Quenched-phosphorescence Detection of Molecular Oxygen: Applications in Life Sciences: Volume 11 (Detection Science Series) - Hardcover

Hardcover

ISBN 10: 1788011759 ISBN 13: 9781788011754

Verlag: Royal Society of Chemistry, 2018

Inhaltsangabe

Significant progress has been made in recent years in quenched-phosphorescence oxygen sensing, particularly in the materials and applications of this detection technology that are open to commercialization, like uses in brain imaging and food packaging. Prompted by this, the editors have delivered a dedicated book that brings together these developments, provides a comprehensive overview of the different detection methodologies, and representative examples and applications.

This book is intended to attract new researchers from various disciplines such as chemistry, physics, biology and medicine, stimulate further progress in the field and assist in developing new applications. Providing a concise summary at the cutting edge, this practical guide for current experts and new potential users will increase awareness of this versatile sensing technology.

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Significant progress has been made in recent years in quenched-phosphorescence oxygen sensing, particularly in the materials and applications of this detection technology that are open to commercialization, like uses in brain imaging and food packaging. Prompted by this, the editors have delivered a dedicated book that brings together these developments, provides a comprehensive overview of the different detection methodologies, and representative examples and applications.

This book is intended to attract new researchers from various disciplines such as chemistry, physics, biology and medicine, stimulate further progress in the field and assist in developing new applications. Providing a concise summary at the cutting edge, this practical guide for current experts and new potential users will increase awareness of this versatile sensing technology.

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Quenched-Phosphorescence Detection of Molecular Oxygen

Applications in Life Sciences

By Dmitri B. Papkovsky, Ruslan I. Dmitriev

The Royal Society of Chemistry

Copyright © 2018 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-78801-175-4

Contents

Chapter 1 Fundamentals of Quenched Phosphorescence O2 Sensing and Rational Design of Sensor Materials Sergey M. Borisov, 1, 
Chapter 2 New Polymer-based Sensor Materials and Fabrication Technologies for Large-scale Applications Efe Armagan, Dmitri B. Papkovsky and Claudio Toncelli, 19, 
Chapter 3 Evolution of Cell-penetrating Phosphorescent O2 Probes Dmitri B. Papkovsky and Ruslan I. Dmitriev, 50, 
Chapter 4 Hydrophilic Ir(iii) Complexes for In vitro and In vivo Oxygen Imaging Toshitada Yoshihara, Yosuke Hirakawa, Masaomi Nangaku and Seiji Tobita, 71, 
Chapter 5 Protection of Triplet Excited State Materials from Oxygen Quenching and Photooxidation in Optical Sensing Applications Mikhail A. Filatov, 91, 
Chapter 6 Progress in Phosphorescence Lifetime Measurement Instrumentation for Oxygen Sensing Angel de la Torre-Vega, Santiago Medina-Rodríguez, Carlos Medina-Rodríguez and Jorge F. Fernández-Sánchez, 117, 
Chapter 7 Optical O2 Sensing in Aquatic Systems and Organisms Klaus Koren and Michael Kühl, 145, 
Chapter 8 Monitoring of Extracellular and Intracellular O2 on a Time-resolved Fluorescence Plate Reader Michelle Potter, Tiffany A. Lodge and Karl J. Morten, 175, 
Chapter 9 Monitoring Parameters of Oxygen Transport to Cells in the Microcirculation Aleksander S. Golub and Roland N. Pittman, 193, 
Chapter 10 Photoacoustic Imaging of Oxygen Chang H. Lee, Janggun Jo, Xueding Wang and Raoul Kopelman, 205, 
Chapter 11 Imaging of Tissue Oxygen Ex vivo Alexander V. Zhdanov and Dmitri B. Papkovsky, 220, 
Chapter 12 Tracking of Hypoxia and Cancer Metastasis with Iridium(iii)-based O2 Probes Xianchuang Zheng and Xiqun Jiang, 244, 
Chapter 13 Probing Tissue Oxygenation by Delayed Fluorescence of Protoporphyrin IX Rinse Ubbink and Egbert G. Mik, 259, 
Chapter 14 Microfluidic Systems and Optical Oxygen Sensors: A Perfect Match for Advancing Bioprocessing and Microbiology Birgit Ungerböck and Torsten Mayr, 278, 
Chapter 15 pO2 Measurements in Biological Tissues by Luminescence Lifetime Spectroscopy: Strategies to Exploit or Minimize Phototoxic Effects in Tumors Veronika Huntosova and Georges Wagnieres, 298, 
Chapter 16 In vivo Brain Functional Imaging Using Oxygenation-related Optical Signal Vassiliy Tsytsarev and Dmitri B. Papkovsky, 319, 
Chapter 17 Applications of Phosphorescent O2 Sensors in Food and Beverage Packaging Systems Malco C. Cruz-Romero, Caroline A. Kelly, Dmitri B. Papkovsky and Joseph P. Kerry, 335, 
Subject Index, 361, 

