Luminescent signalling Subject

The reaction between the analjrte and the bioreceptor produces a physical or chemical output signal normally relayed to a transducer, which then generally converts it into an electrical signal, providing quantitative information of analytical interest. The transducers can be classified based on the technique utilized for measurement, being optical (absorption, luminescence, surface plasmon resonance), electrochemical, calorimetric, or mass sensitive measurements (microbalance, surface acoustic wave), etc. If the molecular recognition system and the physicochemical transducer are in direct spatial contact, the system can be defined as a biosensor [76]. A number of books have been published on this subject and they provide details concerning definitions, properties, and construction of these devices [77-82]. 

Fluorescence applied to oil identification has been an active field, with 17 papers presented on the subject at the last three Pittsburgh Conferences. A number of interesting developments for fluorescence and low-temperature luminescence (LTL) are described by Eastwood et al. (58). These include synchronous scanning, difference spectrofluorometry, synchronous difference spectroscopy, derivative spectroscopy, and total luminescence (or contour) spectroscopy and combinations of these techniques. In a recent presentation, Eastwood and Hendrick (59) reported an extension of their low-temperature luminescence studies to include polarized excitation and emission spectroscopy, and time-resolved phosphorescence. Preliminary studies of polarization effects indicate that differences exist in low-temperature polarized luminescence spectra of oils, which may aid in oil identification. In the time-resolved phosphorescence spectra of oils, the most significant difference observed was enhancement of the vanadyl porphyrin signal at approximately 700 nm for short delay times (20 fxsec). 

Singlet oxygen measurements have not yet been demonstrated in patients, although this is possible in principle, subject to the limitation that the signal is weak so that it will be difficult to detect using fiber optic probes to collect the luminescence. The possibility of using a pulsed diode laser as the source, as recently proposed [25], should also make a clinical system more ergonomic. The most recent advance [26] is to scan the laser... 

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