Luminescent signalling applications

Although in this text they are not described as such, many of the applications described in section 3.5.6 fall into the category of luminescent signalling. For instance, the detection of in section 3.S.6.3, the measurement of pH in section 3.5.6.4, and the use of lanthanide chelates in DNA studies outlined in section 3.5.6.9 all use the change in fluorescence for both the signalling and quantification of the target. 

Within the context of supramolecular devices, re-emission of the radiation by luminescence is of interest in sensing and signalling applications, while chemical reactions are of interest in applications such as molecular switches and photocatalysis. Strictly speaking absorption and re-emission type processes are termed molecular photophysics while light-induced chemical reactions or chemical processes are termed photochemistry . 

It is, however, possible to measure chiroptical properties related to the excited states of molecules - circularly polarized luminescence (CPL) [13]. In this case, the sample is excited by unpolarized radiation and the luminescence signal is analyzed by a circular analyzer. Several variants of this concept have been developed, but the applications are targeted more on electronic structure of the excited states of molecules than to their geometries. 

In conclusion, the new chimeric photoprotein Photina exhibits a robust flash luminescence signal in different expression systems, rendering this protein a reporter well-suited for HTS and uHTS applications. 

The luminescent polynuclear metal complexes may also find utility as chemo-sensors and in signaling applications. 

The other application is the flying-spot scanner. In this set up the information of slides or film can be transfonned into electric signals. The election beam excites a phosphor with short decay time. The luminescence signal scans the object point by point and the transmitted radiation is detected with a photomultiplyer. To reduce blurring of the signal, the decay time of the phosphor should be of the order of magnitude of the time the electron beam scans a picture element ( 50 ns). 

St John PA, McCarthy WJ, Winefordner JD (1966) Application of signal-to-noise theory in molecular luminescence spectrometry. Anal Chem 38 1828... 

The optode transduces the non-optical signal from the environment to the optical one, readable by the photodetector. Various indirect optical sensors and theirs applications are described in literature35. The optode can work as a chemical sensor that detects certain analytes in aqueous solutions or in air on chemical way. It means that changes in the environment cause the changes in the photosensitive material, which is immobilized in the optode matrix. These chemical changes influence the observed light intensity (for example, due to absorption) or one can analyze the intensity or time decay of luminescence. There are numbers of publications devoted to the family of optical chemical sensors36. 

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