Surface-attached fiber sensor

In order to measure vibrations or acoustic wave propagation, an interferometer sensor can be embedded or surface-attached, and then interrogated by using a vibration or AE detection system. When fiber optic sensors are used for measurement of AEs, disadvantages of traditionally used PZT transducers for AE sensing such as their large size and their susceptibility to elec-... 

Fiber optic chemical and biological sensors, based on SPR in continuous metallic films deposited on optical fibers, have been previously reported. " Sensors based on optical fibers have advantages like high response times, ability to be remotely interrogated, and low electromagnetic interference. In our study, fiber optic devices were developed based on excitation of LSPs in gold nanoparticles, deposited on the surface and tip of different optical fiber stractures. As refractive index of the medium around the sensors was varied, or biological molecules attached to the nanoparticles, a shift in the plasmon resonance related dip in the transmission spectram was observed. 

Recent investigations [42] incorporate fluoresceinamine into an N.TV -methylenebisacryl-amide copolymer covalently attached to a glass fiber whose surface is modified by plasma deposition followed by acrylamide photopolymerization. The sensor displays a reversible... 

FIGURE 6.2 Typical configuration of different indicator-mediated fiber optic sensor tips, (a) Indicator is immobilized on the fiber surface, (b) indicator is immobilized on the surface of a membrane attached to the fiber, (c) indicator contained within a chamber created between a membrane and the fiber, (d) indicator contained in a chamber created by a tubular capillary at the end of the fiber, (e) indicator retained in a hollow open capillary at the end of the fiber. (Taken from Otto S. Wolfbeis, Fiber Optic Chemical Sensors and Biosensors, Vol. 1, CRC Press, Boca Raton, FL, 1990.)... 

Fig. 7.13. Different fiber optic sensors (embedded or attached to the surface) as an integrated part of a smart structure...

The manufacturing of adaptive structures requires new production methods that need a lot of experience and expertise for the fabrication of complex systems with embedded or applied actuators and sensors. Patch-like sensors such as 1-3 piezo fiber composites are quite appropriate to be attached to the surface or to be integrated into lightweight multilayer constructions. The bond layer between the piezo element and the base structure determines the transfer behaviour of strain, vibrations and acoustic waves from the actuator to the structure and from the structure to the sensor. Local stress distributions can strongly be influenced by the bonding technique. 

Recently, another type of sensor has been developed to directly detect individual exocytotic events. Xin et al. have simultaneously measured Ca + and catecholamine following their secretion from individual cells using a multidimensional microsensor based on both electrochemistry and fluorescence [45], The surface of a carbon fiber microelectrode is modified with the fluorescent dye calcium green-1 dextran, as this dye is a selective chelator for Ca. The fluorescence response linearly increases with bound Ca +, and the large size of this molecule prevents overconcentration of the reagent at the sensor tip. The dye is attached to the tip of a carbon fiber electrode by cross-linking with 5% glutaraldehyde. 

Randomly dispersed CNT films can be used as electrochemical sensors. For instance, ferrocene was noncovalently attached to acid-treated SWCNT films to detect glutamate. The combination of SWCNTs and ferrocene provided enhanced surface area, direct electron transfer, and catalytic effect. Electrodes can also be coated with CNTs to enhance performance. Indeed, CNT-coated carbon nanoelectrodes significantly outperform the conventional carbon fiber electrodes of similar geometry. ... 

Immobilization Attachment of chemical species to surfaces, polymers, or other insoluble substrates. For example, with optical sensors, indicators are attached to the optical fiber surface. 

Ordered particle packings are also being used in other sensor type applications. Asher et al. ° described a system, where colloidal arrays of polymer particles were embedded in a gel-matrix. Changes in the environment of the particles caused the structures to shrink or expand, which could then be measured through the changes in the optical properties, as exemplified in Fig. 4. The same general idea can be applied to silica particles. This way, very specific sensors could be created when combined with appropriate surface modifications of the silica particles. The latter could be attached to the end of optical fibers or produced as a multisensor array on a chip. 

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