Sensing lifetime-based

Prior to describing the various mechanisms of sensing, we consider it usefiii to expand on the use of decay-lime measurements for sensing. The advantages of lifetime-based sensing are illustrated in Rgure 19.5. In the research laboratory, where clean cuvettes and i cal sutfeces are 

Flgurt 19.4. Optical duotbanoe of tissues and water. Hb. Hemoglobin. Revlaed and reprinted, wi (h permbsion. from Ref. 22, Cc iytight01996, Annual Reviewi, 

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Szmacinski, H. Lacowicz, J. R. Lifetime-based Sensing Using Phase-Modulation Fluorometry. In Fluorescent Chemosensor for Ion and Molecule Recognition. ACS Symposium Series 538, 1993. 

It is even possible to convert changes of the fluorophore emission intensity as a function of the analyte level into lifetime-based sensing devices using phase-sensitive detection. The technique is called dual lifetime... 

Lifetime-based sensing can be mostly insensitive to these real-world effects. This is because these factors are not expected to alter the rate at which the intensity decays (Figure 1.2, middle). In our opinion, phase-modulation sensing provides additional advantages (Figure 1.2, bottom). The instruments take advantage of radio-frequency... 

Figure 1.5. Noninvasive sensing of glucose. Within the optical window (650 nm-1300 nm), lifetime-based sensing by fluoresence is possible through the human skin.

H. Szmadnski and J. R. Lakowicz, lifetime-based sensing of magnesium (submitted for publication). 

Chapter 10 of this volume, entitled Lifetime-Based Sensing, by Henryk Szmacinski and Joseph R. Lakowicz is an excellent complement to the material presented in this section. 

J. R. Lakowicz, H. Szmacinski, and K. W. Berndt, Fluorescence lifetime-based sensing of blood gases and cations, Proc. SPIE 1648, 150-163, (1992). 

Molecular Mechanisms for Fluorescence Lifetime-Based Sensing... 

Lifetime-based sensing can also be based on the existence of two forms of the probe, the fraction of which depends on the analyte concentration. This case is presented in Figure 10.4 where it is assumed that the absorption spectra overlap and both forms can be excited at the same wavelength. The sample displays two lifetimes (TFandifi) which are characteristic of the analyte-free (F) and analyte-bound (B) forms of the probes. The change in lifetime (from rf to zb) is due to binding of the analyte... 

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