CHAPTER 1

Fundamentals of Quenched Phosphorescence O2 Sensing and Rational Design of Sensor Materials

SERGEY M. BORISOV

1.1 Introduction

In the last decades, optical oxygen sensors (oxygen optodes) became indispensable analytical tools, which are nowadays widely applied in academia and industry. Their popularity is explained by the numerous advantages offered by the optical detection method such as the absence of electromagnetic interferences, minimally invasive character (measurement though a transparent wall of a reactor), versatility of sensor formats varying from planar foils and fiber-optic sensors to nanoparticles, suitability for imaging etc. Optical oxygen sensors do not consume the analyte, which favourably distinguishes them from electrochemical sensors such as Clark electrode or galvanic cells. Optodes allow for oxygen measurement in gases and solutions with dynamic ranges, which can be adjusted over many orders of magnitude. Finally, optical oxygen sensors are very useful for measurement of air pressure on surfaces (pressure sensitive paints) or as transducers for enzymatic sensors making use of oxygen consumption such as glucose or lactate sensors.

1.2 Mechanism of Oxygen Quenching

Oxygen is one of the most powerful luminescence quenchers. Quenching of fluorescent dyes (excited singlet state, S1) and phosphorescent dyes (excited triplet state, T1) is spin-allowed. Moreover, the energies of excited states of oxygen (1Sg+ and 1?g) are lower than the energies of the excited states of most organic dyes and metal complexes (Figure 1.1), which makes quenching via energy transfer favourable.

The mechanism of oxygen quenching is rather complex and the exact pathways and formed products depend on many factors. Electron-exchange Dexter-type energy transfer is the predominant mechanism of oxygen quenching. Quenching of fluorescent dyes (D) can result in the formation of the dye in the triplet excited state or in the ground state:

[FORMULA OMITTED]

The triplet state of the dye is deactivated to the ground state:

[FORMULA OMITTED]

For the quenching of phosphorescence, the dye is deactivated into the ground state and singlet oxygen is formed:

[FORMULA OMITTED]

Depending on the triplet energy of the dye, formation of singlet oxygen either only in the 1?g state (e.g. for PtTPTNP, Figure 1.1) or in both 1?g and 1Sg+ states (e.g. for PtOEP) is possible. Notably, O2 (1Sg+) deactivates very fast into O2(1?g) state.

Apart from the energy transfer, electron transfer leading to superoxide is also possible:

[FORMULA OMITTED]

This process can play a significant role for metal complexes with strong reducing properties (particularly in the excited state), for instance Ir(iii) cyclometalated complexes. Rapid back electron transfer can result in the formation of singlet oxygen and the sensitizer in the ground state.

Importantly for all these processes, singlet oxygen represents one of the main products. Since its deactivation to the triplet state regenerates the analyte, optical oxygen sensors do not consume the analyte in theory. However, the lifetime of singlet oxygen in polymers can be much longer compared to that in the aqueous phase (?3 ?s), which can be sufficient for it to react with the sensor components (dye or polymer), see Chapter 1.7.

Independent of the quenching mechanism, the quenching behavior for dissolved dyes is described by the Stern–Volmer equation:

[FORMULA OMITTED] (1.1)

where I0(t0) and I(t) are the luminescence intensity (decay time) in the absence and in the presence of oxygen, respectively, kq is the bimolecular quenching constant and KSV is the Stern–Volmer constant.

From eqn (1.1) it is evident that the efficiency of quenching depends on both the bimolecular quenching constant and the decay time of the luminophore t0. The kq constant is determined mostly by oxygen diffusion since the diffusion of the much larger dye is significantly slower already in solution and is virtually non-existant for immobilized dyes. The kq constant often approaches the diffusion-controlled limit kdiff for quenching of fluorescence but is lower for quenching of phosphorescence. For common phosphorescent indicators such as Pt(ii) porphyrins or Ru(ii) polypyridyl complexes, it is usually close to 1/9 of kdiff, where 1/9 is the spin statistical factor accounting for the formation of both products in the singlet state. However, kq is sometimes higher than this value even in the case of purely energy transfer-based quenching and may be even higher if electron transfer is involved.

