Choice of transducer

The transducer provides the evidence that the reaction of the bioreceptor has occurred. The choice of transducer depends on the reaction type, and the substances liberated or consumed (Table 2.1). Generally, the choice is the appropriate commercialized transducer for the detection method required. There are a large number of electrodes available for electrochemical detection, for example, electrodes that are... 

The choice of transducer also depends on the intended tq>plication of the biosensor. If it is to be used in a biological environment, then it must ftilfil the criteria of biocompatibility, especially with regard to the deporition of proteins, lipids, or cells on its surface. If it is to be used in vivo, then it should be of reduced size, and its fcmn adapted so as not to cause excessive damage to living tissues. Furthermore, the possibility of the release of toxic, metallic, or polymeric components from the transducer should be taken into account when long-term implantation of the biosensor is intended. 

The problem of chemical interference affects the choice of transducer. It is possible to couple urease with a number of different electrodes, such as pH, pNHt, pCX>2, or pNHs electrodes. The best transducers for the determination of urea in a biological sample are the pCOz or pNHa electrodes because they have a hydrophobic membrane to eliminate all possible interference frcrni cations and anions. 

Successful measurement of machine vibration requires more than a transducer randomly selected, installed, and a piece of wire to carry the signal to the analyzer. When the decision to monitor vibration is made, three choices of measurement are available (1) displacement, (2) velocity, and... 

The accuracy of the thermochemical data obtained by this technique has been examined in numerous systems. In general, the data compares well, 1 kcal/mol, with that obtained by other spectroscopic and calorimetric methods. The accuracy and reproducibility of the data is dependent on the magnitude and time scale of the heat deposition detected by PAC that is associated with a given chemical process. Highly exothermic reactions are easy to detect, whereas ones that are not are difficult to detect. A thermoneutral reaction is invisible to PAC. Reactions that occur significantly slower than the response time of the transducer are not detected. Reactions that occur either slightly slower or faster than the response time are difficult to resolve accurately. Clearly, the proper choice of the transducer is extremely important in order to resolve accurately a given chemical event. 

In practice, the time constraint condition may be met by a careful choice of appropriate experimental conditions for a given transducer. Kinetic data for the process of interest is of great help in choosing those conditions. The validity of r <time profile of the calibration and sample waveforms or by varying conditions (e.g., sample concentration) until the experimental waveform reaches a maximum in amplitude. 

Because this detector is found to be universal, have a broad dynamic range, good sensitivity, and a wide choice of carrier gases it is gaining in acceptance. Today there is an instrument commercially available (Figure 5.24)(40). In this detector, sound waves are propagated at one transducer and received at another,... 

Selectivity of the MIP-PZ sensors can be improved by separately optimizing the binding and determination medium. MIPs combined with PZ transducers are unique in selectivity with respect to enantiomers. The proper choice of functional monomers used for imprinting can improve this selectivity at a very low LOD. For instance, paracetamol has been determined with the MIP-QCM chemosensor using VPD and MAA as the MIP functional monomers [109], Affinity of this... 

Many SECM experiments require biasing the substrate. A bipotentiostat in Fig. 1 is used to control both the tip and substrate potentials. Unless transient measurements are made, the response of the bipotentiostat does not have to be fast. More importantly, it should be capable of measuring a broad range of current responses a picoamp scale (or even sub-pA) tip current and a much higher current at a macroscopic substrate. For this reason, it is convenient to have several choices of preamplifiers/current-to-voltage transducers. 

Application of ultrasound enhances transdermal drug transport, a phenomenon referred to as sonophoresis. Proper choice of ultrasound parameters including ultrasound energy dose, frequency, intensity, pulse length, and distance of transducer from the skin is... 

The basic requirement in biosensor development is ascribed to the successful attachment of the recognition material, a process governed by various interactions between the biological component and the sensor interface. Advanced immobilization technologies capable of depositing biologically active material onto or in close proximity of the transducer surface have been reported. In this context, the choice of a biocompatible electrode material is essential. The material surfaces (support) include almost all material tjrpes metals, ceramics, polymers, composites and carbon materials [8]. In most cases, when a native material does not meet all the requirements for... 

In general, a vast number of optical transduction techniques can be used for biosensor development. These may employ linear optical phenomenon (e.g. adsorption, fluorescence, phosphorescence, and polarization) or nonlinear phenomena (e.g. second harmonic generation). The choice of a particular optical method depends on the analyte and the sensitivity needed. Total internal reflection fluorescence (TIRF) has been used with planar and fibre-optic wave-guides as signal transducers in a number of biosensors. 

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