Bulk refractive index sensitivity

BRIS Bulk refractive index sensitivity BSA Bovine semm albumin... 

By employing the approximate expressions for the bulk refractive index sensitivity of the effective index Eq. 58 and low-loss metal approximation of Ipd (Eq. 48), Eq. 63 can be reduced to ... 

In the following section, sensitivity of the sensor output to effective index of a surface plasmon is analyzed for selected sensor configurations, and the merit of different SPR sensor configurations in terms of bulk refractive index sensitivity is evaluated. 

Fig. 11 Bulk refractive index sensitivity as a function of wavelength for SPR sensors with wavelength modulation and prism coupler or grating coupler and three different grating periods. Prism-based sensor configimation BK7 glass prism, gold film, and a non-dispersive dielectric (refractive index 1.32). Grating-based sensor configuration a non-dispersive dielectric (refractive index 1.32) and gold grating...

The bulk refractive index sensitivity can be calculated from the instrumental sensitivity in a similar fashion as in previous sections for the angular and wavelength modulation. The sensitivity to bulk refractive index can be expressed as ... 

Here, m is the refractive-index sensitivity of the sensor Uadsorbate and Ubiank are the refractive indices of the adsorbate (i.e., analyte) and the bulk environment prior to the sensing event, respectively (iadsorbate is the effective thickness of the adsorbate layer and k is the characteristic electromagnetic field decay length associated with the sensor. 

Fig. 15 Sensitivity of the real propagation constant (—) and effective index (---) of a surface plasmon on a metal-dielectric interface to a bulk refractive index change as a function of wavelength calculated rigorously from eigenvalue equation and using the perturbation theory. Waveguiding structure gold-dielectric (nj = 1.32)...

The sensitivity of the effective index of the symmetric and antisymmetric surface plasmons to a surface refractive index change, Figs. 19 and 20, follows basically the same trends as the sensitivity to bulk refractive index changes. 

Fig. 17 Sensitivity of the effective index of symmetric and antisymmetric surface plasmons to bulk refractive index changes as a function of the thickness of metal layer. Waveguide configuration dielectric ( i = 1.32)-gold (sm = - 25 + 1.44i)-dielectric superstate ( d = 1.32), wavelength 800 nm...

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. 

The sensitivity of angular modulation-based SPR sensors to bulk refractive index (herein denoted as (Se)p 5 and (Se)g,ating for SPR sensors using prism and grating couplers, respectively) can be derived from Eqs. 12 and 13, and the equation for Stief/Sn obtained using the perturbation theory (Eq. 58... 

The maximum sensitivity of intensity modulation-based SPR sensors to bulk refractive index can be derived from Eq. 28 (where SrieflSn is from... 

Another classification of detector is the bulk-property detector, one that measures a change in some overall property of the system of mobile phase plus sample. The most commonly used bulk-property detector is the refractive-index (RI) detector. The RI detector, the closest thing to a universal detector in lc, monitors the difference between the refractive index of the effluent from the column and pure solvent. These detectors are not very good for detection of materials at low concentrations. Moreover, they are sensitive to fluctuations in temperature. 

Refractive index detectors. These bulk property detectors are based on the change of refractive index of the eluant from the column with respect to pure mobile phase. Although they are widely used, the refractive index detectors suffer from several disadvantages — lack of high sensitivity, lack of suitability for gradient elution, and the need for strict temperature control ( + 0.001 °C) to operate at their highest sensitivity. A pulseless pump, or a reciprocating pump equipped with a pulse dampener, must also be employed. The effect of these limitations may to some extent be overcome by the use of differential systems in which the column eluant is compared with a reference flow of pure mobile phase. The two chief types of RI detector are as follows. 

Bulk property detectors function by measuring some bulk physical property of the mobile phase, e.g., thermal conductivity or refractive index. As a bulk property is being measured, the detector responses are very susceptible to changes in the mobile phase composition or temperature these devices cannot be used for gradient elution in LC. They are also very sensitive to the operating conditions of the chromatograph (pressure, flow-rate) [31]. Detectors such as TCD, while approaching universality in detection, suffer from limited sensitivity and inability to characterise eluate species. 

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