Clearly, the t0 has a much stronger influence on the Stern–Volmer constant than kq. In fact, assuming a kq = kdiff = 2.1 × 1010 M-1 s-1 for an air-saturated toluene solution (C(O2) ˜ 1.8 mM) of a typical fluorescent dye with t0 of 4 ns, the I0/I value calculated with eqn (1.1) is only 1.15. On the other hand, for a phosphorescent indicator such as PtOEP (t0 = 85 µs) even with much lower kq 2.4 × 109 M-1 s-1 (1/9kdiff) the luminescence intensity and decay time decrease 367-fold in the same conditions. Since the diffusion of oxygen is significantly slower in the polymers compared to the solution, it is evident that only phosphorescent indicators will provide the required resolution when embedded in common polymeric matrices. Additionally, whereas the tunability of fluorescence decay times is usually limited by 1–2 orders of magnitude, the phosphorescence decay time can vary from several microseconds to hundreds of milliseconds. This provides virtually unlimited flexibility in designing oxygen-sensing materials for very different applications.

1.3 Requirements for Phosphorescent Indicators

In order to navigate among hundreds of reported oxygen indicators it is useful to define the important parameters, which should be considered when the indicators are selected. These include:

(i) Spectral properties (absorption and emission maxima). In contrast to fluorescent dyes, phosphorescent indicators possess large Stokes shifts, which simplifies signal separation and reduces interferences caused by scattering and autofluorescence. Nevertheless, indicators excitable and emitting at longer wavelength are preferable for the same reasons. In photosynthetic systems, however, such excitation can result in much higher levels of autofluorescence and dyes with other spectral properties can be a better choice. Clearly, autofluorescence can be completely eliminated in the time domain measurement, but it does interfere with the measurement in the frequency domain unless multi-frequency measurement is performed.

Compatibility of the indicator with the light sources, photodetectors and other optical components should also be considered. Whereas a wide range of light sources is available for the whole spectral range, the detectors are mainly limited to avalanche photodiodes, CCD-arrays and photomultipliers. Although the sensitivity of PMTs is generally very high, it deteriorates fast in the NIR part of the spectrum. In the case of fiber-optic sensors, the quartz glass fibers are compatible with all oxygen indicators. In contrast, much cheaper plastic fibers show strong absorption in the NIR part of the spectrum, which limits the practically useful length to 1–2 meters.

(ii) Brightness of luminescence. Brightness can be defined as the product of molar absorption coefficient e and luminescence quantum yield f. Clearly, in case of phosphorescent indicators high efficiency of inter-system crossing (ISC, S1 -> T1 transition, Figure 1.1) is one of the prerequisites for bright phosphorescence. Bright indicators allow for thinner sensing layers and therefore for faster response times. In the case of very bright but less photostable indicators the operational lifetime of the sensor can be extended by using low intensities of the excitation light nevertheless allowing for acceptable signal to noise ratio.

(iii) Luminescence decay times. The luminescence decay times along with permeability of the polymer govern the sensitivity of the sensor. In order to obtain oxygen sensors for physiologically relevant conditions on the basis of polymeric matrices such as polystyrene (moderate oxygen permeability) the optimal decay times are about 20–100 ?s, the requirement met by most Pt(ii) porphyrins. Indicators with shorter decay times would deliver lower resolution, whereas the sensors based on the indicators with much longer lifetimes (e.g. Pd(ii) porphyrins) will only be suitable for trace sensing. On the other hand, if trace sensing applications are intended, the long luminescence lifetimes (>>1 ms) are highly desirable.

(iv) Photostability. Photodegradation of the indicator results in sensor drift. This can be less critical for the lifetime measurements if no other luminescent species are formed since the decay time remains constant independently on the amount of the remaining dye and only the S/N ratio is affected. In contrast, much stronger drift is expected for intensity-based measurement. This is true for ratiometric measurements where photobleaching of the reference dye will be as critical as the bleaching of the indicator itself unless both bleach with approximately the same speed. It goes without saying that the higher the photostability, the better. However, for many applications indicators with moderate photostability can be fully adequate even for long-term measurements. On the other hand, photobleaching can be an issue if the light densities are very high. For instance, the Eddy correlation technique which gained extreme popularity in the oceanographic community in the last years relies on the use of fiber-optic microsensors with very fast response. Here not only is the density of light exceptionally high, but also high frequency of measurements is required (several times per second). As a consequence, sensors based on even highly photostable dyes will have limited lifetime.

