, especially in the areas of (1) interaction between the light and analyte, (2) device miniaturization and multiplexing, and (3) fluidic design and integration. This has led to drastic improvements in sensor sensitivity, enhanced detection limit, advanced fluidic handling capability, lower sample consumption, faster detection time, and lower overall detection cost per measurement. 

Therefore the flicker noise is expected to grow with 7 as the device size is scaled down. In deep submicron MOSFETs the corner frequency at which thermal noise equals flicker noise may be as large as 100 MHz, indicating that, at low frequency, 1/f noise is the most severe noise source which affects sensor performance. 

In parallel with improvements in chemical sensor performance, analytical science has also seen tremendous advances in the development of compact, portable analytical instruments. For example, lab-on-a-chip (LOAC) devices enable complex bench processes (sampling, reagent addition, temperature control, analysis of reaction products) to be incorporated into a compact, device format that can provide reliable analytical information within a controlled internal environment. LOAC devices typically incorporate pumps, valves, micromachined flow manifolds, reagents, sampling system, electronics and data processing, and communications. Clearly, they are much more complex than the simple chemo-sensor described above. In fact, chemosensors can be incorporated into LOAC devices as a selective sensor, which enables the sensor to be contained within the protective internal environment. Figure 5... 

Abstract In order to improve upon automated sensor performance for secu-... 

The central computer is called the master terminal unit, or MTU. The MTU has two main functions to periodically obtain data from RTUs/PLCs and to control remote devices through the operator station. The operator interfaces with the MTU using software called human machine interface (HMI). The remote computer is called the program logic controller (PLC) or remote terminal unit (RTU). The RTU activates a relay (or switch) that turns mechanical equipment on and off. The RTU also collects data from sensors. Sensors perform measurement, and actuators perform control. 

The model analytes, which were used to show the sensor performance of the microsystems include carbon monoxide, CO, and methane, CH4. The sensor microsystems were designed for practical applications, such as environmental monitoring, industrial safety applications or household surveillance, which implies that oxygen and water vapors are present under normal operating conditions. In the following, a brief overview of the relevant gas sensor mechanisms focused on nano crystalline tin-oxide thick-film layers will be given. 

The model sensitive layer, which will be used for gas sensor performance tests throughout this book, was Sn02 that has been doped with 0.2 wt % Pd. The minute Pd-content leads to a better sensitivity to carbon monoxide. The larger response is a consequence of the increased reaction rate. For the sensor arrays in Chap. 6, two additional materials have been prepared. Pure tin oxide shows a good sensor response... 

The microhotplate was coated with a thick-film tin-oxide droplet as described in Sect. 4.1.2. To characterize the chemical-sensor performance, the chip was exposed to CO concentrations from 5 to 50 ppm in humidified air at 40% relative humidity (23.4 °C water vaporization temperature) (see Sect. 5.1.8 for a description of the gas test measurement setup). 

I. Simon, N. Barsan, M. Bauer, and U. Weimar. Micromachined metal oxide gas sensors opportunities to improve sensor performance . Sensors and Actuators B73 (2001), 1-26. 

One temporal concept to be borne in mind in this context is whether the (bio)chemical reactions and mass transfer separations taking place at the active microzone (one or both of which, by definition, take place simultaneously with detection) are simultaneous or sequential relative to each other. Whether such processes take place at the same or a different time has a marked effect on the sensor performance and type of transient signal obtained. 

The three above-mentioned types of kinetics also influence other aspects of sensor performance (Fig. 2.20). Thus, the signal-time profiles they provide are critically dependent on the kinetics of the processes involved for example, if the sensor regeneration is rather slow, baseline restoration is much too slow. As noted earlier, a slow chemical kinetics can be used to perform reaction rate measurements. 

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