SPR-Transduction

Sur ce plasmons are excited if an electromagnetic wave is coupled into a metal/dielectric interface. These plasmons are charge density oscillations propagating at that surface of the metal. The wave is a perturbation of the electron plasma extending several tens of nm into the metal (depending on the skin depth) and decays exponentially up to 500 nm into the adjacent medium. 

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Comparing the two optical transduction techniques (absorption or SPR) used in this work, we can conclude that SPR technique appears to be more suitable for gas sensing even if it presents some limitation regarding the suitable film thickness for SPR excitation. Moreover, the response and recovery times during the anal5fle/sensing layer interaction appears shortest in the case of optical absorption measurements. Further investigations are in... 

For the application of label-free optical transduction principles like SPR or RIfS, a chiral receptor bound to a transparent polymer layer is required. As various types of these polymers have already been applied to chromatographic separation processes, a substantial wealth of knowledge was achieved during the last few decades. Stationary materials like bonded amide selectors or cyclodextrins were adopted as sensor coatings. Several different applications of these materials in various fields of interest have been reported in the literature [17]. 

Both enantiomers of methyl and ethyl lactate ester and several amino acid derivatives were successfully discriminated by both optical transduction principles. In Fig. 8 the results of SPR measurements of both enantiomers of the valine esters with L-Chirasil-Calix are shown. In accordance with gas chromatographic investigations, the L-enantiomer of the amino acid derivatives shows stronger interaction with an L-Chirasil-Calix sensitive layer. This leads... 

SPR spectroscopy and RIfS were used as optical transduction principles for the detection of halogenated diethers as chiral guests with modified cyclodextrin as the stationary phase [7]. 

In this study, for an accurate understanding of the interaction behaviour of the ultramicroporous polymer Makrolon, as a receptor, under the influence of three alcohols is investigated by three transduction methods Spectral ellipsometry (SE), RIfS and SPR. 

Fiber-optic biosensors are analytical devices in which a fiber optic device serves as a transduction element. The usual aim of fiber-optic biosensors is to produce a signal proportional to the concentration of target analyte to which the biological element reacts. Fiber-optic biosensors are based on the transmission of light along silica glass fiber, or POF to the site of analysis. They can be used in combination with different types of spectroscopic technique, e.g. absorption, fluorescence, phosphorescence, or surface plasmon resonance (SPR) (14). 

Biosensors based on optical fibers as transduction element have been recently reviewed by Wolfbeis [97]. Optical biosensors based on miniattaized SPR or on evanescent field monitoring are not as often found in miniaturized biosensors, especially in comparison to miniaturized electrochemical transducers, yet. Two examples will be given here a miniaturized SPR biosensor by Cullen and co-workers [98] and an evanescent based microchip biosensor by Borchers and co-workers [99]. The best-known SPR biosensor is the BIAcore device from Pharmacia Company, Sweden. It has been on the market for over a decade and is routinely used for hybridization kinetic analyses, specificity analyses, etc. Cullen and co-workers have incorporated a commercially available miniaturized SPR transducer into a field analyzer and developed a competition and inhibition assay for an estrogenic compound in water samples that function as endocrine disrupting compounds (EDCs). 

An optical transduction method that is often used with ultrathin hlms, such as LB hlms, is that of surface plasmon resonance [30, 31]. Surface plasma waves are collective oscillations of the free electrons at the boundary of a metal and a dielectric. These can be excited by means of evanescent electromagnetic waves. This excitation is associated with a minimum in the intensity of the radiation reflected from the thin him system, called surface plasmon resonance (SPR). The sensitivity of SPR is noteworthy, and changes in refractive index of 10 may be monitored thus the technique compares favorably with ellipsometry. The method has been used with LB hlms to provide both gas detectors [29] and sensors for metal ions in solution [32]. 

Different transduction methodologies are employed for the VOCs detection, such as electrical conductivity [9], piezoelectric quartz crystal microbalance (QCM) [10-14], surface acoustic wave [15,16], field-effect transistor (FET) [17], surface plasmon resonance (SPR) [18,19], Kelvin probe [20], color variation [8,21,22], and UV-vis absorption [3,23,24], in the physical properties of the sensing elements. 

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