In respect to photobleaching, two aspects should be mentioned. First, photobleaching rates can be significantly different in the absence of oxygen and under air saturation. In the second case, oxidation of the dye by photosynthesized singlet oxygen may be the predominant mechanism of photodegradation. Second, drift of the sensor properties can be observed not only due to oxidation of the dye but also due to degradation of the matrix polymer resulting in accumulation of the moieties acting as quenchers of phosphorescence of the indicator. In contrast to the first mechanism (photobleaching of the dye itself) characterized by degradation of the luminescence intensity but relative stability of the decay time, in the second mechanism both parameters will be affected to approximately the same degree. Although this effect can be overcome in theory by using an oxidation-resistant polymer, the choice of such polymers is very narrow and the compatibility of the indicator and the polymer can represent a serious problem.

(v) Solubility in polymers. Low compatibility of indicator and the polymer is likely to result in dye aggregation. For instance, even rather hydrophobic indicator dyes based on conjugated structures readily aggregate in silicone rubber. Low solubility of the dye in the matrix can also result in its migration into a polymeric support (e.g. commonly used poly(ethylene terephthalate)). This effect is accelerated at elevated temperatures, e.g. during autoclaving. Covalent grafting of the indicator into the polymer overcomes aggregation, migration and leaching issues but is often synthetically demanding since it requires the introduction of functional groups into the indicator molecule or in both the dye and the polymer.

Only a few indicator classes show the properties which fulfil most of the requirements. Dyes with the best combination of properties will be good indicators for general use covering the majority of applications. However, for some applications one or the other requirement can be a cut-off criterion whereas other properties are of less importance. Here a specialized tailor-made indicator dye may be a much better choice.

1.4 Brief Overview of the Most Common Indicators

An impressive number of phosphorescent dyes were reported in the last decades and most of them qualify as oxygen indicators. However, there is a significant gap between chemists who design the sensing materials and end-users such as biologists, oceanographers, geologists etc. Therefore, the most widely used indicators are either commercially available or can be easily prepared in the lab. Fortunately, some comparably new indicators such as benzoporphyrin complexes have been also commercialized recently.

The structures of the most common oxygen indicators are shown in Figure 1.2 and their photophysical properties are summarized in Table 1.1 Ruthenium tris(4,7-diphenyl-1,10-phenanthroline) (Ru-dpp) is the brightest among the polypyridyl complexes and was applied in many sensing materials. This dye can be synthesized in only one step. The limitations include moderate luminescence brightness and high temperature dependency of the luminescence decay time, which is also comparably short so that immobilization in highly oxygen-permeable matrices is essential to achieve optimal sensitivity. Platinum(ii) and palladium(ii) complexes with porphyrins and their derivatives are extremely popular. The main reasons are simple synthesis and often commercial availability, acceptable photophysical properties and versatility of the porphyrin structure which allows for numerous modifications. Pt(ii) and Pd(ii) complexes with octaethylporphyrin (OEP) possess good brightness upon excitation in the Soret band (UV range). Molar absorption coefficients for excitation with green light are much lower (Table 1.1). The photostability of OEP complexes is, however, moderate. Therefore, for most applications they have been substituted by the complexes of the same metals with meso-(pentafluorophenyl) porphyrin (TFPP) which are known to be very photostable. As a trade-off, the brightness of these dyes is about 2-fold lower than for the OEP complexes.

As was mentioned above, NIR dyes are advantageous for several reasons. Platinum(ii) complex with ocaethylporphyrin-ketone (PtOEPK) enjoyed great popularity as a NIR emitting oxygen indicator. Spectral properties of the Pt(ii) complex with tetra(pentafluorophenyl)porpholactone are very similar to that of the PtOEPK. Although these dyes feature absorption and emission spectra, which are bathochromically shifted compared to the parent porphyrins, the position of the Q-band is not fully adequate for in vivo measurements. Moreover, the brightness of the dyes is moderate. Interestingly, the Pd(ii) complexes with porphyrin-ketones and porphyrin lactones show very weak phosphorescence, which is different from the general trend shown by the porphyrins (~2–3 fold lower brightness of the Pd(ii) complexes, Table 1.1).

(Continues...)

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Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 2018
• Sprache: Englisch
• ISBN 10: 1788011759
• ISBN 13: 9781788011754
• Einband: Tapa dura
• Anzahl der Seiten: 384
• Herausgeber: Papkovsky Dmitri B, Dmitriev Ruslan I
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: Nicht verfügbar