Phosphorescence sensor

Papkovsky D.B., Papkovskaia N., Smyth A., Kerry J.P., Ogurtsov V.I., Phosphorescent sensor approach for non-destructive measurement of oxygen in packaged foods optimisation of disposable oxygen sensors and their characterization over a wide temperature range, Anal. Lett. 2000 33 1755-1777. 

Platinum and palladium porphyrins in silicon rubber resins are typical oxygen sensors and carriers, respectively. An analysis of the characteristics of these types of polymer films to sense oxygen is given in Ref. 34. For the sake of simplicity the luminescence decay of most phosphorescence sensors may be fitted to a double exponential function. The first component gives the excited state lifetime of the sensor phosphorescence while the second component, with a zero lifetime, yields the excitation backscatter seen by the detector. The excitation backscatter is usually about three orders of magnitude more intense in small optical fibers (100 than the sensor luminescence. The use of interference filters reduce the excitation substantially but does not eliminate it. The sine and cosine Fourier transforms of/(f) yield the following results ... 

Nafcillin MTMOS, TMOS, PTMOS Monolithic and film Room temperature phosphorescence sensor based on imprinted xero-gels... 

Brinas RP, Troxler T, Hochstrasser RM, Vinogradov SA (2005) Phosphorescent oxygen sensor with dendritic protection and two-photon absorbing antenna. J Am Chem Soc 127 11851-11862... 

In these sensors, the intrinsic absorption of the analyte is measured directly. No indicator chemistry is involved. Thus, it is more a kind of remote spectroscopy, except that the instrument comes to the sample (rather than the sample to the instrument or cuvette). Numerous geometries have been designed for plain fiber chemical sensors, all kinds of spectroscopies (from IR to mid-IR and visible to the UV from Raman to light scatter, and from fluorescence and phosphorescence intensity to the respective decay times) have been exploited, and more sophisticated methods including evanescent wave spectroscopy and surface plasmon resonance have been applied. 

Following the discovery that the fluorescence of metalloporphyrins is strongly quenched by oxygen57, optical sensor membranes were developed that are suitable for phosphorescent sensing of oxygen58. Table 1 summarizes fundamental articles on optical sensors for oxygen until the year 2000. 

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

O Riordan T.C., Voraberger H., Casey N., Kerry J.P., Papkovsky D.B., Study of migration of active components of phosphorescent oxygen sensors for food packaging applications, Anal. Chim. Acta 2005 350,135-141. 

Keywords Luminescence m Fluorescence m Phosphorescence a Sensors a Switches a Logic Gates a Supramolecular Systems a Truth Tables a Photoinduced Electron Transfer a Molecular-Level Devices... 

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 ... 

From the practical point of view, the radiative decay rate kr may be assumed to be independent of the external parameters surrounding the excited sensor molecule. Its value is determined by the intrinsic inability of the molecule to remain in the excited state. The radiative decay rate kr is a function of the unperturbed electronic configuration of the molecule. In summary, for a given luminescent molecule, its unperturbed fluorescent or phosphorescent decay rate (or lifetime) may be regarded to be only a function of the nature of the molecule. 

The fluorescence and phosphorescence of luminescent materials are modulated by the characteristics of the environment to which these materials are exposed. Consequently, luminescent materials can be used as sensors (referred also as transducers or probes) to measure and monitor parameters of importance in medicine, industry and the environment. Temperature, oxygen, carbon dioxide, pH, voltage, and ions are examples of parameters that affect the luminescence of many materials. These transducers need to be excited by light. The manner in which the excited sensor returns to the ground state establishes the transducing characteristics of the luminescent material. It is determined by the concentration or value of the external parameter. A practical and unified approach to characterize the luminescence of all sensors is presented in this chapter. This approach introduces two general mechanisms referred as the radiative and the nonradiative paths. The radiative path, in the general approach, is determined by the molecular nature of the sensor. The nonradiative path is determined by the sensor environment, e.g., value or concentration of the external parameter. The nonradiative decay rate, associated with the nonradiative path, increases... 

I. Yaropolov, and A. P. Savitsky, Phosphorescent polymer films for optical oxygen sensors, Biosensors Bioelectronics 7, 199-206 (1991). 

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-... 

Optical and laser technologies also offer the prospect for improvements in fluorescence and phosphorescence determinations. An important development is the use of fluorescence and phosphorescence with optical fiber sensors. 

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