Biosensors optical transducers

For optical transducers, the measured signals are directly proportional to [P], so that, once again, reaction layer thickness and mass-transport kinetics determine the sensitivity of the biosensor, and signals are directly proportional to analyte concentration. For potentiometric transducers, signals are proportional to log[P], and therefore to log[S]. ... 

The majority of the biosensors that have been reported are based on the deposition of biologically active species such as enzymes and antibodies at the surface of an electrochemical or optical transducer. The most common principle is to identify the analyte by use of a chemically selective enzyme. The enzyme-substrate reaction produces a secondary chemical signal by means of catalysis, e.g. H" or H2O2. This signal is then recognized and quantitatively converted to an electrical signal, e.g. a potential, a current, or a change of absorption or fluorescence, by a suitable transducer. 

Biosensors are also classified according to the parameter that is measured by the physicochemical transducer of the biological event. Thus, classically biosensors are grouped into optical, electrochemical, acoustic and thermal ones. Optical transducers of most common enzyme biosensors are based on optical techniques such as absorption, reflectance, luminescence, chemi-luminescence, evanescent wave, surface plas-mon resonance, and interferometry. 

Massad-Ivanir N, Shtenberg G, Tzur A, Krepker MA, Segal E (2011) Engineering nanostructured porous SiO(2) surfaces for bacteria detection via direct cell capture . Anal Chem 83 3282 Massad-Ivanir N, Shtenberg G, Segal E (2012) Advancing nanostructured porous Si-based optical transducers for label fi ee bacteria detection. Adv Exp Med Biol 733 37 Mello LD, Kubota LT (2002) Review of the use of biosensors as analytical tools in the food and drink industries. Food Chem 77 237... 

Biosensor Detection. As mentioned above, detection occurs via a measurable change in the biosensor s transducer. Binding of a target molecule to an immobilized chemical receptor may bring about measurable changes that are electrochemical, electrical, thermal, magnetic, optical, or piezoelectric. The principles behind some of these mechanisms are further described in the section entitled Experimental Methods. Additional information can be obtained from a recent review (62). 

Biosensors with optical transducers are distinguished from optical sensors for inorganic species by certain specific features. Differences exist in the importance of specific optical phenomena. 

The previous discussion has focused on the fabrication, characterization and optimization of the transducer. Here, we discuss, coupling of the biomolecular detector to the optical transducer to create a functional nanoSPR biosensor. The two important steps in coupling the biological detector to the optical transducer are presentation of the receptor on the nanoparticle surface and biomolecular binding between receptor and analyte. It has been shown that the density and spatial distribution of the receptor on the surface influences the effective binding affinity of the biomolecular recognition interaction as well as the surface density of the biomolecular complex, so that... 

Optical biosensors based on fluorescence detection often use the combination of a fluorescent bioreceptor associated with an optical transducer. Fluorescent biosensors may also be obtained by immobilizing whole cells on the surface of a sensor layer. This bioactive layer is usually placed in front of the tip of an optical fibers bundle to generate a fluorescent signal. The optical fibers are required to send the excitation radiation to the fluorescent bioelement and convey the fluorescence radiation up to a fluo-rimeter. In order to improve the simpHcity and reliability of fluorescence-based biosensors, optically translucent supports are used because their optical properties enable detection of fluorescence emitted by the algal cells. 

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