Sensing phase-modulation

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... 

Phase-Modulation Sensing of Blood Gases and/or Blood Septicemia... 

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. 

Heideman R.G., Lambeck P.V., Remote opto-chemical sensing with extreme sensitivity design, fabrication and performance of a pigtailed integrated optical phase-modulated Mach-Zehnder interferometer system, Sens, and Actuat. B 1999 61 1 GO-127. 

Figure 1.1. Schemes for fluorescence sensing intensity, intensity ratio, time-domain, and phase-modulation, from left to right.

How can phase-modulation fluorometry contribute to this health-care need It now seems possible to construct a lifetime-based blood gas catheter (Figure 1.3), or alternatively, an apparatus to read the blood gas in the freshly drawn blood at the patient s bedside. To be specific, fluorophores are presently known to accomplish the task using a 543-nm Green Helium-Neon laser,(18 19) and it seems likely that the chemistries will be identified for a laser diode source. The use of longer wavelengths should minimize the problems of light absorption and autofluorescence of the samples, and the use of phase or modulation sensing should provide the robustness needed in a clinical environment. For the more technically oriented researcher, we note that the... 

J. R. Lakowicz and B. P. Maliwal, Optical sensing of glucose using phase-modulation fluorometry, Anal. Chim. Acta 271, 155-164(1993). 

J. R. Lakowicz, H. Szmacinski, and M. Karakelle, Optical sensing of pH and pC02 using phase-modulation fluorimetry and resonance energy transfer. Anal. Chim. Acta 272, 179-186 (1993). 

Figure 13.5. Methods of fluorescence sensing, (a) Single excitation/emission wavelength intensity changes with analyte concentration (b) wavelength-ratiometric A/B changes with analyte concentration (c) liftetime based (time domain) r changes with analyte concentration (d) lifetime-based (phase modulation) Am and A change with analyte concentration.

The fluorescence lifetime can be measured by time-resolved methods after excitation of the fluorophore with a light pulse of brief duration. The lifetime is then measured as the elapsed time for the fluorescence emission intensity to decay to 1/e of the initial intensity. Commonly used fluorophores have lifetimes of a few nanoseconds, whereas the longer-lived chelates of europium(III) and terbium(III) have lifetimes of about 10-1000 /tsec (Table 14.1). Chapter 10 (this volume) describes the advantages of phase-modulation fluorometers for sensing applications, as a method to measure the fluorescence lifetime. Phase-modulation immunoassays have been reported (see Section 14.5.4.3.), and they are in fact based on lifetime changes. 

The fluorescence of quinine and the possibility of its quenching or modulation in the presence of external molecules could provide a method for sensing and assaying these molecules. For example, diastereomeric complexes of quinine and quinidine with (+ )-10-camphorsulfonic acid can be discriminated on the basis of their phase modulation-resolved fluorescence (different fluorescence lifetimes for QN and QD). Thus fluorescence lifetimes of 21.79 and 22.89 ns for QN and QD complex, respectively, have been measured, allowing a quantitative determination of QN and QD with a detection limit of 1.8 and 0.97 pM, respectively [142]. Similarly, room-temperature phosphorescence lifetimes were also shown to differ for diaste-reoisomeric complexes of QN and QD [143]. 

---