Phosphorescence-based sensors

Lifetime [3,9-11] based sensors rely on the determination of decay time of the fluorescence or phosphorescence. Typically, the fluorescence lifetime is 2-20 ps and phosphorescence lifetime is 1 ps to 10 s. Lifetime-based sensors utilize the fact that analytes influence the lifetime of the fluorophore. Thus all dynamic quenchers of luminescence or suitable quenchers can be assayed this way. The relationship between lifetimes in the absence (t0) and presence (t) of a quencher is given by Stern and Volmer ... 

The OLED-based sensors were tested in the 23-60°C temperature range. The values of t are expected to generally decrease with increasing temperature, as the PL quenching is enhanced at elevated temperatures [47]. However, in the 23-60°C studied range, the phosphorescence of porphyrins is only slightly dependent on the temperature [68]. Indeed, the temperature effect on the SV plots was minimal small reductions in tq and t (100% O2) were observed as the temperature increased, e.g., for one film, tq decreased from 91 to 84 js with Sg varying from 36.5 to 37.5. 

Another promising example of a metal-based sensor can be seen in the work of Lee and Okura (239) who used entrapped platinum octaethylporphyrin complexes to form photostable devices. In their study, they found by adding the surfactant Triton X-100 to the sol-gel mixture, they could improve homogeneity and phosphorescence of the dye-containing glass. Encapsulated porphyrin molecules have also been used successfully in the sensing of nitrogen dioxide (240) and, as will be discussed below, can be used to sense metal ions. 

Kautsky 1931 first oxygen sensor (non-fiber optic) based on dynamic quenching of the phosphorescence of adsorbed dyes... 

In addition to the sensors dealt with in Section 3.3.1.1, which could equally have been included in this Section as they use consumable immobilized reagents and regenerable fluorophores, Frei et al. developed a sensor for HPLC determinations based on the solid-state detection cell depicted in Fig. 3.38.B, where they immobilized 1-bromonaphthalene for measuring phosphorescence quenchers. Experiments demonstrated the sensor s usefulness for determining nitrate with a detection limit of ca. 10" M and an RSD of 4% for an analyte concentration of M. However, the scope of application of this sensor to chromatographically separated anions is rather narrow owing to the low sensitivity of the quenched phosphorescence detection for iodide and other halides [268]. 

Notwithstanding the excellent analytical features inherent in molecular phosphorimetric measurements, their use has been impeded by the need for cumbersome cryogenic temperature techniques. The ability to stabilize the "triplet state" at room temperature by immobilization of the phosphor on a solid support [69,70] or in a liquid solution using an "ordered medium" [71] has opened new avenues for phosphorescence studies and analytical phosphorimetry. Room-temperature phosphorescence (RTF) has so far been used for the determination of trace amounts of many organic compounds of biochemical interest [69,72]. Retention of the phosphorescent species on a solid support housed in a flow-cell is an excellent way of "anchoring" it in order to avoid radiationless deactivation. A configuration such as that shown in Fig. 2.13.4 was used to implement a sensor based on this principle in order to determine aluminium in clinical samples (dialysis fluids and concen-... 

The reflecting surface can be a mirror or a membrane with a light-scattering surface. In any case, the sensor has the appearance of a monolithic probe (i.e., a dip-stick probe). Optical sensors based on absorption, fluorescence, phosphorescence, and luminescence can employ such a configuration. Various highly optimized fiberoptic probes for UV-Vis, NIR, and IR ranges are now commercially available, and their designs are shown in Fig. 9.23. 

Vasil ev V, Borisov SM. Optical oxygen sensor based on phosphorescent metal porphyrins immobilized in perfluorinated ion-exchange membrane. Sens Actuators 2002 B82 272-6. 

Figure 27-5 The optical system for measurement of PO The optica system for PO2 is based on the ability of O2 to reduce the intensity and lifetime of phosphorescence from a phosphorescent dye that is in contact with the sample. The optica system comprises a green (519-nm peak) light-emitting diode (LED, that emits light, which is reflected by a dichroic mirror onto the PO2 sensor. Because of the phosphorescence, red light (672-nm peak) is emitted back through the dichroic mirror and onto a photodetector. (From Boaith N,Wandrup J, Larsson L, et al. Blood gases and oximetry calibration-free new dry chemistry and optical technology for near-patient testing. Clin Chim Acta 2001 307 225-33.)...

In this review, the synthesis, properties, and applications in optoelectronic fields of polyfluorenes with on-chain metal centers have been briefly summarized. Metal complexes involving iridium(III), platinum(II), europium(III), rhenium(I), and ruthenium(II) complex coupled with polyfluorene are surveyed. Efficient energy transfer from polymer main-chain to metal-centers can occur in these host-guest systems. These kinds of novel polymers are usually applied in the fields of phosphorescent OLEDs, memory devices, and sensors. In particular, the realization of efficient energy transfer and phosphorescence offers a huge potential for future optoelectronic devices based on these kinds of materials. 

---