Analyte concentrations, measurement using fluorescent lifetime

Advanced process state estimation, prediction, and control via hybrid process modeling, 144-154 Aminophenols, use as sensor for subnanomolar concentrations, 70-80 Analyte concentrations, measurement using fluorescent lifetime, 99-108... 

Many probes are now known that display changes in fluorescence lifetime on complexation of the analyte, photophysical properties some of them are summarized in Table 10.2. While we have listed the lifetimes of the free and the bound forms of the probes, there is no straightforward equation to calculate the analyte concentration using the mean lifetime as was in the case of the absorbance and intensity (Eqs. (10.14) and (10.15)). The mean lifetime depends not only on relative concentration of the probe species (free and complexed) but also on their decay times, quantum yields, and to some extent on the measurement (method or conditions). While the mean lifetime is independent of total probe concentration, this value generally depends not only on analyte concentration but also on excitation and observation wavelengths.03 ... 

This relationship provides an alternative method to determination of the concentration of the analyte of interest. Specifically, lifetime or decay time measurements can be used in fluorescence based sensors to determine the analyte concentration. These measurements provide better results than steady-state measurements. Time-domain lifetime measurements are typically performed by exciting the sensing element with a short optical pulse which is much shorter than the average fluorophor lifetime. For a single population of fluorophors, the rate at which the intensity decays over time can be expressed as ... 

Since the 1950 s fluorescence has enjoyed increased use and acceptance as an analytical measuring tool because of increased instrumental refinements and the method s inherent sensitivity and selectivity. High detection sensitivity results from the fact that the signal-to-noise ratio is large and can be electronically amplified, while selectivity results from the fact that either the emission or excitation spectra can be used to characterize the fluorescing species. In addition, analytically useful information such as sample purity, concentration, metal oxidation state, and number of binding sites can be obtained from consideration of quantum efficiencies and lifetime and polarization measurements. 

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