Sensors refractive-index-type

The interaction phenomenon of the analyte with radiation is governed or modifies the principle on which light is transmitted through the waveguide. Depending on that interaction, we can differentiate three basic types of intrinsic optical sensors [82] refractive-index-type sensors, luminescence-based sensors and absorption-type sensors. 

For refractive-index-type sensors, the waveguide is intrinsically the sensing element, and then chemical processes are measured with the variations of the refractive index, n, of guided modes. The majority of the various sensor types and published configurations make use of grating couplers (Fig. 10a) [83,84], resonant mirrors (Fig. 10b) [52,86-89] or interferometric sensors (Fig. 11) as... 

Refractive-index-type sensors present poor specificity in their response and instabilities due to temperature or pressure variations and on the other hand, interferometric sensors are complex, but more sensitive than other integrated chemo-optical evanescent-field-based sensors. 

The sensors in this section can also be utilized to detect chemicals in liquid through the bulk solution refractive index change induced by the presence of target chemicals. Since no recognition molecules are used, this type of chemical sensing may usually have low specificity. However, these sensors may perform excellently in conjunction with other technologies such as capillary electrophoresis, mass spectrometer, and liquid chromatography in chemical detection. 

The interferometric sensor platform is highly sensitive and is the only one that provides an internal reference for compensation of refractive-index fluctuations and unspecific adsorption. Interferometric sensors have a broader dynamic range than most other types of sensors and show higher sensitivity as compared to other integrated optical biosensors . Due to the high sensitivity of the interferometer sensor the direct detection of small... 

Pannell and coworkers34 described the use of poly(ferrocenylsilanes) as coatings in optical fiber gas sensors. In these devices a small change in refractive index of the polymer film results in a large change in the optical transmission of a tapered optical fiber. This is useful for remote sensing of ammonia or carbon dioxide. Polymers of type 6.20 with R/R = Me/Ph and copolymers from monomers with R/R = Me/Ph and Me/Me were found to be effective for this application. 

One of the most widely studied refractive index sensor, especially for the detection of proteins and other bioanalytes, is the SPR-based evanescent-wave-type sensor. In comparison with evanescent-based sensors, the intensity of the field in the recognition layer deposited over the metal is 2 orders of magnitude higher than that deposited over the glass. 

Flat-surface SPR sensors have a large refi-active-index sensitivity ( 2 x 10 nm/RIU), which is the chief component of their overall sensitivity [54]. LSPR nanosensors have modest refractive-index sensitivity ( 2 x 10 nm/RIU) [55], in contrast. Nevertheless, both types of sensors have approximately equivalent sensitivity for a given adsorbate. In addition to the difference in refractive-index sensitivity, the electromagnetic field decay length Zdis also different for SPR and LSPR sensors. SPR sensors have a decay length on the order of 200 nm. For LSPR... 

The location and type of sensor can greatly affect controllability, safety, and on-time reliability. Controllability can also be improved when a different type of sensor is used. For example, a temperature sensor might be used to infer composition. Such a sensor is easy, robust, and accurate in measuring the temperature. However, the new specifications for the purity have shifted the composition to a range where temperature measurements are no longer sensitive to the composition. Refractive index measurements should be used. 

The first term Srh depends on the method of excitation of surface plasmons and the modulation approach used in the SPR sensor and is hereafter referred as to the instrumental contribution. Sri2 describes the sensitivity of the effective index of a surface plasmon to refractive index and is independent of the modulation method and the method of excitation of surface plasmons. The sensitivity of surface plasmon to refractive index Sri2 depends on the profile of fhe refracfive index tih and has been analyzed in Chap. 1 of this volume [ 1 ] for the two main types of refractive index changes - surface refractive index change and bulk refractive index change. 

Surface plasmon resonance (SPR) sensors are optical sensing devices that take advantage of the sensitivity of a special type of electromagnetic field, a surface plasmon, to changes in refractive index. SPR sensors can be classified based on the method for optical excitation of surface plasmons and the measured characteristic of the light wave interacting with the surface plasmon. 

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